Reservoir Architecture Research Articles

Sedimentary characteristics and reservoir architecture of a lacustrine mixed carbonate/siliciclastic system: the lower member of the ShangGanchaigou Formation, Neogene, in the western Qaidam Basin, China

Lacustrine mixed carbonate/siliciclastic sediment is an important type of oil and gas reservoir with significant potential. Although previous studies have investigated the sedimentary characteristics of the mixed depositional system in numerous oil and gas-bearing basins worldwide, a detailed sedimentary architecture model is still lacking for guiding reservoir characterization at the hydrocarbon reservoir scale. In this paper, a typical lacustrine mixed carbonate/siliciclastic sedimentary system, preserved in the lower member of the ShangGanchaigou Formation, Neogene, in the western Qaidam Basin, Western China, was deeply investigated based on well logging data from 640 wells, 438 m of cores from 3 core wells, and outcrop studies. The results demonstrate that 1) seven types of architecture elements, namely, distributary channel, channel mouth bar, distal bar, sheet-like sand, shallow water mud, algal mound, and marl flat characterized by different lithofacies associations, were recognized based on core and well logging data. 2) The lacustrine mixed carbonate/siliciclastic depositional system can be divided into three facies belts. Along the lakeward direction, the proximal facies belt is dominated by delta front deposits and characterized by gradually downstream bifurcating distributary channels and associated lateral amalgamated delta lobes. The middle facies belt is characterized by isolated and small-scale delta lobes and inter-lobe deposits, including sheet-like sand, small-scale algal mounds, and marl flats, and the distal facies belt is a combination of large-scale algal mounds and marl flats. 3) Within a depression, short-term base-level cycles controlled the facies belt transition, and the proximal, middle, and distal facies belts formed under relatively low, middle, and high base-level conditions, respectively. 4) The scale and connectivity of reservoirs gradually decreased from the proximal to the distal belt.

Early extensional salt tectonics controls deep-water sediment dispersal

Predicting the distribution of sedimentary facies during the early stages of deformation of salt-detached continental margins is key to constraining the location and stratigraphic architecture of hydrocarbon and CO2 reservoirs, as well as to understanding the oceanic carbon cycle. Despite its importance, we still have a relatively poor understanding of salt-sediment interactions during the early phases of extensional salt tectonics, mainly because subsequent salt-related deformation and/or deep burial of the related stratigraphic succession means the related deposits are poorly imaged in seismic reflection data and/or not penetrated by borehole data. We investigated the interplay between early extension-related salt deformation and deep-water sediment dispersal using 3-D seismic reflection data from the northern Levant Basin offshore Lebanon. Our results indicate that salt tectonics has two contrasting impacts: Whereas slope-parallel faults favor early sediment transfer along downslope-oriented corridors to the abyssal plain, slope-normal faults and ramp-syncline basins trap land-derived sediments, hampering or delaying their transport to the abyssal plain. These results help refine source-to-sink models of turbidite systems developing in young salt basins, highlighting the crucial role of extensional tectonics in controlling sediment dispersal and the development of intra-slope depocenters and emphasizing the impact of fault strike, ramp-syncline basin evolution, and salt thinning. Our study has significant implications for predicting the location of deep-water coarse-grained sediment and the preservation of land-derived organic carbon in mature, more structurally complex, salt basins.

The Time-Varying Characteristics of Relative Permeability in Oil Reservoirs with Gas Injection

Relative permeability is a critical parameter in reservoir numerical simulation and production prediction, intimately associated with reservoir architecture and fluid property. During gas injection development, substantial alterations in reservoir properties and fluid phase behavior induce dynamic changes in relative permeability. Clearly characterizing the time-varying features of relative permeability is very useful for an understanding of how gas injection influences fluid mobility within the reservoir and enhances recovery rates. In this paper, core displacement experiments are firstly conducted to obtain the characteristics of the relative permeability of oil and gas under various development stages and displacement conditions, further delineating the comprehensive shifts in reservoir properties at different gas injection stages. Subsequently, a novel reservoir numerical simulation method is proposed that considers the spatial and temporal segmentation of relative permeability curves in the reservoir simulation. Finally, a practical application is presented to clarify the effects of injection and production parameters on the development performance of gas flooding oil reservoirs. The results show the following: (i) Significant time-varying characteristics of relative permeability occur throughout gas injection development, in the early stages of gas injection, where most of the reservoir is at the gas injection front, and a rightward shift in relative oil and gas permeability indicates that gas injection promotes oil mobility. Conversely, in the later stages of gas injection, as the reservoir reaches the trailing edge of gas injection, the change trend in relative oil and gas permeability reverses, shifting leftward, thereby exacerbating the gas breakout phenomena. (ii) Increasing the rate of gas injection causes relative oil and gas permeability to move leftward, effectively enhancing the gas volume sweep coefficient and microscopic oil displacement efficiency at lower injection speeds while reducing development performance at higher injection speeds. (iii) An increase in gas injection pressure causes relative oil and gas permeability to shift rightward, and although it reduces residual oil saturation and enhances microscopic oil displacement efficiency, it also intensifies gas breakout phenomena and lowers the gas volume sweep coefficient. This paper provides theoretical guidance and technical support for the design of gas injection strategies, optimization of injection and production parameters, and production forecasting.

Development of a site-screening method for hydrogen storage purposes and its application to an industrial dataset of Italian hydrocarbon reservoirs

A methodology is presented for the objective and transparent screening of hydrocarbon reservoirs for underground hydrogen storage (UHS), with subsequent testing on a large confidential dataset provided by the energy company Eni. The procedure uses the Analytic Hierarchy Process and the Delphi technique to gather expert opinions and weight 27 screening parameters in terms of: health, safety, and environment; geotechnical performance; and economic performance. A set of scores is produced that characterizes each site in terms of these three categories, as well as a comprehensive site ranking based on their overall suitability for UHS. The results highlight the importance of geotechnical parameters, while the characterization of faults and hydrocarbon type, the onshore or offshore location, the number of wells, and the reservoir architecture yielded the highest individual weights. Potential scores are also estimated for sites with incomplete datasets. Two blind tests evaluated the method's effectiveness against preexisting industrial assessments.

Refined Prediction Method for Production Performance of Deep-Water Turbidite Sandstone Oilfield: A Case Study of AKPO in Niger Delta Basin, West Africa.

Deep-water oilfields frequently employ large or superlarge well spacing, leading to significant production dynamics influenced by reservoir factors. Traditional methodologies often disregard these influences, resulting in poor accuracy. Therefore, an enhanced prediction methodology rooted in reservoir characteristics is proposed. This approach introduces the dynamic relative permeability law as a bridge, capturing macroscopic oil/water movement within the reservoir. For the first time, it integrates production dynamics with key controlling reservoir factors, encompassing reservoir architecture, injection-production connectivity, and reservoir heterogeneity. The results indicate that (1) In deep-water turbidite sandstone fields with ultralarge injector-producer well spacings, the distribution of oil-water movement is primarily influenced by reservoir connectivity and heterogeneity. The injection water sweeping ability coefficient can quantitatively describe the water flooding capacity, with a strong negative correlation between the injection water sweeping ability coefficient and interwell nonconnectivity coefficient and reservoir homogeneity coefficient. This suggests that better reservoir connectivity or weaker heterogeneity results in stronger water flooding capacity, leading to a wider range of water flooding under the same injection volume. (2) For regions with strong water flooding capacity (injection water sweeping ability coefficient 0.30-0.80), the water-free production period is the main production stage, with a focus on improving the planar flooding conditions. For regions with poor water flooding capacity (injection water sweeping ability coefficient 0.00-0.10), the middle and late water-cut periods are the main production stages, with a focus on improving interlayer dynamic differences in the later stages. For regions with moderate water flooding capacity (injection water sweeping ability coefficient 0.10-0.30), the initial focus should be on expanding planar flooding, followed by a focus on improving interlayer dynamic differences in the later stages. (3) The dynamic relative permeability law, capable of comprehensively portraying the reservoir's influence on macroscopic oil/water movement, emerges as a rational choice for production performance prediction in such contexts. Our method can improve the accuracy, compared with traditional method without geographical factors, from 45% to 90% during water-cut rising stage and 31% to 81% during production declining stage. The high prediction accuracy (90%) observed in the AKPO oilfields underscores the method's efficacy in directing on-site optimization and adjustments for the development of deep-water turbidite sandstone oilfields.

Depositional architecture of the tide-dominated late Oligocene hydrocarbon reservoirs in the Tapti-Daman block, Mumbai Offshore basin, India

The intricate interaction between tidal and river currents across a gently sloping shelf area complicates the geological interpretation of sedimentary deposits in subsurface sections. This study comprehensively analyzes the depositional framework and facies architecture in the late Oligocene siliciclastic succession of the Daman Formation, Mumbai Offshore Basin, which shows subtle changes in depositional stacking pattern in response to shoreline shifts. The late Oligocene siliciclastic succession being a major hydrocarbon producer in the Mumbai Offshore Basin; this research also aims to enhance the optimization of reserve exploitation and prospectivity evaluation. A detailed analysis was conducted using well-logs and seismic data integrated with available geological data. The Oligo-Miocene sequence demonstrates a coarsening-upward facies trend until the late Oligocene, followed by a fining-upward facies trend during the early Miocene and characterized by numerous stacked sandstone layers. The facies distribution pattern, sedimentary characteristics, and progradational geometry suggest a deltaic system dominated by tides for the late Oligocene succession and the latter part of the early Oligocene succession. The early Miocene succession shows a reversal in depositional trend with a retrogradation pattern. The late Oligocene deltaic deposits show a very high sediment load deposited during the peak river discharge from the Narmada-Tapti River system. The gentle depositional slope allowed redistribution of sediments by tidal currents. The deltaic system was further resolved into subaqueous mouth bar, delta front, and prodelta facies associations based on facies modeling. The correlation of the facies model with the regional depositional setup indicates that the late Oligocene succession corresponds to a third-order highstand system tract (HST) cycle.

Infinite-dimensional reservoir computing

Reservoir computing approximation and generalization bounds are proved for a new concept class of input/output systems that extends the so-called generalized Barron functionals to a dynamic context. This new class is characterized by the readouts with a certain integral representation built on infinite-dimensional state–space systems. It is shown that this class is very rich and possesses useful features and universal approximation properties. The reservoir architectures used for the approximation and estimation of elements in the new class are randomly generated echo state networks with either linear or ReLU activation functions. Their readouts are built using randomly generated neural networks in which only the output layer is trained (extreme learning machines or random feature neural networks). The results in the paper yield a recurrent neural network-based learning algorithm with provable convergence guarantees that do not suffer from the curse of dimensionality when learning input/output systems in the class of generalized Barron functionals and measuring the error in a mean-squared sense.

Applying seismic sedimentology to characterize the architecture of a fan delta complex: Triassic Baikouquan formation, Mahu Sag, Junggar Basin, western China

Reservoir architecture is often heterogeneous and can affect the migration and accumulation of hydrocarbons. The Triassic Baikouquan Formation in the Mahu oilfield presents a unique opportunity to use seismic data for fan delta channel and lobe belt characterization in an area with a sparse well spacing of about 800–1200 m. The Baikouquan Formation comprises coarse-grained lacustrine fan delta units deposited by traction and debris flows. The occurrence, distribution, and morphology were investigated using petrography, frequency spectrum decomposition, stratal slices, seismic forward modeling, and wireline logs. Fan-shaped lobe complexes and distributary channel complexes (sixth-order architectural units) exhibiting relatively large lateral and vertical variation were identified from 45- and 60-Hz seismic profiles. Channel and fan-shaped lobe belts (fifth-order architectural units) were investigated by integrating provenances, architectural elements from individual wells, the ratio of conglomerate to formation, cross section analysis, and seismic stratal slices. Four channel belts and three fan-shaped lobe belts were recognized, occurring in six evolutionary stages. It was discovered that these channel and lobe belts had distinct geomorphological traits. Reservoir architecture and distribution was governed by paleogeomorphology, fluctuations in accommodation space, and sediment supply. The identified fifth-order architectural units are useful for reservoir modeling and contribute to remaining oil development. This study indicates the suitability of seismic sedimentology for characterizing reservoir architecture in areas with sparse well spacing.

Integrated Insights into Lithofacies, Fracture Networks, and Reservoir Productivity in Basement Reservoirs: A Comprehensive Case Study from the Cauvery Basin, India, Using Well Logs, Petrographic Studies, and Production Logs

Summary The architecture and heterogeneity of basement rocks can play a crucial role in reservoir evaluation and hydrocarbon exploration. This study focuses on the comprehensive characterization of basement reservoir heterogeneities and fracture networks in the Cauvery Basin using a combination of petrophysical and geochemical analyses. The intricate interplay of lithological variations and chemical alteration processes in basement rocks significantly influences their complex nature. In this study, openhole log data acquired in the basement section from wells within the Cauvery Basin were analyzed. These log data were correlated with core studies to understand the lithofacies heterogeneities present within the basement reservoir. Furthermore, fracture data obtained from resistivity image log data were examined to understand the distribution and properties of fractures in relation to lithofacies heterogeneities. Notably, a higher fracture density was observed in the mafic-rich sections compared to the felsic-rich sections. The integration of resistivity image log data with lithofacies contributed to the understanding of the reservoir architecture. Additionally, elemental spectroscopy logging facilitated geochemical analysis, providing measurements of the elemental composition of basement, which were incorporated into the study. Production logging (PL) was performed in the study wells to ascertain the production from the basement reservoir. This analytical approach augmented the characterization of the basement reservoir and contributed to a holistic understanding of its properties. This study emphasizes the role of conducting a thorough analysis of petrophysical log responses in conjunction with detailed core studies to characterize basement reservoirs. The study successfully differentiated two distinct lithofacies units within the Cauvery Basin’s basement reservoirs: mafic-mineral-dominated and felsic-mineral-dominated and their impact on reservoir heterogeneities. Production log data validated hydrocarbon contributions primarily from felsic rocks, underscoring the importance of lithological variations.

Architecture and history of uranium-bearing Palaeocene–Eocene strata deposited on the eastern margin of the Peri-Tethys (Chu-Sarysu Basin, south Kazakhstan)

Deciphering the facies and architecture of alluvial successions provides invaluable insights into the interplay of tectonics, climate, eustasy, and autogenic processes affecting terrestrial sedimentary systems. The stratigraphic response of fluvial systems to variations in discharge and sediment-supply regimes is now well-understood and is tied to changes in climate, precipitation patterns, or sediment sources. The uraniferous Chu-Sarysu Basin in south Kazakhstan occupies the tectonically stable Turan Platform on the eastern margin of the Peri-Tethys, and the study of its Palaeocene–Eocene sedimentary fill offers an opportunity to unravel eustatic and climatic controls that drove the architecture of reservoirs hosting economically important deposits. The stratigraphic succession comprises two multistorey, laterally extensive, sheet-like sandstone bodies floored by prominent erosion surfaces and interpreted as the deposits of channel belts. These packages are interstratified with floodplain, coastal-wetland, and marine-embayment complexes reflecting major extra-channel belt avulsions and marginal-marine incursions on the low-gradient alluvial plain. The stratal architecture was controlled by changes in accommodation likely induced by well-documented sea-level changes in the Peri-Tethys during the Palaeogene, which permitted the development of a chronostratigraphic framework. Eustatic variations culminated in the widespread flooding of the Turan Platform in the middle Eocene, reflected by transgressive lags above a wave ravinement surface capping terrestrial and marginal-marine deposits. Marked changes in fluvial facies, floodplain styles, and inferred channel planforms between Palaeocene and Eocene strata suggest a climatic overprint on river discharge and sedimentation. Upper Palaeocene meandering channel deposits encased in well-drained floodplain strata are indicative of perennial discharge under a semi-arid climate, whereas lower Eocene low-sinuosity channel fills, displaying evidence for transcritical flows and abundant in-situ vegetation, point to intermittent runoff patterns consistent with a humid and seasonal climate. An evolution in atmospheric moisture at the Palaeocene–Eocene boundary from arid to humid conditions has been reported across the Tethys region, and linked to global climatic perturbations of the Palaeocene–Eocene Thermal Maximum.

Geomechanical Response Characteristics of Different Sedimentary Hydrodynamic Cycles—Exampled by Xujiahe Formation of Upper Triassic, Western Sichuan Basin

This study delves into the geomechanical responses of different sedimentary hydrodynamic cycles in deep tight sandstone formations. Employing core observation and thin section analysis, we quantitatively identified and characterized bedding planes, sedimentary microfacies, and tectonic fractures. Then, the intricate relationships between various architectural interfaces and geomechanical parameters were elucidated. Subsequently, utilizing finite element numerical simulation software, in situ stress and fracture parameters were derived. By identifying a fracture facies zone correlated with the sedimentary hydrodynamic cycle and production data, our findings unveil several key insights: (1) Geomechanical parameters (Young’s modulus, Poisson’s ratio, brittleness index) exhibited noteworthy variations within the T3x2−5 sand group, indicative of weak elasticity and robust plasticity. (2) The effective distance, influenced by diverse reservoir architecture interfaces, displayed variability, with each transition between peak-valley-peak or valley-peak-valley pinpointed as a distinct sedimentary hydrodynamic cycle. (3) In environments characterized by strong sedimentary hydrodynamics (between two level 3 architecture interfaces), fractures with larger strike angles and lower dip angles were observed to be more prevalent. (4) Three significant fracture faces—level I, level II, and level III—were discerned within the study area. Notably, reservoirs associated with level III exhibited characteristics suggestive of medium porosity and permeability, indicative of a gas layer. By thoroughly understanding the geomechanical response characteristics of formations such as the Xujiahe Formation, it is possible to guide the exploration and development of energy resources such as oil and natural gas. This helps to improve the efficiency and safety of resource extraction, promoting the sustainable utilization of energy.

Experimental Demonstration of Reservoir Computing with Self-Assembled Percolating Networks of Nanoparticles.

The complex self-assembled network of neurons and synapses that comprises the biological brain enables natural information processing with remarkable efficiency. Percolating networks of nanoparticles (PNNs) are complex self-assembled nanoscale systems that have been shown to possess many promising brain-like attributes and which are therefore appealing systems for neuromorphic computation. Here experiments are performed that show that PNNs can be utilized as physical reservoirs within a nanoelectronic reservoir computing framework and demonstrate successful computation for several benchmark tasks (chaotic time series prediction, nonlinear transformation, and memory capacity). For each task, relevant literature results are compiled and it is shown that the performance of the PNNs compares favorably to that previously reported from nanoelectronic reservoirs. It is then demonstrated experimentally that PNNs can be used for spoken digit recognition with state-of-the-art accuracy. Finally, a parallel reservoir architecture is emulated, which increases the dimensionality and richness of the reservoir outputs and results in further improvements in performance across all tasks.

Numerical modelling of the effects of permeability contrasts on underground hydrogen storage in sandstone reservoirs

Hydrogen is an energy carrier that can balance the divergent variations in seasonal energy demand and energy supply from renewables. Underground hydrogen storage in porous formations, such as depleted gas sandstone reservoirs or saline aquifers, provides the capacities needed for large-scale, long-duration energy balancing. This paper reports on the fundamental behaviour of hydrogen in a model reservoir setup, involving a two-phase (H 2 , water) system and a two well (injector, producer) setup placed at different depths in the reservoir. We specifically focus on the impact of natural heterogeneities, and associated permeability contrasts, on flow and efficacy of hydrogen injection and production. We found that positioning the wells, both injector and producer, at the top of the reservoir facilitates the highest hydrogen production. We also found that permeability contrasts of three to four orders of magnitude significantly affect hydrogen flow; however, factors affecting the pressure gradient also need to be considered. These factors include compartmentalization, the behaviour of co-existing fluids and the localized pressure gradient created by the hydrogen plume. Our research underlines the need to understand the architecture of the whole reservoir, from seismic to sub-seismic scales, not just the zones surrounding the wells and pathways in-between, as this controls capacity, pressure fluctuations and informs operational management decisions. Thematic collection: This article is part of the Hydrogen as a future energy source collection available at: https://www.lyellcollection.org/topic/collections/hydrogen

Elegans-AI: How the connectome of a living organism could model artificial neural networks

This paper introduces Elegans-AI models, a class of neural networks that leverage the connectome topology of the Caenorhabditis elegans to design deep and reservoir architectures. Utilizing deep learning models inspired by the connectome, this paper leverages the evolutionary selection process to consolidate the functional arrangement of biological neurons within their networks. The initial goal involves the conversion of natural connectomes into artificial representations. The second objective centers on embedding the complex circuitry topology of artificial connectomes into both deep learning and deep reservoir networks, highlighting their neural-dynamic short-term and long-term memory and learning capabilities. Lastly, our third objective aims to establish structural explainability by examining the heterophilic/homophilic properties within the connectome and their impact on learning capabilities. In our study, the Elegans-AI models demonstrate superior performance compared to similar models that utilize either randomly rewired artificial connectomes or simulated bio-plausible ones. Notably, these Elegans-AI models achieve a top-1 accuracy of 99.99% on both Cifar10 and Cifar100, and 99.84% on MNIST Unsup. They do this with significantly fewer learning parameters, particularly when reservoir configurations of the connectome are used. Our findings indicate a clear connection between bio-plausible network patterns, the small-world characteristic, and learning outcomes, emphasizing the significant role of evolutionary optimization in shaping the topology of artificial neural networks for improved learning performance.

The architecture of basalt reservoirs in the North Atlantic Igneous Province with implications for basalt carbon sequestration

Abstract Offshore CO 2 sequestration in basaltic formations of the North Atlantic Igneous Province may allow permanent storage of large volumes of CO 2 through rapid carbonate mineralization. Characterizing the internal architecture of such reservoirs is key to assessing the storage potential. In this study, six photogrammetry models and three boreholes on the Faroe Islands have been used to characterize the internal lava sequence architectures as a direct analogue to potential offshore North Atlantic Igneous Province storage sites. The studied formations are dominated by c. 5 to 50 m thick simple and compound lava flows, with drill core observations documenting a transition from pāhoehoe moving towards ‘a’ā lava flow types interbedded with thin (<5 m thick) volcaniclastic rock units. The identification of flow margin breccias is potentially important as these units form excellent reservoirs in several other localities globally. Stacked, thick simple flows may present sealing units associated with dense flow interiors. Connected porous and permeable lava flow crusts present potential reservoirs; however, the degree of secondary mineralization and alteration can alter initially good reservoir units to impermeable barriers for fluid flow. Large-scale reservoir volumes may be present mainly within both vesicular, fractured pāhoehoe and brecciated flow margins of transitional simple lava flows.

Integrated architecture of ITCAM and reservoir computing for time series data

Integrated architecture of ITCAM and reservoir computing for time series data

A Comparative Reservoir Study of Zubair and Nahr Umr Formations in Subba Oilfield, Southern Iraq

The lower Cretaceous sandstones of Zubair and Nahr Umr formations are the main producing reservoirs in Subba oilfield in southern Iraq. Key differences in their petrophysical and depositional attributes exist affecting their reservoir characteristics. The evaluation of well logs and core porosity-permeability data show better reservoir properties in Nahr Formation. The Litho-saturation logs indicate greater thickness of oil-saturated reservoir units for Nahr Unr Formation associated with lower values of shale volume, and higher values of effective porosity. In addition, higher values of permeability for Nahr Umr Formation is suggested by applying porosity-irreducible water saturation cross plot. The reducing reservoir quality of Zubair Formation sandstones is related to finer grains of sandstone reservoirs, higher clay volume, and more effect of compaction resulting from greater depth. A reservoir layering scheme is proposed by sequence stratigraphic analysis leading to the identification of systems tracts and their key surfaces within Zubair and Nahr Umr formations, and forms the basis for predicting of reservoir architecture and quality. Laterally continuous, and thick amalgamated sandstone reservoirs are formed during highstand systems tract in Nahr Umr Formation as a result of low accommodation/sediment supply conditions. Within the transgressive systems tract of Zubair Formation, the sandstone reservoir bodies become isolated as accommodation exceeds sediment supply.

The Influence of Reservoir Architecture on the Connectivity of the Shahejie Formation in the Liuzhong Oilfield

The lack of research on fine reservoir structure and sand body patterns in the Jidong Oilfield currently restricts the efficient development of the oilfield. Therefore, this article mainly focuses on the study of the main types of facies of the Shahejie Formation, sand body splicing patterns, and the degree of sand-body connectivity. The interpretation and analysis of well-logging, three-dimensional (3D) seismic, and production data were used to lay the foundation for the study and evaluate the remaining oil distribution. The results indicate that the reservoir sandstones in the study area were mainly deposited in a submerged distributary channel, mouth bar, and distributary channel flank. Using logging information to identify individual sands, a deltaic sand assemblage pattern is proposed by analyzing the sedimentary architecture. In the vertical direction, the deltaic sand body collocation style can be divided into cut-and-stack and separated types. In the lateral direction, the multi-stage sand bodies exhibit three collocation patterns: the side-cutting type, the mouth bar contact type, and the submerged distributary channel flank contact type. The degree of sand-body connectivity under different splicing patterns was analyzed and verified using production dynamic data. It was found that the sand body splicing pattern with a vertical up-cut stack and the sand body splicing pattern with a lateral up-cut had the best inter-sand-body connectivity.

Structural and stratigraphic controls on reservoir architecture: A case study from the lower Oligocene Vicksburg Formation, Brooks County, Texas

A detailed structural and stratigraphic framework provides a precise understanding of the controls on the vertical and spatial distribution of reservoir units, as well as the identification of the most prospective hydrocarbon accumulation. In southern Brooks County, Texas, the Lower Oligocene Vicksburg Formation (LOVF), is being influenced by the Vicksburg Fault Zone (VFZ). This zone is characterized by listric-normal faults that have formed highly faulted rollover anticlines, which are valuable structural traps for hydrocarbon exploration. This study integrated 568 3D seismic lines, 39 well logs, and three velocity surveys to build a comprehensive conceptual model that explores how secondary synthetic (dipping east), antithetic (dipping west), and Texas Gulf Coast-perpendicular faults are influencing accumulation and spatial distribution of hydrocarbons within the LOVF (La Rucias Field). Results indicate that synthetic, antithetic, and coast-perpendicular faults affecting the V-102, V-17, and V-19 horizons provide conduits for hydrocarbon migration. Antithetic faults and coast-perpendicular faults within the rollover anticline are terminating beneath an overlying shale seal layer between the V-16 and V-17, influencing economic hydrocarbon accumulations through multiple reservoirs. While synthetic faults affect the overlying seal layer migrating hydrocarbon out of the V-102, V-17, and V-19, bidirectional faulting linking antithetic and coast-perpendicular faults provide additional pathways for hydrocarbon accumulation. Spatial distribution of hydrocarbons varies with the targeted horizon. V-102 reservoirs are situated on the western flank of the rollover anticline, whereas the V-17 and V-19 reservoirs are located on structural highs where overlying shale seal layer remains unaffected by the antithetic faults. V-17 and V-19 reservoirs are influenced by bidirectional faulting that terminates beneath the shale seal layer, enabling the accumulation within the rollover anticline. Petrophysical and lithological investigations of the seal layers within the V-102, V-17 and V-19 are highly recommended for better understanding of vertical compartmentalization of reservoir intervals and accumulation estimates within the La Rucias Field. Investigating the control of these fault systems enhances our understanding of subsurface fluid migration and accumulations (oil, gas, groundwater, and contaminants) in the expanded Vicksburg productivity trends. Furthermore, the insights gained from the examination of these fault systems not only contribute to our comprehension of subsurface fluid migrations within the Vicksburg trends but also serve as a valuable reference for similar geological systems and reservoirs worldwide, ultimately aiding in the development of more effective resource management.

Seismic interpretation and sequence stratigraphic analysis of the Bahariya Formation in the South Umbaraka oilfields (Western Desert, Egypt): insights into reservoir distribution, architecture, and evaluation

The integration of multiscale datasets, including seismic, well-logs and stratigraphy, is providing a precise picture about reservoir evaluation and spatial distribution. This study focuses on the seismic interpretation and sequence stratigraphic analysis of the Bahariya Formation in the South Umbaraka oilfields (Selkit, Khepri, and Sethos), located in the Western Desert of Egypt. Seismic interpretations reveal various structural closures, including anticlinal domes and faulted anticlines in different fields. The study area is divided into northern and southern blocks separated by a major fault, and structural cross sections provide valuable information on reservoir zones regarding lateral extension, thickness variation, and fault distribution. The Bahariya Formation is subdivided into two depositional sequences: Lower Bahariya sequence (BAH.SQ-1) and Upper Bahariya sequence (BAH.SQ-2) with distinct wireline-log characteristics, seismic reflections, and lithofacies variations. BAH.SQ-1 comprises mixed siliciclastic-dominated units with some carbonate units, while BAH.SQ-2 consists of mixed siliciclastic and carbonate units. Multiple sequence boundaries, depositional surfaces, and systems tracts are identified within BAH.SQ-1 and BAH.SQ-2, indicating changes in sedimentary environments and sea-level fluctuations. The petrophysical evaluation reveals promising reservoir zones in both the Lower and Upper Bahariya sequences. However, the Lower Bahariya sequence exhibits superior reservoir characteristics in terms of net-pay thickness, shale volume, effective porosity, and water saturation. Particularly, the sandstone-dominated LST-1 within the Lower Bahariya Formation is identified as a favorable reservoir zone. Conversely, the Upper Bahariya Formation has limited reservoir potential. This study underscores the significance of sequence stratigraphy and reservoir architecture, emphasizing the role of faulting, folding, and depositional environments in the distribution and quality of reservoir zones. The findings contribute valuable insights into the structural and stratigraphic characteristics of the Bahariya Formation, enhancing understanding of hydrocarbon plays and reservoir distribution in the studied area.