Sedimentary Characteristics Of Kongdian Formation And The Fourth Member Of Shahejie Formation In The South Slope Of Huimin Depression

This paper takes the red beds of the fourth member of the Shahejie Formation and Kongdian Formation in the south slope of Huimin depression as the research subject. Based on the careful description of drilling cores, combining with the study of the well logging data and the seismic profiles, stratigraphic correlation of the red beds was made, the sedimentary characteristics were studied, then, the reservoir physical properties and favorable facies are summarized and evoluted.The red beds in the south slope of Huimin depression can be divided into the upper part of the fourth member including four sand groups, the lower part of the fourth member of Shahejie Formation including three sand groups and Kongdian Formation including three sand groups.Three types of sedimentary facies which are terminal fan, alluvial fan and shore-shallow lake deposits and corresponding facies models are given. Terminal fan, which can be further divided into proximal, middle and distal subfacies and detailed into microfacies, such as distribute channel, overbank, overflow and mud flat, deposits in the upper part of the fourth member. Alluvial fan, which can be subdivided into main part, fan edge and flood plain, is developed in the lower part of the fourth member of Shahejie Formation and Kongdian Formation. Shore-shallow lake widely spreads in the area north of Xiakou fault in the upper part of the fourth member of Shahejie Formation.Vertically, from the Kongdian Formation to the upper part of the fourth member of Shahejie Formation, sedimentary facies changed from all subaerial deposition to lake deposition in almost half part, form gravity flow dominated alluvial fan to tractive current dominated terminal fan. Laterally, alluvial fan mainly deposited in Qvdi and the eastern areas in Kongdian Formation. While in the lower part of the fourth member of Shahejie formation, alluvial mainly deposited in Qianguantun and Qvdi areas. In the upper part of Shahejie formation, sedimentary facies balanced in the south slope.The reservoir physical properties of the red beds are summarized. The properties in Qianguantun area are better than Jiangjiadian area. In terms of the reservoir property, among the sedimentary facies, terminal fan are the best, alluvial fan follows, and lake is the worst; among the microfacies, distribute channel of terminal fan is the best, braided channel in alluvial fan follows, sand flat and sand bar in lake is the third, and sand beach in shore-shallow lake is the worst. Based on the classification and evolution of the reservoir properties in each microfacies in the south slope of Huimin depression, concerning the sand thickness, sand percentage, property parameter and seismic attribute slices, the reservoir properties of each sand group is evaluated and predicted. The evaluated result shows that: Qvdi Area in Kongdian Formation and the lower part of the fourth member of Shahejie Formation, and Qianguantun Area in the upper part of the fourth member of Shahejie Formation are favorable facies belts, Jiangjiadian Area in the upper part of the fourth member of Shahejie Formation also distributes several favorable facies belts.