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根据晚第四纪地层的物性特征、力学性质及烃浓度值实验资料和孔隙水压力及其消散历时现场试验结果表明，覆盖下切河谷之上的近岸浅海相灰色淤泥质粘土层为区域盖层，下切河谷内的河漫滩相灰—灰黑色粘土及淤泥质粘土层为局部盖层。粉细砂、粉砂、粉砂质粘土、淤泥质粘土和粘土的粒径依次变小，比表面积依次增大，使其孔隙率、孔隙比、天然含水量及孔隙水压力值依次增大。粘土的压缩系数、塑性指数、液性指数及抗剪强度最大，其抗变形能力相对最弱，可压缩相对最大，相对封闭性最好；而淤泥质粘土、粉砂质粘土的封闭性次之。随着埋藏深度的增加，盖层的封闭性增强。盖层的封闭机理主要为物性封闭、烃浓度封闭和孔隙水压力封闭，后者可能对生物气藏保存起着最主要的封闭作用。
Based on the experimental data of the Late Quaternary stratigraphy, the experimental data of mechanical properties and hydrocarbon concentration, and the pore water pressure and its dissipation duration, the field test results show that the gray muddy clay layer near the shallow sea cover above the cut valley is the regional cap rock The river floodplain in the undercut valley is greyish-gray-black clay and muddy clay as partial caprock. The particle sizes of silty sand, silt, silty clay, silty clay and clay decrease in sequence, and the specific surface area increases in turn so that the porosity, void ratio, natural water content and pore water pressure increase in turn. Clay has the highest compressibility, plasticity index, liquid index and shear strength, the weakest anti-deformability, the highest compressibility and the best confinement, while the clay and silty clay are the second most closed . With the increase of burial depth, the sealing of the cap layer is enhanced. The main sealing mechanism of the caprocks is closed physical property, closed hydrocarbon concentration and closed pore water pressure, which may be the most important blocking effect on the preservation of biogas reservoirs.