源盖层替代封闭的有效性及确定方法

Replacing seal validity of caprock with generation gas ability and its determining method

研究了源盖层替代封闭作用形成条件及封闭机理 .通过对替代封闭作用形成时期与气源岩大量排气期的比较 ,提出了源盖层替代封闭有效性的概念及确定方法 .即源盖层的替代封闭作用始于其排气门限 ,并一直贯穿于整个生气过程中 ;替代封闭作用形成时期只有早于气源岩的大量排气期 ,或与之同期 ,源盖层才可依靠替代封闭作用封闭住大量的扩散相天然气 ,替代封闭性最好 ;若晚于大量排气期 ,封闭有效性取决于二者时间差 ,时间差越小 ,封闭住的天然气量越大 ,替代封闭有效性越好 ,反之则越差 .应用该方法评价了松辽盆地北部三肇凹陷登二段源盖层依靠替代封闭作用封闭沙河子组～营城组气源岩扩散相天然气的有效性 .结果表明 ,与实际状况吻合 。

This paper studied the formation conditions and mechanism of replacing seal in caprock with generation gas ability. By contrasting the format ion period of replacing seal in caprock with generation gas ability and the larg e amount of expulsion hydrocarbon period of gas sourcerok , this paper puts forw ard the concept of replacing seal efficiency in caprock with generation gas abil ity and its determining method. If the replacing seal formation period is earlie r than or the same as the period, a lot of gas was expelled from sourcerock, a l ot of gas in diffusion phase is sealed by caprock, the replacing seal efficiency is best. If the replacing seal formation period is later than the period, a lot of gas was expelled form sourcerock, the replacing seal efficiency is determine d by their time difference. The smaller time difference is, the bigger the gas a mount is sealed by caprock, the better replacing seal validity is. On the contr ary, the replacing seal efficiency is bad. The method was applied in studying th e replacing seal validity of the second member of Denglouku formation caprock wi th generation gas ability to the gas in diffusion phase from Shahezi-Yingcheng f ormation gas sourcerock in Sanzhao Sag of Songliao Basin. The result indicates t hat the method is practical and can objectively reflect the replacing seal effic iency of caprock with generation gas ability.