Comprehensive Study On Carbonate Sedimentary Facies And Reservoir Characteristics Of The Ordovician Carbonate Rocks In The South Of The Weibei Region

The Ordovician in the south of Weibei area deposits a set of marine carbonate strata,in Which the exposed surface of the Ordovician strata profile found a lot of bitumen and reefs.Some of the exploration wells in this area also have found gas.Therefore,Weibei area may have a good prospect of natural gas exploration.The purpose of this study is:(1)to study the sedimentary environment and sedimentary facies of the Ordovician in the study area;(2)study the Ordovician reef reservoir in the research area and predict the favorable area for oil and gas exploration..According to the characteristics of rock,age and biology,the strata in the study area were divided and compared.By analyzing the carbon and oxygen isotopes,trace elements and total rock analysis of Ordovician strata in the study area,the Ordovician sedimentary environment was studied,and the evolution rules and patterns of the ordovician sedimentary environment were summarized.Based on the typical profile of outcrop,the lithological characteristics and sedimentary evolution model of the reef are studied,and the sedimentary facies and paleogeographic characteristics of the facies are analyzed and summarized.It is concluded that the Ordovician belongs to the normal seawater carbonate sedimentary environment,and the main sedimentary facies is carbonate facies-residual basin facies.The lithology,physical properties,pore structure and reservoir type of the reservoir were analyzed by using the core photo,the casting sheet,the physical property test,the capillary pressure curve,the imaging logging and the conventional logging,think the Ma5 group of Majiagou Formation dolomite reservoir property is good,have good reservoir space,however,the majority of lithologic densicity and physical property of the micritic limestones in the Pingliang Formation and the marlstone in the Beiguoshan Formation are very poor.By analyzing the influence of sea level change,tectonic evolution,source rock distribution and stratum on the reservoir of the reef(beach)facies,study the reservoir control factors of the region and summarize the Ordovician strata in the source bed,reservoir,caprock,and predict areas favorable for reservoir distribution.According to the comprehensive study,the Ordovician source rocks in the south of Weibei area are mainly distributed in the Beiguoshan Formation and the Pingliang Formation.The reservoirs are mainly distributed in the Pingliang Formation and the Ma5 group of Majiagou Formation,The cover layer is mainly distributed in Dongzhuang Formation,Beiguoshan Formation and upper part of Pingliang Formation,in addition,the coal-bearing strata of Permian and Carboniferous system can be the source rock and the cover layer.This is the formation of the upper-lower storage and self-storage combination type.