Identification and Distribution Characteristics of Mudstone Intercalations in Ultra-Deep Tight Fractured Sandstone Gas Reservoirs: A Case Study of the Keshen A Gas Reservoir, Tarim Basin

The ultra-deep tight sandstone gas reservoirs in the Tarim Basin, exemplified by the Keshen A gas reservoir, face escalating challenges of water invasion and pressure maintenance after years of production. Interlayers within these reservoirs serve as critical geological barriers, yet their spatial distribution remains poorly resolved due to limitations in conventional identification methods. This study integrates core, logging, 3D seismic, and production data within a sequence stratigraphic and reservoir geology framework to establish a ``core-logging-seismic'' collaborative identification system for argillaceous interlayers. Two main interlayer types—argillaceous and physical—are identified within the Bashijiqike Formation. Argillaceous interlayers exhibit distinctive logging responses (``high GR, high AC, low resistivity''), and seismic half-width attributes effectively delineate their lateral distribution. These interlayers are predominantly concentrated in the K1bs2 interval, with thicknesses of 0.8–2.5 m and a NW-SE oriented planar distribution. Based on thickness and lateral extent, they are classified into three levels (single-well, well-group, and reservoir-scale). Interlayers exceeding 1.5 m in thickness with good lateral continuity form effective flow barriers that significantly suppress water invasion. The findings were applied to well-pattern optimization in 2023, reducing overall water influx by 37% and increasing estimated recovery by 8.2%, supporting a transition from empirical to geologically-guided development in ultra-deep tight reservoirs.