The main producing layer in the middle of WY block of Ansai Oilfield is Chang 6₁ sand layer group of Yanchang Formation in Triassic system. Currently, this block has entered the middle-to-late stage of waterflooding development. Due to an insufficient understanding of sand body distribution and superposition patterns, uneven effect of waterflooding exists during waterflooding process. Basic geological data, including core observation, thin-section analysis, laboratory experiment, and well logging, were integrated for detailed analysis of sedimentary microfacies, characterization of spatial configurations of single sandbodies, and evaluation of injection-production correspondence. These analyses provided a geological basis for fine injection-production management in the medium and high watercut stages. Results show that Chang 6₁ sand layer group in the middle of WY block belongs to a meandering river delta front subfacies sedimentary system. Four types of sedimentary microfacies are developed in this group, namely underwater distributary channels, channel flanks, interdistributary bays, and mouth bars. Underwater distributary channels constitute the dominant sedimentary microfacies. Based on the principle of “vertical layering and lateral boundary delineation”, single sandbody superposition patterns are classified into three types: separated type, stacked type, and incised-stacked type. Incised-stacked and separated types are numerically dominant, while stacked types are rare. Sandbody lateral contacts exhibit three modes: isolated mode, butt-jointed mode, and laterally incised mode, in which laterally incised mode is dominant. Influenced by frequent channel diversion and migration, sand bodies show significant superposition characteristics. Along the direction of sediment source, channel sandbodies display strong continuity, and high-quality reservoir sandbodies are concentrated in incised-stacked composite zones of distributary channels. Based on the perforation positions in oil/water wells and single sandbody connectivity, injection-production mismatches are categorized into three types: single sandbody with injection but no production, single sandbody with production but no injection, and single sandbody without production and injection. Injection-production mismatched sandbodies primarily occur in Chang ${6}_{1}^{1-2-1}$, Chang ${6}_{1}^{1-2-4}$, and Chang ${6}_{1}^{1-3-1}$, and single sandbody with injection but no production is dominant. Furthermore, accurate reperforation for single sand layers where injection and production mismatches can improve the reservoir injection-production correspondence, and further enhance waterflooding efficiency.