Characteristics and control factors of fine-grained sedimentary rock lithofacies in Bonan subsag

YANG Wanqin; WANG Xuejun; DING Juhong; WANG Yong; ZHANG Shun

Abstract：Based on detailed description of core,thin sections identification,analysis of whole rock X-ray diffraction and geochemical test data,the primary characteristics of mineral composition,structure and organic matter abundance used as the basis for lithofacies classification were systematically analyzed and a fine-grained sedimentary rock lithofacies classification scheme was established.Meanwhile,the characteristics of main lithofacies types and distribution were studied.It is revealed that the mineral composition is complicated,lithofacies types are diverse,lithofacies characteristics clearly varies,different lithofacies develop in different sedimentary environments,and distribution of lithofacies is mutually controlled by several factors.The results show that mineral composition mainly includes calcite (40％-80％),clay (1％-25 ％),feldspa-quartzose(3 ％-25 ％),and total organic carbon (TOC) falls in the range of 2 ％-4 ％.There are mainly three fine-grained sedimentary rock lithofacies,namely organicrich lamina argillaceous limestone lithofacies,organic-rich stratiform argillaceous limestone lithofacies and organic-lean lamina argillaceous limestone lithofacies.The differences in mineral composition,organic matter abundance and well logging curve are shown to reflect the diverse sedimentary environment.Further analysis shows that the distribution of fine-grained sedimentary rock lithofacies are controlled by paleoclimate,paleosalinity,paleotopography and provenance lithology.Lithofacies characteristics and exploration practice demonstrates that the organic-rich lamina lithofacies is advantageous exploration target.