Abstract
Comprehensive sedimentological studies regarding different facies types and the factors persuading their development were carried out at Eocene (Es1) member of Shahejie formation of Nanpu Sag. To evaluate the sedimentary facies, lithofacies, and reservoir quality, wireline log analysis, a petrographic thin-section study, SEM, grain size analysis, XRD, and CL analysis were used. The Es1 consists of five sedimentary facies and seven lithofacies. Sandstone is classified on the basis of standard rock classification scheme as feldspathic litharenite and lithic arkose. Quartz grains are abundant detrital constituent and feldspars are subordinate followed by mica, chert, rock fragments, and iron oxide as a minor constituent. Primary intergranular pores, as well as secondary dissolution pores and fracture pores, are also present that enhance the reservoir quality. Grain size varies from conglomerate to clay size, with massive bedding, cross-bedding, and fine-grained ripple laminated sandstone, which predicts that formation is deposited in lacustrine and fluvial channel or channel bar environment. XRD and SEM analysis show various clay minerals that reduced the reservoir characteristics. The present study discloses the deposition and distribution of lacustrine, braided, meandering river delta, and delta front sand bodies of Es1 member as well as provides some support for reservoir quality of the correlative sedimentary system that has great significance for further exploration.