Fluvial Reservoir Research Articles

Experimental evidence for bifurcation angles control on abandoned channel fill geometry

Abstract. The nature of abandoned channels' sedimentary fills has a significant influence on the development and evolution of floodplains and ultimately on fluvial reservoir geometry. A control of bifurcation geometry (i.e., bifurcation angle) on channel abandonment dynamics and resulting channel fills, such as sand plugs, has been intuited many times but never quantified. In this study, we present a series of experiments focusing on bedload transport designed to test the conditions for channel abandonment by modifying the bifurcation angle between channels, the flow incidence angles and the differential channel bottom slopes. We find that disconnection is possible in the case of asymmetrical bifurcations with high diversion angle (≥30∘) and quantify for the first time an inverse relationship between diversion angle and sand plug length and volume. The resulting sand plug formation is initiated in the flow separation zone at the external bank of the mouth of the diverted channel. Sedimentation in this zone induces a feedback loop leading to sand plug growth, discharge decrease and eventually to channel disconnection. Finally, the formation processes and final complex architecture of sand plugs are described, allowing for a better understanding of their geometry. Although our setup lacks some of the complexity of natural rivers, our results seem to apply at larger scales. Taken into account, these new data will improve fluvial (reservoir) models by incorporating more realistic topography and grain size description in abandoned channels.

Detailed quantitative description of fluvial reservoirs: A case study of L6-3 Layer of Sandgroup 6 in the second member of Shahejie Formation, Shengtuo Oilfield, China

The steady development of the oil field is facing severe challenges due to the problems of small-layer division, unclear genesis period and unclear river channel distribution in the 4-6 sand formation in the second district of Shengtuo Oilfield. Based on the processing and optimization of logging data, this paper firstly divided the isochronous strata and established the high-resolution isochronous stratigraphic framework. Using the geo-statistics method in the stratigraphic framework, the sand bodies in each small layer were divided according to the principle of equal time of fluvial facies. On this basis, the distribution pattern of the sand bodies in each stage was simulated by the magnetic random walk model. The magnetic random walk model has obtained robust simulation results, which is consistent with the anatomy of reservoir architectures by experienced geologists. The results also show that the number of channels in each small-layer is different, while the overall distribution of NE direction is reflected. At present, the model can well simulate the position of the main channel line, but it cannot reflect the variation of the river width. The method of quantitative fine description based on logging data has great potential application in fluvial reservoir, especially the magnetic random walk model that can reveal the distribution of sand body in every stage. At the same time, the model can also reflect certain randomness and facilitate the uncertainty analysis of geological factors. Cited as : Li, J., Yan, K., Ren, H., Sun, Z. Detailed quantitative description of fluvial reservoirs: A case study of L6-3 Layer of Sandgroup 6 in the second member of Shahejie Formation, Shengtuo Oilfifield, China. Advances in Geo-Energy Research, 2020, 4(1): 43-53, doi: 10.26804/ager.2020.01.05

Dynamic Processes of CO2Storage in the Field: 1. Multiscale and Multipath Channeling of CO2Flow in the Hierarchical Fluvial Reservoir at Cranfield, Mississippi

AbstractA consistent picture of dynamic channeling, invasion, spreading, and breakthrough (CISB) of supercritical CO2 in the hierarchical fluvial reservoir at Cranfield, Mississippi is presented after 10 years of integration and analysis of complementary field monitoring and characterization data. The dynamic CISB with small‐scale CO2‐flow channels in the F1‐F2‐F3 cross section (F1, F2, and F3 are one injection and two monitoring wells) was imaged by daily electrical resistance tomography (ERT) and time‐lapse crosswell seismic surveys. One, three, and four CO2 flow channels logged at F1, F2, and F3, respectively, were dynamically connected with strong temporal variations in CO2 saturation during 221 days of drainage with injection rate doubling twice and 81 days of imbibition. Three intermediate‐scale CO2 flow channels (with highest CO2 saturation) normal to the cross section were ERT‐imaged during late‐time drainage. A large‐scale, sinuous fluvial CO2 flow channel was imaged by repeat surface seismic survey at the end of the imbibition. The fluvial sandstone channel sinuously bypasses the F1‐F2‐F3 cross section in a point bar, but the channel is connected to the cross section through an intermediate‐scale sandstone channel, forming a complicated flow channel network. The multiscale flow channel network (in the fluvial channel‐point bar system) revealed from the observed CISB enables us to consistently interpret the hydrological monitoring data of three tracer tests, each conducted during an injection rate step, and preinjection hydraulic‐thermal‐tracer tests. This interpretation of the CISB and flow channel network can guide future modeling and data inversion to best understand the effects of natural heterogeneity on CO2 storage efficiency and residual trapping.

The Jasmine Field, Blocks 30/06 and 30/07a, UK North Sea

Abstract The high-pressure–high-temperature Jasmine Field lies 270 km east of Aberdeen in the UK Central North Sea and forms part of Chrysaor’s J-Area. Hydrocarbons were discovered at Jasmine in 2006, in Middle–Late Triassic fluvial sandstones of the Joanne Sandstone Member of the Skagerrak Formation. Appraisal proved a greater than 2000 ft hydrocarbon column and, in 2010, the Jasmine Field development was sanctioned. Five development wells were pre-drilled between 2010 and 2013, and the field was brought on line in November 2013, after which one further appraisal and three additional production wells were drilled. Jasmine infrastructure comprises an accommodation platform and a wellhead platform tied back to a riser platform adjacent to the Judy processing and export facility. Rapid early pressure depletion, a highly layered fluvial reservoir, structural complexity and variable fluid types present significant challenges for both static and dynamic modelling. Following production start-up, acquisition of new post-production reservoir pressure and flow data, and incorporation of allocated well production data, have been used to address these modelling challenges, and to provide encouragement for future infill and near-field exploration drilling opportunities.

海上大井距油田河流相储层研究方法

海上大井距油田河流相储层研究方法

Depositional conditioning of three dimensional training images: Improving the reproduction and representation of architectural elements in sand-dominated fluvial reservoir models

Fluvial deposits create significant hydrocarbon reservoirs, although their characterisation can be difficult due to their differing scales of heterogeneity. Whilst numerical modelling methods have advanced to statistically honour fluvial input datasets, geologically realistic features are often lost, impacting hydrocarbon recovery predictions. Two dimensional training images are often used to dictate what heterogeneity is inputted into multi-point statistics based reservoir models. In this study, a three dimensional training image is built, based upon depositional conditions derived from outcrop and modern satellite imagery data of a fluvial system. The aims of this study are to: identify the heterogeneity within the modern and outcrop data and to replicate it in a three dimensional training image; to model such heterogeneity using object-based, sequential indicator simulation and multi-point statistics; and to qualitatively and quantitatively (through static net-connectivity testing) analyse the reproducibility and geological realism of the generated reservoir models. Digital photogrammetric data from Tuscher Canyon, Utah, of the Lower Castlegate Sandstone and satellite imagery from the Jamuna River, northern India, are used to depositionally condition a three dimensional training image. This training image was then used to generate the multi-point statistics models, which were then tested against more traditional object-based and sequential indicator simulation reservoir models. Results indicated that object-based models realistically reproduced heterogeneous architectural elements, however, the connectivity of net-reservoir elements were unrealistically shaped and over-connected. The sequential indicator simulated models produced unrealistic heterogeneous architectural elements and overestimated the connectivity of net-reservoir elements. The multi-point statistical models realistically reproduced heterogeneous architectural elements geometries and the connectivity of net-reservoir elements. Study implications suggest that, based upon limited data, depositional conditioning can generate three dimensional training images to produce reservoir models that are both geologically realistic and reproducible. • Heterogeneity within the Lower Castlegate of Tuscher Canyon, Utah is characterised. • MPS, SIS and OBM models of fluvial reservoirs are compared. • MPS is found to produce the most realistic and reproducible results.

Sequence stratigraphic framework of Paleogene Fluvial and Marginal Marine Depositional Systems of Llanos Foothills Colombia using log character & spectral decomposition

A sequence stratigraphy framework (SSF) was built for the Paleogene Barco and Mirador Formations in the Llanos Foothills southwest of the Cusiana oil field of Colombia, and east of the Guaicaramo fault and Medina Basin. A depositional model was established for these rocks and predicted the geometries of reservoirs, reservoir heterogeneity potential stratigraphic traps. After reviewing the geological section, the study interpreted seismic tied to well logs and established a sequence stratigraphy framework. The seismic attributes from the spectral decomposition of the seismic were integrated with logarithmic gamma-ray (GR) logs, normalized and color-filled, singly or in cross-sections, with their color fill interactively adjusted. This identified the lithofacies and enabled the interpretation of the cyclicity of the depositional facies. Z plots of well logs were used to identify Paleogene sequence boundaries, system tracts, para-sequences, and mapping complex sedimentary fluvial reservoir depositional systems. The paper solved the common difficulty of predicting the siliciclastic geometries of fluvial and marginal marine facies in the stratigraphic record through this integration, enabling the evaluation of the reservoir bodies of non-marine fluvial systems and marginal marine reservoirs. The high definition frequency decomposition (HDFD), distinguishing the difference between the architectures of meandering streams, braided fluvial accumulations, and marine systems that transgress the fluvial domain in the Llanos Foothills. To conclude the study used a powerful tool in HDFD, integrated with well logs to determine the complex sedimentary fluvial reservoir depositional systems and built a sequence stratigraphic framework model of the Paleogene Barco and Mirador Formations of the Llanos Foothills.

A modern analog for meandering rivers of the Mina del Carmen Formation (Albian) at Cañadón Seco oilfield, Golfo San Jorge Basin, Patagonia

Fluvial sandstone reservoirs within the Mina del Carmen Formation (Albian) currently produce up to 10% of the liquid hydrocarbons of the Golfo San Jorge Basin, mainly from isolated channel belts encased in a fine-grained, pyroclastic-rich floodplain. In spite of their economic importance, no modern analogs for the subsurface fluvial reservoirs have been proposed yet, mainly due to the reduced thickness of the channels in relation to the vertical resolution of available 3-D seismic surveys. At Cañadón Seco oilfield (South Flank of the Golfo San Jorge Basin), the planform of a meandering channel belt in Upper Mina del Carmen Formation has been imaged in a 3-D seismic dataset using seismic attributes. The meandering channel belt is up to 13 m thick and 3200 m width, with a sinuosity of 3.61 and has an average channel width of 192 m. Using the measured parameters obtained from the seismic dataset, we tested the applicability of empirical relations developed for modern rivers; the results of the statistical equations showed a close correspondence with seismic measurements and allowed us to estimate data of formative river discharge and upstream catchment area for the subsurface example. Both values were then parallel with a database of river discharge and area of up to 1018 hydrometeorological stations in drainage catchments around the world. Nine rivers of the database show discharge-area values comparable to those obtained using empirical equations. After a review of satellite imagery of the nine areas, a modern analog for the subsurface example was found in the Middle Ebro River (Spain). The analog consists of a meandering fluvial depositional system in a foreland basin setting, with seasonal discharge variability. The approach followed in the research can be of use to any fluvial basin, but considering that fluvial systems are highly variable in scale, geometry, pattern and composition, the extrapolation of results to other regions or even to other strata within the Mina del Carmen Formation, should be done with caution.

Stratigraphic architecture and hierarchy of fluvial overbank splay deposits

Splay deposits represent an important sand-prone component of the otherwise fine-grained stratigraphic record of fluvial overbank systems. This work presents a hierarchical approach to the classification and palaeoenvironmental interpretation of ancient preserved splay deposits supported by the analysis of the stratigraphic architecture of 11 exhumed examples from the Jurassic Morrison Formation and the Cretaceous Mesaverde Group (western USA) and analysis of the morphology of splays from nine modern fluvial systems. A hierarchical arrangement of splay deposits is proposed, categorized into lithofacies, beds, elements and complexes. Recognition criteria for each tier of the hierarchy include identification of bounding surfaces, thinning and fining trends of splay elements and complexes, and palaeocurrent variability. Progradational and compensational stacking trends control the stratal architecture of splay deposits, and these are influenced by the following factors: (1) the rate of local accommodation generation, which influences the erosive power of floodwaters and whether splay elements are laterally offset owing to compensational stacking; (2) the nature of the topographic confinement of the floodplain; (3) the preservation potential linked to migration direction of channel. Splay bodies can contribute volume to fluvial reservoirs and may form significant connectors that link otherwise isolated primary channel bodies, thereby enhancing reservoir connectivity. Supplementary material: Thickness and facies types with global positioning system (GPS) coordinates, length and width v. thickness, and modern data and coordinates are available at https://doi.org/10.6084/m9.figshare.c.4461026

Analyzing the architecture of point bar of meandering fluvial river using ground penetration radar: A case study from Hulun Lake Depression, China

The point bar is one of the most important reservoirs in a meandering depositional system, and accurately building a 3D architecture model for point bars is crucial to predict hydrocarbon distribution within the reservoir. Unfortunately, we can only obtain a qualitative description about the internal architecture of the point bar due to the limited information or the low resolution of available data (such as reflection seismic data). To build a 3D prototype point bar reservoir model, we analyze the architecture of point bars by integrating high-resolution ground penetrating radar (GPR) data and modern deposition. We found that our GPR data have five main reflection patterns (GPR facies), and GPR facies can be used to relate with architectural elements (the depositional facies and geobodies within depositional facies). The concave-down GPR facies is usually related to the abandoned channel. The continuous, subhorizontal, subparallel GPR facies is commonly related with lateral-accretion sand bodies within the point bar. The multiple stacked small-scale, discontinuous reflections GPR facies is interpreted to be shale drapes within the point bar. We further analyzed the geometry parameters of the identified channels. We found that the nonsymmetric [Formula: see text] of abandoned channel near the channel axis is related to the ratio between the curvature of channel radius [Formula: see text] and channel width [Formula: see text] ([Formula: see text]). Finally, we built two 3D channel reservoir models and our models could provide useful guidance for the architecture analysis of buried meandering fluvial reservoirs.

Characterizing meander belts and point bars in fluvial reservoirs by combining spectral decomposition and genetic inversion

Accurately characterizing meander belts and point bars in fluvial reservoirs is significant for reducing drilling risks and improving the recovery of oil and gas. For this goal, we developed a new seismic inversion method that combines spectral decomposition and genetic inversion for improving vertical and horizontal resolution of seismic interpretation and readjusting tuning effects. This method takes advantage of multiple spectral-decomposition seismic cubes. Seismic traces, integrated traces (90°-phase data), sweetness, and root-mean-square volume attributes were input to consider information from a range of seismic data types. Tests using a sample conceptual model and a real-world dataset demonstrate that the proposed method could achieve satisfactory results, improve the resolution of inversions, and readjust tuning effects. The real dataset is a case study from the Chengdao Oilfield in the Bohai Bay basin in China and the Neogene Guantao formation is the interval of interest. Our study area covers approximately 85 km2, and the dataset used includes mainly 441 wells and a post-stack 3D seismic cube with a dominant frequency of 40 Hz. In the spectral-decomposition genetic inversion results, distributions of inversion values were in relatively good accord with the well logs, and several thin adjacent sandstone bodies that could not be distinguished in the conventional genetic inversion results could be distinguished distinctly. We also proposed a workflow for the characterization of fluvial meander belts and point bars by integrating inversion results and quantitative depositional models. According to the surface attributes and red-green-blue blending maps of multiple stratal slices calculated from the inversion cube, one main meander belt, eight narrow channel fills, and several overbank sandstone bodies were accurately imaged; most of these features were confirmed from well observations. Furthermore, 15 point bars and related abandoned channels were characterized in the main meander belt. The proposed inversion method can improve the resolution of seismic interpretations and the undertaken characterization of meander belts and point bars could provide an example for other fields with a similar dataset.

The geometry of fluvial channel bodies: Empirical characterization and implications for object-based models of the subsurface

The distribution of channel deposits in fluvial reservoirs is commonly modeled with object-based techniques, constrained on quantities describing the geometries of channel bodies. To ensure plausible simulations, it is common to define inputs to these models by referring to geologic analogs. Given their ability to reproduce complex geometries and to draw upon the analog experience, object-based models are considered inherently realistic. Yet this perceived realism has not hitherto been tested by assessing the outputs of these techniques against sedimentary architectures in the stratigraphic record. This work presents a synthesis of data on the geometry of channel bodies, derived from a sedimentologic database, with the following aims: (1) to provide tools for constraining stochastic models of fluvial reservoirs in data-poor situations, and (2) to test the intrinsic realism of object-based modeling algorithms by comparing characteristics of the modeled architectures against analogs. An empirical characterization of the geometry of fluvial channel bodies is undertaken that describes distributions in (and relationships among) channel-body thickness, cross-stream width, and planform wavelength and amplitude. Object-based models are then built running simulations conditioned on six alternative, analog-informed parameter sets, using four algorithms according to nine different approaches. Closeness of match between analogs and models is then determined on a statistical basis. Results indicate which modeling approaches return architectures that more closely resemble the organization of fluvial depositional systems known from nature and in what respect. None of the tested algorithms fully reproduce characteristics seen in natural systems, demonstrating the need for subsurface modeling methods to better incorporate geologic knowledge.

Fusing multiple frequency-decomposed seismic attributes with machine learning for thickness prediction and sedimentary facies interpretation in fluvial reservoirs

Abstract Defining the boundaries, thicknesses and sedimentary facies of fluvial reservoirs (sand bodies) is critical for predicting hydrocarbon volumes, designing schemes for petroleum exploration and development and improving oil recovery. Most reservoirs contain thick and thin sand bodies at the same intervals, while the amplitude values of seismic data usually highlight sand bodies near the 1/4 wavelength for the tuning phenomena. Hence, the application of spectral decomposition to seismic attributes and the combination of multiple frequency-decomposed (spectral-decomposed) seismic attributes have gained increasing attention for the readjustment of tuning thickness to predict sand bodies of various thicknesses. However, the popular method of red-green-blue blending is a simple linear combination of three frequency-decomposed seismic attributes that qualitatively analyzes the sand thickness without well-log interpretation. This research proposes machine learning fusion as a new nonlinear method for fusing high-, middle-, and low-frequency seismic attributes. This method uses machine learning to link well-log interpretation and multiple-frequency seismic attributes for the quantitative prediction of sand thickness, which is important for development work in a mature field. Test results of the conceptual model and the real case indicate that the predicted sand thickness after fusing multiple frequency-decomposed seismic attributes is approximately in line with the actual thickness (correlations between 80 and 90%). Combined with the coherence attribute and the red-green-blue blending results, the distributions and histories of sedimentary facies are analyzed based on the predicted sand thickness and well data. The results suggest that the proposed method can effectively readjust the tuning thickness and improve the resolution of seismic interpretation. This method is a potentially effective technique to characterize the sand thickness and sedimentary facies in other fields using a similar geological setting and dataset.

Channel identification using 3D seismic attributes and well logging in lower Shihezi Formation of Hangjinqi area, northern Ordos Basin, China

Channel identification in oil and gas exploration is a vital task due to the importance of fluvial reservoirs. The fluvial sandstone of Lower Shihezi Formation of Ordos Basin is the primary target layer of gas exploration and development which has the maximum potential of producing tight gas sand reservoir in China. Fluvial paleo-channels can be identified easily by core, outcrop and logs data, but due to development of the several faults and limited seismic resolution in the study area, it is difficult to identify them by conventional seismic methods. The study was conducted in Hangjinqi area on the regional level of about 4537.87 km2. The radical objective of this research is to recognize the horizontal distribution and geometry of the multiple channels. Based on the study of integrated analyses of geological cores, geophysical well-logs, and seismic attributes it is confirmed that multiple braided channels are present in the study area. Channel distribution based on seismic attributes and its overlapping on the paleogeographic map showed that the channels are coming from the North and are merging towards South direction.

Past Amazon Basin fluvial systems, insight into the Cenozoic sequences using seismic geomorphology (Marañón Basin, Peru)

This study of the seismic geomorphology of riverine deposits describes and discusses the spatial resolution at which we can detect fluvial features and how the subsequently collected data can help with our understanding of ancient fluvial reservoirs. For this assessment we use three dimensional seismic reflection data, borehole data from ancient deposits in the Marañón foredeep basin of Peru, as well as digital elevation and satellite imagery data from the present day fluvial systems of the Amazonian Basin in the same area of Peru. Based on seismic stratigraphic principles on amplitude display we test parameters to highlight the details of the internal structure of horizons interpreted on continuous wavelets. Seismic attributes such as amplitude, phase, sweetness and spectral decomposition techniques have been successfully applied to make a framework of seismic stratigraphic surfaces that highlight the internal architecture and morphologic details of the studied intervals. This work confirms the presence of a Cenozoic fluvial system in Peru with straight, meandering and anastomosing channels. The observed fluvial features are associated with narrow to medium sized channels (10–∼700 m). Evolution of parameters such as sinuosity allows the variation of load in the identified channel features to be constrained. Cenozoic Marañón Basin rivers/streams size and shape are comparable to those observed in the present-day fluvial Amazon Basin. The fluvial dynamics in the study area are identified to be at least present since the deposition of the Pozo-Chambira Formation (Eocene-Oligocene) in the Marañón Basin.

Challenging Geostatistical Methods To Represent Heterogeneity in CO2 Reservoirs Under Residual Trapping

AbstractGeostatistical methods based on two-point spatial-bivariate statistics have been used to model heterogeneity within computational studies of the dispersion of contaminants in groundwater reservoirs and the trapping of CO2 in geosequestration reservoirs. The ability of these methods to represent fluvial architecture, commonly occurring in such reservoirs, has been questioned. We challenged a widely used two-point spatial-bivariate statistical method to represent fluvial heterogeneity in the context of representing how reservoir heterogeneity affects residual trapping of CO2 injected for geosequestration. A more rigorous model for fluvial architecture was used as the benchmark in these studies. Both the geostatistically generated model and the benchmark model were interrogated, and metrics for the connectivity of high-permeability preferential flow pathways were quantified. Computational simulations of CO2 injection were performed, and metrics for CO2 dynamics and trapping were quantified. All metrics were similar between the two models. The percentage of high-permeability cells in spanning connected clusters (percolating clusters) was similar because percolation is strongly dependent upon proportions, and the same proportion of higher permeability cross-strata was specified in generating both models. The CO2 plume dynamics and residual trapping metrics were similar because they are largely controlled by the occurrence of percolating clusters. The benchmark model represented more features of the fluvial architecture and, depending on context, representing those features may be quite important, but the simpler geostatistical model was able to adequately represent fluvial reservoir architecture within the context and within the scope of the parameters represented here.

Understanding subsurface fluvial architecture from a combination of geological well test models and well test data

Abstract Two decades of geological modelling have resulted in the ability to study single-well geological models at a sufficiently high resolution to generate synthetic well test responses from numerical simulations in realistic geological models covering a range of fluvial styles. These 3D subsurface models are useful in aiding our understanding and mapping of the geological variation (as quantified by porosity and permeability contrasts) in the near-wellbore region. The building and analysis of these models enables many workflow steps, from matching well test data to improving history-matching. Well testing also has a key potential role in reservoir characterization for an improved understanding of the near-wellbore subsurface architecture in fluvial systems. Developing an understanding of well test responses from simple through increasingly more complex geological scenarios leads to a realistic, real-life challenge: a well test in a small fluvial reservoir. The geological well testing approach explained here, through a recent fluvial case study in South America, is considered to be useful in improving our understanding of reservoir performance. This approach should lead to more geologically and petrophysically consistent models, and to geologically assisted models that are both more correct and quicker to match to history, and thus, ultimately, to more useful reservoir models. It also allows the testing of a more complex geological model through the well test response.

Spatial variations in distributive fluvial system architecture of the Upper Cretaceous Marília Formation, SE Brazil

Abstract Conceptual models developed from modern distributive fluvial systems (DFSs) show a predictable spatial variation of facies progression from the margin to the interior of continental sedimentary basins. The Upper Cretaceous Serra da Galga Member of the Marília Formation has recently been interpreted to be a result of DFS deposition in the intracratonic Bauru Basin. This paper describes the spatial variations in stratigraphic architecture from the proximal to medial regions of the studied DFS and presents the implications of the recorded changes for fluvial reservoir characterization. The proximal areas are dominated by amalgamated channel-fill deposits and weakly developed, well-drained palaeosol profiles with only sparse floodplain deposits. The medial areas display a reduction in channel-fill deposits, an increase in the preserved thickness of floodplain deposits and the occurrence of sheetflood deposits and well-developed, poorly drained palaeosols. This spatial trend is accompanied by changes in the net : gross ratios of the geological bodies, forming possible high net : gross reservoirs in the proximal areas and reservoirs with very variable net : gross ratios in the medial areas. This down-system change in preserved stratigraphic architecture is evidenced for the first time in the studied sedimentary succession and follows the same pattern of facies progression described from modern examples of DFSs.

Fused spectral-decomposition seismic attributes and forward seismic modelling to predict sand bodies in meandering fluvial reservoirs

Abstract Understanding the hierarchical architectural elements of fluvial sand bodies is important for planning their development strategy and to enhance oil recovery. Red-Green-Blue (RGB) blending of multiple seismic attributes and forwarding seismic modelling are commonly used in the analysis of compound sand bodies. However, RGB blending of multiple seismic attributes can only qualitatively describe the boundaries and thickness of sand bodies. The forward seismic modelling techniques previously documented in the literature are not effective when depicting the geometry of, and stacking relationships between, sand bodies (i.e., reservoir compartmentalisation). Hence, we propose in this work a new workflow that combines fused spectral-decomposition seismic attributes (SDSAs) and forwarding seismic modelling to quantitatively predict sand thickness, and to characterise stacking relationships between sand bodies. First, we employ a Support Vector Machine (SVM) algorithm to fuse high, middle, and low frequency components (attributes) of seismic data so as to quantitatively predict the thickness of sand bodies. Second, we define the seismic waveform response patterns corresponding to the typical conceptual stacked sand bodies. With the constraints of waveform patterns and predicted sand thickness (fused SDSAs), the geometry and stacking relationships of the sand bodies are characterised by forward seismic modelling. To illustrate the effectiveness of our proposed workflow, we apply it to the Neogene Minghuazhen Formation (Nm) of the QHD 32–6 oil field, Bohai Bay Basin, China. We define five architectural elements of a meandering fluvial reservoir by analysing the hierarchy of sand bodies using our workflow. The predicted sand bodies in this workflow were further proven by horizontal drilling and production data.

Petroleum system in supra-salt strata of extensional forced-folds: A case-study from the Basque-Cantabrian basin (Spain)

Abstract Hydrocarbon accumulations in the Plataforma Burgalesa are located in structural traps that resulted from Mesozoic extensional forced folding. Pre-rift Triassic evaporites favoured the structural decoupling between faulted basement rocks and their supra-salt cover, which includes carbonate and fluvial reservoirs. These reservoir levels record severe syn-extension fracturing, related to the stretching of the supra-salt layers as extensional forced folding proceeded. The observed syn-extension fracture pattern has been partly modified by subsequent Cenozoic shortening. The availability of a large data set of seismic profiles, well data, oil shows, and the exposures of reservoir and seal levels, make the Plataforma Burgalesa an outstanding analogue for petroleum plays in extensional settings with supra-salt reservoirs. Here, we provide a reassessment of recently published structural data from the area, including geometry, kinematics, and fracture pattern of the partly inverted extensional forced fold system. We then compare structural features and occurrence of hydrocarbon accumulations, to discuss the implications for structural traps formation in rift basins with an intermediate decollement level.