The Restoration Of Sedimentary Paleogeomorphology Of Maokou Formation Of Lower Permian In East Sichuan And Karst Reservoir Research

Maokou Formation of Lower Permian in East Sichuan is marine carbonate open platform deposit.In the late Early Permian,influenced by the movement of the eastern Wu Dynasty,the carbonatite strata on the top suffered from the weathering and denudation of fresh air,and developed the weathering crust karst reservoir,which has been proved to have good oil and gas exploration potential through the existing exploration and development.Among them,the analysis of paleogeomorphic characteristics is the key and foundation to predict the favorable development area of karst reservoir,which can provide the basis for the prediction of the favorable exploration area.This paper combines the field geological survey,drilling data,logging seismic data and core slice identification.Sequence stratigraphic division and correlation are carried out for Maokou Formation and adjacent strata.Based on the basic physical characteristics of Maokou Formation karst reservoir,the related control factors of Maokou Formation karst reservoir are studied,and then the favorable accumulation zone of oil and gas is predicted.According to the data of geological survey,drilling,well logging and core,four marker layers of Lower Permian are divided,and the division scheme and standard of Maokou Formation and adjacent formation are established.According to the vertical and horizontal cross well correlation section of Maokou Formation,the true formation thickness of each member of Maokou Formation is calculated.According to the residual stratum thickness and stratum lithology,the division standard of karst highland,karst slope and karst basin is established.It is clear that the paleogeomorphology at the end of Maokou Formation in East Sichuan has the distribution characteristics of "two karst Highlands,two Karst Slopes and three karst basins".Based on the study of the rock types and reservoir characteristics of Maokou Formation,it is found that the physical properties of Maokou reservoir are poor,the development of reservoir mainly depends on the later karst transformation,pure granular limestone and biological limestone are conducive to the occurrence of karstification,which mainly develops fracture cavity reservoir.The development of karst reservoir in Maokou Formation is closely related to karst system.In time and space,the paleogeomorphology,sedimentary facies and tectonism are all well related to karstification,which controls the development of karst reservoir.Hydrothermal dolomitization also has a significant role in promoting karst reservoir.In the work area,Section 2 of Maokou Formation and the Section 3 of Maokou Formation are the layers with frequent karstification.Combined with the plane distribution characteristics of paleogeomorphology,it is predicted that the conditions of hydrocarbon source,reservoir and trap are superior at the karst highland of Kaijiang Dazhu area in the north of the work area and the karst slope in the middle of the work area,which are favorable exploration areas.