盖层封闭能力与盖层厚度的定量关系

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。

RESEARCH OF QUANTITATIVE RELATIONS BETWEEN SEALING ABILITY AND THICKNESS OF CAP ROCK

The ability of caprock sealing free hydrocarbons includes two aspects:one is displacement pressure of the bottom caprock and other is absorption resistance of capillary for water in caprock.The absorption resistance has something to do with lithology,degree of lithogenesis and thickness of caprock.The smaller the grain size of caprock is, the higher the content of clay mineral is, the stronger the degree of lithogensis is and the thicker the caprock is, the stronger the absorption resistance and the sealing ability of caprock are.Based on the mechanism of low velocity seepage of pore fluid in caprock, the absorption resistance is equal to twice as much as ultra pressure value of fluid in the pore of caprock.Calculated results reveal that the absorption resistance of Qingshankou formation in Sanzhao depression of Songliao Basin is approximately twice as much as the displacement pressure of the base for the caprock i.e.The real sealing ability of the caprock is approximately three times as big as the known ability in the past.The research result can be used to explain why Quaternary system caprocks with high porosity, high permeability, and ultra low displacement pressure have sealed a great quantity organic gas in many basins in our country.