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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
41 - 60 of 140 results
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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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