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盖层封闭游离相烃类的能力由两部分组成 ,一个是盖层底部岩石的排替压力 ,一个是盖层毛细管孔隙的吸附阻力 ,盖层毛管孔隙的吸附阻力与盖层岩性、成岩程度、厚度有关 ,盖层岩石的粒度越小、粘土矿物含量越高、成岩程度越强、厚度越大、盖层的吸附阻力越大 ,盖层的封闭能力越强。根据泥质岩盖层中孔隙流体的低速渗流机理研究 ,盖层中吸附阻力的大小恰等于其中孔隙流体超压值的 2倍。通过对松辽盆地北部三肇地区青山口组盖层的封闭能力计算 ,发现该盖层的吸附阻力近似于其底部岩石排替压力的 2倍 ,即实际封闭能力是以前研究的 3倍。由此为我国众多盆地中第四系浅层高孔隙度、高渗透率、极低排替压力盖层封盖了大量生物气的机理解释奠定了理论基础。
The ability of the caprock to seal off free-phase hydrocarbons consists of two components, one is the displacement pressure of the rock at the base of the caprock, the other is the adsorption resistance of the capillarity pores, the adsorption resistance of capillarity and the caprock lithology, the degree of diagenesis , And the thickness. The smaller the cover rock size, the higher the clay mineral content, the stronger diagenesis. The greater the thickness, the larger the adsorption resistance of the cap layer and the stronger the cap sealing ability. According to the low velocity seepage mechanism of pore fluid in the muddy caprock, the adsorption resistance in the caprock is exactly equal to 2 times the pore fluid overpressure. Based on the calculation of the sealing capacity of the Qingshankou formation in the Sanzhao area in the northern Songliao Basin, the adsorption resistance of this layer is found to be about twice that of the rock discharge pressure at the bottom, ie, the actual sealing capacity is three times that of the previous study. This laid the theoretical foundation for the explanation of the mechanism of large amount of biogas capped by the caprock of Quaternary shallow reservoirs of high porosity, high permeability and extremely low replacement in many of China’s basins.