Control factors and classification evaluation of pressure maintenance capability in overpressured shale containing sandstone strips

China has substantial shale oil resources, with the Jiyang Depression alone estimated to contain over 10 billion tons. However, some wells exhibit rapid pressure decline due to sandstone strips encountered during drilling, which impair pressure preservation. This study investigates the LJ Block in the Dongying Sag to clarify the influence of sandstone strips on pressure decline in overpressured shale. Using integrated core, logging, well-test, and simulation data, we characterize pressure distribution and identify key controls on pressure maintenance. Sandstone strips are widespread; about 60% are thinner than 2 m. Although a “high pressure in shale, low pressure in sandstone” profile prevails, not all strips cause pressure drop. Pressure release depends on strip thickness, porosity, and lithology, often forming local “pressure‑decline funnels”. Three first‑order—factors strip scale, sedimentary characteristics, and distribution—control pressure maintenance. A quantitative evaluation system with six second‑order parameters was developed, enabling classification of pressure‑maintaining zones into three categories (I–III) by weighted scoring. The results correlate well with production‑derived pressure indicators, providing a geological foundation for shale oil development in the Dongying Sag.