大民屯凹陷沙河街组四段、三段层序特征及其与油气成藏条件之间的关系

Sequence Stratigraphic Characteristics of No.3 and No.4 Members of Shahejie Formation in Damintun Sag and Relation to Petroleum Exploration

根据层序地层学理论,将大民屯凹陷古近系划分为两个层序:层序Ⅰ相当于沙四段和沙三段,层序Ⅱ相当于沙一段和东营组。层序Ⅰ发育湖侵和高位两个体系域,高位体系域又分上、下两部分。依据对构造、物源、气候和湖平面变化等层序控制因素的分析结果,总结了不同体系域与生、储、盖层之间的关系:生油层主要发育在湖侵体系域当中,也是古生界潜山油藏的区域盖层;储集层主要发育在下部高位体系域,为曲流河—三角洲—滨浅湖、半深湖沉积和冲积扇—扇三角洲—滨浅湖沉积;上部高位体系域底部发育另一区域性盖层。上述有利的生、储、盖组合在该区油气聚集过程中起了重要作用,潜山和下部高位域储集体是深化勘探的潜在目标区。

Based on the sequence stratigraphy theory, the authors recognized two sequences in Paleogene Damintun sag. No.3 and No. 4 Members of the Shahejie Formation belong to Sequence Ⅰ and Sequence Ⅱ is composed of No. 1 Member of Shahejie Formation and Dongying Formation. Sequence I could be further divided into transgressive and highstand system tracts, with the latter comprising the upper part and the lower one. The relationship between different system tracts and source-reservoir-caprock combinations is summarized in terms of the major factors affecting sequence stratigraphy, such as tectonics, climate, sedimentary supply and lake level change. Source rocks are developed dominantly in the transgressive system tract, and can also be considered as good regional caprock beds covering the underlying buried Palaeozoic hill pools. Reservoirs rocks occupy mainly the lower part of highstand system tracts, belonging to the sedimentary systems of meandering river-delta-offshore lake facies and fluvial fan-delta-fan delta-offshore lake-deep lake facies. The bottom of the upper part of the highstand system tract is another regional caprock bed for the lower sandstone reservoirs. Therefore, the favorable source-reservoir-caprock assemblages in the Damintun sag are of great significance in petroleum accumulation. The reservoir rocks of the Palaeozoic buried hills and the lower part of the highstand system tract seem to be the potential exploration targets.