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Shiraz 2009 - 1st EAGE International Petroleum Conference and Exhibition
- Conference date: 04 May 2009 - 09 May 2009
- Location: Shiraz, Iran
- ISBN: 978-90-73781-65-8
- Published: 04 May 2009
1 - 100 of 140 results
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EOR from Carbonates by Using Smart Water
Authors S. Strand, T. Austad and T. PuntervoldSeawater acts as an EOR-fluid, “Smart Water”, in chalk by improving the water wetness at high temperatures, T>90 °C. It has been verified that Ca2+, Mg2+, and SO42- are the active ions in the chemical mechanism for wettability alteration. In this paper, we have identified the chemical reactions involved and compared the reactivity of outcrop chalk and reservoir limestone cores. In general, and as expected, the active ions showed the same chemical reactions towards the chalk and limestone surface, but the reactivity of the limestone surface was significantly lower than that of the pure biogenic chalk surface. It is, however, expected that seawater can act as a “Smart Water” also for limestone at the right conditions.
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Monitoring the Wettability of Oil Reservoir Rocks by AFM during Surfactant Treatment
Authors Omolbanin Seiedi, M. Rahbar, M. Nabipour, S. Ayatollahi and M. GhateiOil recovery from fractured, oil-wet/mixed-wet, carbonate reservoirs by waterflooding is hindered mostly because of the absence of water imbibitions into the matrix blocks. It is believed that the chemical treatments including surfactant flooding improve oil recovery efficiency by wettability alteration and interfacial tension (IFT) reduction. In this paper the effect of surfactants on the wettability of dolomite surfaces are studied. The Two different types of surfactants mainly a cationic (C16TAB) and a non-ionic surfactant (TritonX-100) were used to investigate the wettability alteration utilizing a novel technique of Dynamic contact angle measurement. The treated surfaces which show the most effective changed surfaces are then subjected to the AFM test. Results show that cationic surfactant can remove adsorbed compounds from the surface hence change the wettability. In the case of Non-ionic surfactant as it adsorbs on the surface however the wettability remains unchanged.
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The Effect of Macroscopic Pore Structure Heterogeneities on the Recovery of Waterflood Residual Oil
Authors Rafat Parsaei and I. ChatzisGravity-Assisted Inert Gas Injection performance was investigated in heterogeneous packed model through a number of experiments for recovering waterflood residual oil. These heterogeneous media consisted of isolated regions of large pore-sizes, at the macroscopic scale, randomly distributed in small-size continuum. In such heterogeneous media the waterflood residual oil saturation is proportional to the volume fraction of heterogeneity. Experimental results of tertiary gravity drainage experiments have shown that the presence of large pore-size regions leads to the gas invading through such regions and thus improve the recovery of the large amount of residual oil.
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Recovery Based Ranking Oil Reservoir for CO2 Miscible Injection
Authors F. Kamali, M. Talebian, M. Khosravi, A. Vahidi and E. RoayaeiThe use of CO2 for enhanced oil recovery of the Iranian oil reservoirs offers a unique opportunity to boost incremental oil recovery and reducing emissions of greenhouse gas through geological sequestration. In this paper, oil fields were screened and ranked for CO2 EOR suitability using new rapid and parametric method which can be applied to a large number of reservoirs with considering the technical feasibility of the EOR process and utilized eight essential reservoir properties: API gravity, oil saturation, ratio of reservoir pressure to minimum miscibility pressure (MMP), reservoir temperature, reservoir dip, net oil thickness, permeability and porosity via a developed program. By using this methodology, a systematic screening and ranking of all possible Iranian oil reservoirs was carried out. Evaluation and prediction of the efficiency of CO2 flooding technique were performed for candidate reservoirs by using an analytical method. In addition, a commercial stream-line type model was used to compare the results of this screening which clearly proves the pervious outcomes. Finally, best candidates were chosen by considering suitable distance from CO2 sources.
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Miscible GOGD in Naturally Fractured Reservoirs
Authors M.L. Verlaan and P.B. BoerrigterOil recovery from naturally fractured reservoirs is difficult. Especially in the Middle East where carbonate rocks are oil or mixed-wet. In these reservoirs typical production mechanisms like viscous displacement and counter current imbibition will not work. Gas–oil gravity drainage (GOGD) is then the production mechanism of choice. However, gravity drainage with immiscible (equilibrium) gas could result in low oil rates and/or low ultimate recovery due to capillary hold-up. Miscible gas injection could have significant advantages in a GOGD situation. Miscibility might be achieved with for instance CO2, which has typically a low minimum miscibility pressure. When the injected gas is (first contact) miscible with the oil, density and viscosity will be reduced. Miscibility adds the advantages of single-phase flow and interfacial tension reduction, which further improves GOGD rates and ultimate recovery. This paper evaluates the impact of first contact miscible gravity drainage on oil recovery and discusses the main modelling aspects. The key parameters were identified to be matrix block width over height ratio and vertical heterogeneity. First contact miscible gas injection benefits mainly from IFT reduction and has its application in heterogeneous reservoirs with large capillary hold up and re-imbibition effects.
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Study of Thermally Assisted Gas Oil Gravity Drainage in One of Iranian Fractured Reservoirs
Authors Y. Mahmoodi, R. Kharrat and A. HashemiNaturally fractured reservoirs hold well over 100 billion barrels of heavy oil worldwide. For conventional reservoirs containing heavy oil, steam injection is the most widely used thermal recovery method. In heavy oil fractured reservoirs,steam injection is a challenging problem; however it is a potentially effective improved oil recovery method. In naturally fractured reservoirs containing gas filled vertical fractures, gas oil gravity drainage (isothermal gas oil gravity drainage) is an important recovery mechanism. In dipping fractured reservoirs with high fracture permeability, it may be possible to use steam to accelerate isothermal gas oil gravity drainage. This technique is a new and novel EOR technique known as Thermally (Steam) Assisted Gas Oil Gravity Drainage (TAGOGD (SAGOGD)). This study investigates the feasibility of steam injection and conducting TAGOGD technique in a highly fractured reservoir containing heavy oil in Iran. All data for this study are based on Kuh-e-Mund reservoir which is a highly fractured symmetrical anticline located in the southeastern part of Bushehr in the coast of Persian Gulf. The results of this study showed that this technique could improve oil recovery factor for this field.
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Surfactant Induced Solubilization and Transfer Resistance in Gas-Water and Gas-Oil Systems
Authors R Farajzadeh, A. Banaei, J. Kinkela, T. deLoos, S. Rudolph, R. Krastev, J. Bruining and P.L.J. ZithaTypically, conventional reservoir simulators underestimate the recovery factor of heavy oil reservoirs under solution gas drive. We hypothesize that natural surfactants in oil (e.g. asphaltenes) cause this phenomenon in two ways: 1) by hindering the mass transfer rate of gas molecules through the gas-oil interface and 2) by enhancing the solubility of gas in the heavy oil. We investigate effect of surfactants on mass transfer rate of gas through gas-water interface and on the solubility of gas in oil. In bulk experiments, we observe that the addition of sodium dodecyl sulfate (SDS) does not influence the gas transfer rate while in the presence of a porous medium the growth of gas bubbles becomes increasingly difficult with increasing SDS concentration, which indicates that the interaction of the grain with fluids is an essential element in bubble growth in porous media. The effect a non-ionic surfactant on the solubility of methane in n-dodecane is also examined. The bubble point pressures of the gas+oil+surfactant system are determined experimentally.It is found that the bubble point pressures of the system decrease with increasing surfactant concentration, i.e., the surfactant enhances the solubility of methane in the oil.
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A CT Scan Study of Foam Flooding in Porous Media
Authors M. Simjoo, M. Mahamoodi Nick, R. Farajzadeh, S.A. Mirhaj and P.L.J. ZithaFoam is widely used in oil and gas recovery operations as a mobility control and profile correction agent. A brief list of foam applications includes acid diversion during matrix stimulation, gas blocking and enhanced oil recovery. This paper aims to study the dynamics of foam flooding assisted liquid displacement in a porous media. We report core-flood experiments performed using Bentheimer sandstone and N2 foam with the aid of X-ray computed tomography. A detailed description of CT images and quantification of local fluid saturation revealed that foam is formed in-situ and giving a mobility control. Furthermore, oil can be produced by a liquid slug induced by this strong immiscible foam front.
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A Petroleum system study in the Persian Gulf
More LessAbstract A comprehensive geochemical study and research on crude oil samples from different producing oil field in the Persian Gulf resulted in preparation of the first phase of Atlas of Iranian oils which is unique in its own kind. Detailed measurements on oil physical properties included determining of API gravity, viscosity, pour point, sulfur content, Ni/V and stable carbon isotope 13C. Complementary geochemical analyses such as SARA tests, Gas Chromatography and Gas Chromatography and Mass Spectrometry were carried out for the purpose of oil to oil correlation and in order to identify characteristic biomarkers of organic origin, depositional environment, thermal maturity and geologic age. Based on physical and chemical properties and characteristic geochemical fossils, three major petroleum systems with respective oil families were recognized in the Iranian offshore of the Persian Gulf. Most oils produced from Aboozar, Dorood, Foroozan (1 and 3) and Reshadat fields were sourced from Paleozoic petroleum system. Oils encountered in Nowrooz, Hendijan 3, Bahregansar 1and 2, Salman 2and 3 and Reshadat 2 fields are assigned to Jurassic petroleum system. Oils produced from fields including Hendijan 1and 2, Foroozan 2, Salman1, SirriA and C are sourced from Cretaceous petroleum system. Keywords: Petroleum system, Persian Gulf, Atlas of Iranian Oils
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Origin of Transfer Faults in the Fars Folded Belt, Zagros Mountains
Authors M. Sepehr, S.F. Mirhashemi and M. YavariTransfer Fault describes a broad category of structures that accommodate lateral variations of deformation. They form in various scales and in different tectonic setting. In the southeastern part of the Zagros Fold-Thrust Belt of Iran number of transfer faults, ranging from a few to tens of Kilometers has been identified. These transfer faults in which all accommodate the lateral variation of shortening as a result of continental collision along the northeastern margin of Arabian Plate interpreted as oblique/lateral ramps and have various modes of origin. The development of these fault zones in the sedimentary cover, their relation to the inherited and active basement faults and their importance in the hydrocarbon exploration is discussed. Based on evidences presented in this paper we have argued that probably most of the transfer faults in the Fras Folded Belt are not basement origin as was suggested previously.
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Fold-diapir Interactions and the Building of the South Fars Fold and Thrust Belt
Authors JP Callot, S. Jahani, J. Letouzey and D. Frizon de LamotteThe southeastern Zagros is situated at the eastern tip of the Zagros system, close to the Makran accretionary prism and Oman Mountains. This orogenic system results from the ongoing collision between the Arabian and Central-Iran plates. In this context, the main features of the studied area are; (i) the existence of numerous emerged or buried salt diapirs, made up of Late Precambrian Hormuz salt moving since the early Paleozoic, and (ii) the irregular along-strike shape of the collision-related detachment folds, with frequent apparent bending, change in width and structural association with salt diapirs which express the control of deformation by the pre-existing salt structures.
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Salt Activity and Halokinesis in the Zagros Fold-thrust Belt and Persian Gulf (Iran)
Authors S. Jahani, D. Frizon de Lamotte and J. LetouzeyAt eastern tip of the Zagros fold thrust belt (ZFTB) and Persian Gulf numerous salt diapirs emerged which originated from pre-Cambrian–early Cambrian Hormuz salt layer. We show that almost all the diapirs were already active prior to Zagros folding either as emergent diapirs forming islands or as buried domes initiated at as early as the Lower Paleozoic. They have been reactivated by subsequent sedimentary supply, tectonic events and surface erosion. A quite continuous halokinesis exists since the early Paleozoic, i.e. just after the deposition of the Hormuz salt, up to the present. In fact, each salt diapir shows individual evolution depending of their position in the system. Abundance of emergent salt diapirs and presence of recycled Hormuz debris mostly in the Miocene in the onshore suggest that during the Zagros folding nearly all salt diapirs has been emerged.
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Neogene Sequence of Folding in the NW Zagros Fold Belt Dating Non-marine Foreland Growth Strata
More LessThree magnetostratigraphic sections across the Pusht-e Kuh Arc in NW Zagros and Izeh Zone constrain the ages of syntectonic foreland deposits as well as the timing of folding. These sections are located in the front of the Pusht-e Kuh Arc in the Changuleh growth syncline, in the centre of the arc in the Afrineh growth syncline and in the hinterland along the footwall of the High Zagros Fault. The ages for folding onset are well constrained in Changuleh at 7.65 Ma and in Afrineh at 11.8 Ma. In Chaman Goli growth syncline the age of initial folding could be as old as 13.5 Ma that fits with even older ages (early Miocene) along the footwall of the Main Zagros Thrust. Folding propagated towards the foreland during at least 20 My, which implies an older age and a longer duration than previously assumed.
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Field Evidence for a Major Early Paleogene Folding Phase Across the Zagros Simple Folded Zone (Lurestan Province, Iran)
Authors E. J.-P. Blanc, J. Verges, P. Gillespie, E. Casciello, H. Emami, T. Egebjerg, M.H.G. Ghoodarzi, M. Valinejad, S. Homke, D. Hunt and I. SharpWe report here the presence of fold growth strata in lower Paleogene beds across Lurestan. Those are associated with a compressional phase much older than the typical Zagros folding which affected the eastern side of the Simple folded zone 12 Ma ago (Emami, 2008) and spread to the mountain front, on the western edge of the Simple Folded Zone around 8 Ma ago (Homke et al., 2006) with the deposition of Agha Jari-Bakhtyari and Quaternary sediments. Early folding accounts there for up to half of the total shortening measured in cross section and corresponds to a shortening of around 10%.
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Development and Folding of the NW Zagros Foreland Basin, Lurestan Povince, SW Iran
Authors S. Homke, E. Saura, J. Serra-Kiel, G. Bernaola, D. Hunt, I.R. Sharp, J. Verges, E. Blanc, E. Casciello and M.H. Hasan GoodarziIt is crucial for exploration in fold-and-thrust belts to get robust understanding of foreland basin evolution and deformation, in order to constrain the timing of hydrocarbon generation, migration and trap formation. Although it is widely accepted that the main phase of deformation in the Zagros belt occurred in the Miocene and Pliocene, recent field studies have demonstrated that folding started in the NW Zagros (Lurestan Province) as early as the Late Cretaceous and Paleocene. The objective of this work is to constrain the timing of the development and folding of the NW Zagros foreland basin, on the base of accurate dating of the Amiran, Taleh Zang and Kashkan syntectonic foreland formations at different places through Lurestan Province. A multidisciplinary approach has been used, combining benthic foraminifera biostratigraphy, calcareous nannoplankton biostratigraphy, palynostratigraphy and strontium isotope stratigraphy. Dating results show that the Amiran-Kashkan clastic wedge prograded south-eastward in the NW Zagros foreland basin between the late Cretaceous and the early Eocene. The dating of associated syn-depositional folding structures permits to establish that an early folding of the NW Zagros foreland basin progressed south-westward during the same period.
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Style and Age of Deformation in the Northwest Persian Gulf
Authors B. Soleimany and F. SabatThe study area is located in the foreland of the Zagros (Persian Gulf) where important oil and gas fields are present. Data consist of two orthogonal sets of 2D seismic sections. Both NNE-SSW folds (Arabian trend) and NW-SE folds (Zagros trend) are documented. These folds formed during two folding stages: the older one Late Cretaceous in age and the younger one Plio-Quaternary. Older folds formed according to the Arabian trend. During the younger folding stage older folds has been reactivated and tightened, and some of the new folds also with Arabian trend formed on top of them. This occurs in front of the advancing Zagros trend folds front.
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Quantification of Stress and Strain Using Calcite Twins and Anisotropy of Physical Rock Properties in a Folded/Fractured Reservoir
Authors K. Amrouch, O. Lacombe, J.M. Daniel, P. Robion, J.P. Callot and N. BellahsenThe description of folded/fractured reservoirs requires the understanding of mechanical behaviour of rocks during deformation. In folds, at the decametric scale, deformation is accommodated by flexural slip, faulting and formation of macroscopic fracture sets. The role of LPS has been recognized for years using magnetic fabric analysis which shows that in siliciclastic deposits the deformation is mainly accommodated by pretilting strain. This paper thus combines analyses of calcite twins, Anisotropy of Magnetic Susceptibility and Anisotropy of P-wave Velocity, together with petrological study to investigate the relationship between fold development and stress/strain. The results are compared to already available and newly collected mesoscale fracture and fault slip data. The Sheep Mountain anticline was chosen as a natural laboratory.Our results show a good agreement between calcite twinning and anisotropy of rocks properties, and with macroscopic fracturing on the other hand. Our study points toward a better description of deformation mechanisms of folded strata. A major result is the consistency of the record of deformation at microscopic and macroscopic scales, emphasizing that core scale data can be relevant to fold-scale structuring. This study yields important constraints for forthcoming modeling of stress distribution during fold development.
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3D Fold Pattern Formation: a FEM Study
Authors D.W. Schmid, M. Dabrowski and M. KrotkiewskiThe numerical study of three dimensional (3D) fold patterns formation in randomly perturbed layers requires large resolutions. We have developed BILAMIN, a geometry fitted mesh implementation of the finite element method for incompressible Stokes flow that is capable of solving such systems. We use BILAMIN in a case study of fold pattern evolution. Folds are ubiquitous in nature, and contain both mechanical and kinematic information that can be deciphered with appropriate tools. Our results show that there is a relationship between fold aspect ratio and in-plane loading conditions. We propose that this finding can be used to determine the complete parameter set potentially contained in the geometry of three dimensional folds: mechanical properties of natural rocks, maximum strain, and relative strength of the in-plane far-field load components. Furthermore, we show how folds in 3D amplify and that there is a second deformation mode, besides continuous amplification, where compression leads to a lateral rearrangement of blocks of folds. Finally, we demonstrate that the textbook prediction of egg carton shaped dome and basin structures resulting from folding instabilities in constriction is largely oversimplified. The fold patterns resulting in this setting are curved, elongated folds with random orientation.
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Multilayer Properties Revealed by Anticline Distribution, the Case of the SE Pusht-E Kuh Arc (Lurestan)
Authors E. Casciello, J. Vergés, E. Saura, G. Casini, N. Fernández, E. Blanc, S. Homke and D.W. HuntFolding in the south-eastern Lurestan Province was analysed by measuring anticline’s wavelength and axial-length and by comparing the fold distribution with the available paleofacies maps. It was found that the large variability of the measured parameters occurs in relation with facies changes within the Cretaceous Bangestan Group, which acts as the competent carbonate unit that governs buckling in this region. The Oligocene-Miocene Shahbazan-Asmari unit folds harmonically with the Bangestan Group, except in the areas where the Paleogene deposits interposed between the two units exceed 1300m of thickness. In these areas the Shahbazan-Asmari carbonate displays short wavelength folds that indicate a complete decoupling from the underlying folds of the Bangestan Group. It is suggested that this decoupling occurs because the summed thickness of the incompetent units separating the Shahbazan-Asmari from the Bangestan Group exceeds the extension of the effective zone of contact strain of the Bangestan Group folds.
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Disharmonic Folding (Related to Different Mechanical Behaviour of Rock Formations) of Lurestan Region in the Zagros Fol
Authors A. Farzipour Saein, A. Yassaghi, S. Sherkati and H. KoyiThree main decollement units whithin the sedimentary pile of the Lurestan region were distingushed based on the field observation, seismic data and dipmeter logs from drilled wells. The effect of these decollement units on folding style was studied based on the constructed balanced regional cross section.
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Uplift in Sedimentary Basins Revisited - New Insights from the Voring Basin, Norwegian Sea
Authors L. Rupke, D.W. Schmid, S.M. Schmalholz and Y.Y. PodladchikovMany sedimentary basins show subsidence pattern that cannot be explained by uniform stretching models. In fact, uplift, or reduced subsidence, appears to be common during basin evolution. In this study we review the causes and consequences of different uplift mechanisms. Using a two-dimensional basin model we explore how differential thinning, mineral phase transitions, and magmatic underplating affect the structural and thermal evolutions of sedimentary basins. The paper is divided into two parts: the first part explores the characteristics of different uplift mechanisms, while the second part shows the results of a reconstruction case study. The case study focuses on the structural and thermal evolution of the Gjallar Ridge, a structural high in the Norwegian Sea that was uplifted to sealevel during the last rifting phase. The key findings are: (i) all discussed uplift mechanisms show characteristic structural and thermal evolutions that can potentially be used to discriminate between them, (ii) mineral phase transitions can enhance mantle thinning induced uplift, (iii) uplift of the Gjallar Ridge is explainable by different scenarios but phase transitions and differential thinning appear the most likely, and (iv) integrated basin modeling is key for discriminating between different uplift scenarios.
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Early Foreland Basin Depositional Evolution in NW Zagros from Latest Cretaceous to the Early Eocene
Authors E. Saura, J.C. Embry, J. Vergés, S. Homke, D.W. Hunt, E. Casciello, N. Fernández, G. Casini, J. Serra-Kiel and G. BernaolaWe present an analysis of the evolution of the eastern Lurestan arc after own detailed paleobathymetric and thickness maps, based on paleofacies analysis and dating of our own field stratigraphic logs and existing borehole data. Integration of these maps in a geomodel was used to generate step-by-step subsidence maps, which illustrate a south-westward migration of the basin depocenter. However, WNW-ESE trending, relatively uplifted areas can also be recognised in the internals parts of the basin, which fit the location of the main anticlines of the area. These uplifted areas migrate to the SW and we interpret them as recording an early folding stage, spanning at least from the Maastrichtian to the early Eocene.
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Kopet-Dagh Basin Evolution During Middle-late Jurassic
Authors M.A. Kavoosi, M. Sepehr and S. SherkatiIn this paper with the help of latest available data including field, well and seismic data, palaeoenvironments and depositional sequences of Kashafrud, Chaman Bid and Mozduran formations constructed in order to determine the basin evolution of the Kopet-Dagh during Middle-Late Jurassic. Our study reveals that wedge-shaped sedimentary units, onlap surfaces, high sedimentation rate along with deepening- and fining-upward, assign extensional regime as the result of rifting during Middle Jurassic. The sequence of initial rapid continental stretching during the Middle Jurassic, followed by slower and thermally driven subsidence in the Late Jurassic. Tectonosedimentary evolution of the Kopet-Dagh Basin during Middle-Late Jurassic has a great interest for the future exploration and production in this rich but poorly understood hydrocarbon province.
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Origin of Gaseous Hydrocarbons of the Outer Carpathians and Palaeozoic-Mesozoic Basement in Southeastern Poland
By M.J. KotarbaNatural gases accumulated both in the Polish Outer (Flysch) Carpathians and the Palaeozoic-Mesozoic basement are genetically related to thermogenic and microbial processes. Thermogenic gaseous hydrocarbons accumulated in the Dukla and Silesian units were generated from Type-II and -II/III kerogen of the Menilite Shales. Thermogenic gaseous hydrocarbons accumulated in the Sub-Silesian Unit migrated from the Silesian Unit. Natural gases accumulated in traps within the Middle Devonian, Lower Carboniferous and Upper Jurassic strata of the Palaeozoic-Mesozoic basement were mainly generated during thermogenic processes and only sporadically during microbial processes. The themogenic gases accumulated within Palaeozoic complex were generated from Type-II kerogen of the Ordovician-Silurian strata and gases accumulated within Mesozoic complex from Type-III (II/III) kerogen of the Middle Jurassic strata. In some traps within the Dukla and Silesian units of the Outer Carpathians and Palaeozoic-Mesozoic basement had already been formed and sealed as early as the initial, microbial transformation stage of the source rocks. These traps were successively supplied with thermogenic gaseous and liquid hydrocarbons generated from the same source organic matter at successively higher maturation stage.
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Acoustic Emission Associated with the Formation of Sets of Fractures in a Sandstone
Authors M.S. King and W.S. PettittA laboratory ployaxial loading system has been employed to study acoustic emission (AE) associated with the failure of a sandstone specimen. The minor principal stress is maintained at a low level, while the two other principal stresses are raised until failure takes place. The AE events associated with the formation of micro-cracks, and resulting through-going fractures, are located precisely by an array of AE sensors in each of the loading platens. The mechanisms indicate tensile failure during initial fracture failure, but shear failure as the fractures approache the platens.
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Seismic Facies Analysis Based on K-means Clustering Algorithm Using 3D Seismic Attributes
Authors H. Sabeti and A. JavaherianIn seismic interpretation, clustering seismic data can be used to extract more information about structures and geology of underground units. In this paper, an efficient clustering method called k-means clustering algorithm is utilized to categorize seismic facies based on seismic attributes. By a given k value (i.e. the number of clusters), k-means clustering algorithm uses an iterative algorithm that minimizes the sum of distances from each sample to its cluster centroid over all clusters. This algorithm moves samples between clusters until the sum cannot be decreased further. The result is a set of clusters that are as compact and well-separated as possible. By applying this method over a synthetic seismic cube it is concluded that lateral changes in layer boundaries are detectable. In the case of real data, in order to increase the information needed for clustering, eight seismic attributes were calculated using Paradigm software. By applying k-means clustering algorithm to real dataset, it is shown that more seismic facies appears by increasing the k value and this leads to extract useful information about underground beddings.
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3D Pore Pressure Prediction Using Seismic Data in an Oil Field in SW Iran
Authors P. Hadian, E. Nosrat and M.R. TorabiThe pore pressure prediction method based on seismic velocity field is a common method for constructing a 3-D pore pressure cube. In this study, the resolution of stacking velocity was improved using sonic logs and a geostatistical calibration method. In this calibration procedure, the differences between velocity derived from sonic logs and stacking velocity were calculated and, then, the calibration parameters were obtained. These parameters were interpolated in the velocity grids. Effective pressures were calculated using the measured pore pressures and the calculated overburden pressures at well locations. The coefficients of Bowers equation were calculated using well data. Using the Bowers equation the calibrated stacking velocity cube was converted to the effective pressure cube. The pore pressure cube was constructed by computing the differences between the overburden pressure cube and the effective pressure cube. Finally the predicted pore pressure cube was calibrated with regard to the measured pore pressures at well locations. In the area of study, the stacking velocity was improved and, then, the pore pressure cube was made accordingly. The predicted pressures show good agreement with regard to the measured pressures at well locations.
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A New Technology for Enhanced Hydrocarbon Production
Authors I.G. Kerimov and S.I. KerimovOur Technology has an aim of equal influence on medium in order to save oil deposit, increase oil production and recovery and minimize negative effects from outside impacts. This Technology is capable resolving these problems successfully and with the high rate result.
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Determination of Bin Size and Migration Aperture in 3D Seismic Survey Design for AHWAZ Oil Field
Authors E. Pegah, B. F. Aghaei, A. Javaherian and D. NowrooziIn oil exploration, because of anisotropy of the earth, velocity of the waves in horizontal and vertical directions are not uniform; but we can apply the assumption with good accuracy in exploration procedure that in a layer, velocity changing is limited as a result of slow variation in density and elastic properties of the layers in this horizontal directions. In general, variation of above parameters in horizontal directions is very slowly than vertical directions. For this reason often divide acquisition area to smaller areas and ignore horizontal variations and apply same vertical velocity distribution in any sub-areas. Conventional formula for Bin size and migration aperture is based on constant velocity assumptions. In this paper calculation of Bin size and migration aperture for AHWAZ oil field is carried out base on linear model between velocity and depth. On the other hand Bin size and migration aperture have the firstorder effects on acquisition and processing cost, thus method of this paper steer to optimize and reduce the cost of acquisition.
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Direct Detection of Hydrocarbon by Matching Pursuit Decomposition in One of the Reservoirs of South West Iran
Authors M. Radad, A. Javaherian, B. N. Araabi and M.R. TorabiSpectral decomposition has many applications in processing and interpretation of seismic data. In present, there are several methods for spectral decomposition. Each of spectral decomposition methods is useful for a special application, but it has been proved that matching pursuit decomposition has more efficiency in various cases. In the present work, the performance of matching pursuit decomposition was compared with STFT and CWT methods in improving the resolution of thin beds and studying the tuning effect on synthetic data. Moreover, efficiency of MPD method has been shown to detect hydrocarbon directly in oil Bearing sandstone reservoir at south west area of Iran.
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Estimation of Well Log Data by Conjunctive Use of Seismic and Petrophysical Data (Hendijan Oil Field, Iran)
More LessWell logs are of the important tools for reservoir characterization. Parameters such as porosity, volume of shale, water saturation, permeability, lithology and production zones could be computed from processing and interpreting of well logs. Such information is obtained from petrophysical logs. Considering coverage and continuity of seismic data, log estimation in each location of reservoir by using seismic data, not only before the drilling but also after it will be applied and invaluable. So that using the predicted wells log from seismic data, reservoir evaluation and assessment over the seismic data coverage is possible. In this research, a formulation is established between well log data including sonic and density logs and their corresponding seismic attributes using neural networks in Hendijan oil field, Persian Gulf. For this purpose, optimal input seismic attributes were obtained using a forward stepwise regression. The results show a good agreement between measured and neural network predicted data at test wells. So, the estimated well logs could be used for reservoir parameters evaluation and reducing risks of future exploration and field’s development. Also such predicted well logs enable us to gain more vital parameter about a reservoir.
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Seismic Velocity – Reservoir Permeability Relations within Hydraulic Units in an Oil Field Southwest Iran
Authors M. Emami Niri and A. MisaghiEstablishing a relation between permeability and velocity has met with little success so far. Different types of uncertainties usually make this relationship not very straightforward. Categorizing the pore systems in different hydraulic units may reduce the uncertainties. This study tries to improve characterization of a carbonate reservoir with complex pore systems which is located in southwest of Iran. A combination of classification methods was used to build a robust determination of Hydraulic Units using porosity and permeability values. Then the concept of grouping porosity and permeability data according to their FZI (Flow Zone Indicator) values were tested. It was shown that such relation can be extended to seismic parameters to create strong correlation between velocity and permeability. Strong correlation between P and S waves' velocity and permeability in this field was observed, i.e. the correlation coefficient for Vp-Permeability lies between 0.72-0.96 and for VS-Permeability lies between 0.62-9.98. Such a relation is invaluable as a prediction tool. We understood that by grouping rocks into hydraulic units, we can control and predict flow properties such as permeability via seismic velocity in this field.
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Seismic Attribute Redundancy Reduction Using Statistical Feature Extraction Technique
Authors H. Hashemi Shahdani and A. JavaherianCombining seismic attributes and building a meta-attribute section is a useful stage for seismic object detection (fault, gas chimney and …), seismic facies analysis and many other applications. Many seismic attributes used in classification tasks are redundant, which yield a useless higher-dimensional feature space. In this paper, a criterion based on RDA with two sub-optimal forward and backward algorithms is presented to accomplish this problem. Then, classification based on four different MLP neural networks is done and the average error is plotted versus the ranked feature space. As a flexible method, the algorithm introduces dissimilar ranks as the training set changed by the user. This makes it possible to introduce several seismic attributes in input stage of the classification. Based on the proposed training set, the interpreter can find the most important seismic attributes for the classification.
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Side View Seismic Location Method Helps Fracture Characterization in a Giant Fractured Carbonate Heavy Oil Field in Iran
Authors A. Shafiei, M.B. Dusseault and B. Samimi-SadehKuh-e-Mond heavy oil field is the largest onshore naturally fractured heavy oil carbonate field in Iran with a resource base of 6-10 Bb OOIP. The heavy oil is found in two formations with oil viscosities of 570-1160 cP in situ. Having a clear picture of the natural fracture fabric of the reservoir will help petroleum engineers and development geologists to determining orientation and flow characteristics of the dominant fracture sets in order to optimize production well placement. In this article, results from fractured media investigations using the Side View Seismic Location (SVSL) method are presented. The SVSL results indicate a transversely oriented zone of minimum values of open fracturing in the NW part of the field, which separates the field into two isolated blocks. The SE part is characterized by a high concentration of abnormally fractured zones and is considered to be the most promising area for primary field development. Based on this study a number of suitable locations for production well placement are proposed. Also, implementing proper down-hole operations in some of the existing wells are recommended to further assess the fabric and arrive at a development strategy.
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Quantitative Seismic Attributes in a Fractured Reservoir
Authors S.M. Haghighi and E. AngererSeismic attributes provide critical information in characterising the heterogeneous fractured basement reservoir of the presented case study. Azimuthal anisotropy caused by open subseismic scale fracture networks is directly linked to the hydrocarbon production of existing wells. Further, acoustic impedance inversion shows the distribution of an additional, thin productive layer that was considered below seeismic resolution.
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Application of Seismic Attributes for Identification of Gas Hydrate Bearing Zone and Free Gas Beneath it
Authors B. Hosseini Shoar, M. Sadiq Arabani and A. JavaherianGas hydrate is an ice like form of concentrated gas (>99% methane) and water found in the sediments of permafrost regions, marine continental margins and seafloor of deep sea at depths far shallower than conventional oil and gas. The first indicator of gas hydrate in deep sea is bottom simulating reflector (BSR). BSR approximately mimics sea-floor and cuts across reflection of statigraphic origin and have reverse polarity respect to seabed reflection. A second significant seismic characteristic of gas hydrate-cementation is called amplitude blanking. The presence of hydrate and free gas change the seismic properties of host sediments. Relative acoustic impedance and absorption quality factor attributes can be used for analyzing them. In this study, we have analyzed the gas hydrate indicators in 2-D seismic sections of deep sea sediments of Iran with seismic attributes.
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Multiple Attenuation by F-X Parabolic Radon Transform
Authors V. Minaeian, A. Javaherian and A. MoslemiMultiples constitute one of the most troublesome forms of coherent noise in seismic exploration. Multiple reflections often destructively interfere with the primaries of interest. Therefore, suppressing multiples from reflection seismograms during processing stages is necessary. Radon transform is a robust tool for suppressing multiples from seismic data. The key idea in Radon based multiple attenuation is to map the CMP gather to a new domain where seismic reflections collapse to point-like events and, therefore, primaries and multiples are separable. The time invariant parabolic Radon transform is widely accepted for multiple suppression. The benefit of time invariance is that the computations can be performed in the frequency-space domain and so the computational costs are reduced. In this procedure, the first step is to replace hyperbolic events in offset domain with parabolas by applying NMO correction using velocities of primaries. In the next step, the data are transformed to the Radon domain by stacking amplitudes along parabolic trajectories. In this paper, a MATLAB coding for multiple attenuation using the parabolic Radon transform has been implemented and successfully applied on a synthetic model and a real data set. KEYWORDS: Radon transform, multiple attenuation, SNR enhancement, coherent noise
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Rayleigh Wave Suppression in the RT Domain
Authors J. Jamali, M. Bagheri, M.A. Riahi and Z. FarajporAlways on seismic data record, reflection event will be masked with Ground_roll and observation of this event is not usually easy. Radial trace transform is a simple transform for mapping x-t gathered data into apparent velocity and travel time domain. The apparent frequency of Ground_roll will be changed completely in RT domain. With knowledge of this changes and the application of frequency filters in RT domain, these events can be attenuated. In this paper the result obtained from F-K method and RT method on one common shot gather acquired from oil field has been compared. The results showed that the RT filters is much better attenuate those events with respect to F-K method without much reducing amplitude spectrum.
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Solving the Problem of Conflicting Dips in Common-Reflection-Surface (CRS) Stack
Authors M. Soleimani, I. Piruz, J. Mann and P. HubralCRS stack procedure is a data-driven imaging method which is independent of an explicit velocity model. The pragmatic search strategy for CRS attributes consists of three one-parameter searches. This implementation determines only one optimum stacking operator for each ZO sample to be simulated. Consequently, conflicting dip situations are not taken into account. In one of the efforts to overcome this problem, the strategy has been extended in order to take into account up to five conflicting dips at each sample. Here, we propose a strategy which considers all possible angles and, thus, accounts for all the conflicting dips that may exist at one sample. This strategy has some advantages that improve the continuity of reflection events as well as diffractions in the presence of conflicting dip situations. It also generally emphasizes diffraction events in the stacked section such that we may call it common-diffraction-surface stack. Here, we processed the Sigsbee 2A synthetic data and a real land data set with the new method. The stacked result of Sigsbee 2A and the results of the poststack depth migration of the real data also proved that the stacked section of the CDS stack is a suitable input for migration.
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Using Singular Spectrum Analysis and Autoregressive Methods for Improvement of Temporal Resolution of Seismic Data
More LessOne of the goals of seismic processing is to improve the temporal resolution of seismic data. Seismic data usually have not enough temporal resolution because of band-limited nature of source signatures. In this paper we introduce a method in which we extrapolate deconvolved seismic spectrum for recovery of missed frequencies. The introduced method takes a certain part of both real and imaginary parts of the spectrum, where S/N is high compare to the rest of the spectrum, and extrapolates lower and higher portions of the spectrum using Singular Spectrum Analysis (SSA) and Autoregressive model. The selected part of spectrum is decomposed into some principal components. Each principal component has periodic pattern without trend, a narrow band frequency spectrum, and well defined characteristics to be extrapolated. After extrapolation of each principal component, the spectrum is reconstructed by combining the associated extrapolated principal components.
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A Novel Drilling Fluid for Underbalanced Drilling
Authors E. Karimyan, H. Dashtian and K. ShahbaziInterest in underbalanced drilling is growing worldwide. UBD, when properly designed, eliminates problems associated with the invasion of particulate matter into the formation. However, experience has indicated it is difficult to maintain a condition of continuous underbalance pressure throughout the complete drilling operation, resulting in fluid losses to the formation due to no mudcake on the borehole wall and leading to possible significant damage. So, in this paper a new drilling fluid was developed. It contains a kind of nanomaterial particles called Carbonblack. It is currently the most widely used carbon nanomaterial. This is the first time which Carbon block particles are used as a drilling fluid. Insoluble Carbon black maintains its individual particle identity through high levels of pressure. Coated with lubricant, the ultra-fine particle size penetrates openings and scratches not normally penetrable with other solids in the drilling fluid system. When overbalanced situation is happening, the Carbonblack particles can bridge and form a thin plugging layer as soon as possible in the pores or fractures in the borehole wall. This plugging layer can stop further fluid invasion into the formation.
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Underbalanced Drilling Technology, the Key for Solving Drilling Problems
Authors A. Shadravan, M. Khodadadian, K. Shahbazi and A. RoohiRS 12 well is the twelfth well in the 2 year underbalanced drilling project involving NIDC and Weatherford. NIDC supplied the UBD equipment and Weatherford supplied the UBD expertise to assist NIDC personnel on UBD techniques. National Iranian South Oil Company was the operating company whose oil wells were drilled under the contract between NIDC and Weatherford. RS 12 is a deviated well with the 9 5/8" casing shoe at 2,138 m and 7" liner shoe at 2,328 m and 5" liner shoe at 2824 m. The UBD interval will be from 2,905 m to TD of 3,250 m. Underbalanced conditions will be established by injecting nitrogen gas down the drill string along with native crude four objectives.
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Underbalanced Drilling in Depleted Formation Achieves Great Success: A Case Study
Authors A. Shadravan, M. Khodadadian, A. Roohi and M. AmaniThe drilling technologies have evolved over the years. The prime reasons for the advancements in these technologies are the ever increasing demand for energy and the increase in ‘energy price’. Underbalanced drilling (UBD) is gaining popularity as a drilling methodology to overcome some of the problems encountered in conventional overbalanced drilling. UBD was initially adopted for resolving drilling problems; it is defined as a drilling operation where the pressure of the circulating drilling fluid is lower than the pore pressure of the target formation of interest. By far, it has also been proved that the advantages of underbalanced drilling are most evident in depleted reservoirs. Well Parsi 70 was the 3rd well of National Iranian Drilling Company (NIDC) UBD campaign in Parsi oil field. Well PR 70 is the first well that produced while drilling.
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Wellbore Stability Analysis in UBD Wells of Iranian Fields
Authors S. Salehi, H. Emadi Baladehi, A. Mojdeh and R. Darvishi1. Severe lost circulation during overbalanced drilling condition is reported during drilling depleted carbonate fields in Iran, for this reason using the underbalanced drilling technique with proper wellbore stability analysis is recommended for drilling in these fields. 2. An elastoplastic model combined with a finite explicite code was used for mechanical wellbore stability analysis of underbalanced drilling technique in two depleted Iranian fields. Based on the results and compared with field data using elastoplastic models gives good predictions for wellbore stability in these fields. 3. A criterion based on size of yielded zone or NYZA (Normalized Yielded Zone Area), was used to assess stability condition. Based on the simulation results and for keeping UBD condition in most of the time the critical value of NYZA was adjusted to 1.20 instead of unity in Iranian carbonate fields. Choosing this critical value an ECD of 5.06-5.30 Lb/Gal was proposed for drilling the well in field A.
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Integrated Modeling of the Crust and Mantle Structure in the Zagros Fold and Thrust Belt and the Mesopotamian Foredeep
Authors M. Fernandez, J. Vergés, I. Jiménez-Munt, J. Fullea, H. Zeyen, M. Pérez-Gusiñé and D. García-CastellanosThe Zagros mountains formed by collision between Arabian and Eurasian plates from Miocene times. The region is characterized by intermediate seismicity, a low mantle velocity, a deep foreland basin, and an irregularly folded sedimentary cover. Despite extensive acquisition of geophysical data major unknowns are related to i) the nature of the crustal deformation during collision and the resulting crustal structure; ii) the existence of a mantle root and the possible strain partitioning between crust and mantle lithosphere; and iii) the basement deflection caused by the building of the Zagros mountains and the associated deep geometry of the foreland basin. These items are addressed in two ways. An integrated approach, combining the use of gravity, geoid and absolute elevation allows us to infer the 3D regional crustal and lithospheric structure. The resolution of the gravity inverse problem for that lithospheric configuration allow us to separate the regional and local field components which, in turn, allows for a more detailed 2D lithospheric modelling along selected geotransects. These geotransects are constrained by existing seismic profiles, surface elevation, gravity and geoid data. The crustal and lithospheric structure is modelled by using a numerical code that simultaneously solves the geopotential, lithostatic, and heat transport equations.
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Determinnig of Optimum the Length of Profile in Normalized Full Gradient Method
Authors H. Aghajani, A. Moradzadeh and H. ZengLength of profiles and number of stations for measuring gravity anomalies play an important role in the amount of cost for exploration projects. Also, length of profile relates to estimate of depth to anomalous bodies. Normalized full gradient (NFG) method applied to detect bodies is a special downward continuation of gravity anomaly. This method eliminates the perturbations which appeared during downward continuation when passing through mass depth. In this study, in order to determine the optimum length of profile for measuring gravity effects due to anomalous body, a horizontal cylinder with a known radius and depth have been used to produce synthetic anomalies to calculate NFG values on different profiles. The results show that the length of the profile and dimension of the area should be 13 times greater than the expected depth of the study to determine the depth of anomalous body with the least error.
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A 3D Forward Method for Modeling Magnetic Anomalies Due to Tabular Bodies
Authors H. Jahandari and V. Ebrahimzadeh ArdestaniThis paper presents a new method for computing the magnetic anomaly due to a tabular dipping body, based on approximating a dipping prism by a large number of rectangular prisms. The magnetic anomaly due to this body would be the sum of anomalies resulted from all the small prisms. To test the efficiency of this approximation, we generate the 3-D synthetic anomaly due to a known dipping prism, perform a forward modeling scheme on these data using approximated models, and compare the resulted parameters with the known parameters of the dipping prism. In order to corrupt the synthetic data, we add pseudorandom noise with zero mean and standard deviation of 10% of the datum magnitude. To perform the forward modeling we use a FORTRAN program that inputs the ranges due to different parameters, calculates the anomaly for all possible conditions inside the ranges using the discretized body model, and chooses the best fit parameters. The remanent magnetization information, if available, can be incorporated into the modeling scheme. To show the practicality of this method, we apply the modeling on a real field magnetic data set from Zanjan province in the North-West of Iran.
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Geostatistical Modeling of Radiometric Survey Data, Using Sequential Gaussian Simulation
By M. JamieA radiometric investigation has been done in Bandar-e-Abbas in the south of Iran. Geostatistical analysis, using WinGsLib, have been performed in order to model the anomaly distribution. As geostatistical estimators result more reliably in normal distributions, raw data were normalized by normal scores method. By drawing variograms in four major directions, the trend due to maximum anomaly concentration can be determined. The trend azimuth of 45 degrees shows hole-effect, indicating obvious cyclic-bedding with a hole effect signature which could be well interpreted by the rhyolit, gypsum sequential bedding. Because of geometrical anisotropy, the direction of maximum and minimum continuities must be defined. By drawing the 2D plot variogram map, these directions are shown to be 315 and 45 degrees respectively. Afterwards, the best theoretical model, here a spherical one, fits into these two directions. The map resulted from 100 Sequential Gaussian Simulations(SEG)was drawn. In order to reduce uncertainty resulting from simulations E-type map of 100 simulations was drawn. Also, by cross validation method, the estimation error histogram was drawn to assess geostatistical estimation accuracy. The cross-plot of estimated values versus true values shows the correlation coefficient of 82 percent which is desirable.
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Integrated Rock Typing in Asmari Formation of Gachsaran Field
Authors V. De Groen, M. Fuchs and S.M. MirzadehAs part of an integrated reservoir modelling and simulation project, a rock-typing study has been performed on the carbonate Asmari Formation of Gachsaran Field (Iran). The current paper presents the challenges and results of integrating different disciplines in the definition of rock-types. Rock-types represent geological aspects such as stratigraphy, log facies and porosity, but their true added value is the dynamic characterization of facies and strong link with geology, which allows spatial distribution. This study has allowed definition of integrated rock-types representing geological facies and groups with similar dynamic rock properties, and identifying these from their log signature. As log data is much more abundant and presents a good spatial distribution over the field, this is the ideal means to refine the conceptual geological models (sedimentary environment, stratigraphy, diagenesis) and trace the extent of stratigraphic sequences. These subsequently allow propagating the rock-types away from the wells, and combined with the dynamic rock properties, allow simulation of these properties in a 3D reservoir model. The definition has resulted in a classification of 10 rock-types with a unique set of geological, log and dynamic properties along some 150 wells.
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The Prediction of Permeability in a Carbonate Reservoir Using Adaptive Neurofuzzy Inference System
Authors Y. Beiraghdar, M. Nabi-Bidhendi and C. LucasIn this paper a new approach for the prediction of permeability from well logs is presented. It is based on adaptive neurofuzzy inference system (ANFIS) which is fuzzy inference system implemented in the framework of adaptive networks. A combination of back propagation and least-squares method referred to as hybrid learning method is applied to estimate membership function parameters of fuzzy inference system and learning purpose of ANFIS. The constructed model is optimized for the number of epochs to avoid overfitting and to provide maximum generalization by considering the error index of validation sets during training. To verify the effectiveness of the methodology, a case study in one of the carbonate reservoirs of Iran is carried out. Core and well-log data from two wells that are located in the center of the field provide the data for the learning task. Model validation of proposed ANFIS model is implemented by using core permeability and well-log data from a third well that is located on the corner of the field. Numerical simulation results show that the adaptive neurofuzzy inference system is capable for the prediction of permeability.
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Stochastic Porosity and Shale Percentage Modeling Controlled by Different Seismic Attributes
Authors S. A. Miri, M. Yousefpoor and H. PourhosseinAcoustic Impedance (AI) as a densely sampled data from seismic is traditionally used to guide modeling of reservoir properties. In this study, a new approach is tested and other seismic attributes such as instantaneous phase and quadrature amplitude will help modeling of porosity and shale percentage. Ilam Fm in the Sirri D Oil Field which is an Iranian offshore carbonate reservoir is studied in this work. The spatial directional variogram analysis is done for each zone of Ilam separately. The stochastic methods, Sequential Gaussian Simulation (SGS) and also SGS with a seismic trend are used and their results are compared in this work. The seismic attributes showed a correlation coefficient of 40 % with porosity and 60% with shale percentage for the zone 5 that is the main oil-bearing zone and the modeling is focused on this zone. To validate the models, some wells were dropped out, and the modeled results were compared with the actual well values. When a seismic trend was used as a secondary variable, the SGS algorithm generally yielded better results. This study suggests that in absence of AI, other seismic attributes can be helpful for the reservoir property modeling.
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New Methodology for Estimation and Sensitivity Testing of STOOIP in Carbonate Reservoirs: The Pore-type Concept
By ARVE LonoyTraditional methods for estimating STOOIP (Stock Tank Original Oil In Place) is based on the use of average input parameters for different reservoir zones, and by the application of a variety of cut-offs in net-to gross evaluations. This methodology creates a significant uncertainty in the STOOIP calculation, especially related to saturation and to the application of cut-offs. A new methodology has been developed for estimating matrix-related STOOIP and for predicting the sensitivity of the estimates. This method does not apply fixed input parameters, but uses measured and/or predicted, pore-type related input parameters that vary continuously through the reservoir. Well data are normally preferred as input data, although it is possible to use data from geological models. The methodology is to a large degree based on pore-type control of reservoir parameters. The new methodology has been applied to a Middle East oil field, and STOOIP estimates are significantly different to those obtained from traditional methodology.
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Determination of Reservoir Rock Fracture Properties Using Wireline Logs
By A. HeidariThis fracture study focuses on the Asmari Formation of south-western Iran. The FMS (Schlumberger's Formation Micro Scanner) data were analyzed for dip azimuth, dip, height and quantity of the fractures. The fracture width was measured from the FMS images and flushed zone resistivity (Rxo) after which, fracture porosity was calculated. Fracture properties distributions were similar to those of published work. The evaluated fractures exist in sets and assemblages and the majority of them lay along the axis of the fold. Finally a fracture log was made, plotted versus open-hole logs and correlated to mud loss and PLT logs. The good correlation shows the contribution of fractures to oil recovery.
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Geostatistical Modeling of Permeability by Simulated Annealing in Clastic Reservoirs
Authors S.S. Zabihi and S.K. ShiroodiAboozar oil field is located approximately 72 km west of Khark Island in offshore Iran. The main reservoir of this field is an Oligo-Miocene stratum called Ghar which is a member of Asmari formation composed of loose sand with thin beds of shale. The present study developed the application of simulated annealing to generate stochastic model of Ghar permeability. Simulation of permeability of Ghar is based on porosity model which can be considered as secondary variable. Ordinary Kriging was used to construct the porosity model. In order to perform ordinary kriging to determine spatial distribution of porosity, 10 experimental variograms were calculated. Variograms show that the porosity in Ghar sand has both zonal and geometrical anisotropy. Then by using porosity model and permeability data of available data, 100 realizations of permeability distribution was generated by simulated annealing. At the end 3D probability model was generated from all realizations. By this model high permeable zone which indicate high reservoir quality was determined.
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Diagenesis of the Asmari Formation (Oligo-Miocene; SW Iran): Implications on Reservoir Modelling of a Giant Oilfield
Authors F. H. Nader, M. Moradpour, P. Samani, Y. Hamon, A. Hosseiny, J.M. Daniel, A. Moallemi and N. PickardThis contribution refines the diagenetic evolution of the Asmari Formation (Oligocene – Early Miocene) in southwest Iran. It presents diagenetic maps providing invaluable data for assessing reservoir heterogeneities and optimising rock-typing. The major results of this work bridge the gap between classical geological study (which includes conceptual dolomitisation models, burial history and paragenesis) and the actual reservoir heterogeneity encountered in the investigated field and demonstrated by the production distribution. Diagenetic maps (Limestone %, Dolomite %, Anhydrite %, Total Porosity %, Dissolution Porosity %, Cementation %) covering six stratigraphic intervals that are bounded by key sequence stratigraphic surfaces reveal spatial and vertical distribution characteristics in the investigated oil field. Integrating these diagenetic maps shows dolomite, anhydrite, porosity and dissolution relative distribution across the study area and per stratigraphic interval, resulting in better understanding of the diagenetic processes and their products. Thus, a comprehensive, generalized diagenesis model explaining the reservoir properties evolution prior to oil charging was succeeded.
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Secondary Porosity Evaluation on Permeability Forecasting Using Fuzzy Logic and Neural Networks in Heterogenic Carbonate
Authors M. Khanian, M.A. Riahi, S.K. Shiroodi and M. RezaeiDirect measurements of permeability through core analysis and well test are expensive and may not be possible for all boreholes, whereas all wells are almost petrophysicaly logged which permeability from open-hole logs can be estimated. One of the major challenges in carbonate formations is to analyze and quantify non-effective pores like secondary porosity. If this can be achieved, permeability evaluation will be more accurate. For this purpose, three wells of the Iran offshore Balal oil field were chosen; the focus of interest was Surmeh (Arab) formation. The permeability estimation model was built in well BL-1P through core and well logs data using two methods fuzzy logic and back propagation neural network (BP-ANN). Moreover, secondary porosity index (SPI) was calculated and imported in the model. This model was applied to predict permeability in control wells 3I and 3W-2. The outputs were cross checked against core data. The results of this study showed that fuzzy logic prediction was a bit better than ANN and in accordance with elimination the effect of discontinuous porosity after adding SPI, the prediction became better.
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Fractured Reservoir Characterization and Modelling of a Basement Field in Yemen
Authors P. Neff, Y. Boisseau and R. BischoffThe characterization and modelling of a basement field in Yemen was achieved through the creation of a reservoir model. This reservoir model consistently integrates the available data, 2D seismic lines, borehole interpreted images, classical log suit and core data to allow capturing flow characteristics and establishing relevant production forecasts for the field development. Considering the geological context of this field, a particular attention has been given to characterize the fracture network and its associated flow behaviour. This paper describes the implemented approach starting with the creation of a structural model. Then the analysis of fracturing related data that lead to the development of a conceptual model for the fracture network. Finally the realisation of a Discrete Fracture Network DFN model in accordance to the developed concept and calibrated towards dynamic data allowed establishing key production characteristics of the field.
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The Effects of Far-field Stress in Multiphase Flow Simulations in Naturally Fractured Reservoirs
Authors J. Xiang, M. Belayneh and J.P. LathamGeomechanics plays a very important role in understanding and predicting the behaviour of naturally fractured reservoirs (NFRs). In order to develop the predictive capability of the physical phenomena that occur in NFRs including compaction related to production, reservoir subsidence, induced fracturing, reactivation of pre-existing fractures and faults, the interaction between rock matrix and the fractures, it is necessary to couple reservoir simulations with geomechanics. In this study, we present a novel approach which considers both the static and dynamic behaviour of the fracture network based on length, orientation and their spatial distribution. For simulating single phase and multiphase flow simulations, we use combined Finite Element – Finite Volume Method in which the pressure equation is solved using the finite-element method and the transport equation using finite-volume method. For capturing the dynamics of the fractured system, we apply Combined Finite-Discrete Element Method with combined single and smeared crack model, that has the advantages of both continuum and discontinuum techniques to simulate intact behaviour, the initiation and propagation of new fractures, and reactivation of pre-existing fractures. We use realistic fracture geometries to compare changes in the static and dynamic behaviour by varying the magnitude and orientation of far-field stresses and boundaries conditions.
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Porosity Type and Distribution in the Shu’aiba Reservoir, Southern Iranian Persian Gulf
Authors S. Reali, A. Ortenzi, D. Sartorio, R. Galimberti and F. RighettiThe Late Aptian-Early Albian unconformity, widespread in the Persian Gulf, marks the boundary between a seal facies, Nahr Umr shale, and carbonate units belonging to the Upper Thamama Group. The latter includes the Shu’aiba Formation, a major hydrocarbon bearing reservoir in several Middle East giant fields. At regional scale the gross facies distribution can be referred to a carbonate ramp. Depositional textures controlled the predominant secondary pore type, while the overall reservoir properties seem related to diagenesis. In order to establish the role played by depositional environment and diagenesis process on the Shu’aiba reservoirs, data from cored wells Alpha 1, Alpha 2, Rakish 6, IM-R4 and IM-O2 (Central Gulf, Iranian waters) have been studied. The early diagenetic evolution of the Shu’aiba Formation was dominated by fresh water influx as a consequence of the emersion during Late Aptian-Early Albian time, as indicate by stable isotope of Carbon and Oxygen and trace elements analysis. This influx determined secondary porosity and cementation. The late diagenesis is represented by minor dolomitization along fractures and by a probable porosity enhancement linked to H2S as a product of TSR, which is proved by the presence of thiaadamantanes.
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Heterogeneity of High Temperature Dolomite (HTD) Reservoirs in the Sarvak Formation, Anaran Anticline, Ilam, Islamic Republic
Authors F. Lapponi, A. Amilibia, J. Garland, P. Gillespie, D. Hunt, T. Needham and I. SharpSpectacular outcrops of dolomite of hydrothermal origin are described from the Anaran Anticline, in the Simply Folded Belt of the Zagros Mountains, Ilam province, SW Iran. Dolomite replaces Cretaceous carbonates of the Upper and Lower Sarvak formation (Albian to Turonian). The typical paragenetic association includes a matrix replacing dolomite phase followed by a void-filling saddle dolomite. Both are interpreted to be of hydrothermal origin. The contact between dolomite and precursor lithology is typically sharp on the scale of the outcrop, with contacts being both stratigraphically, structurally and diagenetically (reaction front) controlled. Dolomite bodies in both the Lower Sarvak and Upper Sarvak have been described and sampled systematically in order to constrain lateral and vertical textural and poro-perm variations. Systematic collection of structural data has also been undertaken to evaluate the possible control of fractures (joints + faults) on fluid flow, and to place constraint on the timing of the dolomitisation event within the geological evolution of the Zagros Mountain belt. Comparison between fracture pattern inside and outside the dolomite bodies is taken into account to evaluate a possible impact on reservoir modelling.
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A New Analytically Derived Shape Factor for Gas-oil Gravity Drainage Mechanism
More LessMatrix-fracture exchange term is an important parameter in simulation of NFR using double porosity concept. Matrix block located in gas-cap is going to be produced under gravity drainage retarded by capillary force. Hence, oil can be produced as long as gravitational force is greater than capillary force. Interaction of these forces which controls oil production from matrix block may be expressed by a factor named matrix-fracture transfer shape factor. Customarily, this factor has been used as history matching parameter because it isn’t still well understood and formulations used in commercial simulators arenot precise. Therefore, a mathematically derived shape factor reflecting gravity drainage behavior into exchange term using shape factor concept is essential. Traditionally, constant shape factor has been used in most of commercial reservoir simulators. Here, we use analytical modeling to develop a time dependent shape factor for gas-oil gravity drainage mechanism for a single matrix block in gas-cap. Obtained model is verified against several fine-grid numerical simulations as well as two major existing models being used in commercial simulators. Results obtained here will improve understanding of gas-oil gravity drainage in NFR and will find application in more accurate representation of process.
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Cold Production from a Fractured Carbonate Heavy Oil Reservoir in Iran - Case Study
More LessA successful case study on a carbonate heavy/extra-heavy oil field is presented and the techniques and challenges behind the production from highly fractured carbonate Bangestan reservoirs are discussed in this study. The field consists of two fractured carbonate reservoir with about 3.6 billions barrels of initial oil in place of 7.5-18º API heavy/extra heavy oil. The oil viscosity at reservoir temperature (139.3 oF) is around 700-800 cp. The pressure is 927 psi at 1119 mdd but heavy oil does not naturally flow to the surface. Based on field conditions and reservoir characterization, it was decided to implement initially cold production by two experimental methods of lifting with no injection but only swabbing and use of PCP (Progressing Cavity Pumps). simulation showed a good match with the further field data when the cold production scenario was employed. The challenges and techniques employed on field pilot including various techniques of production are summarized and optimized production methods of cheaper lifting procedures of heavy oil to surface is described. Consequently lifting heavy and extra heavy oil to surface using PCP is applicable for this field in stage of cold production prior to any expensive and complicated thermal method implementation in future phases of production.
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Formation of Traveling Liquid Bridges between Matrix Blocks: Modeling and Simulation
More LessIt is widely accepted that under reservoir conditions there exists some degree of block to block interaction that may result in capillary continuity. The formation of liquid bridges causing capillary continuity between blocks will significantly affect ultimate recovery. In this work a mechanistic model with original thought from hydrology for a given steady feeding volumetric flow rate from an upper block (under both gravity and matrix capillary pressure effects) is developed which considers the formation, growth and detachment of pendant liquid droplets perpendicular to the horizontal fracture (assuming to be smooth and parallel walled) between blocks. The length of detached liquid droplet is observed to be weakly related to the flow rate but it increases as the fracture capillary pressure increases. By neglecting the impact of the flow rate, the simple relation is derived for determination of the length of detached pendant droplet which depends on the fracture capillary pressure, liquid density and the gravitational acceleration. Comparison between the horizontal fracture aperture size and the length of detached pendant liquid droplet is then used to evaluate the formation of traveling liquid bridge between upper and lower blocks.
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Sedimentary Control on Early Diagenesis in Shallow-marine Carbonates: Control on Fracturation (Madison Formation)
Authors J. P. Callot, M. Barbier, Y. Hamon and B. VincentThe carbonates of the Madison Formation outcrop in the core of the Laramide fold of Sheep Mountain (Wyoming). The sedimentation is organized in stacked meter-scale fining-up cycles, illustrating a repetitive evolution from (1) a "deep" subtidal environment (mid ramp system), to (2) a subtidal environment subjected to storm reworking, and finally (3) a quiet lagoon environment separated from the open marine setting by migrating oolithic shoals. The diagenetic evolution is controlled by the initial sedimentary facies: (1) mudstones present an intense early dolomitization; (2) oolithic grainstones display isopachous marine calcite cements; (3) mud-supported facies (wacke- to packstones) are poorly impacted by early diagenesis (little early dolomitization of the carbonate mud). The multi-scale characterization of the fracture network reveals a strong control by the coupled depositional pattern and diagenetic imprint.
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Revised Biostratigraphy and Sequence Stratigraphy of the Gadvan, Dariyan and Kazhdumi Formations, SW Iran
Authors F.S.P. van Buchem, D. Baghbani, L. Bulot, M. Caron, F. Gaumet, A. Hosseini, F. Keyvani, R. Schroeder, R. Swennen, V. Vedrenne and B. VincentA regional sequence stratigraphic model is presented for the Barremian to Lower Albian sedimentary systems of southwest Iran. Illustrated with nine seismic scale outcrop sections, and constrained by new biostratigraphic and chemostratigraphic age dating (ammonites, pelagic forams, orbitolinids and carbon and oxygen isotope curves), it proposes a fundamental revision of the geometrical relationships between classically used lithostratigraphic units. The relative influence of both eustatic sea-level fluctuations and regional tectonic control are demonstrated. These new insights have significant implications for both the understanding of the factors controlling sedimentation, as well as the architecture of the mid-Cretaceous petroleum systems in the studied region.
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Microfacies Analysis and Environmental Interpretation of Tertiary Reefs in the Osmaniye-Iskenderun Sub-basins, SE Turkey
By M. IkramThese studies are about the sedimentology and environmental interpretation of middle Miocene reefal carbonates found in the SE Turkey. These rocks comprises hydrocarbon reservoirs in the region. Therefore, detailed sedimentological studies of the outcrops provided a unique opportunity to see the reservoir characters of these rocks.
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Sequence Stratigraphy and Sr Isotope Stratigraphy of the Oligo-Miocene Deposits in the Dezful Embayment (Asmari and Pabdeh Formations, SW Iran) - Implications for Reservoir Characterisation
Authors F.S.P. van Buchem, T. Allan, G.V. Laursen, M. Lotfpour, A. Moallemi, S. Monibi, H. Motiei, N. Pickard, A.R. Tahmasbi, V. Vedrenne and B. VincentA sequence stratigraphic model is proposed for the Oligo-Miocene Asmari and Pabdeh Formations in the Dezful Embayment of South-West Iran. The model is based on both detailed sedimentological observations in outcrops, core and well logs, and an improved high resolution chronostratigraphic framework constrained by Sr-isotope stratigraphy and biostratigraphy. The better understanding of the stratigraphic architecture allows distinguishing four, geographically separated types of Asmari reservoirs.
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The Influence of Obduction on the Late Cretaceous Deposits in the Fars Province-Zagros, Iran
Authors A. Piryaei, J. Reijmer and F. van BuchemDuring the Late Cretaceous the northeastern margin of the Arabian plate (Zagros-Fars Area) is characterized by significant variations in sedimentary facies, sedimentation patterns, accommodation space and by shifting depocentres. A succession of events recording the evolution of the region from a passive to an active margin is documented by the study of eight outcrop sections and one well. This new study uses new age dating (benthic and planktonic foraminifera, nannoplankton and radiolarian biozonations and strontium isotope stratigraphy). Three tectono-sedimentary phases are recognised indicating the evolution from a passive to an active margin: Phase I (Late Albian to Cenomanian, before obduction) comprises three depositional 3rd order sequences comparable to the other parts of the Zagros and Arabian Plate. This interval is composed of shallow-water platform carbonates and intrashelf basins. Phase II (Turonian to Late Campanian, obduction phase) is characterized by major changes in depositional environments and sedimentary facies, due to obduction and foreland basin creation. Phase III (Late Campanian to Maastrichtian, after obduction) shows the development of rudist-dominated carbonates in the NE ,deep basinal facies in the centre of area. In the most-NE no sediments of this age have been recorded suggesting uplift at that time.
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The Asmari Formation Revisited: Changed Stratigraphic Allocation and New Biozonation
Authors G.V. Laursen, S. Monibi, T.L. Allan, N.A.H. Pickard, A. Hosseiney, B. Vincent, Y. Hamon, F.S.P. van Buchem, A. Moallemi and G. DruillionThe essential biostratigraphy of the Asmari Formation was outlined in the early 1950’s and thereby the only published record of the biostratigraphy before the Asmari Formation was formally described in the mid 1960’s. The traditional Iranian biostratigraphy is based on unpublished reports. Unfortunately, these reports were written in a period when the Aquitanian stage was under debate. Recent studies have shown that sediments ascribed to the Miocene “Aquitanian” are in fact Late Oligocene, Chattian in age. This was proved by the application of Sr-isotope stratigraphy to cored sections from 10 Iranian oil fields and 14 outcrop sections, within the framework of a high resolution sequence stratigraphic study down to fourth order cycles (van Buchem et al., in press). For each section, the strontium dates were plotted against the fossil ranges. The strontium ages necessitate a revision of the interpretation of the Chattian-Aquitanian boundary. The Chattian/Aquitanian boundary is marked by a major faunal turnover, with the general extinction of Archaias species and Miogypsinoides complanatus. The previous age interpretation of the early, unpublished zonations necessitates a revision, and the establishment of an updated biozonation. This new zonation and the stratigraphic ranges of selected key-species are presented here.
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Platform to Basin Facies Transition in the Lower Cretaceous Fahliyan Formation: Evidence for the Formation of Garu Intra
Authors M. Khosravi, Y. Lasemi and M. FeiziThe Fahliyan Formation (Berriasian-Valanginian) is an important petroleum reservoir in southwest Iran. Field and microscopic investigation of the Fahliyan Formation in the Izeh Zone, west of Kazroon Fault, resulted in recognition of platform and off platform basinal (calciturbidite and pelagic) facies. Lateral and vertical facies variations of the Fahliyan Formation in the study area indicate deposition in settings related to a carbonate shelf with an east facing shelf margin. Platform facies in the type locality (Fahliyan section) changes towards the northwest in the Eshgar section to chiefly basinal pelagic and calciturbidite facies. In the Eshgar section, mainly calciturbidite facies, sharply overlies the platform facies of the lower part of the Fahliyan Formation suggesting the onset of tectonic activity along the Kazroon Fault system in Early Cretaceous leading to the formation of the north to south trending Garu Intrashelf Basin in southwest Iran
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New Findings on the Dasycladacean Algae from the Fahliyan Formation in the Zagros Basin (SW of Iran)
More LessA very detailed biostratigraphical analysis, sequential interpretation and paleoecological investigations have been carried out based on the Dasycladacean algae and accompanied benthic foraminifera on the Fahliyan Formation in Kuh-e-Khartang and Kuh-e-Gavbast and correlated with Kuh-e-Surmeh, SW of Iran. Vertical variations of lithofacies and cyclic deposits in the shallow water carbonates can be interpreted in terms of sequence stratigraphy. Sequential interpretations reveal at least three 2nd-order and 3rd-order sequences with several parasequence sets throughout the studied successions. The sequences are given in Berrisian – Early Valanginian, Early Valanginian and Hauterivian age. Family Dasycladacea and subfamily Clypeineae are the most frequent and occasionally reported for the first time from the Zagros Basin and/or from the Southern Tethys. The paleoecological and paleobathymetrical investigations indicate that these strata have been deposited in a shallow internal subtidal (protected lagoon) to external subtidal and platform margins with the interval depths of 5 m to 40 m and their salinity ranges from normal marine to super saturated (hypersaline) conditions.
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Evidence for Top Shuaiba Exposure and Incision in Block 5, Offshore Qatar, and Regional Consequences
Authors F. van Buchem, M. Raven, P.H. Larsen, F. Surlyk, H. Steinhardt and M. EmangAn integrated subsurface data set of core, vertical and horizontal wells and seismic has provided evidence for the presence of karstification and quartz sand filled platform incision at the top of the Shuaiba Formation in offshore Qatar. These observations have significant implications for the late Aptian palaeogeography and related understanding of the distribution of late Aptian/early Albian siliciclastics in the region. In addition, it provides a Late Aptian reference curve for the Arabian plate.
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Possible Mechanisms in MIOR Processes
Authors M. Shabani Afrapoli, C. Crescente, O. Torsaeter and S. OstvarAbstract: Microbial Improved Oil Recovery, MIOR, consists in increasing the population of bacteria with beneficial properties for mobilizing additional oil in the reservoir, and thereby generating improved oil recovery (IOR). Determining which mechanisms allow bacteria to increase oil recovery and how these mechanisms occur and interact is the key to understanding, predicting and planning MIOR projects successfully. The authors have carried out experimental works with Rhodococcus sp. 094 and the main objective of the works was to get a better insight into the complex mechanisms allowing this bacterium species to increase oil recovery. This includes investigations of interfacial tension reduction, wettability changes due to the bacteria solution, glass micromodel flow tests and core flood experiments. From the results, it is possible to propose a theory of how Rhodococcus sp. 094 improves the oil recovery. The theory suggests which type of bacteria is most active and thereby gives IFT reduction, wettability alteration to both oil- and water-wet systems and gives favorable changes in the flow pattern.
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Micromodel Studies of Bioplugging Efficiency in Heterogeneous Porous Media by Means of Mixed Culture of Microorganisms
Authors M.S. Karambeigi, M. Schaffie, M.H. Fazaelipoor and M. SaadatOn of the most important problems of water-flow control and water flooding is heterogeneity of porous media. This problem causes water to canalize through high permeable zones and low permeable zones remain intact A possible method for decreasing this unwanted phenomenon is bioplugging of high permeable zones. In this study the efficiency of microbial treatment for improvement of water flooding of Persian gulf in a heterogeneous micromodel with 2 layers of low and high permeable zones was visualized using 2 sets of experiments. The first one was water flooding and the other was microbial treatment with a mixed culture of microorganisms that followed by water flooding. Results of visualization and image analysis studies showed that water canalizing through high permeable layer in the first experiment decreased considerably via bioplugging of this layer and the oil recovery enhanced considerably.
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The Comparison of Effects of Immiscible Injection of Natural/Nitrogen Gases on Asphaltene Precipitation Process
Authors R Rostami Ravari, A. Hajizadeh and M. AmaniAsphaltene and wax deposition in the course of production of many Iranian reservoirs has become a serious problem. In order to investigate the effect of injecting rich and dry natural gases and also nitrogen, on the asphaltene precipitation process a comprehensive research study was launched. Three phase equilibrium calculation of NGHIEM and his co-workers is used. In the method pure asphaltene in the oil is considered as solid and the heavy part of the oil is split as precipitating and non- precipitating. The provided model is able to describe the phase behavior of reservoir oil encountered with a compositional disturbance caused by injecting light fluids into the reservoir during the production period. In this work, first, the natural depletion model of each case is constructed and then the changes of behavior by injecting rich and dry natural gases and also high nitrogen content gas is investigated. Also the change in onset of asphaltene precipitation for different injections is shown. The achieved results show that the nitrogen gas has more moderate effect on precipitation process compared to more vigorous effect of dry and rich gases.
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Fractal Analysis of Surface Roughness Induced by Asphaltene Deposits: Effect of Surface Topography on Wettability Altera
Authors EHSAN Nikooee, J. Sayyad Amin, S. Ayatollahi, A. Alamdari, H. Jahromi and M. EscrochiAsphaltene precipitation is known as one of the side effects of gas injection in the depleted oil reservoirs. In this study surface topography alteration during high pressure precipitation process on different substrates (mica and glass) was studied. Fractal analysis of the surface images was performed which led to the calculation of fractal dimensions (D). The difference statistics method was used to calculate fractal dimensions. To obtain the images of asphaltene deposits on the surface, in micro scale size, a high pressure cell was designed. The condition for asphaltene precipitation in a solution of Asphaltene/Toluene/ Heptane was maintained by changing the pressure of the cell. Results showed that by increasing of pressure, the mica and glass surfaces tend to be altered to the oil wet conditions because of the increase in fractal dimension which is the representative of surface roughness. It was also observed that fractal dimension of asphaltene-deposited glass surface is more than the one for asphaltene-deposited mica surface at the end of experiment. Since number of nucleation- growth sites on mica surface are much more than those of glass surface thus asphaltene growth on mica surface is much more noticeable which can fill micro-asperities.
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Comparison Between Natural and DFN Models in Water-flooding Numerical Simulations
Authors M. Belayneh and S.K. Matthaithis method is error prone due to post-burial processes. Mineralised fractures (vein) attributes are good candidates as analogues for open fracture formed under in-situ conditions and to establish the relationship between length versus aperture and help to reveal the conditions at the time of their formation. Vein attributes were used to condition stochastic generation of fractures using the Discrete Fracture Network (DFN) code, FracMan. Comparison of water breakthrough time and oil saturation at breakthrough were then determined by applying constant pressure gradient for each realisation to simulate water-flooding numerical simulation using the combined finite element – finite volume method (FEM – FVM). Stochastic realisations were compared with the actual system. The results indicate that, depending on the variability of the above attributes, fluid flow in fractured rocks vary from pervasive where the fractures play subordinate role to a highly localised flow where most of the flow occurs through single or connected network.
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Challenges of Modelling Naturally Fractured Reservoirs: IOR/EOR Studies
More LessCharacterization of naturally fractured reservoirs is complicated. The reservoir model of such reservoirs must represent both fracture and matrix systems and interaction between the two. It is important to choose correct dual continuum model parameters to build the most representative of a fractured reservoir. In this study, we try to improve our understanding of interaction between matrix and fracture and how this can be captured by dual porosity/permeability model. We look at a homogeneous, a simple heterogeneous and a detailed pore-type based heterogeneous model. Fracture act as boundary conditions. First, interaction of forces during various depletion scenarios is studied. Then, oil recovery by gas/water injection is simulated in the fine scale. Dual continium models corresponding to the fine scale models have been built and it has been tried to achieve a good match between fine scale and dual continuum model, by adjusting dual continium model parameters. Observations from this study highlight the importance of capturing the fine scale heterogeneity in fractured reservoir modeling. Furthermore, the ability of reproducing fine scale results, by final simulation model will depend upon selected upscaling/coarsening methodology and how parameters of the coarse scale model are generated/tuned.
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Evaluation of Different Flooding Scenarios as Enhanced Oil Recovery Method in a Fractured Reservoir: A Case Study
Authors B. Moradi and A. ShahvaranfardBecause of technological complexity and financial requirements to initiate a gas flooding project, a thorough evaluation before it is performed would be necessary. In this paper reservoir modeling approach was used to evaluate different flooding processes (miscible and immiscible) in a fractured oil reservoir. This study included: 1) equation of state (EOS) modeling of experimental PVT data, 2) determining MMP for different gas compositions using an slimtube model and studying the effect of grid number on results (numerical dispersion), 3) studying the effect of completion pattern and injection rate on recovery performance, and 4) comparing recovery performance in different flooding scenarios(CO2, N2, methane, enriched methane and water injection)
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Simulation Study of Conventional Fire Flooding (CFF) in Fractured Combustion Cells: A Promising Tool along Experiment
Authors R. Kharrat, S. M. Fatemi and C. GhotbiThe Conventional Fire Flooding (CFF) process application feasibility on fractured carbonated reservoirs remained questionable. In this paper first combustion parameters and reaction kinetics of a naturally fractured low permeability carbonated heavy oil reservoir in Iran called Kuh-E-Mond applied to simulation study. After that, simulator has been validated with Kuh-E-Mond combustion tube experiment. Recovery mechanism in single block matrix is different from one in conventional model since oxygen first flows into the fractures and then diffuses from all sides into the matrix. Combustion of the oil in the fractures produces some water ahead of fracture combustion front which prohibits oxygen from early breakthrough through fractures into production well. Water imbibes to the matrix and causes matrix oil drainage to the producer. This oxygen diffusion/water imbibition based recovery mechanism is slower in production rates compare to conventional model recovery mechanism, and causes lower produced oil quality since less oxygen is available for matrix. Further, sensitivity analysis on air injection rate, formation thickness, injection well depth of perforation, horizontal fractures and also effect of water alternating air process on fracture model results have been studied.
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Noise, the What, the Where and the How To
Authors S. Taylor, T. Ulrych, B. Nedilko and I. Weir-JonesThe ability to deliver drastic improvements in signal to noise ratio are a key step to enhancing the results of passive seismic surveys - whether short or long term; carbonate or clastic formation; deep or shallow; and fluid or steam stimulated. Across the board noise is the primary enemy of passive seismic. The authors detail advances in noise filtering and reduction techniques and detail the journey to automation of this technique as an embedded DSP routines directly onto the data acquisition system. Selected case studies will be detailed and explained in terms of data fidelity and the practical relevancy of associated benefits.
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Detection of Micro Faults in Dipping Layers in 3D Seismic Data by Coherency Attributes
Authors A. Hashemi Gazar and A. JavaherianCoherency attribute is a measure of lateral changes in acoustic impedance caused by variations in structure, stratigraphy, lithology, porosity, and fluid content. When coherency attributes are applied to seismic data, they might indicate the continuity between two or more traces within a seismic window. The rate of seismic continuity is an index of geological continuity. Areas of traces that change with a fault or other geological phenomena have lower coherency in contrast with the adjacent traces. There are three solutions to calculate coherency attributes that include cross-correlation, semblance and eigenstructure. To study the ability of coherency attributes in delineating micro faults, we generated several 3-D synthetic seismic cubes including horizontal, dipping, and cross dipping layers with micro faults. We also studied the effect of the dominant frequency and the size of analysis cube in calculating coherency attributes using MATLAB. We applied all three approaches of coherency attributes to 3-D real data. Coherency attributes proved to be very effective in defining micro geological discontinuities even up to 4 ms.
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Relationship Between Velocity and Permeability Using Hydraulic Flow Units
Authors A. Pouladi, E. Kazemzadeh, G. Norouzi and M. ShabanEstimation of Relationships between velocity of P-wave and permeability by using usual method is difficult. In this study that is first research in Iranian oilfield we show that by grouping and sorting rocks into hydraulic units, we can establish relationships between velocity and permeability. We can determine the hydraulic units by using measured porosity and permeability values from core analysis. Correlation between velocity and permeability is significant within each hydraulic unit. In the first part of study we determine this relation and the correlation coefficient (R2) lies in the range 0.67–0.80. We know that the compaction and cementation history of sediment can have effects on porosity and permeability and velocity of P-wave. At this study we determine relation between permeability and velocity within specific case study and then by comparison to one wave theory (Biot model of wave) we demonstrate that the good match is between them. This relation can be used to predict permeability from velocity in well logs by zoning the data from training wells into hydraulic units.
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Application of Artificial Neural Network for Estimation of Formation Permeability in an Iranian Reservoir
Authors M. Yeganeh, M. Masihi and S. FatholahiThe permeability is one of the most important reservoir parameters and its accurate prediction is necessary for reservoir management and enhancement. Although many empirical formulas are derived regarding permeability and porosity in sandstone reservoirs [1], these correlations cannot be modified accurately in carbonate reservoir for the wells which are not cored and there is no welltest data. Therefore estimation of these parameters is a challenge in reservoirs with no coring sample and welltest data. One of the most powerful tools to estimate permeability from well logs is Artificial Neural Network (ANN) whose advantages and disadvantages have been discussed by several authors [2]. In this paper, 767 core data sets and their corresponding well logs were taken from five wells of a reservoir in south west of IRAN. Depth, NPHI, PHOB, DT and total porosity were used as the input data and horizontal permeability obtained by coring was as target data. 60% of these data points were used for training and the remaining for predicting the permeability (validation and test).An ANN was developed and a correlation coefficient of 0.965 was obtained by comparing permeability predictions and the actual measurements. Data sets are well log and core data of a reservoir.
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Estimate of Porosity Distribution by Using Seismic Inversion and Geostatistics Methods in one of the Oil Fields of Iran
Authors Z. Farajpour, M. Nabi-Bidhendi and M.R. TorabiWe analyse data acquired over a part of studied field how 3D seismic inversion and 3D geostatistical analysis can be used to predict porosity. The adopted techniques in this study are ordinary kriging and cokriging using well to well, well to seismic and seismic to seismic variograms. The result is a set of porosity simulations, all of which are equally probable. The simulations, computed as 3D volumes, are constrained to be in agreement with both log and seismic data and the geologic model for the reservoir. Summary maps can be used to view the average porosity in any layer or combination of layers. The integration of 3D geologic modelling and high resolution constrained model based seismic inversion has proven to be a useful tool in the exploration for hydrocarbons (Pendrel and Van Riel, 1997). We use the constrained model based inversion cube corresponding to the project data as a co-simulator. This is computed using all of the available information seismic, interpreted horizons, geology and logs. We using the estimated probability density functions (pdf’s) and variograms, we do 3D sequential spherical co-simulation of the porosity logs with the inversion impedance cube as the secondary input.
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Seismic Inversion and Multi Attribute Analysis to Prediction of Porosity Distribution in an Oil Field in SW of Iran
Authors A. Rahimi Zeynal and M.A. RiahiThis paper describes a methodology for the integration of well logs and a series of grid-based attributes extracted from interpreted seismic data for prediction of porosity distributions. The studied area is located in the southwest Iran. Before finding a relationship between the target logs and predicted logs from 3D seismic data, we have interpreted the 3D seismic data in the studied area. Also we matched and combined well data with seismic for forward modeling and seismic inversion. Inversion produces a full band acoustic impedance model of earth which improves the vertical resolution. Then we have checked other different inversion methods such as spare spike and model based. Since the model based method resulted with a better resolution outcome, therefore we decided to apply model based inversion method in the reservoir level. In the next step we applied a linear and a non linear transforms between a group of seismic attributes and porosity logs. Then we obtained a relationship for estimating of a volume of the porosity at all locations of the seismic volumetric data. Finally we found an improvement in the porosity prediction from linear multi attribute transforms when using neural network methods.
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Petrophysical Evaluation and Sequence Stratigraphy of Upper Surmeh (Arab) Formation in Reshadat Field (Persian Gulf)
Authors S. Sohrabi and B. ArbabAbstract The upper Jurassic, Upper Surmeh (Arab) Formation in Block R in Iranian territorial Reshadat field in the Persian Gulf , subdivided into the A, A1, B, C and D members, is overlain by Hith formation and underlain by the Darb and Diyab formations. The Arab members consist of a thick sequence of carbonates and evaporites which is deposited in Shallow marine. The typical Parasequences consist of shoal Grainstone, representing Transgressive System Tracts, that pass upward into Thin-Bedded Lagoonal burrowed mud/Wackstone, representing the Maximum Flooding surface. Intercrystaline Porosity and moldic pores is recorded as very good, but locally decreasing because of the presence of large secondary Anhydrite Patches.The Porosity map shows a downflank deterioration In reservoir quality. Dolomitization process increased the porosity. The studies demonstrated 16 Shallowing-Upward Paresequences. It was recognized for Arab members as follows: A and A1 (6 Cycles), B (2Cycles), C (2Cycles) and D (6Cycles). Petrophysical Characters of each Microfacies are extracting from Log and Core Analysis in key wells. Microfacies modeling is done and petrophysical characters are populated into each facies bodies.
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Reservoir Characterization Using Local Linear Models (LLMs) Approach Applied on Seismic Attributes
Authors H. Jamali, N. Keshavarz Faraj Khah, S.M. Behrouz, G.H. Montazeri and I. MaddahiIn this research we used one of the most advanced neuro-fuzzy algorithms called Local Linear Models (LLMs) to estimate the resistivity log from seismic attributes in an oil field in south-west of Iran. Local Linear models belong to the class of intelligent Neuro-Fuzzy approaches which are based on a neuron growing strategy. This method has been developed primarily for the purpose of control in electronic engineering, as it has been shown here, it also can be used as a strong predictor of estimating reservoir characteristics by its application on seismic attributes. In addition, this method can act as an appropriate substitute for conventional methods that have been applied in petroleum industry previously. The input space dividing strategy, used in this method, makes it less affected by the choice of seismic attributes for multi-attribute analysis. Also, this approach can be applied when we have limited number of wells.
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Permeability Prediction from Petrophysical Logs Using Fuzzy Logic in Clastic-Carbonate of Asmari Formation
Authors S. Zare, S.K. Shiroodi and B. NooriAboozar field is located approximately 72 km west of Khark Island in offshore Iran. Main reservoir of this field is an Oligo-Miocene stratum called Ghar which is a member of Asmari. Permeability plays important role in reservoir flow and always has much difficulty to be defined and modeled. This property is directly measured based on core analysis and drill stem test. This paper presents the use of fuzzy logic molding to prediction permeability from wireline log data in clastic-carbonate reservoirs of Asmari formation. Fuzzy logic allows quantifying qualitative information and modeling complex not linear relation. In essence, the problems consist in finding some explicit relation between log and core in well. After training the fuzzy model with subtractive clustering in a given well, permeability prediction were made for other layers in the same well. In subtractive clustering a one and quick way shall be selected for training which based on this a Takagi-Sugeno-Kang method can be generated. The number of membership functions and laws doesn’t need to be defined because inferring system is able to define those by using clustering input-output data. These predictions were in excellent agreement with permeability values obtained from core.
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Using NMR Log to Estimate Permeability in One of the Carbonate Formations in South of Iran
Authors M. Roustaie, M. Nabi-Bidhendi, M. Tadayoni and S. TorabiPermeability is an elusive parameter in hydrocarbon reservoirs as it is very difficult, if not impossible, to determine precisely and directly from current subsurface logging technologies. In this research, an attempt is made to test some methods for estimating permeability as a function of depth from Nuclear Magnetic Resonance (NMR) logging in one of carbonate reservoirs in south of Iran. For accurate permeability estimation, an Artificial Neural Network (ANN) model with two different inputs is applied. In the first case, NMR porosity has been used as input data but in the second case there is no NMR data as input and core porosity has been used. Also three NMR models such as average-T2, free-fluid and Swanson model, have been used for permeability estimation. The results of all these methods are compared with the core permeability. The trends of permeabilities obtained by NMR models have good compatibility with core permeability, so they can be used for in-situ permeability estimation. The results of ANN model shows that using NMR porosity, beside traditional log data, as input for ANN leads to considerably increase in correlation coefficient relative using core porosity. So it can be used as a reliable method for permeability prediction.
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Geostatistical Modeling of Reservoir Properties in an Iranian Oil Field from Upper Bangestan Group, Southwest of Iran
More LessIntegration of various data types available on different scales by using appropriate statistical tools is necessary for building an appropriate static reservoir model. It is very important prior to the reservoir simulation to estimate reservoir performance uncertainty and to aid reservoir management decisions. The oil field of this study is from upper Bangestan group in the SW of Iran which consists of several reservoirs, including Ilam and Sarvak. The information from 5 wells along with the acoustic impedance in time domain in the field was used to generate stochastic images of porosity and permeability with their inferred associated probability. Data from various scales including logs, cores and AI were available. We used AI to improve the reservoir characterization by providing information on the spatial variation of the reservoir porosity away from the existing well. The velocity model for depth conversion was developed by using first check shots in the wells and second Collocated Co-Kriging method with stacking velocity in the field and the check shots. Variogram contour maps of AI were generated to evaluate the underling anisotropy. These are then used in the framework of the various sequential simulation techniques to produce realizations of 3D porosity and permeability models.
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Pressure-volume-temperature Correlations For Iranian Crude Oils
Authors B. Moradi, E. Malekzadeh, R. Kharrat and P. MoradiABSTRACT Pressure-Volume-Temperature (PVT) properties are necessary to reservoir engineering calculations in porous media and it is important for calculations in pipeline as well. This work presents a new set of correlation for estimating Iranian Crude oils properties based on some experimental data. Whenever, these is no representative experimental PVT data, these correlations can be used for oils of API ranging between 19 to 42. New correlations was developed to calculate Oil Formation Volume Factor (Bo), Bubble point pressure (Pb) and solution Gas oil Ratio (Rs). Finally, a comparison is made between these correlations and other published correlations such as Standing, Vazquez & Beggs, Glaso, Farshad and et al, Al Marhoun, Petrosky & Farshad, Hanafi and et al and it is found out that these new correlation are more accurate then the other ones.
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Implementation of Ensemble Kalman Filter (EnKF) Technique in Well-test Analysis of Gas Condensate Reservoirs
Authors G.H. Montazeri, S.M. Behrouz and H. JamaliIn this paper the Ensemble Kalman Filtering technique (EnKF) is implemented to remove noise from well testing data of a gas condensate reservoir and estimate some important parameters such as critical condensate saturation, irreducible water saturation and distribution index which can be used in drawing relative permeability curves. In order to use EnKF, we developed a MATLAB computer program which dynamically interfaces with ECLIPSE300 numerical reservoir simulator. The conventional approches for interpretation of transient data in gas condensate reservoirs can be criticized in several ways. Because of complex nature of flow in such reservoirs, many simplifying assumptions have been made in order to find analytical solutions for diffusivity equation which is theoritical foundation for most of well test analysis techniques , but these assumptions cause a great deal of error in final results. In addition to this, the available methodologies for well testing in such reservoirs are sensitive to measurment errors and flactuation in test data, consequently, any inaccurate mesuarment can be really misleading. Therefore, we used EnKF technique to cover the deficiencies appear in previous analysis methods. Furthermore, extracting relative permeability curves is the unique advantage of this technique.
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Multitransform of Seismic Attributes to Petrophysical Properties Using Committee Fuzzy Inference System
Authors A. Kadkhodaie-Ilkhchi, M.R. Rezaee, P. Hatherly and A. ChehraziThis paper presents an intelligent model based on fuzzy systems for making a quantitative formulation between seismic attributes and petrophysical data. The methodology consists of two main steps. In the first step, petrophysical data including water saturation (Sw) and porosity are predicted from seismic attributes using fuzzy inference systems (FIS) including the Sugeno (SFIS), Mamdani (MFIS) and Larsen (LFIS) fuzzy inference systems. In the second step, a committee fuzzy inference system (CFIS) is constructed using a hybrid Genetic Algorithms-Pattern Search (GA-PS) technique. The inputs of the CFIS model are the outputs and average of the fuzzy inference systems. Each of them has a weighting factor showing its contribution to the overall prediction. For this paper, 3D seismic data and petrophysical data from 11 wells of the Iranian Offshore Oilfield in Persian Gulf Basin are used. The performance of the CFIS model is compared to that of a probabilistic neural network (PNN). The results show that the CFIS method performs better than a neural network, the best individual fuzzy model and a simple averaging method.
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Microfacies and Sedimentary Environment of the Asmari Formation in Lali Oil Field (NW Masjed-e-Soleyman)
By A. EynollahiThe Oligocene-Miocene Asmari Formation is a thick sequence of carbonate rocks in the Zagros basin. The Formation has been studied in Lali oilfield, which locates at 40 kilometers of south-west Masjed-e-Soleyman. It lacks the Lower Asmari but involves the Kalhur Member and Basal Anhydrite at that area. The study of the Asmari thin sections from available cores and cuttings at wells no. 20 and 22 of Lali oilfield, led to recognize 10 microfacies, related to six facies zone, including: supratidal, intertidal, shelf lagoon, barrier or shoal, shallow open marine and basin margin. The Asmari Formation represents sedimentation on a homoclinal carbonate ramp.
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Unsupervised Seismic Facies Analysis Using Singularity and Self-organizing Maps in Southern Pars Oil Field
Authors S. Hadiloo, H. Siahkoohi, A. Edalat and R. TaherkhaniUnsupervised seismic facies analysis provides an effective way to estimate reservoir properties by combining different seismic attributes through pattern recognition algorithms. In many cases important information is carried by singularities that are not necessarily associated to certain amplitude patterns. We use Hölder exponent (α) as a seismic attribute which captures the locations and strengths of irregularities in the data. It is demonstrated that α is a natural attribute for delineating stratigraphy boundaries due to its excellent abilities in detecting detailed geologic features from seismic data. We use wavelet transforms and Hölder exponent to identify seismic trace singularities in each geologically oriented segment, and then we build the seismic facies map using the clustering ability of the SOM. We tested method using real seismic data from Southern Pars oil Field. The results confirm that we can estimate the appropriate number of seismic facies through the clustering of the SOM. We also showed that we can improve the seismic facies analysis by using trace singularities detected by the wavelet transform and Hölder exponent technique. Key words Seismic Facies Analysis; Time-Frequency Analysis; Hölder exponent; SOM
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New Data on Sequence Stratigraphy of Dashtak and Khaneh Kat Formation and Re-evaluation as Effective Cap Rock in Zagros Basin
Authors M. Khoshnoodkia, H. Mohseni, M. Hajian, M. Fallah Kheirkhah, K. Khosro Tehrani and M. KhaleghiDashtak Formation composed of dolomite, anhydrite and limestone acts as an effective seal whereas Khaneh Kat Formation composed of dolomite, shale and limestone excluding evaporites has no cap rock characteristics. Both Formations deposited in a homocline carbonate ramp with depositional facies including supratidal, tidal flat, lagoon, shoal and mid ramp. However a relatively more deep setting wherein no more evaporites were deposited for Khaneh Kat Formation.These formations were evaluated in 8 subsurface and 3 outcrops. Data gathered from field observation, thin sections, geophysical data (GR, Sonic and Neutron logs) and strontium isotope. Dashtak Formation comprises 4 sequences and Khaneh Kat Formation has 5 sequences. Southeast ward part of uppermost sequence of Dashtak Formation has been removed due to post depositional erosion. Lowermost sequence extends in whole of basin with carbonate facies,is equivalent of Kangan Formation. Sequences 2 to 5 of Khaneh Kat Formation are equivalents of Dashtak Formation. These sequences show a distinct lateral facies changes from Sartal#1 borehole toward Kuh-E-Manghasht and OshtoranKuh from evaporite dominated facies to carbonates. An increase in thickness of Dashtak Formation has been revealed toward boreholes Dalan#1, Kuh Siah#1, Dashtak#1; however high anomalously thickness in Sartal#1.
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Applicability of New Production Logging Tools in Horizontal and Deviated Wells of One of Iranian Fields
Authors A. Qazvini Firouz, K. Shahhoseini and A. MortezapourWe found out gas is producing from the beginning section of open hole interval. We recognized this happened after increasing the wellhead choke size in order to increase oil production without bearing in mind that the field is natural fracture carbonate reservoir which has very large numbers of vertical and horizontal fractures in reservoir rock. Also in spite of starting gas injection project, pressure drop continued to increase as a result of increasing oil production rate which caused more oil loss. Consequently gas oil contact has gone down and we had additional gas production in our producing wells.
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Drilling Optimization in the World's Largest Offshore Gas Field by Optimizing the BHA Design
More LessDrilling is an expensive industry these days which consist of tools, services, rig and etc. so it's important for drilling engineers to optimum drilling parameters to reduce costs and avoid problems. In this paper an integrated drilling system with specific focus on BHA design which has been used to improve drilling performance in the world's largest offshore gas field will be discussed. The effect of this optimization was reduction of actual drilling time to more than half of the budget time.
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Casing Design Reevaluation in South Iran Oil Field
Authors M. Shaban, A. Pouladi and S. Behzadisize and type of the casing is chosen based on the geology and formation properties of the field. Cost of the casing design is more than 30% of overall drilling cost which make it an expensive operation for each well. Saving in this operation causes huge reduction in total expenditures of drilling. It seems that it is accessible to reach an optimum method by complete analyzing and reevaluating of the relevant factors in customary design programs which are done traditionally in the Iranian Oil fields. In this paper, by using minimum-cost casing design two methods are proposed for Iranian oil field. In the first proposed method, 30 in conductor casing is used and completed with 7 in liner which make it suitable for high producing field. This method save 17.31% cost of casing design compare to traditional method. The application of the second method is not restricted to special condition and it is compatible to the all cases. This method saves 17.4% cost and also providing sufficient stability and safety in casing program by using two liner and prevent unnecessary cost and time-consuming operations. Finally these two methods are applied to south and southwest Iranian oil field.
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