湘鄂西区寒武系层序划分及其对油气勘探的意义

通过对湘鄂西区寒武系大量露头和钻井剖面的系统分析及对寒武系主要储层样品和下部暗色泥页岩样品的分析测试,认为湘鄂西区寒武系可划分为6个三级层序,其层序界面主要为不整合面和岩性转换面;鲕粒云岩/灰岩是寒武系物性最好的储集岩,其主要分布于SQ5的海侵体系域,另外在SQ4和SQ5的高位体系域也有少量发育;寒武系下部暗色泥页岩中有机碳含量相差悬殊,丰度较高的暗色泥页岩主要分布于SQ1高位体系域,之上的泥页岩有机质丰度均较低。发育了较厚鲕粒云岩/灰岩的SQ5海侵体系域是常规油气勘探的主要目的层,而有机碳含量较高的SQ1高位体系域为页岩气勘探的主要目的层。 

Sequence stratigraphic division of Cambrian in western Hunan-Hubei and applications for petroleum exploration

The systematic analyses of outcrops and drilling profiles and the tests of reservoir samples and dark mudstones from Cambrian in the western Hunan-Hubei indicate that the Cambrian in the study area can be divided into 6 third-order sequences, and the sequence boundaries are mainly unconformity surfaces and lithologic transitional surfaces. Oolitic limestones/dolomites are the most favorable reservoirs in Cambrian. They mainly distribute in the transgressive system tract of sequence 5, and a few of them locate in the highstand system tract of sequences 4 and 5. The content of total organic carbon (TOC) varies obviously among dark mudstones in the Lower Cambrian. The dark mudstones rich in TOC distribute in the highstand system tract of sequences 1, while those in the upper formation have lower TOC content. The transgressive system tract of sequence 5 which deve-lops thick oolitic limestones/dolomites is the main target for normal exploration. The highstand system tract of sequences 1 which has higher TOC content is the main target for shale gas exploration.