The middle sub-member (Es3z) within the third member (Es3) of the Eocene Shahejie formation is the main source of the generation and accumulation of hydrocarbons in the lacustrine deltas of Bonan depression. Exploration and research work in different blocks is carried out separately. Types of sedimentary facies, and their vertical and lateral evolution in Es3z are not studied in detail. To fill this knowledge gap, we did a detailed analysis of facies and lithological characteristics through integrative studies of cores, well logs and seismic data. Identification of sedimentary structures and lithology of the reservoir zone from cores are calibrated with high-quality well logs and seismic data. Depositional facies in Es3z reservoirs are identified through analysis of sedimentary structures, grain size, log’s trends and seismic sections. Es3z was deposited in the fan delta front setting where five facies associations are found, among them distributary channels consisting of MCS, CSg, PCSs, MS, RCL, WCS, PBSs, RCS and GBS lithofacies, natural levee containing DFs, and furthermore, sheet sand are associated to CBS and SSM lithofacies. GM, GGM and DGM lithofacies are related to inter-distributary deposits, whereas mouth bars consist of PLS, CS and CFS. Depositional history, flow direction of the sediments, and facies distribution are investigated through detailed facies mapping and cross-section profiling to show that the sediments were sourced from southeast to northwest. We found thicker succession of sedimentary profiles towards north and north-west directions. Belt distributary channel deposits, covering a wide range of areas, act as potential reservoirs along with mouth bar deposits, while mudstones in interdistributary channels act as a good source and seal rocks. The methodology adopted has great potential to explore the reservoirs of fan delta front in lacustrine deltas.
Introduction: Oilfield development’s primary objective has changed in recent years as a result of a deeper focus on oilfield exploration and possible reservoir oil extraction. These days, the distribution and characteristics of residual oil are hot topics.Methodology: This research study provides a physical simulation of the remaining oil distribution in the third-order architectural unit in the beach reservoir. Based on the reservoir geometry and compositional sequence, the third-order architecture unit in a beach sand reservoir can be divided into three types: layered, plate-like, and trough-like architecture units.Results and Discussion: A water-flooding simulation experiment is performed to find the distribution pattern of remaining oil (shortened as RO and used hereafter) and the controlling effect of the mudstone interlayer. The simulation results revealed that in the layered architecture unit with reverse-graded bedding, RO is mainly distributed between interlayers and accumulates at the bottom in fine-grain sands. The horizontal distribution of the mudstone interlayer has a profound effect on blocking the longitudinal migration of fluid. Second, in the plate-like architecture unit with uniform grain size, RO is mainly found in the middle portion of the model, separated by clay interlayers, with irregular presence of RO in the upper and lower part of the model. The oblique distribution of the clay interlayer has a significant effect on blocking the lateral migration of the fluid. Thirdly, in the trough-like architectural unit with normal-graded bedding, the RO is mainly distributed on top of the model in fine-grain sands and on the ridge-like parts formed by the interlayer’s intersection.Conclusion: A trough-like clay interlayer can promote fluid movement. RO distribution patterns from the current experiment can be used to explore the remaining oil in beach sand reservoirs of similar oilfields.
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