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75th EAGE Conference & Exhibition incorporating SPE EUROPEC 2013
- Conference date: 10 Jun 2013 - 13 Jun 2013
- Location: London, UK
- ISBN: 978-90-73834-48-4
- Published: 10 June 2013
151 - 200 of 1113 results
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The Importance of Modelling High Frequency Cycles in Carbonate Reservoirs When Assessing Fluid Flow Performance
Authors J.R.H. Shaw Stewart, R. Wood, C. Van Der Land, P.W.M. Corbett and S. GeigerWe have investigated the role of high-frequency cycles (HFCs) in carbonates during water flooding. These are normally sub-seismic and therefore below grid resolution and must be upscaled, both in terms of single- and multiphase flow behaviour, to predict time to water breakthrough, recovery factors, and the habitat of remaining oil properly. Particularly the latter could be important when designing appropriate enhanced oil recovery schemes that target the remaining oil. The importance of selecting a high vertical resolution grid has been demonstrated for HFCs with continuous petrophysical log gradients and discontinuities, and the consequence these high permeability ranges have on waterflood velocity has been presented: capturing all of a continuous gradient requires increasing the vertical resolution so as to predict a fast enough water front, and a realistic distribution of the residual oil within the HFCs. In addition, the importance of selective diagenesis has been investigated by considering the effect of early-stage diagenesis at the top of HFCs in end-member Greenhouse and Icehouse climates. HFCs are very common in carbonates, even if they are nested within larger-scale heterogeneous geobodies, and the value of this investigation is in its application to real reservoir models.
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Using Microseismicity to Identify and Verify Increased Fracture Complexity During Hydraulic Fracture Stimulations
Authors T.I. Urbancic and A.M. BaigWe examine microseismicity associated with hydraulic fracture stimulation in a naturally fractured shale formation. The stimulation program was designed to assess the potential for increasing fracture complexity by considering the number of perforations, injection pressure rate changes, and different fracture hesitation approaches. In addition to event locations, multi-array and multi-well configurations allowed for the assessment of general moment tensor solutions for observed events. This approach provided an opportunity to examine the relative spatial and temporal behavior of fracture orientations (azimuths and dips) as a function of the stimulation program. In general, derived fractures typically grouped into two orientations (sets), similar to mapped natural fractures or secondary (induced) fractures. Reducing the number of perforations resulted in increased fracture variability and complexity whereas sequential failure of different mapped fracture sets occurred as a result of pressure rate changes. Our results also suggest that the hesitation approaches achieved their objective, with the dominance of natural fracturing early in the sequence as compared to induced fracturing upon re-injection, a direct result of localized stress re-orientation during the stimulation. Our observations suggest that varying the stimulation program can potentially be used to control fracture complexity and potentially result in a direct impact on stimulation effectiveness.
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CO2 - EOR Methods Applied in a Heterogeneous Reservoir with Light Oil under High Pressure and Low Temperature
Authors H.F.A. Scanavini, E.L. Ligero and D.J. SchiozerThe use of enhanced oil recovery methods (EOR) is motivated by the characteristics of the Brazilian pre-salt fields, such as heterogeneous reservoirs under high pressure and low temperature, light fluids with a certain amount of CO2. This produced gas cannot be all released to atmosphere in order to prevent the greenhouse effect. So, this work presents the study of a light oil with 8% of CO2, with an Equation of State (EOS) well-adjusted, applied in three different compositional simulation cases: miscible continuous CO2 injection, WAG – CO2 with or without relative permeability hysteresis. As the hysteresis effect can reduce the gas mobility, causing its displacement through areas that were not initially swept, it was included in the WAG modelling. The results were analysed in terms of average reservoir pressure and production parameters. Both WAG processes (with and without hysteresis) resulted in higher oil production than the continuous CO2 injection, attesting that the water injected in WAG reduced the gas mobility. In the results, it was observed that when the reservoir simulation is a tool applied to predict the oil production, the hysteresis phenomenon should be considered to model a WAG injection, once relative permeability changes with the injection fluids alternation.
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Pilot Testing Practices for the Assessment of Best Approach for Viscous Oil Recovery in the Russkoe Field
Authors I. Edelman, A. Shandrygin, E. Severinov and L. GaidukovThe work presents approaches for development of the Russkoe viscous oil field based on the results of pilot operations and laboratory tests of the EOR methods. The field is unique in terms of both hydrocarbon reserves and problems associated with its development. It is located above the Polar Circle and is characterized with a complex geological structure of highly permeable heterogeneous poorly cemented reservoirs saturated with high-viscosity oil (250-300 mPa*s). Significant factors making field development difficult include presence of extensive gas cap, underlying water, and weakly consolidated sand. Field development has been started with pilot operations whose results make it possible to find the approaches for the full-field development strategy. The pilot design is based on experimental core studies of EOR methods and on reservoir simulation. The following EOR methods have been tested and analysed: hot water, steam, and polymer injection. The first pilot, implemented based on both lab and simulation data, involves hot water injection testing. The work describes the results of experimental and field testing, and full-field development scenarios considered.
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Incorporation of 3D Fault Zones in Field-sized Simulation Models - A First Case Study
Authors M. Fachri, J. Tveranger, A. Braathen and P. RřeConduit faults and faults that can accommodate vast long-distance along-strike flow are well-documented phenomena. In reservoir simulation models, flow within these features are more correctly captured using a volumetric representation of fault zones rather than employing 2D fault planes. We here demonstrate a method for implementing fault zone grids and features on a full-field case study. The fault zone grid is populated by fault rocks and fractures. We investigate the resulting effect on the modelled forecast of field-wide reservoir flow. Membrane slip zones cause the fault zones to form barrier-conduit systems. Along-strike positioned injector-producer pairs focus flow into the fault zone, decreasing sweep efficiency. On the other hand, injector-producer pairs positioned to drain perpendicular to faults partition the injection fluids and therefore tend to increase overall sweep efficiency. In models with conduit slip zones, the fault zones act as thief zones. Fluids preferentially move through the fault zones towards the producers. Consequently, sweep efficiency is more related to injector-producer distance than the geometric relation of well pairs to the faults. Our study suggests that the improved realism added by incorporating volumetrically expressed fault zones substantially influences forecasts of field behavior, and consequently should be considered during oil/gas production planning.
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A Connectivity Criterion to Select the Best Coarse Reservoir Model
Authors C. Preux, M. Le Ravalec and G. EncheryReservoir models are commonly built to represent hydrocarbon reservoirs and study fluid flows. To properly capture reservoir heterogeneity and to account for resolution data, engineers build very detailed geological models. However, this contributes to strongly increase the number of grid blocks, hence the computational overburden. A possibility to circumvent this weakness is upscaling: it consists in converting the fine geological model into a coarser reservoir model. The resulting decrease in the number of grid blocks makes it possible to perform flow simulation in a reasonable amount of time. The coarse reservoir model does not reproduce exactly the dynamic behavior of the fine geological model as upscaling induces a loss of information. An issue is the choice of the upscaling techniques. Distinct criteria have been proposed to evaluate the information loss induced by upscaling without performing flow simulation, but none of them has focused on connectivity. We introduce a new quality indicator depending on reservoir connectivity, the leading idea being that upscaling must preserve connectivity between wells. The potential of such a criterion to evaluate the value of upscaled reservoir models is investigated by considering two types of numerical experiments inspired by the SPE10 case.
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Pore-elastic Plastic Modeling with Non-linear Diffusion Using the Graphical Processing Unit (GPU) Architecture
Authors S.A. Miller, B. Galvan and T. HeinzeA potential major advance in simulating hydro-mechanical processes is the use of the Graphics Processing Unit (GPU) architecture. The inherently parallel platform of the GPU allows fast and high resolution simulations of the underlying physics governing the nucleation, growth, and coalescence of fracture networks and coupled to the highly non-linear behavior of fluid flow through evolving permeable pathways. We have developed a model (that runs entirely on the GPU) that simulates a pore-elastic plastic rheology with hardening, softening, and damage, and coupled to a non-linear diffusion model for fluid pressure propagation and fluid flow. The model demonstrates how fractures develop and evolve in response to far-field stresses and local stress perturbations that arise by crack growth and interaction, and how the evolving network feeds back on the permeability field. The model has direct applications to reservoir simulations, fracking, and enhanced geothermal systems.
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Relative Permeability Homogenization by a Regression Technique
Authors F. McKee, C. Preux and C. BerthonGeological and geophysical expertise coupled to numerical simulation allow the petroleum industry to build increasingly detailed reservoir models. These models integrate the whole set of available data but involve geostatistics and stochastic approach. A large number of simulations is required to estimate hydrocarbon reserves and optimize oil recovery. Geoscientists begin by building a geological model respecting the real geometry of the reservoir and containing possibly million of cells. A reservoir model containing less cells is then built in order to ensure that numerical simulation is feasible within a reasonable time. Upscaling is the link between the geological model and the reservoir model. Multiphase flows upscaling is still an actual issue. In particular, relative permeability curves are characteristic of twophase flow equations. Upscaled relative permeabilities are called pseudo-functions. These functions are often computed for each different case, assuming special flow conditions. The purpose here is to propose a homogenization method for relative permeability by an optimization approach. Non-linear regression analysis can also generate pseudo-relative permeabilities. Such a method is here adopted. Production curves are to be matched by an optimization algorithm in order to generate a homogenized relative permeability model.
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Multi-Objective History Matching Allowing for Scale-Difference and the Interwell Complication
More LessThis study presents a new multi-objective history matching model to predict the individual well performance. Typical single-objective history matching, reducing the linearly averaged form of different-scaled objectives, has not covered the individual well performance properly. Previous multi-objective history matching, which could demonstrate the individual performance, shows the poor applicability as the number of objective function increases. This work aims to develop the accurate and diversity-preserved methodology to accomplish the global optimization. The scheme consists of dynamic goal programming and successive linear objective reduction incorporated with non-dominated sorting genetic algorithm-II. Dynamic goal programming grants priorities to solutions satisfying the expectation values for the objective functions with goal adjustment. SLOR removes redundant objective functions at the fitness evaluation in genetic algorithm. For the case study of waterflood history matching, the model is less sensitive to the form of objective functions and gridblock size. This study proves that reflecting relativity of different performances is able to improve prediction ability of the conventional single- and multi-objective approaches. The model provides a reliable range of uncertainty from diversity-preserved concept. The developed multi-objective optimization algorithm can easily apply to solve the convergence problem and the unrealistic estimation caused by scale-difference and the complication among multi-objective functions.
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Integration of Multiscale Carbonate Reservoir Heterogeneities in Reservoir Simulation
Authors M.G. Correia, C. Maschio and D.J. SchiozerThe link among geological carbonate heterogeneities, such as fractures and vugs, upscaling procedures and simulation flow models remains a challenge. This work perform an methodology aiming a suitable representation of simulation flow model and upscaling procedures approach according to small and large scale carbonate reservoir heterogeneities. The methodology is applied to one flow unit considering diffuse fractures, sub-seismic fractures and vugs. The methodology has shown several advantages: sequential control over static properties and pseudo functions along upscaling procedure; simplification of the match procedure as is done sequentially by heterogeneities scale over the upscaling; reduction of the uncertainty in the accurate simulation flow model approach; reduction of time consumption in flow simulation and project development as the methodology can be implemented for uncertainty workflows; improvement of the integration of multiscale heterogeneities in reservoir simulation. This work presents a significant methodology and analysis that can be useful for multidisciplinary areas of expertise since it integrates geostatistical modeling of carbonate reservoir heterogeneities with reservoir simulation.
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Influence of Hydraulic Heterogeneity of Rocks on Pore Pressure Changes Induced by Reservoir Stimulations
Authors C. Dinske, C. Langenbruch, J. Galindo Guerreros and S.A. ShapiroWe interpret borehole logging measurements from the German Continental Deep Drilling Program (KTB) to construct a hydraulic diffusivity profile for the central part of the main borehole. The profile indicates strong fluctuations of diffusivity ranging over three orders of magnitude. We find that the variations can statistically be described by a log-normal distribution and by a power-law scaling in the corresponding power spectrum. We generate 2D fractal random media which obey the statistical properties of the derived diffusivity log as representations of hydraulically heterogeneous rock. We numerically simulate the diffusion of pore pressure perturbations caused by a fluid injection in such a rock model. We compare the result of the modelling with a model where a homogeneous distribution of an effective hydraulic diffusivity (equal to the mean of the log-normal distribution of diffusivity variations) was applied. We find that the magnitude of pore pressure changes is affected, in particular in the vicinity of the injection borehole where regions of strong enhancement as well as reduction exist. Another feature is the development of flow paths along which the injection pressure is transported. We assume that these flow paths reflect higher permeable fractures embedded in the low porosity rock matrix.
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Reservoir Management through Frequent Seismic Monitoring at Ekofisk Field
Authors A. Grandi, B. Lyngnes and N. HallerA permanent reservoir monitoring system was installed at the Ekofisk field in summer 2010. Four seismic surveys have been acquired between winter 2010 and summer 2012. Excellent repeatability of the acquisition geometry and 3-4 week processing turnaround enable to exploit time lapse seismic results to optimise the reservoir management. Three examples are discussed where 4D results add information key to characterisation, prediction and decision making. The first example demonstrates an area where a few wells lack pressure support and production is affected. A second example shows how 4D data enabled diagnosis of a well failure, and how the lessons learnt from this well are being used to prevent mechanical issues at other wells. The third example shows a seismic PLT in a well giving valuable information regarding distribution of influx in the well within 1-1/2 months of the well coming online.
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The Ravva 4D Seismic Study - A Multidisciplinary Approach for Identification of Bypassed Oil
Authors K. Reddy, R. McClenaghan, K. Saikia, S. Mishra, C. G. Rao, M. Gupta, S. Joysula, G. Sanghvi and V. ShankarA 4D seismic survey was carefully planned, executed and interpreted on the Ravva Field. The geoscience and 4D seismic studies have provided key information that defines fault compartments, position of the current OWC and reveals potential undrained areas in field. In this paper, we describe a multidisciplinary approach for the identification of potential areas of bypassed oil. We show examples of how geoscience and engineering disciplines work together and explain the 4D responses which have delineated the areas of the undrained hydrocarbons. The recent infill drilling results along with on-going dynamic reservoir surveillance programs are in line with the 4D interpretations. All these results are being used to up-date the reservoir model for optimal reservoir management and development.
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Seismic Detection of Fractures from Injection - A Field Example
Authors A. Tura, Y. HajNasser, B. Keys and L. BrownDetection of fractures using geophysical methods has proven elusive. A significant amount of theory has been developed, however, convincing applications of the theory to observed data have been lacking. In this paper we show a clear example of seismic amplitude changes due to controlled fracturing from injection at the Alpine field in Alaska. We use the ability of time-lapse seismic data to remove the background medium so that seismic amplitude changes due to the creation of open fluid (gas or liquid) filled fracture systems are clearly exposed around injectors. Additionally we utilized rock-model-based seismic forward modelling to test against three different models of fractured media. We conclude that the Kuster-Toksoz randomly distributed fracture model is the most appropriate for Alpine. Using this model we are able to calibrate the fracture parameters (fracture pressure, fracture aspect ratio, and fracture porosity) to match observed data. Our results show that fracturing can introduce 4D velocity changes significantly larger than what would be expected from using velocity-pressure trends from core measurements alone. Finally, using time-lapse AVO modelling we show that at Alpine it may be possible to discriminate between gas- and oil/water-filled fractures.
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An Interpretation of the 4D Seismic Response to Gas Exsolution and Dissolution
Authors R. Falahat, A. Shams and C. MacBethThis study examines the 4D seismic signatures of gas exsolution and dissolution in a producing hydrocarbon reservoir. The physical mechanisms for these reservoir processes are investigated using a series of simulation studies, and the primary controls on the seismic response are thus identified. It is concluded that gas can attain a steady state approximately three to six months after a major reservoir pressure change, and that in this state the seismic responds to the thickness of gas accumulations existing at either the critical and/or maximum gas saturation. Application to multiple repeated surveys over a North Sea turbidite field demonstrates the practical consequences of our findings and how this insight can be used to interpret the seismic amplitudes. Interpretation of the field example confirms a low critical gas saturation of less than 1% for the reservoir rocks. However, it is not found possible to quantify the maximum gas saturation using the 4D seismic amplitude only. Quantitative estimates of the volumes of gas liberated and dissolved in the oil are found possible by integrating material balance principles with the seismic response. It is shown that the insights gained from this application can be generalised to other moderate to high permeability hydrocarbon reservoirs.
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Breaking the Limitations of Pressure and Saturation Inversion With a New Dynamic Constraint
Authors T.D. Blanchard and P. ThoreThe seismic inversion of 4D prestack amplitude information (AVO) can be very non-unique, leading to dubious estimates of dynamic properties. Here we demonstrate a workflow that simultaneously uses the 4D time shift, 4D amplitude and a novel dynamic constraint to invert for much more robust and reservoir consistent changes in elastic parameters. The conversion of these elastic parameters to pressure and saturation yields very promising results. Previously undetectable small-scale changes in pressure are now observed that are coherent with the completion zones of a water injection well.
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Quantitative 4D Reservoir Property Determination
By U. TheuneEstimation of pressure and saturation changes from seismic data is an important step in reservoir characterization and planning of future IOR programs. In addition to estimating such reservoir property changes, the assessment of the estimation uncertainties is important for risk assessment and quantitative integration of observed and modelled data in reservoir model updating. This paper describes a quantitative petro-elastic inversion approach that determines pore pressure and saturation changes from inverted seismic data and assesses the asociated uncertainties. An application to a field where repeated saturation logs are available demonstrates its applicability and correctness.
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Utilizing a Pseudo-State Flow Equation for Estimation of Pressure and Saturation Changes
Authors S. Witsker and M. LandrřIn this paper we present simple, first order expressions for pore pressure predictions and time lapse seismic travel timeshifts to discriminate between pressure and saturation changes as a result of hydrocarbon production or CO2 injection. To account for reservoir seals, the pressure distribution is modeled by employing a pseudo-state flow equation in combination with a superpositioning method. The approach is successfully applied to a synthetic and a real data example, investigating travel timeshift changes during CO2 injection. We find a good correlation between synthetic and modeled data. Since our method is valid for homogeneous reservoir conditions and returns spatially low frequent results, capturing the complex heterogeneities of the real data example is challenging. The advantage of our method is its fast application to estimate first order effects of pressure and saturation changes on time lapse seismic data using a simple inversion algorithm instead of time consuming simulations.
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Geophysical Monitoring Of CO2 at the Ketzin Storage Site - The Results of the Second 3D Repeat Seismic Survey
Authors M. Ivandic, C. Juhlin, S. Lüth, P. Bergmann and A. KashubinVarious geophysical methods applied at the Ketzin storage site have successfully imaged migration of the injected CO2 within the target reservoir zone of the ~ 650-680 m deep saline aquifer. Results from the first 3D repeat seismic survey conducted in 2009, after about 15 months of injection (~22,000 t), showed that the CO2 plume was concentrated around the injection well with a lateral extent of approximately 300-400 m and a thickness of about 5–20 m. The plume, however, was not radially symmetric, but had a rather westerly trending tendency, revealing the heterogeneous nature of the reservoir. A second 3D repeat seismic survey was acquired in the Summer/Fall of 2012, when ~ 61,000 tons of CO2 had been injected. Preliminary results show further growth and migration of the anomaly which has been interpreted to be induced by the CO2 injection. It is similar in shape to the one observed at the time of the first repeat survey, but larger by approximately 100-200 m and much stronger with the highest amplitudes nearly centered at the injection well. There is still a pronounced westward propagating tendency. The new seismic data show no indication of upward migration into the caprock.
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Integrated Geosteering Studies in Real Time - Mockup or Reality?
More LessGeosteering is a systematic engineering which integrates multiple disciplines. In many oilfields of China, three major problems, including multi-disciplinary resources sharing, collaborative working in geosteering monitoring and controlling, decision-making support in real time among different departments, need to be solved in order to really realize integrated geosteering studies. For those problems, this paper proposed a model-driven method including rationalization of geosteering businesses and building of two-tier business models and related logic models. Furthermore, an IT solution including Service-oriented Architecture (SOA), Enterprise Service Bus (ESB), Data Service Bus (DSB) and etc were introduced. Two platforms including an integrated research platform and a collaborative decision-making support platform were developed and integrated. Multi-disciplinary resources sharing, real/near real time collaborative working methods in integrated geosteering studies have been fully applied in B oilfield of China and were validated in practicability.
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The Importance of Fault Analysis in Prospect Volumetrics and Screening
Authors S.R. Freeman, J. Campbell, S.D. Harris, D. Hemingway, B. Goosen and M. ThomasInaccurate volume assessments can lead to expensive drilling of low volume targets or, more often, the by-passing of potentially economic prospects. It is therefore critical for efficient exploration that we have confidence in the approaches being applied. In this paper we will examine gross rock volume approaches derived from top reservoir surface form, discounted for net-to-gross and effective porosity (a very common technique) and 3D model creation linked with stratigraphic population and volumetric analysis (with single, low/mid and high stratigraphic cases, a less common approach but becoming more so). We compare and contrast these techniques and assess the reliability of the resultant volume estimates. Due to recent advances in 3D modeling, useful geological models for prospects can be produced more quickly, and more recent advances allow the automated identification of 3D spill points on faulted traps which can be linked to computations of volumetrics. Linking these techniques to stochastic stratigraphic population routines provides a powerful technique to independently assess the value of the different approaches and identify the key factors that need to be considered when assessing which technique to use in a particular geological setting or the likely accuracy of the volume estimate technique being applied.
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Integrating Fault Throw Uncertainty into Reservoir Modelling - Applications to Exploration and Development Workflows
Authors D. Hemingway, S.R. Freeman, S.D. Harris, J. Campbell and B. GoosenIn exploration and development settings the modelled throw in geocellular grids can have a critical influence on the volumetric fill levels and cross-fault production behaviour, based on the juxtaposition of the flowing units across the fault and the fault seal processes that occur. The exact fault throw is almost impossible to define based on fundamental seismic imaging limitations around fault zones. This uncertainty is typically overlooked during the modelling of fault and horizon interpretations within the geocellular grid. Historically, predicting the effects of modifying the fault throw is a time consuming process, based on the vertical heterogeneity of stratigraphy and the varied response that this may have on the fault properties. We present a method that allows for fault throw uncertainty to be automatically incorporated into both exploration and development evaluation cases. We demonstrate how modifying the fault throw by realistic uncertainty values (i.e. defined from seismic) can grossly under- and over-estimate reserve volumes (by up to 50%) and significantly change the predicted flow behaviour in fault-bound traps. The method we demonstrate allows these uncertainties to be routinely incorporated into exploration and development workflows, allowing for the effects to be captured and included in more concise risk evaluations.
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Application of Two-phase Pseudo-pressure in Gas-condensate Well-testing With and Without Positive Coupling and Inertia
Authors H. Hamdi, P. Ghahri, M. Costa Sousa and P. CorbettWell-test interpretation in gas condensate system is particularly challenging when condensation happens within the reservoir. This is not only due to the natural reduction of near wellbore mobilities, but also the existence of the velocity effects (i.e. positive coupling and inertia), which compete to revamp the relative permeabilities. In this study, a set of realistic build-up tests are generated using a compositional reservoir simulator, where measured (velocity dependent) relative permeabilities and a real gas condensate fluid model are used. The transient build-up tests are analysed using the real-gas and steady-state two-phase pseudo-pressures, and the (velocity dependent) reservoir integral transforms. The results show that the application of steady-state two-phase pseudo-pressure transform can result in a remarkable over-prediction of the reservoir permeability, when the velocity dependent relative permeabilities are in effect. Moreover, the traditional real-gas pseudo-pressure transform fails to estimate the reservoir properties particularly when the reservoir is initially below the dew point pressure. However, in either of situations (i.e. with and without velocity effects), using the reservoir integral transform leads to an excellent liquid analogy solution, where the reservoir properties can be accurately estimated.
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Turning One-sided Illumination into Two-sided Illumination by Target-enclosing Interferometric Redatuming
Authors J. van der Neut, C. Almagro Vidal, N. Grobbe and K. WapenaarWe present a novel method to transform seismic data with sources at the surface and receivers above and below a selected target zone in the subsurface into virtual data with sources and receivers located at the initial receiver locations. The method is based on inverting a series of multidimensional equations of the convolution- and the correlation-type. The required input data can be computed from surface seismic data with a new iterative scheme that is currently being developed. The output data contains virtual sources that illuminate the target not only from above (as in the original data), but also from below, facilitating the needs of seismic imaging and inversion in an optimal way. The method is nonlinear in the sense that all internal multiples are correctly accounted for and true amplitude in the sense that the virtual sources are forced to inherit uniform radiation patterns even though the overburden is strongly heterogeneous.
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Data-Driven Green's Function Retrieval from Reflection Data - Theory and Example
Authors K. Wapenaar, E. Slob, F. Broggini, R. Snieder, J. Thorbecke and J. van der NeutRecently we introduced a new approach for retrieving the Green's response to a virtual source in the subsurface from reflection data at the surface. Unlike in seismic interferometry, no receiver is needed at the position of the virtual source. Here we present the theory behind this new method. First we introduce the Green's function G and a so-called fundamental solution F of an inhomogeneous medium. Next we derive a relation between G and F, using reciprocity theorems. This relation is used as the basis for deriving a 3D single-sided Marchenko equation. We show that this equation is solved by a 3D autofocusing scheme and that the Green's function is obtained by combining the focusing wave field and its response in a specific way. We illustrate the method with a numerical example.
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Receiver-pair Seismic Interferometry and the Cosine Method
Authors E.N. Ruigrok and K. WapenaarIn this paper we consider ambient seismicity with an a priori unknown, but strong, directionality. We develop methods to use the recorded Rayleigh waves for estimating an average dispersion curve and for estimating the directionality of the (noise) field. With the first method: receiver-pair seismic interferometry, a well-sampled circular array of receivers is used. The method consists of two steps. In the first step the recordings are crosscorrelated for opposite receiver pairs. From these crosscorrelations, the backazimuth of the source(s) are found with a stationary-phase analysis. In the second step, the crosscorrelations are stacked, yielding the actual surface-wave response between two positions on the circle. From the retrieved response, the dispersion curve is extracted. With the second method: the cosine method, there are only a few receivers on the circle. The backazimuth of the source is found from the crosscorrelations through an inversion scheme. A minimum of 4 receivers is required. Subsequently, we generalize the cosine method for non-circular arrays of receivers. For the generalized case a minimum of 3 receivers is required. In both latter cases, the dispersion curve can be found directly from the crosscorrelations after estimating the backazimuth of the source.
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Tangent-Phase Interferometry, Time Lapse Application and Sensitivity Analysis
Authors F. Poletto, B. Farina and G. BoehmSeismic interferometry by crosscorrelation is a known representation method used in seismic exploration to reconstruct the Green's function between receivers and to remove the overburden effects when buried receivers are used to record the seismic signals. An issue in conventional seismic interferometry applications for exploration purposes may be the lack of illumination coverage by real sources with a given receiver geometry for natural, i.e., data-based, Kirchhoff-Helmholtz representation of crosscorrelation type for the propagating wavefields. This shortcoming may be overcome by modified representation based on tangent analysis for selected events, and using partial model knowledge to locate new projected points where to calculate virtual signals. This interferometry method uses a generalized-phase operator in a modified representation integral. We investigate the sensitivity of the generalized phase interferometry (GPI) method to velocity variation, and the use of this approach for time-lapse purposes. We present crosswell examples where the acquisition geometry has no complete coverage for the illumination of a buried velocity lens by conventional seismic interferometry application. The results show that the GPI provides a set of new seismogram gathers for each couple of receivers, sensitive to time-lapse variations.
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Progress towards a Passive Shallow-subsurface Continuous-monitoring System at Valhall Using the LoFS Array
Authors J. Dellinger, S. de Ridder, A. Mordret, N. Shapiro, O.I. Barkved and J. YuThe Valhall Life of Field Seismic (LoFS) OBC seismic array was installed in 2003 for the purpose of regular long-term 4D monitoring of the Valhall oil field. With academic collaborators, BP has investigated whether it could be used to synthesize virtual sources using passive seismic interferometry, allowing continuous monitoring of the field. The ambient noise background consists of Scholte waves, which propagate with a limited depth of penetration below the subsurface. Furthermore, although the noise is broadband, it only has the necessary statistical properties required for interferometry over a frequency range of about 0.18 to 1.75 Hz. At such low frequencies, however, Scholte waves do penetrate the top few hundred meters. Preliminary results give hope that it may be possible to use the Valhall OBC array to monitor the shallow subsurface in near real time.
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Inverting for a 3D Shear-wave Velocity Model of the Valhall Subsurface - Results from Seismic Interferometry
Authors A. Mordret, N.M. Shapiro, S. Singh and P. RouxWe present a 3D Shear-wave velocity model of the subsurface at Valhall obtain using seismic interferometry. After computing the Scholte-wave group and phase velocity maps at different frequencies we obtained local dispersion curves at each point of our model. We used a Monte-Carlo approach to invert these local dispersion curves at depth as 1D S-wave velocity models. The collection of these models allowed us to create a 3D model. Our model that is well resolved down to 300 m below the sea level shows geomorphological features with very heterogeneous velocities and could be used as a starting model for Full Waveform Inversion. The monitoring of the shallow subsurface could also be a future application for ambient seismic noise based methods.
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From Seismic Interferometry to Resonant Ultrasound Spectroscopy in Rock Acoustics
Authors S. Barbouteau, P.N.J. Rasolofosaon, N. Dubos-Sallée and P.F. RouxThe aim of this paper is to introduce an alternative laboratory technique for measuring the elastic constants of solid samples, including rock samples, simultaneously using the principles of Seismic Interferometry (SI) and Resonant Ultrasound Spectroscopy (RUS). The solid sample is randomly excited by a pneumatic air gun and hang to a minimal number of contact points in order to allow free vibrations. The sample is in point contact with two passive piezoelectric transducers which measure the sample response. According to the principle of SI, the cross-correlation between the two recorded noisy ultrasonic signals allows to retrieve Green’s function of the sample between these two contact points. The Fourier transform of the correlation function is closely related to the resonance spectrum of the solid sample, and can be analysed using the principles of RUS. Then the resonance peaks are identified and inverted in terms of the elastic constants of the solid samples. The method is checked on a standard aluminium cylinder. The inverted elastic constants are quite consistent with those independently measured on the same material with the conventional ultrasonic pulse transmission technique. Similar successful results on rock samples are shown to illustrate the relevance of the method to rock acoustics.
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Selective Interferometric Imaging of Internal Multiples
Authors M.A.H. Zuberi and T. AlkhalifahInternal multiples deteriorate the image when the imaging procedure assumes only single scattering, especially if the velocity model does not reproduce such scattering in the Green’s function. If properly imaged, internal multiples (and internally-scattered energy) can enhance the seismic image and illuminate areas otherwise neglected or poorly imaged by conventional single-scattering approaches. Conventionally, in order to image internal multiples, accurate, sharp contrasts in the velocity model are required to construct a Green’s function with all the scattered energy. As an alternative, we develop a three-step procedure, which images the first-order internal scattering using the background Green’s function (from the surface to each image point), constructed from a smooth velocity model: We first back-propagate the recorded surface data using the background Green’s function, then cross-correlate the back-propagated data with the recorded data and finally cross-correlate the result with the original background Green’s function. This procedure images the contribution of the recorded first-order internal multiples and is almost free of the single-scattering recorded energy. This image can be added to the conventional single-scattering image, obtained e.g. from Kirchhoff migration, to enhance the image. Application to synthetic data with reflectors illuminated by multiple scattering only demonstrates the effectiveness of the approach.
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Internet-Based Information System of Digital Geological Data Providing
Authors L.E. Chessalov, M.G. Soukhanov and E.M. YuonThe experience of creating Internet-based information system of digital geological data providing, including the developing of web-service of NGKIS-system allows to tell, that technological realization of presenting Russian geological-cartographical data with using of international standards is possible. While realizing, it could be some difficulties, associated with geological material depth. Russian informational geological model is more deep and wide, than foreign. This means the main problem of using international standards and formats: Russian geological data presentation is possible only with decreasing the data detalisation. But, such a problem becomes not very important, if the service publishes also Russian vocabularies, not associated with international vocabularies. In this case, the international format could be the interchange format to change data between Russian users. The integration into the international projects reaches developing of the correlation schemes between russain and foreign classificators and vocabularies.
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Information Technologies for Efficient Management of Natural Resources
Authors E.N. Cheremisina and A.V. LyubimovaTechniques and technologies of information and analytical support of nature-use management problems are disscussed. We present new approach to the solution of the problem allowing for integration of available information resources and combination of all tools of information technologies. Technological implementation of this approach is based on integrated distributed information environment, realized as a modular program complex. At the report we present the main block of the complex, its keynote features and possibilities for nature-use management problems.
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A Data‑Centric Approach to Data Provenance in Seismic Imaging Data
Authors A. Al-Naser, M. Rasheed, D. Irving and J. BrookeSeismic imaging data is noisy and visually complex and thus its interpretation requires human intuition. However, we do not often have a single feature but multiple views of a feature. Managing multi-user and multi-version interpretations, combined with version tracking, with the existing application-centric software is challenging since feature objects are stored separately from their seismic surveys and possibly in different local machines. In this work, we restructure the seismic volume data and the interpreted features into a combined central storage, implemented in a relational database. Features, by multiple user sessions, are presented as a metadata. A parallel data fetching mechanism is linked to this structure to produce an intermediate object that can be graphically rendered on the user screen. We present case studies that illustrate our system's ability to reproduce users' modifications to the interpretations of others and the ability to retrace the history of modifications to a visual feature. We believe that the implications are significant in that a data provenance architecture can be imposed on multiple remote, visually-rich, user interactions with data and derived data products. This can enable workflow logic to be transferred from the application domain to the data management platform.
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Online Seismic Attribute Database for Efficient Literature Research
Authors C. Eichkitz, J. Amtmann and M.G. SchreilechnerSeismic attribute interpretation is an essential part in interpretation of seismic data. Commercial software packages offer a variety of seismic attributes and the amount of seismic attributes described in scientific articles is overwhelming. For seismic interpreters it is often difficult to keep track of the variety of seismic attributes, their capabilities, and their application. In the course of a research project we accumulated and read many scientific articles dealing with seismic attributes and their application. These articles need to be sorted and stored in an efficient way. Therefore, we have decided to develop a seismic attribute database that contains metadata of the various articles as well as a keyword system that allows quick querying for given situations.
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Maximizing TTI RTM Throughput for CPU+GPU
Authors D. Wade, A. Narang, S. Kumar, J. Soman, M. Perrone, K. Bendiksen, V. Slĺtten and T.E. RabbenThere is a continuous interest for increased computational performance in seismic modelling and migration based on discretization of the 2-way wave equation. In many complex exploration settings the acoustic tilted transverse isotropic (TTI) approximation is preferred. Traditionally the CPU hardware architecture has been used, but during the recent years the GPU technology has been gaining popularity because of its significantly higher theoretical peak performance. However, not all problems are equally suited to take advantage of this potential and the low-level programming model is more demanding. In this work a comparison between a CPU only and a hybrid CPU and GPU implementation is presented. The starting point is a code well optimized for CPU systems by using long operators, coarse grids and cache optimization. The performance optimizations required to get good GPU performance are described. The success measure in the CPU+GPU port is migration throughput, not speedup of individual kernels. A comparison on a system with Intel Westmere CPU and nVidia Fermi GPU shows a performance improvement of 4.4x.
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