松辽盆地三肇凹陷油气下排的地质条件及找油方向

Geologic conditions of oil-gas downward discharging and exploration direction in the Sanzhao Sag,Songliao Basin

三肇凹陷青山口组一段是质量尚好的烃源岩层,该地层普遍存在较高的孔隙流体超压,为油气的向下排放提供了充足的动力来源。扶杨油层的油气来自于其上覆的青一段源岩层。数值模拟和油气纵向分布规律表明岩石的孔隙、微裂缝及干酪根网络不是油气下排的输导通道;断层的分布规律、断穿层位、演化历史及油气的纵向分布规律研究发现:大量发育并在源岩有机质成熟后频繁活动开启的断穿T_2—T_(06)的断层是青一段油气下排的主要通道,该类断层即为油源断层。青一段在油气下排之后即变成了封闭能力极强的封盖层,青一段下排的油气被严格地限定在了青一段之下的扶杨油层之中。受地层倾向和起通道作用断层活动性的影响,油源断层的下降盘扶杨油层很难形成较大规模的油气聚集,油气主要在油源断层的上升盘一侧聚集成藏,故上升盘是油气勘探的主要方向。

The mudstone of Member 1 , Qingshankou Formation was preferable source rock,with common pore fluid abnormal pressure in the strata, which was dynamic resource of oil discharging downward. The sources＇ comparison revealed the oil in Fu-Yang oil layer being from Member 1 of the formation in the Sanzhao Sag. The numerical analogue and longitudinal distribution laws of oil-gas demonstrated that lithologic pores, microcrack and kerogen network could not be transfusion pathway of oil discharging downward. Based on a study of faults＇ distribution, the horizons cut by faults, the evolving history and longitudinal distribution of oilas, it was discovered that the faults cutting T2-T06 were main transfusion pathway of oil discharging downward into Member 1 ,Qingshankou Formation. The faults reactivated and opened frequently alter organic matter in source rock becoming mature,and the faults were oil source fault. The Member 1,Qingshankou Formation became excellent cap rock after oil discharging downward, and the oil was rigorously limited in Fu-Yang oil layer. Affected by formation trend and fault activity, larger scale accumulation of oil-gas might be very difficult to creat in the downthrow block of oil source fault in Fu-Yang oil layer, and oil accumulation might chiefly form in uplifted side of oil source fault. The uplifted side of oil source fault should be main exploration target in Fu-Yang oil layer.