Controlling effects of depositional microfacies on reservoir development in the Es₃^s formation, Jin9 Block, Jinjia...

Understanding the spatial heterogeneity of clastic reservoirs is essential for effective hydrocarbon development, yet the controlling factors remain poorly constrained in the Es₃^s Formation of the Jin9 Block, Jinjia Oil Field. This study integrates core descriptions, well logs, 3D seismic data, and production tests to investigate how depositional microfacies influence reservoir architecture and quality in this under-explored interval. Petrographic analysis of core samples shows that the reservoir rocks are fine-grained feldspathic litharenites and lithic arenites with moderate sorting, subangular grains, and primary porosity-characteristics indicative of proximal sediment sources and limited diagenetic modification. Sedimentological interpretation reveals deposition in a delta front environment fed by the Luxi Uplift to the south and the Qingcheng Uplift to the west. Five microfacies are identified: mouth bar, distributary channel, distal bar, interchannel, and blanket sand. Mapping these microfacies across multiple sublayers documents systematic lateral heterogeneity, with sand bodies thickening northward and westward-a pattern that reflects compensational stacking and differential accommodation. Integration with production data demonstrates that reservoir quality is strongly facies-dependent: wells completed in mouth bar sandstones (thick, clean, coarse-grained) yield the highest productivity with oil-bearing layers exceeding 6 m, whereas wells in distal bar or interchannel facies show lower rates and earlier water breakthrough. Our findings establish that depositional microfacies, rather than structural position alone, exert the primary control on reservoir development in the Es3s. This microfacies-based framework offers a practical tool for predicting sweet spots and optimizing well placement-not only in the Jin9 Block but also in analogous delta-front settings where conventional structure-oriented approaches fall short.