泥岩盖层的超压封闭演化特征及封气有效性

Seal evolution characteristics of overpressured mudstone and its seal efficiency

在松辽盆地汪家屯气田青山口组泥岩盖层超压发育特征研究的基础上,对不同井青山口组泥岩超压演化特征进行了探讨.结果表明:汪家屯气田只有升65井青山口组泥岩盖层曾在嫩四段沉积中期发生过破裂超压释放,已完成了1次演化,目前进入第2次演化阶段;其余井青山口组泥岩盖层目前均未发生破裂超压释放,仍处于第1次演化阶段.在此基础上,对该气田青山口组泥岩盖层超压封闭性演化特征进行了研究,得到汪家屯气田除升65井青山口组泥岩盖层超压在嫩四段沉积中期封闭能力降低外,其余井青山口组泥岩盖层封闭能力自形成后均逐渐增强,且具有较强的封闭能力.通过青山口组泥岩盖层超压封闭性形成演化与沙河子组源岩排气期之间的匹配关系得到,汪家屯气田青山口组泥岩盖层超压封闭能力形成时期远远晚于沙河子组源岩的大量排气期,造成沙河子组源岩排出的天然气,大部散失,升65井处在嫩四段沉积中期超压释放造成的天然气散失,可能是该气田虽然青山口组泥岩盖层封闭能力强但只形成了中等气田的一个重要原因之一.

Based on the study of development characteristics of overpressured mudstone caprock of K1qn mudstone in Wangjiatun gas field of Songliao Basin, the evolution of overpressure of K1qn mudstone in different wells was studied. Only mudstone caprock of K1qn in well Sheng 65 has been broken and overpressure has been released. Thus the first evolution was completed and the second evolution began. Mudstone caprock of K1qn in other wells has not been broken and overpressure remained unreleased, its evolution is in the first evolution stage. Based on this, the seal evolution characteristics of overpressured mudstone caprock of K1qn in Wangjiatun gas field was studied. It was considered that except the seal ability of ovepressured mudstone of K1qn in well Sheng 65 decreased in the middle of K1n4 sedimentary period, the seal ability of overpressured mudstone of K1qn in other wells increased since overpressure formed. There are strong seal ability of overpressured mudstone caprock of K1qn in all wells now. By the study of the relation between seal formation and evolution of overpresssured mudstone caprock of K1qn and expulsion gas period of K1sh soucerock in Wangjiatun gas field, it was considered that the seal formation period of overpressured mudstone caprock is much later than the period that a lot of gas was expelled from K1sh sourcerock ln Wangjiatun gas field, which made a lot of gas expel from K1sh sourcerock lose. If gas is lost in the middle of K1n4 sedimentary period because overpressure was released, it is one of important cause that a middle gas field was only formed in Wangjiatun though there is a strong seal ability in overpressured mudstone caprock of K1qn.