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杭州湾地区晚第四纪浅层生物气藏盖层存在孔隙水压力封闭和烃浓度封闭机理,但其是否存在物性封闭机理目前尚存在较大争议。研究区浅层生物气藏盖层埋藏浅、时代新、结构松散,对其物性封闭能力的评价不能直接套用深部成岩盖层的评价参数和方法。通过变水头渗透实验测定盖层和储层样品渗透率数值,以渗透率作为评价浅层生物气盖层物性封闭能力的参数,对研究区浅层生物气藏盖层的物性封闭特征及其影响因素进行了详细研究。结果表明盖层渗透率数值比储层小3个数量级,具有较强的物性封闭能力,有利于浅层生物气藏的保存。研究区浅层生物气盖层物性封闭能力的影响因素包括黏土含量及黏土矿物成分、含水饱和度和盖层厚度,黏土含量及黏土矿物成分对盖层物性封闭能力起决定性作用,较高的含水饱和度促进了盖层物性封闭能力的增强,盖层厚度对物性封闭能力起到了极为重要的补偿作用。
There is pore-water pressure sealing and hydrocarbon concentration sealing mechanism in the caprock of the Late Quaternary shallow biogenic gas reservoir in the Hangzhou Bay, but there is still much controversy about whether there is a physical sealing mechanism. The cover of the shallow bio-gas reservoir in the study area is shallow, with a new age and loose structure. Evaluation of its physical sealing ability can not directly apply the evaluation parameters and methods of deep diagenetic cover. The permeability of caprock and reservoir samples were measured by variable head penetration experiments. The permeability of caprock was used as a parameter to evaluate the physical sealing ability of shallow caprock. Factors were studied in detail. The results show that the permeability of cap rocks is 3 orders of magnitude smaller than that of reservoirs, which has strong physical sealing ability and is favorable for the preservation of shallow biogenic gas reservoirs. The influencing factors of the physical sealing ability of the caprock of shallow biogenic gas in the study area include clay content, clay mineral composition, water saturation and caprock thickness, clay content and clay mineral composition, which play a decisive role in cap property closure. Higher water content Saturation promotes the enhancement of physical properties of caprock, and the thickness of caprock plays a very important compensation role on physical captive ability.