Use Of 3D Seismic Data Research Articles

Four-Dimensional History Matching Using ES-MDA and Flow-Based Distance-to-Front Measurement

The use of 4D seismic data in history matching has been a topic of great interest in the hydrocarbon industry as it can provide important information regarding changes in subsurfaces caused by fluid substitution and other factors where well data is not available. However, the high dimensionality and uncertainty associated with seismic data make its integration into the history-matching process a challenging task. Methods for adequate data reduction have been proposed in the past, but most address 4D information mismatch from a purely mathematical or image distance-based standpoint. In this study, we propose a quantitative and flow-based approach for integrating 4D seismic data into the history-matching process. By introducing a novel distance parametrization technique for measuring front mismatch information using streamlines, we address the problem from a flow-based standpoint; at the same time, we maintain the amount of necessary front data at a reduced and manageable amount. The proposed method is tested, and its results are compared on a synthetic case against another traditional method based on the Hausdorff distance. The effectiveness of the method is also demonstrated on a semi-synthetic model based on a real-case scenario, where the standard Hausdorff methodology could not be applied due to high data dimensionality.

The influence of curvilinear form of boundaries on reflected wave field

The paper is devoted to the influence of curvilinear reflection boundaries on kinematic and dynamic 1haracteristics of reflected seismic waves. First of all, the paper describes the major reasons of low geological efficiency of CDP seismic survey in the areas of Azerbaijan, characterized by complex surface and deep seismic and geological environmental features and in this aspect, the special attention is paid to curvilinear boundaries. The paper displays statistical data for Shamakhy-Gobustan province, where of 132 anticlinal folds only a few are under production currently. It is considered, how the spatial curvilinear nature of reflection surfaces influence reflection waves propagation. In addition, by use of 3D seismic data the formula is given for breakdown of reflection waves along propagation planes in space. As the example, VSP data from a well in Absheron peninsula are displayed and on the seismic records, it is possible to clearly observe the out of plane waves, which do not propagate in the section plane (in the vertical plane). Velocity analysis is based on evaluation of coherency measure, which allow to assess the correlation level of reference point of seismic traces in the given time window along the hyperbolic trajectory of curvature depending on time and velocity. It is known that in case of curvilinear reflection boundaries the observed travel time graphs are far from hyperbolic by their shape, and due to this, in the process of velocity analysis we derive both optimal stacks, which are the subject to the rule of velocity change versus time, common to this area, and also quite different stacks, which we name as “anomalous”. The great importance is to make clear the nature of these “anomalous” stacks at the initial stage of study as they keep some hidden information about the geology of the area. Analysis display that in addition to folded reflections, the cause of these anomalous stacks may be the curvilinear boundaries, horizontal gradient of the velocity. Curvilinear boundaries influence also the dynamic parameters, wave amplitudes in particular, as in the case of curvilinear boundaries the seismic rays are focusing due to the concaved shape of boundary. It has been noted that if the curvature of a syncline form boundary is not constant, then at the defined reception points the reflections arrive from several parts (points) of syncline and the reflected energy will be recorded as several branches (most frequently as three). As the light is focused when it passes through the lens, the seismic waves are similarly focused by curvilinear boundaries and due to the refraction the seismic rays are bended and we observe intensive reflections on seismic sections.

Impact of model and data resolutions in 4D seismic data assimilation applied to an offshore reservoir in Brazil

Data assimilation is the process where reservoir models are calibrated using dynamic data. The goal is to reduce uncertainties related to reservoir properties for more assertive model-based forecasts and decisions. The use of 4D seismic data as input to this process allows model properties to be updated so that dynamic changes are better represented in the entirety of the reservoir. However, in many cases, the higher the number of grid blocks, the more time consuming are the models' simulation. Thus, the balance between the fidelity of models and simulation runtime in a project is crucial in the planning of activities. The objective of this work is to discuss the impact of using grids with different resolutions and explore options to incorporate 4D seismic maps in data assimilation and production forecast. Through a real field application, we evaluate the use of two grids with different vertical and lateral resolutions, using the Ensemble Smoother with Multiple Data Assimilation (ES-MDA) method. The available high-quality seismic data, applied to a Bayesian inversion, generated 4D impedances that helped identify important dynamic changes that happen at intermediate layers of a thin reservoir (averaged 25 m thickness), located in Brazil. Thus, we also evaluate two approaches for models updating with 4D seismic data: treating the entire reservoir as a single interval, and considering a greater vertical resolution by adding information at intermediate layers. Overall, well production misfits between posterior models and observed data were considerably reduced when assimilating seismic and production data simultaneously, presenting even smaller errors than production data only cases. This happened for both grids. By adding further 4D information at intermediate layers with the use of two maps, we observed (in both grids) that posterior models could predict important reservoir behaviors, such as the gas trapping in the deeper interval. The coarser grid presented lower well production data misfits compared to the refined grid, but showed to be insensitive to the use of different seismic data in data assimilation, resulting in alike models. Furthermore, the posterior models for the coarse grid presented similar behaviors when performing production forecast, which indicates that the uncertainties may be underestimated in these cases. The refined grid presented slightly greater production misfits but was more sensitive to the different 4D seismic inputs. In this grid, an increased ensemble variance was observed between the posterior models, which is also observed in the long-term forecasts. Also, the most refined grid yielded estimates of acoustic impedance changes visually closer to the observed data than those obtained from the coarser grid. As a real case application, the definition of the best procedure is not straightforward. Results suggest that both grids can be used depending on the project's objective. The coarser grid is a good option for short-term studies, since it is able to properly represent the near future with much cheaper models. The refined grid may be suitable for long-term decisions, because it better represents models' uncertainties and provides safer risk analyses.

Sigmoidal normal faults and evidence for vertical-axis block rotation in an oblique convergent margin: A 3D seismic example from offshore Colombia

Sigmoidal fold and fault geometries are typical kinematic indicators of strike-slip fault zones. We document kilometer-scale, normal faults with sigmoidal plan-view geometries within the dextral pull-apart Bahia Basin, at the rear of the obliquely convergent South Caribbean Deformed Belt, offshore Colombia. Using 3D seismic reflection data calibrated to wells, closely spaced, low-displacement, planar normal faults are mapped within the Miocene strata. A series of seismic horizontal (time) slices and computed seismic attributes are used to interpret the 3D configuration of these faults. The closely spaced faults display an east–west trend with a progressive rotation into a northwest–southeast trend. In map view, the fault traces curve toward their tips, describing a sigmoidal-Z geometry that terminates at discrete northeast–southwest-trending fault zones. The structures observed may correspond to either tension fractures, which form theoretically at 45°, or antithetic shear fractures with normal displacement formed at 50°–70° to the boundaries of a dextral shear zone. These scenarios lead to a clockwise block rotation of between 20° and 40° within the shear zone. This study shows the first example of vertical-axis block rotations observed offshore in the western end of the South Caribbean margin and is an important example of the use of 3D seismic data to identify rotations where paleomagnetic studies are not available.

Evaluation of hydrocarbon prospects by the use of 3D seismic data at the Cretaceous formations in Jade field, Matruh Basin, North Western Desert, Egypt

Evaluation of hydrocarbon prospects by the use of 3D seismic data at the Cretaceous formations in Jade field, Matruh Basin, North Western Desert, Egypt

Distribution of Mid‐deeply Buried Sand‐bodies and their Hydrocarbon Significance at Basin Margins: Case Study of the Paleogene in the Eastern Liuzan Area of the Nanpu Sag, Bohai Bay Basin, China

AbstractThe current research aims to unlock the temporal and spatial distribution of sand‐bodies and their relationship with hydrocarbon accumulation in the mid‐deep layer of basin margins, located in the eastern part of the Liuzan area of the Nanpu Sag, Bohai Bay Basin, China. Through this study, the main target interval of the area was divided into two fourth‐order sequences. The lean sand mixed sedimentary belt with great importance in controlling hydrocarbon accumulation was identified through the comprehensive use of 3D seismic data, logging data, lithological data and seismic inversion data. A detailed analysis of sand‐body development characteristics and their role in controlling hydrocarbon accumulation was conducted. The results reveal that the study area mainly develops two distinct fan‐delta lobes from the NE‐trending sediment supply direction. Due to the relatively high influence of the lacustrine transgression event, the scale of the lean sand mixed sedimentary belt within the SQ1‐1 (the lacustrine transgressive systems tract) is relatively small, showing a relatively continuous distribution of sand bodies in the plane. Conversely, due to the relatively high impact of the lacustrine regression event, the scale of the lean sand mixed sedimentary belt developed within the SQ1‐2 (the highstand systems tract) is relatively large, the two east sets of fan‐delta sedimentary systems being clearly separated. The lean sand mixed sedimentary belt formed a good lateral occlusion belt in favor of hydrocarbon accumulation. Through composite analysis of structural interpretation results, sand‐body distribution and well test data, it is evident that the lean sand mixed sedimentary belt located in the structural high is not a favorable zone for hydrocarbon accumulation. In contrast, the wing of the high part of the structure is the zone of sand‐bearing bodies and is a favorable zone of hydrocarbon accumulation.

On the Formation Mechanism of Mud Volcanoes in the South Caspian Basin According to 2D and 3D Seismic Data

Identifying the mechanism and formation time of a mud volcano is one of the most debatable issues concerning the geological phenomenon of mud volcanism. As of now, the use of 3D seismic data is a unique technique that allows documenting the main formation stages of mud volcanism and revealing the connection of this process with the formation of hydrocarbon deposits in the South Caspian Basin (SCB). It is shown that the formation of mud volcanoes began after the accumulation of the Maikop (Oligocene–Lower Miocene) series stratum and continued in parallel with the deposition of sediments. As the thickness of the sedimentary cover increased, mud volcanoes periodically became active. A paragenetic relationship may perhaps exist between the formation of mud volcanoes and the formation of petroleum hydrocarbons.

Mineral precipitation sequence and formation of the lacustrine hydrothermal sediments in the Lower Cretaceous Tenggeer Formation in the Baiyinchagan Sag, China

Cores from the Lower Cretaceous Tenggeer Formation in the Baiyinchagan Sag of the Erlian Basin present dolomitic mudstones and argillaceous dolostone with white grains and laminae. Thin section, X-ray diffraction (XRD), electron microprobe (EMPA), and scanning electron microscopy (SEM) analyses show that in addition to terrigenous clastics, dolomite, analcime, natrolite, pyrite, pistomesite, fluorite, talc, barite, etc. are abundant. Compared with the conventional lacustrine sediments, these rocks contain highly abundant exhalative textures and structures, such as laminae and banded textures, disseminated textures, mesh-vein structures, breccia structures, and contemporaneous deformations. These types of mineral associations, rock textures and structures are specific and uncommon. Previous works indicate that these rocks are of hydrothermal origin. In this study, we provide supplementary evidence and recognition to support the lacustrine hydrothermal sediment origin and further study the mineral precipitation sequence and formation conditions and processes. With the use of 3D seismic data, the magmatic intrusions, hydrothermal ducts, and hydrothermal vents are first identified on seismic sections. The Ni-Co-Zn and Fe-Mn-(Cu + Ni + Co) × 10 ternary diagrams confirm the hydrothermal origin of these sediments. The Sr/Ba ratio, V / (V + Ni) ratio, oxygen and carbon isotope values of carbonate, pH and EH values suggest anoxic, reducing and alkaline sedimentary conditions. Based on the analysis of fluid inclusions, rock textures and structures, we find that the precipitation of minerals occurred in a specific sequence: pyrite-pistomesite-analcime-natrolite-dolomite. The nature of the magmatic intrusions, the changes in environmental variables and fluid energy, and the flow distance may be the controlling factors of this specific sequence. A mode of lacustrine “white smoker”-type hydrothermal sedimentation is presented in this study: as the hydrothermal fluid sourced from the intermediate-basic magmatic basement enriched in Fe2+, Mg2+, Al3+, Si4+, Ca2+, Na+, and CO32– rose and mixed with cool lake water, ferromagnesian, aluminosilicate, and carbonate minerals formed successively from the ducts to the vicinity of the vents. Pulsing exhalation and overflow formed alternating deposits of hydrothermal sediments and lacustrine mudstones.

Practical aspects of working with 2D migrated seismic data

Despite the ever-increasing use of 3D seismic data in today’s exploration and production activities, 2D seismic data continue to play an important role in the oil and gas industry. Interpretations of 2D regional and megaregional surveys are essential elements of integrated exploration programs, establishing frameworks for basin analysis, structural synthesis, and play fairway identification and mapping. When correlating and mapping horizons on 2D migrated seismic data, interpreters use certain practical techniques for handling structural misties, which are caused by the fundamental limitation of 2D migration to account for out-of-plane components of dip.

Image-oriented distance parameterization for ensemble-based seismic history matching

Time-lapse (4D) seismic data provides spatial information about dynamic changes in a reservoir. This information can be used in combination with production data from wells to adjust reservoir models through a history matching procedure. However, quantitative use of 4D seismic data for history matching is generally challenging. This is partly because of the high dimensionality and the large uncertainty associated with the seismic data. To circumvent these difficulties, some methods have been proposed with a focus on reparameterization of seismic attributes and reformulation of seismic objective functions so that the integration of 4D seismic data is more robust and efficient. A distance parameterization of seismic anomalies due to saturation effects was previously proposed to history match reservoir models in combination with the ensemble Kalman filter (EnKF). Because the parameterization reduces both nonlinearity and the effective number of data, an improved functioning of the EnKF could be achieved. The distances measured from simulated fronts to observed fronts were used as innovations in the EnKF such that the same number of simulated measurements is obtained for each simulated model realization. However, it turns out that this definition is not always an effective measure of the actual differences between simulated and observed fronts as we demonstrate through the experiments in this paper. Using concepts from the field of image analysis, we generalize the defined innovations as a directed local Hausdorff distance, providing a one-directional dissimilarity measure (from simulated to observed fluid fronts, or in a broader sense, to detected features in 4D seismic data). A more robust distance parameterization approach is proposed based on the full local Hausdorff distance that measures the distances between observed and simulated fronts in both directions. Additionally, a comparison is made between contour-based and area-based characterizations of the differences between images that are commonly used for shape matching within the field of image analysis. Numerical experiments in a synthetic 2D case and realistic synthetic 3D case based on the Norne field are presented in which improved functioning of the proposed method is demonstrated.

The spatial, temporal and volumetric analysis of a large mud volcano province within the Eastern Mediterranean

This paper documents and describes through the use of 3D seismic data a prolific mud volcano province within the Eastern Mediterranean. As many as 386 mud volcanoes were mapped within the post-salt succession of the western slope of the Nile Cone, offshore Egypt, using high resolution 3D seismic data. The mud volcanoes within this field display significant geometrical variability in diameter (c. 550 m to c. 5660 m), height (c. 25 m to c. 510 m) and volume (c. 0.1 km3 to c. 3.3 km3) and lie at depths ranging from c. > 6000 m subsea to c. 3100 m at the seafloor. A close spatial relationship between mud volcanoes and base-salt depressions and regions of anomalous thinning within the immediate pre-salt succession, combined with documented core samples taken from mud volcanoes within this region present a powerful argument for a pre-salt source of mud. 3D seismic interpretation and volumetric analysis of these mud volcanoes and their source region permit the definition and quantification of their depletion zones. A conceptual model for a dynamic liquefaction and sediment withdrawal process is proposed whereby mud is fed into a central conduit as the depletion zone propagates radially and episodically outwards resulting in a the formation of a concentric depletion zones. Prolonged mud volcanism within this region over the last ∼5.3 Ma implies the potential for long lived pre-salt overpressure and continued mud volcanism following the catastrophic hydrodynamic impact of the Messinian Salinity Crisis. It is suggested that the scale of mud volcanism means that this region should be considered as among the largest mud volcano provinces in the world.

A simple procedure for handling misties on 2D migrated seismic lines

Despite the ever-increasing use of 3D seismic data in modern exploration and production environments, 2D seismic data are still widely used in many projects. Mapping of horizons interpreted on 2D migrated seismic lines must necessarily address the problem of misties at line intersections, whether the data are migrated in the time or the depth domain. These misties are the result of the inability of 2D migration to account for the dip of reflections out of the vertical plane of the migrated section. This tutorial describes the technical basis for a simple procedure by which the deeper of the values for an interpreted horizon at the intersection of two 2D migrated seismic lines is used to guide mapping of the horizon.

Evaluation of inter-well connectivity using well fluctuations and 4D seismic data

An integrated methodology is proposed to quantitatively evaluate interwell connectivity by uniting available data from the production and seismic domains, while simultaneously honouring reservoir geology. The Capacitance Model approach for interwell evaluation is selected initially to obtain prior understanding using well production and injection fluctuations. Then, to make proper use of 4D seismic data, we extend the newly developed “well2seis” technique to further predict the well-to-reservoir connectivity by correlating multiple seismic monitor surveys to the well behaviour data. Based on the prior information provided by the Capacitance Model, appropriate wells are selected to provide robust 4D seismic correlation. The final result is generated as a 3D attribute volume, which directly reveals spatial patterns of reservoir connectivity. The proposed methodology is firstly tested on a synthetic case, where it is shown that the well2seis correlation attribute can correctly identify key reservoir flow barriers and conduits. When applied to observed data from the Norne field, the pressure diffusion and fluid flow pathways from injectors to producers are detected, which are consistent with bottom-hole pressure measurements and observed sea water production breakthrough. We also discover a key fault barrier which was not considered in the reservoir model previously and successfully improves the history matching quality. The understanding of the reservoir connectivity is significantly improved compared to using conventional methods or the 4D seismic method independently.

Advanced Modeling of Interwell-Fracturing Interference: An Eagle Ford Shale-Oil Study

Summary To investigate interwell interference in shale plays, a state-of-the-art modeling workflow was applied to a synthetic case on the basis of known Eagle Ford shale geophysics and completion/development practices. A multidisciplinary approach was successfully rationalized and implemented to capture 3D formation properties, hydraulic-fracture propagation and interaction with a discrete-fracture network (DFN), reservoir production/depletion, and evolution of magnitude and azimuth of in-situ stresses by use of a 3D finite-element model (FEM). The integrated workflow begins with a geocellular model constructed by use of 3D seismic data, publicly available stratigraphic correlations from offset-vertical-pilot wells, and openhole-well-log data. The 3D seismic data were also used to characterize the spatial variability of natural-fracture intensity and orientation to build the DFN model. A recently developed complex fracture model was used to simulate the hydraulic-fracture network created with typical Eagle Ford pumping schedules. The initial production/depletion of the primary well was simulated by use of a state-of-the-art unstructured grid reservoir simulator and known Eagle Ford shale pressure/volume/temperature (PVT) data, relative permeability curves, and pressure-dependent fracture conductivity. The simulated 3D reservoir pressure field was then imported into a geomechanical FEM to determine the spatial/temporal evolution of magnitude and azimuth of the in-situ stresses. Importing the simulated pressure field into the geomechanical model proved to be a critical step that revealed a significant coupling between the simulated depletion caused by the primary well and the morphology of the simulated fractures within the adjacent infill well. The modeling workflow can be used to assess the effect of interwell interferences that may occur in a shale field development, such as fracture hits on adjacent wells, sudden productivity losses, and dramatic pressure/rate declines. The workflow addresses the complex challenges in field-scale development of shale prospects, including infilling and refracturing programs. The fundamental importance of this work is the ability to model pressure depletion and associated stress properties with respect to time (time between production of the primary well and fracturing of the infill well). The complex interaction between stress reduction, stress anisotropy, and stress reorientation with the DFN will determine whether newly created fractures propagate toward the parent well or deflect away. The technique should be implemented in general development strategies, including the optimization of infilling and refracturing programs, child well lateral spacing, and control of fracture propagation to minimize undesired fracture hits or other interferences.

Using 3D seismic data to map shallow-marine geohazards: a case study from the Santos Basin, Brazil

This paper documents a study that used high quality, conventionally processed, speculative 3D seismic data for two specific purposes: first, to identify and avoid any health, safety, security and environmental (HSSE) issues regarding the water bottom and, secondly, to avoid shallow (<1 s below the mud line) geohazards when drilling the wells. The study integrated existing legacy well data, new 3D data from the BM-S-52 concession and a targeted programme of water-bottom grab samples from the BM-S-52 concession, Santos Basin, offshore Brazil. Two aspects of the analysis are described: the first addresses the problem and solution adopted for characterizing the water-bottom environment in this area; the second addresses the interpretation of the data for shallow geohazards. The results of this case study have been accepted by the regulatory authorities as representing sufficient evidence of risk evaluation that no further dedicated site-survey data acquisition is required. This has led to savings in time and in costs which would otherwise have been expended on deep-water site-survey campaigns. Furthermore, the use of 3D seismic data for well-location planning brings benefits in improved imaging of the near-mud-line geology, full coverage over the whole concession, operational flexibility for changing well location and timely availability of data. The analysis workflow may also be applicable in other, similar deep-water areas.

Stochastic Data Integration: History Matching Production and Time-Lapse-Seismic Data

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 146418, ’A Comparison of Stochastic Data-Integration Algorithms for the Joint History Matching of Production and Time-Lapse-Seismic Data,’ by Long Jin, SPE, Faruk O. Alpak, SPE, and Paul van den Hoek, SPE, Shell International E&P, and Carlos Pirmez, Tope Fehintola, SPE, Fidelis Tendo, and Elozino Olaniyan, SPE, Shell Nigeria E&P, prepared for the 2011 SPE Annual Technical Conference and Exhibition, Denver, 30 October-2 November. The paper has not been peer reviewed. Quantitative integration of spatial and temporal information provided by time-lapse (4D) -seismic surveys into dynamic reservoir models requires efficient and effective data-integration algorithms. The particle-swarm-optimization (PSO) method emerged as more effective compared with the neighborhood algorithm (NA) and very-fast-simulated-annealing (VFSA) methods in the Imperial College Fault Model (ICFM) problem. The PSO method was also effective in the field application. The VFSA method required comparatively more iterations to converge because of its sequential nature, but it has advantages when moderate computing resources are available. Introduction The use of 4D-seismic data is increasingly important for reservoir monitoring and management. However, quantitative integration of 4D-seismic data with historical production data into reservoir-simulation models is a challenging task. A key issue of joint history matching, involving production and time-lapse-seismic data, is proper processing of 4D-seismic data such that physical information (fluid saturations) is captured by geophysical measurements properly. Various types of geophysical measurements have been assimilated in the literature, including inverted impedance, inverted saturation, and fluid fronts. Another important issue centers on appropriate selection of model parameters to be adjusted to obtain a history match. In this work, three stochastic data-integration methods were evaluated: NA, VFSA, and PSO. They were compared on the joint history-matching problem involving production and time-lapse-seismic data. Stochastic Data-Integration Methods Data integration in the presence of time-lapse-seismic data consists of updating reservoir dynamic models by jointly assimilating both 4D-seismic and production data. The goal is to use the complementary nature of 4D-seismic data (spatial and temporal information) and production data (temporal information) to produce more-predictive reservoir models, and in turn, make optimal reservoir-management decisions. In this work, the focus was on nonintrusive stochastic data-integration methods. No special information (e.g., adjoint sensitivity coefficients or gradients of the objective function) was needed from the flow and seismic forward models. A generic iterative workflow for joint 4D-seismic and production history matching conducted by a stochastic sampling engine (optimizer) is shown in Fig. 1. The main idea was to perturb the uncertain (model) parameters identified by comparing the synthetic data (production and 4D-seismic) with the measurements simultaneously. The basic idea is also shown in Fig. 2.

History Matching of Production and 4D Seismic Data: Application to the Girassol Field, Offshore Angola

Time-lapse seismic provides a source of valuable information about the evolution in space and time of the distribution of hydrocarbons inside reservoirs. Seismic monitoring improves our understanding of production mechanisms and makes it possible to optimize the recovery of hydrocarbons. Although 4D seismic data are increasingly used by oil companies, they are often qualitative, due to the lack of suitable interpretation techniques.Recent modeling experiments have shown that the integration of 4D seismic data for updating reservoir flow models is feasible. However, methodologies based on sequential interpretation of 4D seismic data, trial and error processes and fluid flow simulation tests require a great effort from integrated teams. The development of assisted history matching techniques is a significant improvement towards a quantitative use of 4D seismic data in reservoir modeling.This paper proposes an innovative methodology based on advanced history matching solutions to constrain 3D stochastic reservoir models to both production history and 4D seismic attributes. In this approach, geostatistical modeling, upscaling, fluid flow simulation, downscaling and petro-elastic modeling are integrated into the same history matching workflow. Simulated production history and 4D seismic attributes are compared to real data using an objective function, which is minimized with a new optimization algorithm based on response surface fitting. The gradual deformation method is used to constrain the facies realization, globally or locally, which populates the geological model at the fine scale. Moreover, a new method is proposed to update facies proportions during the optimization process according to 4D monitoring information.We present here a successful application to the Girassol field. Girassol is a large, complex and faulted turbidite field, located offshore Angola. First, a detailed geostatistical geological model was built to describe reservoir heterogeneity at the fine scale, while respecting 3D base seismic data. Second, the model was constrained to production data and 4D seismic attributes, applying gradual deformation to facies realizations and varying facies proportions. The integration of 4D seismic data led to better production forecasts and improved predictions confirmed by a new seismic survey shot two years after the history matching period. 4D seismic data also contributed to better characterize the spatial distribution of heterogeneities in the field. As a result, the fine scale geological model was improved consistently with respect to the fluid flow simulation model and the observed data. The Girassol study, already presented in (Roggero et al., 2007, 2008), has been updated with recent information and a more detailed presentation concerning the construction of the geological model based on 3D seismic data.

4D Seismic for Reservoir Management in Carbonates: Does It Work?

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 144228, ’Application of 4D Seismic for Reservoir Management in Carbonates: Does It Work?,’ by Mohamed Saleh Efnik, SPE, and Samsudin Haj Taib, University of Malaya, prepared for the 2011 SPE Enhanced Oil Recovery Conference, Kuala Lumpur, 19-21 July. The paper has not been peer reviewed. In the past 10 years, time-lapse (4D) seismic has evolved from an academic research topic to a typical method of monitoring reservoir performance. The method is used to provide evidence of saturation changes within the reservoir at field scale. 4D seismic provides data that describe the dynamic behavior of reservoir fluid between wells that otherwise would be limited to small-scale monitoring at borehole scale. Thus, 4D seismic provides sophisticated techniques of reservoir monitoring and management that rely on the integration of geological models, static and dynamic properties of the reservoir rock, and detailed field-production and -pressure data. Introduction The feasibility of 4D seismic has evolved with studies that showed that certain rock properties, such as acoustics and pressure, are affected by changes caused by hydrocarbon production over the life of the field. The use of 4D-seismic data in conjunction with reservoir-simulation models and production data enables creation of an internally consistent subsurface model. It has been shown that acoustic impedance (AI) and Poisson’s ratio are related closely to porosity and water-saturation changes in Arne chalks. An increase in porosity causes a decrease in AI; increasing water saturation (at constant porosity) results in a strong increase in Poisson’s ratio. An extensive seismic program was carried out over a CO2-injection area during a 5-year span to monitor the CO2 storage in a saline aquifer in the North Sea Utsira sand. 4D seismic and other geo-physical techniques were used to obtain information that could help determine reservoir-quality characteristics and predict fluid contacts. Forward modeling of 4D seismic has been shown to be a useful reservoir-management tool. Here, the simulation model was combined with the streamline method for modeling flow, and the ray-Born method for synthetic seismograms was used to compensate for the numerically expensive model because of the large volumes in the subsurface.

Towards quantitative evaluation of gas injection using time-lapse seismic data

Of particular concern in the monitoring of gas injection for the purposes of storage, disposal or improved oil recovery 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 recognized 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 the gas volume injected into a clastic reservoir. Despite good results using three accurately 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, which can be explained by several possible causes. Of most impact are the effects of processing and migration, wave interference effects and noise from non-repeatability of the seismic surveys. This subject highlights the need for a more careful consideration in 4D acquisition, amplitude processing and use of true amplitude preserving attributes in quantitative interpretation.

Permeability Updating of the Simulation Model by Use of 4D-Seismic Data

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 125632, ’Permeability Updating of the Simulation Model Using 4D-Seismic Data,’ by R. Villegas, University of Leeds, and C. MacBeth and M. Paydayesh, Heriot-Watt University, prepared for the 2009 SPE/EAGE Reservoir Characterization and Simulation Conference, Abu Dhabi, UAE, 19-21 October. A method is presented for updating a reservoir-simulation model by incorporating permeability that is derived directly from time-lapse-seismic data. The proposed method builds new permeability distributions by integrating a previous 3D-simulation model with 2D-permeability maps from the time-lapse-seismic results. These updates provide an alternative to use of a conventional gradient-based history-matching tool by itself. The largely uncertain petroelastic model can be avoided when history matching to the time-lapse-seismic data. Introduction New high-resolution 4D-seismic-acquis-ition techniques have led to many advances, especially in static-reservoir-property estimation. A common reservoir-engineering-context question is to what extent can time-lapse seismic be used to refine the flow-simulation model. Although time-lapse seismic is used to solve challenges such as pressure-/saturation-change separation, researchers have been less successful in estimating reservoir properties such as permeability. Permeability is a reservoir property that has a first-order effect on simulation-model predictions and is important for optimizing the simulation-model predictions. Recent research has focused on developing a history-matching process or seismic-history-matching process to estimate permeability iteratively by use of an objective function matched exactly to the seismic data. There has been little investigation of direct transform of time-lapse-seismic attributes into average-permeability maps of the reservoir. Direct estimation of reservoir properties from 4D seismic, by transformation procedures similar to those used to estimate properties such as porosity and net-to-gross ratio, could be a viable approach. However, a major drawback of all approaches is that permeability is defined as a 2D map rather than a 3D volume. Current work addresses this challenge by designing a scheme to effectively integrate the depth-averaged mapped estimates from seismic to update the 3D-permeability field in the simulation model.