Sedimentary System In The Fourth Member Of The Shahejie Formation Of Zhanhua Sag

Guided by sedimentary theory, analogy mapping method is used to compose lithofacies-paleogeography map. Based on cores, loggings data,sedimentary facies types of the fourth member of the Shahejie Formation in the study area is summaried,and lateral distribution and vertical evolution of the sedimentary system are also studied. Two major sedimentary systems are developed: alluvial fan, fan-delta system and lacustrine system, which include fan-delta facies , nearshore subaqueous fan facies, lake facies, and salt lake facies. the early period of the fourth member of the Shahejie Formation is in the early stages of the basin evolution, when alluvial fan and shallow deposition dominate the area, and the lake water level is low, controlled by season and flood changes. As a result, a thick red layer is deposited. Glutenite rock is extensively developed along the provenance area except Yidong fault. To the late periods of the fourth member of the Shahejie Formation, the sedimentary environment is semi-arid to semi-enclosed salt lake. Alluvial fan, fan -delta and lacustrine deposition are extremely developed. sedimentary facies pattern is described as: gyprock developed in deep water of sub-sag, Limestone developed on the edge and near the provenance in uplift is glutenite.This reservoir of research area mainly divided into two categories: limestone reservoir of beach bar and glutenite reservoir. limestone reservoir of beach bar is also divided into fan-delta front type and lake type. The former is mainly developed at outer edge of the siliceous beach bar, which is mixed deposition with clastic in the same layer. The latter is mainly developed in underwater uplift, limestone and clastic is deposited as alternate layer. Based on the thick and content of the glutenite, favorable reservoir bed is upper of the fourth member of the Shahejie Formation, and favorable facies is also clear. Furthermore, with the analysis of sedimentary facies and physical properties data, Luojia fan-delta front and limestone beach bar sand, fan-delta front in the west of Guxi fault, reef body at Yidong fault, fan-delta front in the south of Chengnan fault and the middle of subaqueous fans and beach bar in the east of Gubei sub-sag in the upper of the fourth member of the Shahejie Formation and the middle of fan in Luojia, Boshen 4 in the west of Guxi fault, in the south of Chengnan fault and at the Chengdong fault in the west of Gubei sub-sag in the bottom of Es4 member is the favorable reservoir area.