- Home
- Conferences
- Conference Proceedings
- Conferences
72nd EAGE Conference and Exhibition incorporating SPE EUROPEC 2010
- Conference date: 14 Jun 2010 - 17 Jun 2010
- Location: Barcelona, Spain
- ISBN: 978-90-73781-86-3
- Published: 14 June 2010
301 - 400 of 797 results
-
-
Excess Conductivity of North Sea Chalk and Its Influence on Cementation Exponent and Saturation Prediction
Authors M. M. Alam, A. K. Shaik and I. L. FabriciusArchie’s equation utilizes the electrical conductivity of rock to predict brine and hydrocarbon saturation in rock. Based on laboratory data we investigated how Archie’s cementation exponent varies with the excess conductivity of chalk. Excess conductivity arises form the Cation Exchange Capacity (CEC) of the minerals. We studied Ekofisk and Tor Formation chalk samples from the South Arne field of North Sea. CEC of pure calcite was measured to 0.6 (+-0.1) meq/100g, where as CEC of Ekofisk Formation varies between 1.5 to 5.5 meq/100g. CEC of Tor Formation is very close to the pure calcite. Due to the excess conductivity effective pore water resistivity becomes smaller than the actual pore water resistivity. In the process of cation exchange a diffuse layer is formed on the mineral surface, which could increase the magnitude of cementation exponent, m. We found that predicted water saturation increases by one to two percent due to the excess conductivity and increased cementation exponent.
-
-
-
Evaluating Different Approaches of Permeability Modeling in Heterogeneous Carbonate Reservoirs
Authors F. Khoshbakht, M. Mohammadnia, A. M. Bagheri, A. A. RahimiBahar and Y. BeiraghdarPermeability, the ability of rocks to flow hydrocarbons is directly determined in the laboratory on cores taken from the reservoir. Due to high cost associated with coring, many empirical models, statistical methods and intelligence techniques were suggested to establish robust relationships between permeability and various easy to obtain and frequent data such as wireline logs. This study launched to put different approaches of permeability modeling into practice to predict permeability in a heterogeneous carbonate reservoir (Fahliyan formation in SW Iran) and compare results in order to determine the optimal approach for utilizing in this formation. Considered methods divide into four groups; a) empirical models (Timur and dual water), b) regression analysis (simple and multiple), c) clustering methods (MRGC, SOM, DC & AHC) and d) artificial intelligence techniques (ANN, fuzzy logic and neuro-fuzzy). This study shows that clustering techniques predict permeability in a heterogeneous carbonate better than other examined approaches. Among four assessed clustering methods, SOM performs best and could handle dimensionality and complexity of input data sets. Artificial intelligence techniques are average in modeling permeability, in addition empirical equations and regression techniques are not capable for predicting permeability in studied heterogeneous carbonate reservoir.
-
-
-
Eolian Sandstone’s Pore Space Examination Based on Nuclear Magnetic Resonance and Computed Microtomography Techniques
Authors M. Dohnalik, D. Cebulski, J. Zalewska and A. PoszytekAnalyzed samples had a different origin, petrology and reservoir properties. Micro-CT results led to pore spaces’ structures interpretation: analysis of pore network expansion and classification of pores according to them volume. Three eolian sandstone types’ NMR data were analyzed. Correlation between T2 time distribution and the micro-CT pores’ volume distribution was found. The larger pores, the longer transverse relaxation times. The best petrophysical properties had the A-type eolian sandstones. Rock core samples properties estimated by computed roentgen tomography very well correlates with NMR results.
-
-
-
Analysis of Sedimentary Cyclicity Based on X-ray CT Images and Ultrasonic Measurements of Core Samples
Authors T. M. Mueller, M. H. Grochau, E. Campos, D. Nadri, B. Clennell and B. GurevichWe present a methodology to assess rock properties by using X-ray computed tomography (CT) images along with the ultrasonic P-wave velocity measurements in laboratory under different confining pressures, and borehole logs from a stratigraphic interval in Campos Basin, offshore Brazil. The higher resolution of sampling in the core data overcomes the aliasing and smoothing effect of log-based measurements and enables the delineation of stratigraphic cycles. In addition, we observe a good correlation between X-ray CT value and ultrasonic P-wave velocity. Large variation in measured ultrasonic P-wave velocity between different samples is related to variations in calcium content. This improved understanding of the cyclic nature of physical property variations may help to correlate stratigraphy between wells and provide valuable information for paleo-climate studies. This study also helps to understand the facies heterogeneity in fine scale which is needed for choosing the correct rock physics model for further undergoing studies such as time lapse in this field. Given the periodic nature of sedimentary facies, the unique combination of X-ray CT images, ultrasonic P-wave velocities, and high resolution well logs in this field could be used as an example for seismic wave propagation studies in periodic media.
-
-
-
Functional Network Softsensor for Determination of Porosity and Water Saturation in Sandstone Reservoirs
Authors G. M. Hamada, M. A. Elshafei and A. M. AdernianThe proposed methodology makes use of appropriate well logs and core measurements. A portion of the data available was retained for verification of the prediction of water saturation and porosity. This paper presents a novel method for estimating these two important parameters directly from conventional well measurements. The recently proposed Functional Networks technique is applied for rapid and accurate prediction of these parameters, using six and five basic well log measurements as data for estimating porosity and water saturation respectively. Functional network is a generalization of the conventional Feed Forward Neural Networks, which overcome many of the drawbacks of the conventional neural network techniques. The proposed functional network was trained using data gathered from two wells in the Middle East region. Results obtained from this case study of sandstone reservoir using the proposed intelligent technique have shown to be fast and accurate referring to core samples porosity and water saturation values.
-
-
-
Basin Modeling Along Emergent Island Arcs and Oblique Convergent Margins – Impact on Petroleum System – SE Caribbean Case
Authors A. Escalona, W. Fjeldskaar and P. MannWe performed a study using forward basin modeling in the southeastward Caribbean region in order to evaluate the effect of active volcanic arcs and oblique convergence on the evolution of petroleum systems in the adjacent sedimentary basins. The study is done along a geologic profile based on the interpretation of a regional 2D seismic line across the Lesser Antilles island arc, oriented NW-SE with a length of ~650 Km and covers the SE corner of the Caribbean region. The Grenada and Tobago basins are the backarc and forearc of the Lesser Antilles island arc respectively, and record sedimentation since the early Eocene-recent with more than 14 km of thickness. Our interpretation suggests that both basins were a large basin during the Eocene and that were split by the impinging Lesser Antilles arc during the middle Miocene which remains as an active volcanic island arc until present. Basin modeling results of paleo- heat flow, temperature history and simple shear restorations shows that the impinging Lesser Antilles arc in the middle Miocene was key on the maturation of possible Paleogene source rocks in the Grenada and Tobago basins.
-
-
-
Influence of Surface Temperatures on Source Rock Maturity – An Example from the Arctic
Authors O. Abbink, S. Nelskamp, T. Donders and J. D. van WeesUsing paleontological and geochemical techniques the long-term temperature development of the central Arctic was documented from sedimentary records for the first time. With the help of the new paleo-climatic evolution a tectonic paleo heat flow prediction of the Kara Sea area was performed to show the influence of paleo temperatures on the temperature and maturity history of that region.
-
-
-
Maikop Hydrocarbon System of the Caucasus Region
Authors N. P. Fadeeva, M. L. Saint-Germes and E. N. PoludetkinaThe Maikop Series widely distributed in the Caucasus-Skythian region consists of clayey rocks with abundant organic matter (OM). Sequences of similar geological age accumulated in marginal basins are characterized by high petroleum potential and in certain cases contain petroleum accumulations. Marine sedimentation environments, clayey composition, sapropelic OM type and presence of petroleum accumulations make MS a classical example of an oil-producing sequence. It is the main oil source present in Cenozoic and, most probably, Upper Cretaceous strata in the Caucasus-Skythian region. However, oil reserves pooled in the Cenozoic reservoirs of the region are incomparably lower than that which could be expected in view of the above conditions.
-
-
-
Nitrogen Source for the Main Dolomite Natural Gas in the Sulecin Isolated Platform Area – Verification of Existing Theory
Authors P. Zdanowski and K. WozniakIn the Southern Zechstein Basin there is an exploration risk related with high nitrogen content in the Main Dolomite (Ca2) reservoir. Existing theory of nitrogen-rich gases origin in Ca2 reservoirs (the Sulecin isolated platform) states, that natural gas was generated from type III kerogen at high-temperature stage of thermogenic processes and probably migrated from the Carboniferous/Rotliegend deposits, sourced by the post-mature Carboniferous shales. A comparison of isotopic composition of gases from Ca2 and the Rotliegend reservoirs from Wedrzyn-1well does not confirm this theory. δ15N values from these reservoirs are significantly different, around +1,3‰ for the Rotliegend and +9,8‰ for Ca2 what excludes their common source. The comparison of isotopic composition of methane indicates that both gases are thermogenic. The methane from Ca2 is isotopically lighter, what suggest it contains biogenic components or was generated from organic matter of lower maturity or different composition. Nitrogen content in Ca2 gas can result from the specific organic matter type. Sedimentary conditions during deposition allowed strong development of microorganisms. Their activity during and after sedimentation might lead to nitrogen formation through biochemical reactions starting from atmospheric N2 fixation through ammonification, nitrification, ending on denitrification and sulfate reduction.
-
-
-
Modeling of the Petroleum System in Reggane Basin, Algeria
Authors F. R. Monreal, A. Eid and R. AfrazmanechFour regional sections have been modelled in Reggane Basin to evaluate the risk of the petroleum system and to discuss the overpressure related drilling hazards. Main generation occurred previously to the Hercynian orogeny, at around 360 and 324Ma for the Silurian and Frasnian source rock source rocks respectively. The basin became highly overpressured due to the Upper Devonian regional sealing. After the Hercynian uplift, pressure started to be dissipated through the outcropping areas. The drop of the pressure in the Lower Devonian reservoirs accumulations induced gas expansion, phases changes and oil flushing. Generation was frozen until 200 Ma when a thermal anomaly evidenced by AFTA data took place triggering extra generation and extensive cracking. At present day both source rocks are overmature in the center of the basin. Hydrocarbon accumulations are mainly in gas phase. Overpressure events in the Emsian reservoirs are related with a process of “fossil” pressure preservation from pre-Hercynian times plus pressure transference from Upper Devonian overpressured shales. This can be traced back to the confinement of the Emsian reservoir by the Upper Devonian top seal and the Muralla China base seal coupled with low permeability faults acting as lateral seals resulting in a overpressured closed system.
-
-
-
Migration Mechanisms and Pathways in the Nile Delta Fan
Authors U. Boeker, A. C. Aplin and T. DoddUnraveling natural gas migration mechanisms and pathways in the Nile Delta fan is a major challenge due to the ubiquitous occurence of locally generated microbial gas. We applied a coupled isotope-and-concentration model in order to substract this methanogen fingerprint from our hydrocarbon gas data. Variations in thereby isolated thermogenic gas properties relate to formation temperature and result from biodegradation rather than maturity. Our results strongly indicate that there are three distinct categories of thermogenic gas: unaltered, biodegraded, and mixed unaltered-biodegraded. Unaltered gas has been sampled mostly beyond 90°C, whereas degraded gas is found within reservoir and mud-rich caprock sections between 40-58°C. Stratigraphy with intermediate temperatures hosts a remarkably constant mixture of biodegraded and unaltered gas, implying re-charge of formerly biodegraded gas with fresh thermogenic gas from below. We conclude that the reservoirs are in part being charged through the pore space of the sub-reservoir sections, and we can see leakage via the pore network of the caprock as well as via caprock bypass systems. Our observations support the concept of a dynamic charge-leak scenario.
-
-
-
Decompartmentalisation of a Multiepisodic Fault System, Barcelona Plain, NE Spain
Authors I. Cantarero, A. Travé, G. Alías and V. BaquésThe Catalan Coastal Ranges are formed by a NE-SW fault system that is the result of two extensive events (Mesozoic and Neogen) and a compressive event (Paleogen). We have studied two fault zones involving basement and Triassic materials within the Barcelona Plain in the NE Iberia stated from petrological and geochemical studies. These fault zones have a core formed by brittle fault rocks that present three kinds of cements: silicic, calcitic with δ18O values between -20 and -15‰ vPDB and calcitic with δ18O values about -5‰ vPDB. The temporal and spatial relationships between these cements show the evolution of the compartmentalisation in front of fluids linked with the different deformation events from Mesozoic to recent. During the early history, both faults acted as conduits for very different fluids, silicic cements precipitated in one of the faults and very δ18O-depleted calcite cements precipitated in the other fault. Later, a reactivation of both faults allowed the connectivity for fluids along the two zones. Finally, when the faults reached the surface, low-temperature meteoric fluids percolated downward along the fault zones.
-
-
-
Diagenetic Evolution During Progressive Development of Neogene Faults, NE Spain
Authors V. Baques, A. Travé, A. Benedicto, P. Labaume and I. CantareroDifferent fractures, cements, breccias and karstic sediments identified on the Mesozoic carbonates attest to establish the diagenetic processes that have taken place during the Neogene evolution of the Penedès half-graben. Six families of fractures are identified. The first generation trending NNW-SSE is compatible with the Alpine compression whereas the fractures 2 to 6 have been attributed to the Neogene extension. The fractures 2, without preferred orientation, generated a fault breccia related to the initial propagation of the Neogene normal faults. The fluid involved during this deformation, shows a high interaction with the host-rock, in a closed hydrological system. The fractures 3, enlarged by the subaerial exposure of the Mesozoic horsts, are filled by different karstic sediments. The geochemistry of the sediments indicates the opening of the system to meteoric water. When the normal faults reached to the surface, fractures 4 to 6 are formed. The fractures fillings are a mixture of tectonic and karstic processes and resulted from multi-stages movement of the normal faults.
-
-
-
A Hierarchical Database on Carbonate Geobodies and its Application to Reservoir Modelling Using Multi-point Statistics
Authors A. Jung, T. Aigner, D. Palermo, S. Nardon and M. PontiggiaQuantitative data on geobodies are crucial both for standard reservoir modelling processes as well as new modelling technologies such as Multiple Point Statistics (MPS). While abundant quantitative data for siliciclastic systems are available in the literature, so far such data are scarce for carbonate systems. In addition, a method for organising and classifying the data is so far missing for carbonates. Carbdb, one of the outcomes of the TETRIS (TEmplate for TRaining ImageS) R&D project driven by ENI E&P to provide quantitative geological information for MPS training images, is an interactive database system on carbonate geobodies. Carbdb uses a hierarchical modular genetically based structure with the following levels: depo-time (geological time), depo-system (carbonate platform type), depo-zone (facies belt), depo-shape (geological body), depo-element (archi-tectural elements) and (6) depo-facies (litho- and biofacies). Carbdb works as a central server providing a web-based interface to its users over the network. Practical application of the system is demonstrated by training image (Ti) construction on basis of a well studied Cretaceous outcrop in southern France. Even in the context of complex carbonate systems the employment of relatively simple and schematic training images generates geological meaningful realisations.
-
-
-
Fractures Characterization in Carbonate Rocks
By B. SapiieFractures can act as a major control on porosity distribution in carbonate reservoirs. In general, three different types of open fractures can be found; shear fractures, extensional fractures and stylolites. All types can be equally important in controlling porosity and permeability distribution. Detailed outcrop study of the Tertiary carbonate complex has been carried out to characterize fracture type, distribution and density. The field observations were made using the one dimensional scan-line method and the data was analyzed utilizing standard statistical methods. The results of the study show that there are fracture characteristics that are strongly dependent on carbonate facies. Based on the data analysis, both fracture spacing and length followed power law distribution. The statistical analysis show the average R2 of fracture spacing is ranging between 0.85-0.97 meaning the data showing excellent correlation coefficient. This indicates that small scale fractures form an important part of the overall porosity. However, fracture density is also clearly controlled locally by the presence of faults and folds. Secondary processes such as dissolution along stylolite surfaces due to the groundwater interaction have also played a major role in enlarging fracture apertures.
-
-
-
Structural Controls and Plattendolomit Reservoir Description of the Wissey Field, UK Southern North Sea
Authors C. Duguid and J. R. UnderhillZechstein Supergroup carbonates have in general formed a highly disappointing exploration target beneath UK waters. The Wissey gas field, situated on the southern margin of the UK Southern North Sea is the first gas field in that region to produce solely from Zechstein Supergroup Carbonates and specifically the Z3 Plattendolomit Formation. Investigation, integrating seismic interpretation with well data analysis has explored the stratigraphy and structural complexity of the region surrounding Wissey. Furthermore, the nature of the naturally fractured Plattendolomit Formation reservoir and controls on the observed reservoir quality have been identified and are set in the context of both the Z3 depositional system and the subsequent deformation observed. Suggestions are presented for consideration in existing and new exploration opportunities with Zechstein Supergroup reservoir targets.
-
-
-
Using Duplex Wave Migration for Mapping of Fracture Zones in Oil-fields from Northern Russia
Authors I. U. Khromova and B. H. LinkThis paper describes examples of mapping fracture zones in carbonate reservoirs using duplex wave migration (DWM). This method is used following conventional pre-stack depth migration with a new and very different type of pre-stack depth migration called DWM plus interpretation. The theoretical basis of the DWM process enables its ability to provide accurate and detailed detection of the position and properties of vertical boundaries and of the fracture zones confined by them. Fracture zones revealed using the DWM process are compared with available well information that verifies the existence or absence of anomalous permeability, its direction, and most importantly, information about the intensity of open fracturing in productive wells. The locations of open fracturing are verified by the productivity factors and interconnection of these wells. Also, the DWM results are compared with the results of standard methods for seismic data interpretation, which are widely used for mapping of small-scale faults and fracture zones.
-
-
-
Estimating In-situ, Anisotropic, Principal Stresses from 3D Seismic
Authors F. D. Gray, P. F. Anderson, J. Logel, F. Delbecq and D. SchmidtThe principle stresses, vertical, maximum horizontal and minimum horizontal, and rock strength parameters can be estimated from wide-angle, wide-azimuth seismic data. This is demonstrated using a small 3D seismic survey over the Colorado Shale Gas play of Alberta, Canada. It is demonstrated that this information can be used to optimize the placement and direction of horizontal wells and hydraulic fracture stimulations.
-
-
-
Geology of a Giant Bitumen Reservoir – Grosmont Formation, Northeast Alberta, Canada
More LessThe Grosmont Formation contains one of the world's largest accumulations of bitumen. The reservoir rock facies is a karsted dolomite with very high porosity (25-40%) and permeability. A four stage reservoir model is put forward to explain the reservoir development and bitumen accumulation. Core photos, SEM, XRD and thin section data are used to support the model.
-
-
-
Reactivity of Dolomitizing Fluids and Evaluation of Mg Sources in the Benicassim Area (Maestrat Basin, E Spain)
Authors E. Gomez-Rivas, M. Corbella, J. D. Martín-Martín, A. Teixell and E. CardellachHydrothermal dolomitization is one of the most important processes in enhancing or degrading carbonate porosity and permeability. This type of dolomite forms due to the circulation and/or mixing of different types of solutions, mainly seawater-derived or deep brines. The Lower Cretaceous Benicassim dolomitized ramp is an excellent example to study and evaluate the impact of hydrothermal dolomitization on reservoir quality distribution. In this contribution, the possible magnesium sources for the Benicassim case study are evaluated, as well as the reactivity of different dolomitizing fluids at variable temperatures. The results show that dolomitization at Benicassim occurred due to the circulation of a high temperature (> 80ºC) fluid that had its origin from evolved seawater that interacted with K-rich rocks, probably from the Paleozoic basement. Reactivity evaluation of four possible dolomitizing fluids, by means of geochemical modelling, reveals that evolved seawater can be considerably more reactive than high-salinity brines. Fluid mixing between seawater and saline brines at 100 ºC does not seem to affect the volume of fluid required to dolomitize the whole rock, but it considerably alters the saturation index of calcite. The variation of saturation index is a strongly non-linear process when two fluids are mixed.
-
-
-
An Acquisition Model for an Interim Life of Field Seismic Project at the Azeri-Chirag-Gunashli Field in the Caspian Sea
Authors R. Seaborne, D. J. Howe, W. Slopey and A. TalibovThe Chirag Azeri Reservoir Seismic Project (CARSP) is the latest phase of seismic acquisition for reservoir management on the Azeri-Chirag-Gunashli (ACG) oil field complex in the South Caspian Sea, Azerbaijan. This paper describes the philosophy behind a semi-permanent Life of Field Seismic (LoFS) configuration deployed over the field, the details of the equipment used, the operational challenges that were confronted and overcome and the timeline of events to acquire two sets of time-lapse (4D) four component (4C) OBC surveys during 2007 and 2008.
-
-
-
Implementing the Long Term Seismic Strategy for the Azeri-Chirag-Gunashli Field, South Caspian Sea, Azerbaijan
Authors N. D. Robinson, M. C. Riviere, K. Tough and P. A. WatsonThe objectives of this paper are to show how a robust seismic strategy has been developed for the ACG Field and to provide an overview of how the implementation of that strategy has provided significant advances in 3D imaging and 4D surveillance. The strategy was underpinned by a willingness to deploy and develop new acquisition and processing techniques and a determination to ensure that the best quality processing result was obtained from our investment in acquisition.
-
-
-
Improvements in 3D Imaging over the Azeri-Chirag-Gunashli Field, South Caspian Sea, Azerbaijan
Authors K. Tough, M. C. Riviere, N. D. Robinson and P. A. WatsonThis paper describes how the results from new seismic acquisition and processing have led to progressive improvements in the seismic data and the static description of the reservoir interval over ACG. In particular, we will concentrate on two significant contributors to improved data quality. Firstly, the change from towed streamer to OBC seismic acquisition and secondly, the use of full waveform inversion as part of the velocity model building flow.
-
-
-
4D Seismic Surveillance over the Azeri-Chirag-Gunashli Field, South Caspian Sea, Azerbaijan
Authors M. C. Riviere, N. D. Robinson, K. Tough and P. A. WatsonThis paper describes the progress made with 4D seismic to image fluid movement within main ACG reservoirs. It will briefly review results from a pilot 4D project using streamer-tow seismic, which demonstrated the viability of 4D monitoring. The results from the streamer-tow 4D together with the uplift in imaging seen from a 2002 Ocean Bottom Cable survey (OBC) provided the impetus to acquire further OBC seismic data in 2007 and 2008 using a dedicated acquisition model under the name CARSP (Chirag Azeri Reservoir Seismic Project).This paper will review results from comparing CARSP back to legacy data (both streamer-tow and OBC), and comparing CARSP 2008 to CARSP 2007 data.
-
-
-
Is Your Prospect Sealed – From a Geophysical and Pore Pressure Perspective
Authors J. H. Yu and M. PottorfFor a typical prospect evaluation, the three main technical elements are migration, reservoir and trap. Traditionally geoscientist employs structural interpretation to assess the trap or seal integrity. In this paper we focus on how to use pore pressure to evaluate the seal integrity since without a proper trap mechanism or seal integrity, the hydrocarbons would continue to migrate out of the reservoir and result in no prospect. To be able to extract accurate pore pressure from seismic data, we must understand the causes and mechanisms of abnormal pressure. When they are better understood, a mathematical model can be built to estimate the formation pore pressure. We present a systematic workflow to condition the input seismic data and build a well-calibrated pressure model to estimate a high density high resolution (HDHR) 3D pore pressure volume from seismic data. This calibrated pressure model is unique because it takes into account burial depth, temperature gradient and shale diagenesis as well as the compaction and loading and off-loading trends. We discuss how to visualize and interpret pore pressure with seismic data and demonstrate the usefulness of this calibrated pressure model with real case studies for seal capacity evaluation.
-
-
-
Integrating Seismic & Potential Field Data in Hydrocarbon Prospectivity Assessment – Pantelleria Region Offshore Sicily
Authors S. J. Coomber, J. Field and D. HarrisonSeveral oil and gas/condensate accumulations have been discovered offshore north-eastern Tunisia. These discoveries are south-west of the volcanic island of Pantelleria, which is situated within the NW-SE trending Pantelleria Graben, in the Straits of Sicily. The last two years have seen renewed exploration efforts to the north-east of the graben. This included 600 km's of 2D marine seismic data acquisition, with simultaneous potential field (i.e. gravity and magnetic) data, in 2009. Some of the oil fields to the south-west of the graben are coincident with gravity highs relating to structural uplift. The recent exploration to the north-east of the graben was originally targeted to investigate a similar gravity and structural high, initially identified from regional satellite gravity data. By modelling marine gravity and magnetic data, integrated with interpretation of the seismic data, it has been possible to achieve a clearer understanding of the geological history of the area. This has made a significant contribution to the assessments of the area's hydrocarbon prospectivity and decisions regarding future exploration in the area.
-
-
-
Exploration Challenges in the Valencia Trough, Offshore Spain – The Lubina and Montanazo Discoveries
In 2009, two discoveries were made in the Valencia Trough (offshore Spain): Lubina and Montanazo. The Valencia Trough is an oil bearing province that presents important challenges such as geohazards, reservoir imaging and evaluation. This study presents the successful experience that resulted from the use of different technology to overcome the dificulties to explore carbonate reservoirs.
-
-
-
Unlocking Resources in Mature Basins Using Seismic Technology
Authors L. Ben-Brahim, F. Cailly, M. P. Duval-Valentin, J. Guerra, M. Rowlands and K. PatelMost of the UKCS basins are very mature with a high well density and well known plays. The continued search for additional resources both through exploration or delineation, is fuelled by the presence of nearby infrastructures and facilitated by improved technology. Seismic plays an important role, both at exploration (prospect identification and derisking) and appraisal-development stages (field evaluation and uncertainty reduction) thanks to continued improvements at various steps of the geophysical chain. This paper will illustrate through several recent examples (West of shetlands, Northern North Sea, Central Graben)how a better understanding of the geological key elements was made possible thanks to optimized seismic data
-
-
-
4D Joint Pre-stack Seismic Stratigraphic Inversion of the Sleipner-CO2 Case
Authors N. Delepine, K. Labat, V. Clochard, P. Ricarte and C. Le BrasTime-lapse seismic data acquisition and processing is a mature technology to monitor changes of rock properties due to hydrocarbon production. The same efficiency is expected from this technology to monitor carbon dioxide (CO2) injected in underground reservoirs. Since 1996, Statoil has injected more than 11 million tons of CO2 in a saline aquifer of the Sleipner field (Norwegian North Sea). This Carbon Capture and Storage (CSS) industrial pilot is now considered as an international reference site. To insure an accurate monitoring, seismic surveys are carried out every two years or so, thus providing the research community with an exceptional series of 3D seismic datasets. In order to further characterize the CO2 injection into the Sleipner saline aquifer, we present here the results of a joint stratigraphic inversion of time-lapse seismic data. This approach has been applied to the 1994 and 2006 vintages to obtain detailed estimates of the elastic parameters within the aquifer. After a presentation of the joint pre-stack stratigraphic inversion methodology, we focus on the quantitative analysis of the inverted elastic parameters to demonstrate the efficiency of the joint inversion with respect to independent inversions of the successive datasets.
-
-
-
Data-driven Quantitative Analysis of the CO2 Plume Extension from 4D Seismic Monitoring in Sleipner
Authors P. N. J. Rasolofosaon and N. Dubos-SalléeAmong the measures to reduce the amount of greenhouse gases in the atmosphere, the geological storage of carbon dioxide (CO2) is one of the most promising. Since 1996, more than 11 million tons of CO2 have been injected in a saline aquifer, the Utsira sand, of the Sleipner field (North Sea). An extensive seismic monitoring programme over the CO2 injection area have been carried out. Using more or less sophisticated rock physics models, seismic images of the injected zone were previously interpreted quantitatively in terms of the total volume and of the total mass of CO2 in place. In this study, starting from the cubes of the prestack-inverted seismic impedances, we propose a method for computing the cube of CO2 saturation, and for estimating quantitatively the CO2 plume (volume and mass) without using any petroelastic model. In contrast we exploit some characteristics of the particular flow regime associated with CO2 injection in a saline aquifer, namely the first drainage regime. To our knowledge, such a detailed CO2–saturation cube has not been published before. Summation over the whole cube provides an acceptable match for the known injected CO2 mass.
-
-
-
Passive Seismic Monitoring of CO2 Storage at Weyburn
Authors J. P. Verdon, D. J. White, J. M. Kendall, D. A. Angus, Q. J. Fisher and T. UrbancicPassive seismic monitoring has been ongoing at the IEA GHG Weyburn-Midale Project since 2003. We present the microseismic activity recorded during a 5 year period, showing event timings and locations, and discussing the implications for storage integrity. We link passive seismic observations with predictions about event locations and seismic anisotropy made by a simple geomechanical model, demonstrating the importance of combining observation with modelling in order to guarantee successful storage.
-
-
-
Seismic Monitoring in the Framework of the Pilot Project CLEAN
More LessThe joint research project "CLEAN" (CO2 Largescale EGR in the Altmark Natural-gas field) is a scientific program accompanying the Enhanced Gas Recovery (EGR) project within the Almark Natural gas field. During the period of three years an amount of 100,000t of CO2 will be injected into the reservoir layer. The Injection is accompanied by a large number of biological, chemical and physical monitoring experiments, which are designed to monitor the spatial and temporal evolution of the CO2 front within the reservoir as well as the related processes. The instrument to achieve this aim are active and passive seismic measurements. Therefore a time-lapse VSP/MSP survey as well as the installation of a borehole seismometer network for the monitoring and analysis of potential injection-induced seismicity are planned. In preparation to the VSP/MSP experiments rock physical estimates and simulations of the seismic wavefield were performed in order to get information concerning the implementation. These information are boundary conditions for the survey design as well as the expected ampitude changes and their detectability.
-
-
-
Quantitative Seismic Monitoring of CO2 at Sleipner Using 2D Full–waveform Inversion in the Time–lapse Mode
Authors S. C. Singh and M. QueisserGeological sequestration of CO2 is considered to be an important greenhouse gas mitigation technology (Washington et al. 2009). Current public resistance to onshore sequestration sites makes offshore sites an attractive alternative. The Sleipner gas field in the North Sea is such a site and has been the worlds first industrial scale CO2 storage project. An effective CO2 storage requires monitoring and verification over large areas. Time lapse seismic monitoring is an integral tool to do so. Here we use time lapse elastic 2D full wave form inversion (FWI) to monitor CO2 in the Sleipner aquifer reservoir and retrieve the amount of free CO2. Inverted P-wave velocities (Vp) are related to gas saturations using a fluid substitution model employing Gassmann theory assuming patchy saturation. We find that a considerable amount of the injected CO2 could be in dissolved form by 2006 and hence saline aquifers could be a natural reservoir for CO2 storage.
-
-
-
From Surface Deformation to Permeabiltiy – A Case Study
Authors A. Rucci, A. Ferretti, F. Novali and D. W. VascoInterferometric Synthetic Aperture Radar (InSAR) measurements provide accurate, large-scale estimates of displacements within material overlying a producing reservoir. Such deformation proves useful in deducing spatial and temporal changes in reservoir fluid pressure. Starting from the pressure field we estimate the diffusive travel times, and then, as the solution of a linear inverse problem, the effective permeability of the reservoir. We apply the formulation to subsidence in the material overlying a thin gas production zone at the Krechba field in Algeria.
-
-
-
Mineral Sequestration of Naturally Occurring CO2 in Rankin Trend Gases, Carnarvon Basin, Australia
Authors E. Tenthorey, C. Boreham, A. Hortle and J. UnderschultzHigh-CO2 gas fields serve as important analogues for understanding various processes related to CO2 injection and storage, including assessing the relative importance of mineral precipitation and/or solution trapping efficiency. In this paper, we present a high resolution study focused on the Gorgon gas field and associated Rankin Trend gases on Australia’s North West Shelf. The gas data we present here display clear trends for CO2 abundance (mole %) CO2 and d13C CO2 both areally and vertically. Generally, CO2 mol % decreases and becomes depleted in d13C with decreasing depth and towards the north; a pattern which also holds true for the greater Rankin trend gases in general. We propose that these variations were driven by the precipitation of a carbonate phase, namely siderite, which is observed as a common late stage mineral. The results from this study have important implications for carbon storage operations and suggest that significant volumes of CO2 may be sequestered from a gas plume over short migration distances.
-
-
-
Effect of Mixing on Acid Gas Sequestration Processes
Authors A. Lukyanov, A. Garipova, A. Priestley and S. HurterThis paper presents different models of mixing rule allowed to calculate a corresponding density, viscosity and relative permeability of the aqueous phase containing dissolved acid gas in it. It has been shown that the mixing process under different geological condition (e.g., mechanical dispersion, variable water saturation) has an important effect during the geological storage of acid gas.
-
-
-
Fast 3D ZO CRS Stack – An FPGA Implementation of an Optimization Based on the Simultaneous Estimate of Eight Parameters
Authors P. Marchetti, D. Oriato, O. Pell, A. M. Cristini and D. TheisWe show over 200x speedup of our proprietary data intensive application, 3D-ZO-CRS, utilizing a FPGA-based solution, compared to conventional x86_64 CPU cores. As well as performance a second, but no less important, target was to maintain the portability of the basic C/FORTRAN source code for other platforms. A third important point considered in this paper regards maintaining the capability to “recompile” the code in case of small modifications and/or discovery of bugs. In this paper we present our approach and some general considerations regarding the use of such acceleration technology on the data grid environment previously developed for this application.
-
-
-
Running 3D Finite-difference or Spectral-element Wave Propagation Codes 25x to 50x Faster Using a GPU Cluster
Authors D. Komatitsch, D. Michéa, G. Erlebacher and D. GöddekeWe first accelerate a three-dimensional finite-difference in the time domain (FDTD) wave propagation code by a factor of 50 using Graphics Processing Unit (GPU) computing on a NVIDIA graphics card with the CUDA programming language in the case of the fully heterogeneous elastic wave equation. We also implement Convolution Perfectly Matched Layers (CPMLs) on the graphics card to efficiently absorb outgoing waves on the fictitious edges of the grid. The methodology can be used for Maxwell's equations as well because their form is similar to that of the seismic wave equation written in velocity vector and stress tensor. We then implement a high-order spectral-element seismic wave propagation application on a cluster of GPUs. We compare it to a C+MPI implementation on a classical CPU cluster. We use mesh coloring to efficiently handle summation operations over degrees of freedom on an unstructured mesh. Using non-blocking MPI communications allows us to overlap the communications across the network and data transfers between the GPUs and the CPUs with calculations on the GPUs. We validate the CUDA and MPI implementation and analyze performance measurements. In average we obtain a speedup of 20x to 25x.
-
-
-
On Efficiency of Data Compression for Acceleration of Seismic Processing
Authors V. G. Tulchinsky, I. V. Nazarenko and O. K. IushchenkoEfficiency of data compression for computer clusters processing the massive seismic datasets is examined. A compression isoefficiency estimate is proposed to verify a compression method applicability for acceleration and to compare different methods. 5 algorithms of time cube compression are compared to accelerate duplex wave migration.
-
-
-
A Massively-parallelised Spatially-registered Data Structure for Integrated Subsurface Data Management
Authors D. H. B. Irving, M. Rasheed and N. O‘DohertyWe demonstrate the application of a massively parallel architecture to subsurface datasets, specifically Terabyte scale multi-attribute seismic volumes and derived interpretation. We decompose subsurface data into spatial, attribute and metadata components. Subsurface attributes are stored by their location whilst retaining the spatial scope (e.g. bin size), their original format (e.g. SEG-Y) and source file in a MPP storage array. We have developed a hashing algorithm which permits computationally efficient recovery of multi-resolution data as a near-instaneous operation regardless of the size and complexity of the dataset. We demonstrate efficiencies both computationally - when working with derived seismic parameters and attributes (e.g. instantaneous phase, variance); and in retrieval - when extracting arbitrarily oriented seismic profiles in a timely manner for use by a visualisation application. We compare this to the performance of enhanced GIS-based systems and suggest that a fully integrated architecture is more appropriate interacting with enterprise-scale data volumes.
-
-
-
RTM High Performance I/O Considerations
Authors A. Farrés, M. Hanzich and J. M. CelaRTM was proven to be an industrial-strength application that is crucial in seismic imaging. However, it is a resource-consuming application that demands a high I/O performance. Moreover, HPC platforms are changing and the I/O structure of those systems evolve. This encourage RTM developers to take into account underlying I/O architecture in order to maximize its efficiency and hence RTM performance. Among the considerations are the kind of global and local file systems, the size of the system transfers and buffers, and the directory locking policy and data distribution. How to set those parameters are a main concern if high performance I/O has to be extracted from modern HPC systems.
-
-
-
Practical VTI RTM
Authors M. P. Perrone, H. Zhou, G. Fossum and R. ToddIn this abstract we describe a production implementation of 3D anisotropic VTI RTM using a finite-difference scheme on production cluster. Our end-to-end code is about four times faster than a blade that consists of dual Intel quadcore Harpertown running a similar VTI RTM code, including vectorization. It is interesting to note that in the final implementation disk IO is the bottleneck. This means that faster compute nodes (increased FLOPS per core) will not improve performance. What is needed is more disk bandwidth (>200MB/s per processor) to make it run faster, and/or more computationally intensive versions of RTM to generate better images.
-
-
-
Automated Software Development in Heterogeneous GPU/CPU Environments for Seismic Modeling
Authors A. Varanovich, V. Tulchinsky, E. Burmako, V. Falfushinsky and R. SadykhovRecent studies in the field of seismic modeling show us that utilizing graphical processors as a part of computing clusters give significant performance benefits. There are different types of applications available for the most common cluster configuration. We introduce a research program framework called Conflux, which allows efficient utilization of the new paradigm of writing mixed GPU/CPU algorithms. Conflux provides a parallel programming framework to use CPUs and GPUs in collaboration as components of an integrated computing system. The paper shows advantages of using the framework to solve most typical tasks in the field of seismic modeling. The performance metrics were obtained from two approaches in the implementation of 2-D finite-difference acoustic modeling: native C implementation for NVidia CUDA library and Conflux based on C#. The results given allow to conclude that keeping the same level of performance we gain an advantage in the overall development efforts for writing seismic algorithms as well as flexibility of targeting different types of hardware architectures including GPU-enabled clusters.
-
-
-
Integrated Mobility of G&G Data
Authors I. Zulfiqar and M. S. Bokharipetroleum venture, from the initial opportunity analysis and exploration, through appraisal, production and the abandonment phase. E&P companies accumulate data from many sources which are in many different formats. However, the identification of the relevant data and its availability in the required form takes substantial time in the evaluation process. E&P companies are increasingly trying to leverage from data management and GIS technologies in order to overcome these barriers. Data management encompasses three key areas: physical assets management, electronic data management and digital data management. GIS more coherently manages spatial data and makes cross-discipline spatial data available to users. But the mammoth size of each individual repository foils the very criterion of relevance and ease of use. This paper discusses Eni Pakistan’s experience regarding its execution of G&G data management and GIS project. It examines the use of business objects as an integrating factor across multiple repositories and how PetroBank / PowerExplorer, ArcSDE and ArcIMS technologies were utilized to create a holistic view of G&G data. Furthermore, it also discussed the concept of Integration Mobility that it used in its implementation.
-
-
-
Flow Patterns of Dolomitizing Solutions in a Buried Carbonate Ramp – The Benicassim Case Study (Maestrat Basin, NE Spain)
Authors E. Gomez-Rivas, S. L. Stafford, A. G. K. Lee, M. Corbella, J. D. Martín-Martín and A. TeixellGeometric, petrographic, and geochemical observations suggest that sub-stratiform dolomitization in a Lower Cretaceous Benicassim ramp (Maestrat Basin, E Spain) was due to the circulation of high temperature brines through faults and high permeability layers. In this study, fluid and heat flow numerical simulations are applied to investigate the controls on hydrothermal flow in this area, depending on the tectonic activity at the time of dolomitization. The results indicate that flow caused by rapid release of overpressured fluids below seals in recurrent pulses through large-scale faults may drive enough fluid for dolomitization, but not enough heat. Thermal conduction dominates advection over large-time scale. However, long-term fluid circulation, due to differences in pressure and temperature within the basin, can pump dolomitizing fluids at high temperature during long periods of time if the system is open. Moreover, a permeability contrast of two orders of magnitude is required to have lateral flow preferentially in some layers and to form relatively sharp, sub-stratiform dolomitization fronts.
-
-
-
Constraining Fracture Distribution in an Atoll-like Carbonate Platform - Results from Field Observations and 3D Geomec
Authors H. Boro, G. Bertotti, F. Beekman and S. M. AgarIt is known that the presence of fractures in carbonate reservoirs will have significant impact on the fluid flow. Depending on their properties, fractures could act either as a conduit or as a barrier, therefore understanding their distribution throughout reservoir is really important. In this study we present our results on fracture analysis affecting the Latemar carbonate platform. The newly developed fracture acquisition method, equipped with GIS application, has been applied in the field to acquire full description of outcrops. Through statistical analysis, fractures are then characterized from various domain and structural setting to observe the controlling factors. The numerical modelling approach has been incorporated into this study. Guided by hi-res Lidar images interpretations, the 3D geological model of Latemar is produced to constrain the geometry of different domains for the mechanical modelling. Through finite element method, several loading scenarios have been applied to the 3D model, to observe the distribution of the deformation, i.e. fracturing. The results from numerical modelling and field observation will provide better insight to predict fracture distribution in subsurface reservoirs.
-
-
-
A Combined Numerical-experimental Approach to Study Sub-grid Transport Processes in Real 3D Carbonate Rocks
Authors S. Geiger, C. Fricke, K. S. Schmid, Y. Zaretskiy, I. Butler, S. Elphick, K. S. Sorbie and M. I. J. van DijkeWe have developed a new finite element – finite volume based simulation approach to study flow and transport processes at sub-grid scales, i.e. at scales below the typical size of a reservoir simulation grid block, using real 3D geometries in carbonate reservoirs. We complement the simulations by high-resolution X-Ray CT experiments which provide us with the 3D structures, allow us to visualise flow processes at the core-scale in real time, and help us to compare the observed processes to numerical simulations to validate and verify the latter. We use this combined numerical-experimental approach to analyse the fundamental processes controlling fluid flow in carbonates at sub-grid scales. Results can be incorporated in existing reservoir simulation workflows to increase the confidence in reservoir performance forecasting. We show applications related to fractured carbonate reservoirs and enhanced oil recovery processes due to injection of low-salinity fluids and hot water.
-
-
-
Multi-scale Approach 3D Facies Modeling Applied to an Inner Carbonate Ramp Setting (High Atlas, Morocco)
Authors F. A. Amour, M. M. Mutti, N. C. Christ, A. I. Immenhauser and L. K. KabiriThe quality and level of resolution of 3D facies models are crucial factors for reservoir characterization and fluid flow prediction. This study presents a newly developed workflow from field acquisition to modeling approach, which can be used to model heterogeneities at different scale ranging from lithofacies, to Environment Of Deposition (EOD), to system tract deposited on a carbonate dominated ramp setting. This multi-scale approach integrates different data sets (stratigraphic sections, d-GPS points, LiDAR data) and allows to build three coherent models from these three scales of observations.
-
-
-
Fracture Field-data Acquisition and Processing, Customized Software and Datamodel Development
Authors N. Hardebol, G. Bertotti, N. de Reus and H. BoroThis study presents a work-flow and software development initiative that aims at the digital field acquisition of fracture-network datasets and is devoted to the characterization and upscaling of fractured-reservoirs from outcrop analogs. The workflow and Digifract software that we present make it possible to make use of the full potential of outcrops to capture the 3-D spatial arrangement of individual fractures. DigiFract is an innovative software package designed and developed by the VU University (Amsterdam) and Delft University of Technology in the last few years to acquire fracture data from vertical outcrops more efficiently and more completely than done with more traditional (scan-line) methods. The purpose of the Digifract development initiative is to embed GIS functionality in our custom application to meet our purpose for digital field-data acquisition. This implementation makes full use of GIS capabilities, among which are spatial referencing of outcrop photos, digitizing of geometries and spatial relationships, and user-friendly intuitive graphical user interface. This study shows the advantage of direct digital acquisition of the fracture networks from outcrops and outlines the development of a software that facilitates this. The DigiFract software has been used in various research projects.
-
-
-
Fault–associated Dolomites in the Benicàssim Area, Maestrat Basin, E. Spain – Macro– to Micro–scale Fluid Flow in Carbon
Authors J. D. Martín-Martín, A. Travé, E. Gomez-Rivas, J. P. Sizun, R. Salas, D. Gómez-Gras and J. VergésPartial dolomitization of the middle to late Aptian carbonate succession from the SE Maestrat Basin (E. Spain) occurred during shallow burial in relation to the circulation of high temperature fluids (>60º C) through regional extensional faults and most permeable host limestone facies. The timing of replacement is constrained between the early Albian (syn-rift) and the Campanian (post-rift). Analytical data suggest that most likely dolomitizing fluid is evolved Aptian/Albian seawater, probably mixed with basinal waters. The resulting replacive dolomite texture has very low porosity, mainly of vuggy type, that was successively enhanced by dissolution and occluded by burial dolomite and calcite cementation during Late Cretaceous. Dolomite hosted Mississipi Valley-type ore deposits, and associated saddle dolomite, formed due to hydrothermal alteration through large-scale faults during the onset of the Tertiary. Later Alpine uplift and fracturing promote meteoric calcite cementation and dedolomitization through fractures and fault zones. Porosity and permeability data evidence a very bad potential reservoir quality of the host limestone, being only slightly higher in the dolomites due to the reported pervasive burial calcite cementation. Results provide a new case study of partial dolomitization that can be used in the characterization of equivalent hydrocarbon reservoirs worldwide.
-
-
-
Fracture Modeling Using Advanced Numerical Techniques
More LessExtensional strain in the brittle crust is usually accommodated by opening mode natural fractures. These opening mode fractures grow perpendicular to the direction of least compressive principal stress and can form under a combination of loading conditions, including elevated pore pressures, folding of geological strata, burial/uplift of heterolithic layers, and slip along preexisting faults. Fractures occur in varying orientations, form clusters, and have different propagating lengths and apertures. Analytical solutions such as curvature analyses, restoration techniques, elastic continuum models and stochastic approaches for natural fracture prediction have been favored over more sophisticated continuum and hybrid (finite-discrete) analyses because of their computational efficiency and ease of implementation. This argument is somewhat dated in light of advances in computer processing speed and capabilities. Truly predictive methodologies must emphasize accurate modeling of the material response throughout the deformation. This study demonstrates recent advances in natural fracture predictive capabilities using advanced discontinuum and continuum analyses. Advanced numerical analysis coupled with a fracture initiation criteria enable geologically realistic fracture modelling at a range of scales. These new numerical capabilities help identify fracture sweet spots that can form due to a variety of loading conditions.
-
-
-
Sensitivities to Flow–modeling Assumptions for a Heterogeneous Carbonate Ramp – An Example from a Jurassic Carbonate Ramp
Carbonate reservoirs pose significant challenges for reservoir simulation and flow prediction due to lateral and vertical heterogeneities that are difficult to predict. Limits to seismic resolution, heterogeneities in rock properties and limited constraints on subsurface data require the consideration of multiple geologic scenarios for flow predictions. Hence, a systematic and streamlined approach is needed to construct geologic models and to quickly evaluate key sensitivities in the flow models. This paper discusses results from a reservoir analogue study in a Mesozoic carbonate ramp in the High Atlas of Morocco. Here, geologic models have been constructed from the integration of sedimentological, diagenetic and structural studies in the area. Novel methods have been applied to develop a consistent approach for rock property definitions in outcrops and incorporate multi-scale fractures to test the response in flow simulations. In these simulations we have tested the response of presence or absence of specific geologic features, including hardgrounds, stylolites and fracture populations as a way to guide the level of detail that is suitable for modeling objectives. Based on these studies, we have been able to evaluate the relative impacts of some of the geologic features on flow behavior and gain further insights to effective recovery strategies.
-
-
-
From RESCUE to RESQML – The Open Standard Format of Reservoir Earth Model Takes Up New Dimensions and Momentum
Authors R. Henri-Bally, J. F. Rainaud, L. Towery, J. Schey, D. Heath, P. Sabharwal and C. SewellToday’s reservoir studies are, more than ever, integrated both upstream with geophysical and geological data, and downstream with flow simulation benchmarked by fast time-lapse production data. Additionally, for such studies there has been an increased use of multiple scenarios, aimed at better understanding uncertainties and reducing risk. BP, Total & Shell, with the strong support of most prominent software companies and institutes, initiated the RESQML Special Interest Group (SIG) and decided to open the concept of consistent Earth Model exchange using XML technology. They defined an initial set of use cases like Import from and to Flow Simulation , Attribute Extraction , Horizon TimeDepth Import , Combine matrix and fracture properties and Update Fault for History Match. Draft XML Schemas of reservoir characterization objects were delivered along 2009 , and were tested and validated against a set of real data provided by Total. By the end of 2009 the first version (V1) was drafted including Structural and Grid Features. The infrastructure has been defined, configured and tested. This includes the global architecture with geolocalization capabilities and a link between XML and a binary file (HDF5). RESQML has gained steady momentum, with the objective to release V2 by year end 2010.
-
-
-
A Knowledge-driven Shared Earth Modeling Workflow for Seismic Interpretation and Structural Model Building
Authors J. F. Rainaud, P. Verney and L. MastellaWe have been claiming for several years that Shared Earth Modeling should be “knowledge-driven”. This approach considers geology as a key knowledge to which all expert fields necessarily refer. According to this approach, a permanent link can be established at each stage of the modeling process between the various objects considered (seismic reflectors, well markers, geometrical surfaces) and the geological objects (GeologicalUnits, GeologicBoundaries) to which they have been associated thanks to geological interpretation. In this paper we explain how we formalize, populate, reuse, extract and exploit this knowledge for opening the communication between several processing stages (prospect initiation, well marker, seismic interpretation, structural modelling) and for offering the possibility of permanently completing and updating the various representations. This solution, based on a semantic approach, basically consists in formalizing knowledge attached to geological, seismic and well log data by means of Domain Ontologies, operating a knowledge based method for seismic interpretation and providing results allowing automated building of a structural model, opening the possibility of retrieving all useful information concerning the interpretations operated at the various stages of the modeling workflow by means of various knowledge management tools. This solution will be described in reference with a practical example.
-
-
-
Seismic History Matching in Fractured Reservoirs Using a Consistent Stiffness-permeability Model – Focus on the Aperture
Authors A. Shahraini, M. Jakobsen and A. AliThis paper proposes a method for characterization of naturally fractured reservoirs by quantitative integration of seismic and production data. The method is based on unified (T-matrix) model for the effective hydraulic and elastic properties of fractured porous media and a (nonlinear) Bayesian method of inversion which provides information about uncertainties as well as mean (or maximum likelihood) values. We consider a fractured reservoir as a porous medium containing a single set of vertical fractures characterized by an unknown fracture density, azimuthal orientation and aperture. We then look at the problem of fracture parameter estimation as a nonlinear Bayesian inverse problem and try to estimate the unknown fracture parameters by joint inversion of seismic AVAZ data and dynamic production data. Once the fracture parameters have been estimated the corresponding anisotropic stiffness and permeability can be estimated using consistent models. A synthetic example is provided to explain the workflow. It shows that seismic and production data complement each other, in the sense that the seismic data resolve a non-uniqueness in the fracture orientation and the production data helps to recover the true fracture aperture and permeability, because production data are more sensitive to the fracture aperture rather than the seismic data.
-
-
-
Effect of Natural Fracture on Hydraulic Fracture Propagation in Naturally Fractured Reservoir – A Finite Element Modeling
By M. RahmanNumerical results have shown that at high angle of approach and differential stress, it is more likely for the hydraulic fracture to cross the natural fracture, whereas for a case where angle of approach and differential stress are low the hydraulic fracture is more likely to be arrested and then reorient the existing path and propagate through natural fracture. In the case of 90o (close to 90o) angle of approach the hydraulic fracture always crosses the natural fracture and the differential stress has no significant effect on the trajectory of the hydraulic fracture propagation. It was, however, observed that for the high fracture half length and the high width of the natural fracture, long injection time, hence high injection pressure, is required for the hydraulic fracture to cross the natural fracture. Results of our study also suggest that when a hydraulic fracture intersects a natural fracture it is initially arrested. With increased pressure due to continuous pumping, this intersection causes the natural fracture to dilate, or dilate and cross or break out at the far end of the natural fracture. Every case we observed the width discontinuity when induced fracture cross the natural fracture or propagate through the natural fracture.
-
-
-
Impact of Three-phase Relative Permeability Model on Recovery in Mixed Media – Miscibility, IFT and Hysteresis Issues
Authors V. Alvarado and S. H. BehzadiThe most widely used three-phase relative permeability models are Stone1 and Baker. Two advanced models have been developed more recently (Blunt, 1999; Jerauld, 1997). The mixed-wet condition is perhaps the most frequently encountered wetting condition worldwide. Blunt’s model is complex to employ in simulators in contrast with the relative ease of use of Jerauld’s model. An advantage of Jerauld’s model is that it incorporates the effect of IFT between phase pairs. The ability to model mixed wettability and to incorporate IFT makes this an attractive option to investigate recovery in mixed wet reservoirs. In this paper Stone1 and Jerauld’s models are compared. We illustrate the differences in performance prediction between these two models in three-phase kro for the same two-phase relative permeability data sets. Then we show how these two formulations can be cast on one another to be able to use them in commercial simulators. Recovery prediction differences as well as the effect of gas miscibility on krow are shown here. Analysis of hysteresis in mixed-wet system reveals that it has less effect on recovery in comparison with water-wet systems and it does have much less effect than wettability.
-
-
-
New Techniques for Auto-regionalisation of Reservoirs
Authors R. G. Parish, D. A. Wooff, J. G. Hamman and D. H. CaldwellHistory matching and appraisal of reservoirs usually include a partitioning of the reservoir for each physical property that is to be sensitised. Different engineers or geo-scientists often regionalise the reservoir differently. However, the choice of regionalisation can significantly affect critical results such as reserves estimates. Two auto-regionalisation methods were developed. The first method utilises small scale dimensional models to generate new property arrays compatible with those from the original geo-modelling. This approach also provides the option to regionalise using statistical fitting algorithms and the method of Principal Variables. The second method employs user-tailored distance measures to generate regions automatically. In trials the results were superior to the results obtained by conventional methods. Fewer runs were required to obtain a history match, with the second method performing the best.
-
-
-
Natural Cross-flow Rate Modeling in Complex Reservoirs
Authors M. R. Jalali, J. M. Embry, F. J. Santarelli and M. B. DusseaultDuring fluid injection into a complex reservoir, different pressure gradients are generated in the sandface of each layer because of differences in reservoir properties such as permeability, compressibility, thickness, porosity and depletion. Upon shut-in, these differences cause flow from high-pressure layers, usually of lower permeability, to low-pressure layers, usually of higher permeability, a process known as natural cross-flow. Cross-flow may lead to sanding problems [e.g. Santarelli et al. 1998]. In this study, one-dimensional (axisymmetric) natural cross-flow in a complex reservoir is simulated using a finite difference approach. The problem is solved for multiple layers with different permeabilities, separated by impermeable layers. In the paper we emphasize various means of establishing input parameters and apply the model to several well-documented field cases, demonstrating its capacity to predict accurately measured cross-flow.
-
-
-
The Quest for Subsalt Imaging – The Next Chapter
Authors S. Kapoor, N. Moldoveanu, D. Vigh and H. LiPrestack depth migration and wide-azimuth towed-marine acquisition provided step-change improvements in subsalt imaging during the last decade. However, interpreting and incorporating salt geometry into the velocity model is the weakest link in our ability to consistently image subsalt sediments. Building velocity models with full waveform inversion and improving ilumination with full azimuth and long offsets could provide the next step change in subsalt imaging.
-
-
-
Sub–basalt Strata Geophysical Imaging
Authors R. Fainstein and D. JoshiThis paper concerns primarily with the imaging of sub-basalt strata and its worlwide prospectivity. It deals with deep seated features of seismic sections, the seismic resolution of syn-rift sub-salt and sub-basalt layers. These are performed mainly by time and depth migrated interpretation of seismic in the context of basin formation, source rock maturation, migration and entrapment, and by integrating diverse geophysical data.
-
-
-
Incorporation of Sediment Inclusions in Detailed Salt Modeling Improves Subsalt Imaging in the Gulf of Mexico
Authors M. Schoemann, S. McLallen, D. Valasek, B. Yu and R. ZhongIt is well-understood that accurate salt interpretation is critical to subsalt imaging. As our ability to create more accurate velocity models for imaging progresses, we must pay attention to the details required to create better images. The standard work flow for subsalt imaging generates a model with a homogeneous constant velocity salt body. Incorporation of both the detailed external and internal geometries of allocthonous salt in velocity models is proving to be critical in achieving a superior subsalt image. Each contributes to a more accurate and valid velocity model which in turn creates better-defined base salt and subsalt reflectors. Incorporating sediment inclusions in the imaging velocity model on a 3D Gulf of Mexico dataset provides significant uplift in the quality of the seismic image.
-
-
-
Simultaneous Joint Inversion of Seismic, Gravity, and EM Data for Subsalt Depth Imaging in Gulf of Mexico
Authors M. Virgilio, M. De Stefano, S. Re, F. Golfré Andreasi and F. F. C. SnyderThis paper illustrates an advanced process for integration: 3D simultaneous joint inversion (SJI) of seismic, electromagnetic, and gravity data to better define the base salt in the Green Canyon-Garden Banks-Keathley Canyon-Walker Ridge areas. SJI enhances the ambition of improving the existing velocity models for prestack depth migrations and the consistency of seismic and non-seismic representations of the subsurface in complex salt geometries. We produced a new structural framework with renewed interpretations of the allochthonous and autochthonous salt, providing new tools for interpretation of the complex salt, reducing inversion uncertainties, and most importantly, defining a new strategy for subsalt interpretation, thereby enhancing the role of non-seismic methods as supporting complex seismic depth imaging.
-
-
-
3D Seismic Among Icebergs in a Volcanic Provenance – A Successful Project Offshore Greenland Using Dual-sensor Streamers
Authors P. E. Dhelie and L. R. MillerIn the summer of 2009, PGS acquired two 3D seismic surveys in Arctic waters offshore West Greenland for Husky Energy. Dual-sensor GeoStreamer technology was used, and the project seemed ideal to benefit from its apparent advantages. Challenges included a short 3 – 4 month ice-free season, avoiding icebergs during acquisition, a hard water-bottom notorious for strong multiple energy, and volcanic flows with associated dikes and sills within and overlying prospect objectives. Since the dual-sensor streamer technology allows for deep-towed source and receivers without compromising higher frequencies in the amplitude spectrum, operating windows in rough seas were increased. The increased energy recorded in the amplitude spectrum lower than 20 Hz was found more appropriate to penetrate primary energy through attenuative volcanic rocks than what conventional tow depths have achieved historically. Project planning was critical to the success of the surveys. Ray tracing was conducted to ensure the survey outline provided an adequate migration aperture to fully image complex structures. 3D survey design analysis ensured that the most suitable parameters were being prescribed, particularly specific to sub-basalt imaging. Special considerations in operations included radar imaging for iceberg detection, and methodical infill analysis tailored to the subsurface geology.
-
-
-
Effects of Interface Rugosity on Elastic Wave Propagation
Authors S. Del Giudice, D. Rovetta, G. Bernasconi and A. RavasioInterface rugosity affects wave propagation and it can produce poor imaging of the interface itself and of the underlying reflectors. We explore this effect on data generated with a full-wave elastic modeling code on 2D models. A variable rugosity top interface overlies a second plane interface. Seismic data is acquired on the surface with a standard split spread layout. We use the semblance computed along hyperbolic events on the common shot gather as “target detection” indicator. Interface rugosity is parameterized by the vertical amplitude and by the horizontal variability, defined respectively by the standard deviation with respect to the plane case, and by the maximum spatial frequency. Results show that, even for severe rugosity, the reflection from the deep interface is still detectable, whereas the reflection from the rough interface itself disappears when rugosity amplitude is higher than half the signal wavelength. This study can help in understanding wave propagation in volcanic media.
-
-
-
Advances in Sub-basalt Exploration in the Faroe-Shetland Basin
Authors R. Fletcher and J. W. GallagherRecent advances in sub-basalt seismic imaging and a growing well database has allowed the basalt-covered Faroese sector of the Faroe-Shetland Basin to be explored, and sub- and intra-basalt prospects evaluated with more confidence than ever before. We present new 3D seismic data over one of Statoil's operated licences in Faroese waters (FL011), indicating a complex volcano-stratigraphy overlying sub-basalt siliciclastic sediments.
-
-
-
Probabilistic Seismic Inversion of a West of Shetlands Deepwater Turbidite Field
Authors G. Jenkins, M. Floricich, D. McComirck, J. Copp, K. Martin, P. Allan, S. Day, J. Fletcher, C. Macdonald, A. Mannini Ltd, R. Gilham Ltd and F. Boundy LtdThe Schiehallion Field oil reservoir, located West of Shetland on the UK Continental Shelf, lies in a Palaeocene deep marine turbidite complex characterized on seismic data by direct hydrocarbon indicators. A new subsurface model for the Schiehallion Field is being built for infill drilling, field management, reserve estimations and production forecasting. To use this model with confidence and to achieve a satisfactory production history match in a shorter time, it is important for the model to honour all the subsurface data available. Seismic amplitude attributes significantly influence the sand distribution in this new subsurface model. A comparison of 3D synthetic seismic generated from the model and real seismic data is a fundamental quality check for subsurface models. A probabilistic 3D inversion, using the Shell proprietary software (PROMISE) to update the Net-to-Gross in the model, has improved the match between synthetic and real seismic data while honouring petrophysical and geological constraints. This probabilistic inversion approach allows for property updating of the reservoir model without a full model rebuild and also provides a means to define subsurface uncertainty and generate associated high and low case models that still honour the seismic response.
-
-
-
Using Time Domain Seismic Data for History Matching Processes
Authors E. Tillier, M. Le Ravalec and F. RoggeroSophisticated workflows have been designed to build reservoir models consistent with geology, production history and also seismic attributes. Seismic attributes are usually expressed as a function of depth. In such a case, their integration of in matching workflows is straightforward as reservoir grids depend on depth. This approach relies on a basic assumption: the velocity model used to transfer seismic data from time to depth domain is fixed for once, whatever the perturbation applied to the geological model during the history matching process. Moreover, the resolution of this model is usually low. Therefore, we propose to integrate the seismic data given as a function of time instead of depth. As fluid flow simulators yield saturation and pressure values over the reservoir grid, the corresponding seismic attributes are first computed against depth. Then, they are transfered from depth to time domain thanks to the fine resolution velocity model derived from the petro-elastic model. Thus, the depth to time conversion step is fully integrated in the history-matching loop. A numerical example is presented to stress the potential of the proposed methodology. The results are compared to the ones derived from a more conventional workflow involving seismic data against depth.
-
-
-
Observation Sensitivity in Computer-assisted History Matching
Authors M. V. Krymskaya, R. G. Hanea, J. D. Jansen and A. W. HeeminkThis study concerns computer-assisted history matching of reservoir simulation models, i.e. systematic updating of model parameters to minimize the mismatch between observed and simulated production data, with the aim to improve the predictive capacity of the model. The goal of our research is to quantify the information content of the observations. Following a method developed in meteorology, we employ an observation sensitivity matrix to quantify the effect of observed data on predicted data. The use of this matrix is illustrated with an example in which we adjust the permeability field of a two-phase two-dimensional reservoir model by means of a particular history matching technique, the representer method. This method particularly allows for efficient computation of the observation sensitivity matrix. Conceptually, however, the use of an observation sensitivity matrix is equally valid for other history matching techniques. In our example the information content of the updated model comes mostly (96%) from a priori knowledge and to a much lesser extent (4%) from the observations. This finding is in line with the practical experience that in computer-assisted history matching using production data the results are strongly influenced by the prior model.
-
-
-
Business Impact of Frequent Time-lapse Observations Around Valhall Water Injection Well
Authors J. van Gestel, G. Tjetland, M. J. Parikh, J. H. Kommedal and O. I. BarkvedIn 2003 the Life of Field Seismic system was installed on the Valhall Field as the first full field ocean bottom permanent monitoring system. Monitoring of the waterflood was one of the main objectives of the installation of this seismic system. Dedicated water injection at Valhall started with two water injection wells in 2006 in the Central Crest and South Central Basins, followed in 2008 by water injection in the Northern Crest Basin. All these three wells show clear time-lapse observations of the injected water. In this paper we discuss the expected and the observed responses from these water injectors for the various seismic surveys. For all the wells we show how the time-lapse observations have improved the understanding of the waterflood and have had a clear impact on the reservoir management of the individual wells and the full field. Individual examples illustrate how this improved understanding was used to make better informed business decisions on new well placement and well work.
-
-
-
Experiences on Seafloor Gravimetric and Subsidence Monitoring Above Producing Reservoirs
Authors H. Alnes, T. Stenvold and O. EikenDuring the last 12 years, Statoil has collaborated with Scripps institution of Oceanography to develop a method for precision seafloor measurements of time-lapse gravity and depth changes. The precision is now at a level where effects of pressure depletion and hydrocarbon production are visible, and the data can be used in history matching the reservoir simulation model. This paper shows some results from two ongoing monitoring programs offshore Norway. At Troll, a subsidence of about 1 cm/year is observed, and both gravity decrease due to hydrocarbon production and gravity increase due to edge water influx are seen. At Sleipner, the gravity data yields an estimate on water influx to the producing gas reservoir. In addition, a clear signal from the CO2 injected into a nearby aquifer is seen. Finally, the potential of the method in various geological and production settings is discussed.
-
-
-
4D Seismic Benefits to Development Drilling at Enfield – North–West Shelf – Australia
Authors G. P. Thomas and M. SmithEnfield oil field is the site of Australia’s first dedicated 4D seismic monitoring program, which has proved to be an outstanding success. The technique is particularly applicable in Enfield due to faulting and baffles within the reservoir, the need for multiple water injection wells, and the presence of a gas cap. Two full-field monitor surveys have together made major contributions to reservoir management and identification of infill drilling opportunities. We highlight the 2009 development drilling in the field’s Sliver Block, where 4D not only supported the business case for new development wells, but also provided important information to enhance safe and efficient drilling. 4D AVO analysis was undertaken, driven by a calibrated rock property model in which near/mid offsets are shown to indicate pressure changes, while far/ultra-far offsets indicate saturation changes. This work showed the target area was strongly overpressured by a distant injector, contrary to expectations, but not swept by water. The two monitors confirmed this was a stable situation, hence the viability of the drilling project. The overpressures required an extra casing in each well for safe drilling. The actual drilling and well completions went smoothly, and confirmed pressures predicted from 4D.
-
-
-
Norne 4D and Reservoir Management – The Keys to Success
More LessTime-lapse seismic is playing an important role in reservoir management on the Norne, Stær and Svale oil fields. The total value of the 4D data is estimated to 4.3 billion NOK. The keys to the success has been a strong focus on the whole value chain from acquisition, processing, 4D interpretation and reservoir management. Also very important is continuous use of the 4D data in reservoir management also between the acquisitions. We here show how each of these factors have been important for the success, illustrated by case examples. On Norne infill drilling targets are defined using 4D seismic data, and already on the first monitor survey on Svale unexpected barriers in the reservoir and out of target injection were observed. The importance of a good quality base survey, and frequent monitoring surveys have been clearly demonstrated.
-
-
-
Modelling of the Steam Chamber Growth During SAGD – Effects of Reservoir Heterogeneities on 4D Seismic
Authors A. Baroni, O. Lerat, F. Adjemian, G. Etienne, G. Renard, E. Bathellier, J. Cotton and E. ForguesThe performance of heavy-oil production by Steam-Assisted Gravity Drainage (SAGD) can be affected by near-well reservoir heterogeneities. However, as many factors interact during thermal production such as changes in oil viscosity, fluid saturations, pore pressure, stresses..., the monitoring of the steam chamber growth by 4D seismic data is not direct. An integrated workflow is presented. Based on a Canadian heavy oil field, the approach consists of three steps: 1/ the construction of an initial static model, 2/ the simulation of the thermal production of heavy oil with two coupled fluid-flow and geomechanical models, 3/ the production of synthetic seismic cubes at different stages of steam injection. The impacts of heterogeneities, production conditions and reservoir properties are evaluated for several production stages. Results show that heterogeneity distribution has a strong impact on mechanical results and then on the synthetic 4D seismic data. This study also highlights the impact of the shale mechanical behaviour on the steam chamber development during thermal production. Finally, this study demonstrates the added value of 4D seismic data in the context of steam-assisted heavy oil production.
-
-
-
4D seismic monitoring using horizontal wells – A synthetic case study from Troll
Authors E. Janska, S. A. Petersen and G. ToxopeusWhen producing from a thin oil layer with a gas-cap, gas is generally an unwanted component, because the reservoir looses pressure and its dynamic is changed. In this paper we validate by numerical simulations if permanent placing of the seismic tools in the horizontal production well would provide sufficient information about the gas-oil contact position. To our knowledge this type of seismic acquisition has not been done. Result for two out of six acquisition setups are presented: the best setup in terms of the gas-oil contact resolution and the most economical setup. An alternative way of data interpretation is utilized and the Troll field is used as the case example.
-
-
-
A Neumerical Method to Investigate the Effect of Ultrasonic Waves on Capillary Imbibition
Authors C. Ghotbi, B. Keshavarzi, R. Karimi, I. Najafi and M. GhaedianA lot of laboratory experiments have been carried out to investigate each aspect of ultrasonic wave’s role on fluid flow behavior through porous media. Despite all experimental works, little attention has been paid for modeling the ultrasonic wave influence on capillary imbibition, which is the main mechanism of production in fractured reservoirs. At this work the process of imbibition with and without applying ultrasonic waves is mathematically modeled by modification of piston-like model. In contrast to this model’s assumption, in which mobility ratio is assumed to be constant, here permeability variation due to increase in water saturation is considered in numerical solution. To evaluate our modeling, experimental results are compared with that of numerical modeling solution for both conditions, i.e. with and without applying ultrasonic waves. The results of this paper presents a new model for imbibition assisted ultrasonic radiation, which can be considered in future simulation softwares.
-
-
-
Empirically Derived PVT Correlations for Murzuq Basin in Libya
Authors M. A. Benrewin, A. Gaaim, M. Samama and A. NaasPVT data are essential in conducting reservoir engineering studies, and whenever experimentally derived PVT data are not available, correlations are commonly used. These correlations are applicable in a limited range of reservoir fluid properties and some are based on local geographical regions. Murzuq basin crude oils are characterized by their low bubble point pressures and low gas oil ratios. This paper evaluates the most frequently used PVT correlations for application in crude oils of the Murzuq Basin in Libya. The oil formation volume factor was predicted with reasonable accuracy by most of the correlations without modifications to the original forms. Most of the tested correlations for predicting bubble point pressure and solution gas oil ratio, however, were not comparable with the experimental data. Modified forms were generated and gave better estimates of the bubble point pressures and solution gas oil ratios than the original published correlations. These modified forms could now be used to predict oil properties for crude oils with low bubble point pressures and low gas oil ratios.
-
-
-
Integration of 3D Seismic and Reservoir Simulation for Exploitation of Remaining Oil in a Heavy Oil Field–A Case Study
Authors X. Guo, X. R. Huang, Y. Ling and Y. T. CaiBased on a full azimuth 3D seismic (cell size 6.25m x 6.25m and coverage area 14km2) and reservoir simulation on one well group (64 vertical wells and 5 horizontal wells in an area of 600m x 400m), integrated research on a SAGD (Steam Assisted Gravity Drainage) production is carried out in an oilfield in Northeast China. The results indicate that the configuration of steam chambers caused by steam flooding could be estimated from high precision 3D seismic data, and it is more accurate than the reservoir simulation model with locally varying descriptions of the chambers (the accuracy of the simulation model is influenced by density, porosity and permeability data). But with only seismic data, it is difficult to differentiate the influence of geological sedimentation or small sized fractures from the steam chambers, and further predicate the distribution of residual oil. Integrating the 3D seismic data with the reservoir simulation model (thus forming a 3.5D seismic method), we can predict the residual oil. This approach is free from many technical difficulties facing time-lapse applications such as no baseline survey and non-repeatable noise.
-
-
-
Hydraulic Fracturing Design and Investigation Cumulative Production in one of Iranian Gas Condensate Reservoirs
Authors H. Askari, E. Sahraei and A. TahamiHydraulic fracturing is a method of choice to improve production for the most of gas-condensate wells. In this work, hydraulic fracture effect on well production has been considered in one of Iranian gas condensate reservoirs. The target for propped hydraulic fracturing treatments is two sandstone layers with gross thickness of 101.7 ft and 95.1 ft at average depths 8725.45 of ft-TVD and 8823.75 of ft-TVD. In this study, different seven scenarios have been defined. For any scenarios, a hydraulic fracture has been designed. In the scenarios design, has been tried to attend all possible options of hydraulic fractures. In following, well cumulative production has been forecasted in both conditions without and with fracturing operation. The production forecast of seven scenarios represent that all scenarios increase cumulative production more than %19. In final, NPVs of the scenarios have been calculated and compared together and selected optimum scenario. The results are shown average fracture permeability is more effective than fracture length. Comparing NPVs of the scenarios represents NPV of Fourth Scenario is optimum. Since this is the first hydraulically fracture design in Iran, the design and results can be very useful for production planning of other Iranian tight gas reservoirs.
-
-
-
Acoustic Impedance Inversion for Static and Dynamic Characterization of a CO2 EOR Project, Postle Field, Oklahoma
Authors A. P. R. Robinson and T. L. D. DavisSeismic inversion was applied statically and dynamically to characterize the Morrow A sandstone, a thin fluvial channel sand with a low impedance contrast, located in Postle Field, Texas County, Oklahoma. A CO2 flood enhanced oil recovery project was initiated in Postle Field in 2008. Two seismic surveys over a 6.25 square mile study area were acquired, the first in March 2008 (prior to most injection) and the second in December 2008. Colored Inversion was chosen over model based inversion due to limited well control producing a sub-optimal low frequency model. Inversion enabled multi-attribute static reservoir characterization for important properties such as gross sand thickness. Four potential drilling locations were identified in areas of increased sand thickness, with one set to spud February 1, 2010. In addition, time-lapse changes related to the CO2 injection can be detected in the acoustic impedance inversion difference volumes. Integration of these data with production and surveillance data enables the identification of CO2 flow pathways and bypassed zones, thereby optimizing the CO2 flood management and improving recovery.
-
-
-
Conceptual Uncertainty in Geological Interpretation of Borehole Image Logs
Authors P. Zarian and S. N. DymmockWe often interpret borehole image logs to better understand subsurface geology. Our interpretation can be used for making many critical decisions in hydrocarbon exploration and exploitation. Contradictory assumptions, individual bias and differing experience which are all referred to as “concept uncertainty” are the basis for most of our interpretations. The main focus of the very few studies that have been previously published on the subject of “conceptual uncertainty” is on seismic interpretation. This study is about the conceptual uncertainty that can exist in our interpretation of borehole image logs. A controlled experiment was designed to quantify this conceptual uncertainty. We created synthetic borehole images from core scans of a dataset where the geology is known. We invited a group of Geoscientists with borehole imaging expertise to participate in our experiment and interpret these borehole images. The role of their prior knowledge and bias in their interpretation was studied in detail. The results of this study show that conceptual uncertainty exists within a large range of interpretations from a single borehole image data set. This information can help in developing best practices to minimize the effect of conceptual uncertainty, by recognizing and evaluating possible alternatives to a single borehole image data.
-
-
-
Bias in Geophysical Interpretation
Authors P. S. Rowbotham, P. Kane and M. R. BentleyThe E and P business takes decisions based on accurate description of the subsurface and the uncertainty in that description. We commonly observe biases in this description due to cultural influences and over-confidence in estimates of uncertainty. From the geophysical perspective, there is a lack of insight into the end impact of uncertainty on the business leading to a mis-match between the effort expended on uncertainty analysis and its value. Multiple deterministic scenario modeling is one tool for overcoming some of these biases, and for maintaining a realistic uncertainty range from the geophysical domain and through the modelling lifecycle.
-
-
-
Assessing Geometric Uncertainties in Solid Earth Models
Authors A. L. Tertois, J. L. Mallet, E. Gringarten and A. HaouesseReservoir studies aim at estimating hydrocarbons in place to determine whether a prospect is viable. Assessing the uncertainty on the geometry of the reservoir is as important to the end result as assessing the uncertainty on rock properties. Geometric uncertainty modelling in surface-based models poses the challenge of maintaining geological consistency. To perturb structural models in a geologically consistent way the UVT-Transform is used. Geological objects such as faults and horizons are embedded in a meshed volume. A set of geochronological coordinates links the structural model to the property model, enabling coherent geometric uncertainty modelling without invalidating the property model. Effects of different sources of uncertainty (e.g. the velocity model, fault position, horizon position and geometry, etc.) are applied successively to a reference model. Fault to fault and horizon to fault contacts are always consistent because of the way the structural model is defined. Additional constraints on the simulations ensure that the model is valid and that the horizons do not intersect. Each realisation results in a coherent volume model from which uncertainty on rock properties can then be assessed.
-
-
-
Seeking a Common Resources Reporting Code – The Mapping Option
More LessA United Nations task force has completed a study that compared major energy and minerals resources classification standards to those being developed by the UN. The resulting "mapping" indicates close alignment such that assessments conducted using the SPE's Petroleum Resources Management System (PRMS) or CRIRSCO's International Minerals Reporting Template and their associated guidelines can be translated into the United Nations Framework Classification (UNFC) common 3-dimensional matrix format. Use of this "mapping" option allows the UNFC to take advantage of linkages of these existing two systems to evolving international accounting standards and the regulatory disclosure rules of the major stock exchanges.
-
-
-
Model Based Control Techniques for Control and Optimization of Oil Wells Segments – Example of Applications
Authors O. T. Taha, N. M. Nabil and M. R. KhanSerious decisions have to be made on a daily basis that affect the volumes produced and the cost of production. These decisions are taken at different levels in the organization. The sensors provide permanent downhole measurements of properties such as temperature, pressure, resistivity, etc., which can lead to a better understanding of the reservoir, thereby enabling more accurate modeling and optimization. The aim of this paper is to discuss applications of Advanced Multivariable Control algorithms with Intelligent Well technologies to improve oil production and recovery and demonstrate the capabilities using real time and simulation results. This is done by using the real time (I-field) information and Smart completion technologies to monitor and control in-real time segments, multilaterals, multiple completions and systems of the oil / gas well. This real time controls will allow addressing some key issues of in petroleum production oil or gas wells that suffer from e.g. instabilities or an unexpected decline in production and ultimately to increase the recovery of oil fields.
-
-
-
What Would Be the Minimum Subsurface Information Before Making Decision to Develop the Field – A Case Study from El Toor
Authors M. M. Elmahi and A. A. MohamedField Development Plan (FDP) is highly needed after long term of production for reserve Estimations, technoecnomics, to achieve the maximum knowledge of the field in terms of Geological and Reservoir context and to understand lateral reservoir Quality. The minimum subsurface information before making FDP are: Good control of seismic data, Structure maps, Pay zone thickness, Facies information, Pertophysical Information, Core analysis, Fluid Contact, Fluid properties, Water Salinity, Estimated STOIIP, and well test analysis.
-
-
-
Improved Well Delivery Using Advanced Technology and Integrated Processes in the Planning Phase
Authors R. S. H. Pettersen, R. Flatebø, J. Kvernstrøm and V. UlenDrilling of new wells at the Valhall field is a challenge. The reservoir is thin and structurally complex. The field has been on production since 1982. Due to low permeability there are significant lateral changes in pressure. The reservoir rock is compacting, thus the complex and overpressured overburden is subject to subsidence and associated stress state changes. Because of this, past drilling performance has been mixed. Recent advances in use of geomechanical modelling tools, 4D seismic, rigorous pressure estimation and thorough well planning processes have changed these trends by mitigating the key risks for delivering the well. In this paper we discuss the planning and implementation of the third consecutive well where the use of advanced technology has helped in designing the optimal well trajectory and pre-drill predictions. This trajectory design is somewhat counter-intuitive when seen without the context of the data and technology employed. A horizontal water injector, was placed in the reservoir with no overburden problems or sidetracks. Great improvements were made in the drilling phase of this well. The integrated subsurface planning together with high class drilling performance resulted in a highly successful operation with a significantly reduced Non-productive time finishing 32.5 days ahead of plan.
-
-
-
New Opportunities from 4D Seismic and Lithology Prediction at Ringhorne Field, Norwegian North Sea
Authors D. H. Johnston, U. Tiwari and B. P. LaugierTime-lapse (4D) seismic data from the Ringhorne field in the North Sea are used to monitor water movement in both Paleocene and Jurassic age reservoir sands, improve existing geologic and simulation models, and enable more cost-effective field operations. The structural complexity of the reservoirs, their proximity to the high-impedance Cretaceous chalk, and a relatively small 4D response required a significant effort in seismic acquisition and processing which resulted in a highly repeatable survey. In addition to the 4D interpretation, Vp/Vs derived from simultaneous elastic inversion is diagnostic of sand and provides additional constraints on Ringhorne subsurface models. Connected volumes based on Vp/Vs correlate to areas of water sweep seen in the 4D data and reduce uncertainty in 4D interpretation. Relative P-wave impedance changes calculated from 4D inversion are consistent with pre-survey predictions. The 4D seismic and inversion results help explain water breakthrough timing, improve our understanding of field production history, and were critical inputs to an updated geologic model used for reservoir simulation. The data have resulted in an increase in the reserves base and the identification of additional infill well opportunities.
-
-
-
Ekofisk Time-lapse Seismic – A Story of Continuous Improvement
Authors P. J. Smith, H. Haugvaldstad, B. Lyngnes and A. I. ThompsonFive time-lapse seismic surveys have been acquired over the Ekofisk field. Progressive improvements in survey repetition accuracy has resulted in demonstrably higher fidelity time-lapse seismic data. The information obtained from this data is crucial for effective reservoir management and calibration of geomechanical models, leading to greater operational efficiency, higher recovery factors and safer operations.
-
-
-
Seismic Monitoring of an Old Underground Blow-out – 20 Years Later
Authors M. Landro, M. Thompson, A. S. Pedersen and L. AmundsenIn January 1989 Saga drilled a well into a rotated Jurassic fault block on the Steinbit Terrace in block 2/4 in the North Sea. At 4734 m the well kicked, and the drill pipe started to come out of the hole. The well was cut on the 20th January, and it developed into an underground blow out. Shallow seismic surveys were performed 4, 6, 10 and 12 months after the blow out. Last year, Statoil acquired 5 2D lines over the well location again. The old and the new data are now 4D processed again, and initial interpretation will be presented. Based on preliminary results from fast track processing of the 2009 data it seems reasonable to conclude that there has been some gas migration into shallower sediments. However, the co-processing of the old and new datasets is required to verify this initial conclusion.
-
-
-
4D Case Study in the Deep Water Gulf of Mexico – Hoover, Madison and Marshall
Authors M. B. Helgerud, D. H. Johnston, B. G. Jardine, M. Udoh, N. Aubuchon and C. HarrisA 4D monitor survey was acquired over Hoover, Madison and Marshall in the deep water Gulf of Mexico in late 2005 early 2006. Analysis and interpretation of the 4D data delineated water movement in all three reservoirs and revealed gas exsolution at Marshall. Potential unswept pay was identified at Hoover. In order to fully integrate the 3D and 4D data into the geological and reservoir simulation models at Hoover, 3D and 4D seismic modeling was performed. 4D modeling helped support the presence of a subseismic flow baffle and aided in bracketing its transmissibility. From the integrated analysis, drilling opportunities have been progressed for future drilling at Hoover.
-
-
-
4D Fast Track Advanced Interpretation on Dalia Field, Block 17, Angola
Authors E. Brechet, H. Jorge, P. Turpin and S. MaultzschThe Dalia field, located deep offshore Angola in Block 17, is composed of confined and unconfined unconsolidated turibidites sands aged from Miocene. After 30 development wells, a first 4D seismic survey was acquired in order to monitor these development wells, understand reservoir communications, but also prepare the next development and infill wells. Due to the fact that sands are very unconsolidated and with a low burial, 4D effects are very strong: time shifts larger than 10 ms are observed due to fluid changes. Post-stack processing and interpretation techniques were optimized in order to fully interpret 4D and integrate it into the reservoir model. For fast track interpretation purposes, performed within a 2 months time frame, we used amplitude difference cube and dV/V attribute (i.e. relative P-wave velocity change) issued from warping. Starting from these attributes, advanced interpretation and upscaling techniques were applied. 4D anomalies were compared to dynamic monitoring parameters such as MDT and PLT measurements in order to calibrate it. 4D seismic data was useful to understand areas of water injection, depletion, rise of the WOC, fault sealing character and reservoirs communications.
-
-
-
4D Seismic in Deep Water at the Dikanza Field, Offshore Angola, West Africa
Authors P. C. Mitchell, R. H. Paez, D. H. Johnston, G. D. Mohler and C. C. NetoA 4D seismic program was acquired over the Dikanza field with the objectives of monitoring water sweep, OWC movement, gas exsolution and to identify infill well opportunities to optimize the field’s depletion and ultimate recovery. The baseline survey was acquired in 2002 and a subsequent monitor survey in 2008 approximately two and a half years after the start of production in 2005. Excellent seismic repeatability was achieved with a NRMS value of around 0.12 measured in an interval above the reservoir. Dramatic production related 4D effects were observed consisting of strong reflectivity changes and large time shifts associated with gas exsolution, water injection, water sweep and increases in pore pressure due to water injection. The observed responses were validated by forward modelling and comparison to well production data. The 4D data generally confirmed the effectiveness of water sweep in the field and showed excellent agreement with the production data. It confirmed the presence of off-axis channel systems and indicated the presence of stratigraphic barriers to fluid flow. The interpreted 4D response will be integrated into the geologic model to improve the simulation and history match of field performance and to optimize future producer and water injector locations.
-
-
-
High Resolution Timelapse Imaging – Salt Creek Case Study
Authors J. Moran, G. Wilburn, S. Morris, J. Andersen and O. QuezadaWe present a methodology for high resolution timelapse monitoring over an onshore oilfield and demonstrate the method with a case study from the Salt Creek Field, Wyoming, USA. Key aspects of the method are: 1. High reproducibility in acquisition through the use of permanently emplaced geophones, 2. Consistent processing of all surveys, with an amplitude-friendly processing flow, and 3. Detailed characterization over time by recording multiple monitor surveys at time intervals of 10 – 14 weeks. This case study vividly demonstrates the ability to monitor CO2 movement in an onshore field with high spatial and temporal resolution and illustrates the flow patterns that can be identified with this technique.
-
-
-
Towards Quantitative Evaluation of Gas Injection using Time-lapse Seismic
Authors R. Falahat, A. Shams and C. MacBethOf particular concern in the monitoring of gas injection for the purposes of storage, disposal or IOR is the exact spatial distribution of the gas volumes in the subsurface. In principle this requirement is addressed by the use of 4D seismic data, although it is recognised that the seismic response still largely provides a qualitative estimate of moved subsurface fluids. Exact quantitative evaluation of fluid distributions and associated saturations remains a challenge to be solved. Here, an attempt has been made to produce mapped quantitative estimates of gas volume injected into a clastic reservoir. Despite the accuracy of the calibration using three repeated seismic surveys, time-delay and amplitude attributes reveal fine-scale differences though large-scale agreement in the estimated fluid movement. These differences indicate disparities in the nature of the two attributes themselves and highlight the need for a more careful consideration of amplitude processing for quantitative 4D seismic interpretation.
-
-
-
3D Geological and Seismic Modelling for Reservoir Characterization Workflow Optimization
Authors S. Bardini, D. Grana, F. Maffioletti, E. Paparozzi, L. Ruvo, C. Sala and C. TarchianiThis work concerns a 3D elastic seismic modelling of a complex reservoir integrated within a multiattribute reservoir modeling workflow in order to generate, rank and include seismic attributes with uncertainty evaluation and reduction. The correspondence between seismic data and reservoir properties is complex and non univocal. The problem has been approached by constructing a synthetic reservoir model that exhibits the geometrical and petrophysical complexity of a real field - from deep offshore West Africa – and generating a 3D synthetic seismic response by means of forward convolutional modelling. Synthetic seismic data have been processed through a seismic inversion methodology in order to include inverted seismic attributes in reservoir simulation steps and to compare the final reservoir model with the actual one. The proposed workflow takes into account different types of data to optimize quantitative interpretation through the integration of various disciplines, such as geophysics, petrophysics, rock physics, geology and reservoir simulation.
-
-
-
Application of Distance Based Random Field Models to History Match a North Sea Field
By D. KachumaWe demonstrate a simple technique of using distance based random function generation to generate history matched models by applying the technique on a North Sea field. We perform simulation on the models and use multidimensional scaling to project an ensemble of reservoir models into a lower dimensional space. In this space we simply look for linear combinations of the projected models that give us a projection of the true data. Taking the same linear combinations in the parameter space then gives us history matched models. This technique can be used not only to history match but also to visualise the quality of an ensemble of model realisations. The applied technique is promising and gives quite good results on our North Sea example.
-
-
-
Bilondo Oil Field – How To Deal with Sand Injections? Static and Dynamic Evidence, Modelling and Consequences
Authors A. Mazeraud, B. Carbonnier, Y. Painchaud, J. F. Poilpre, P. Ferrand and M. BourgeoisBilondo is a Miocene turbiditic oilfield located in deep offshore Congo Republic. Bilondo reservoirs are made of 5 sandy flow units separated by continuous shaly barriers. Bilondo is also divided into 3 main compartments by normal faults. Pressure measurements recorded in one well, drilled 8 months after first oil, show that all the reservoirs are depleted, including the non produced ones. The presence of vertical connections between all the sandy reservoirs, crossing the shaly barriers, was apparent. These connections are linked to the development of sandy injections identified and clearly confirmed by borehole imageries recorded in horizontal wells. The main challenge was to incorporate these injectites in our geological model to better reproduce the dynamic behaviour. By performing a trial and error cycle between Dynamic and Geological models, it was possible to match the field history: pressure measurements and water breakthrough after 3 months notably. Finally, the locations of future wells were optimized according to our new geological model. This study underlines the importance of a phased development with the drilling of horizontal producers and an adapted acquisition data for such heterogeneous turbiditic fields.
-
-
-
High Permeability Zones and Their Impact in Reservoir Model Simulation, Postle Field, Texas County, Oklahoma
More LessA permeability model was developed for Postle Field, Texas County, Oklahoma. The reservoir is under CO2 flood and the challenge to sweeping the reservoir effectively is the permeability heterogeneity within the reservoir. The presence of high permeability zones and its distribution can have profound repercussions in terms of flood performance. The permeability model is based on core data available in the study area. Since these data are limited, sandstone petrofacies from the cores were distributed throughout the reservoir by the use of petrophysical attributes from the logs. The permeability model is based on permeability distributions linked to the different petrofacies interpreted in the area. The integrated permeability model was tested against a binary (sandstone-shale) model. A base case history match of liquid production (oil+water) was performed. This match showed that the performance of the integrated permeability model was better than the binary model with respect to matching early liquid arrival in specific wells. High permeability zones were the cause of early arrival, and the integrated permeability model accurately predicted these zones The accuracy of the reservoir model is dependent on the integration of various geophysical, geological and petroleum engineering data used to constrain and validate results
-
-
-
Predicting Net Pay by Pushing the Boundaries of Seismic and Rock Properties in Complex Lithologies Offshore Angola
More LessReservoir description can be challenging in Block 31 offshore Angola, owing to the complex arrangement of Lithologies, combined with variable rock properties and fluid fill, often in proximity to salt or less than benign overburden. All types of sands can contain hydrocarbons. The seismic response of a typical stack of reservoirs can be highly variable, as a result of the range of rock properties. In order to populate the reservoir simulation model the development team had to decide whether to estimate N:G values for the reservoir model from seismic amplitudes or to use a stochastic approach. The challenge was to use Seismic derived Net to Gross where data quality from both seismic and seismic rock properties could be shown to give a confident prediction. Net to gross was calculated from EEI logs for a range of chi angles at control wells, and the seismic EEI response as a function of chi was examined. The results provided the asset team with confidence that chi-angle CI-volumes would give a good prediction of Net to Gross and could be used to populate the reservoir model.
-