A Study On The Characteristics Of Sedimentology And Reservoir Of Lacustrine Carbonate Rocks In The First Member Of Shahejie Formation In Western Huimin Sag

It is proved that lacustrine carbonate rock is one of the most important oil/gas reservoirs through the practice of oil and gas exploration, but the research of lacustrine carbonate rocks is less than marine carbonate rocks. Studying the sedimentary and reservoir characteristics of lacustrine carbonate rocks is important to enrich the sedimentary theory and support the research of oil/gas reservoirs. Directed by the theories such as Sedimentology, Sequence stratigraphy and Reservoir geology, sequence stratigraphic characteristics, sedimentary characteristics and reservoir characteristics of the lacustrine carbonate rock in the first member of Shahejie Formation in Huimin sag are systematically studied in this paper on the basis of geology, seismic, logging and chemical analysis data.Through the comprehensive analysis on the geologic background of paleostructure, paleoclimate, volcanic activity and seawater intrusion in first member of Shahejie Formation in Huimin Sag, the result shows that Huimin Sag is suitable to develop lacustrine carbonate rocks.Based on the theory of sequence stratigraphy, the sequence stratigraphy of the first member of Shahejie Formation in Huimin Sag is studied. The comprehensive analysis of the core, well logging and seismic data in Huimin Sag shows that the first member of Shahejie Formation in Huimin Sag may be divided into one third-order sequence. There are lots of lacustrine carbonate rocks during the transgression systems tract. The research of high-resolution sequence stratigraphy of the lacustrine carbonate rock shows that the carbonate parasequences of different sedimentary environments have different distinguishing symbols.The analysis of sedimentational geochemical characteristics of the lacustrine carbonate rock in the first member of Shahejie Formation in Huimin sag indicates that the dolomite takes an important proportion in the research area, and they are interbedding with oil shales, mud rocks and biolithitesand siltstones. It is suggested that there are mass lacustrine carbonates rocks in the first member of Shahejie formation in Huimin Sag through the comprehensive analysis of core and microcospic dentification. It can be divided into grain dolomite(limestone), grain-bearing micritic dolomite (lime- stone) and micritic dolomite(limestone). Grain types include intraclasts,ooids, chondruie,bioclast and algae agglomerate, and the bioclast is found usually. According to their lithology-electric characteristics and single-well facies, the sedimentary facies are determined. Biologic beach facies of near volcanic cone which is easily affected by storm comes into being the mixed aggradation of the volcanic debris and the bioclast. The distributional characteristics research of the depositional system shows that the biologic beach facies distributes above palaeohigh, near volcanic cone and the slope belt. According to the comprehensive analysis of sedeimentary characteristics, a comprehensive sedimentary model is established in this area.Based on the analysis of petrology characteristics, types of reservoir space and pore microgeometrical of lacustrine carbonate, the lacustrine carbonate rocks in the first member of Shahejie Formaion in Huimin Sag are given classification and valuation. The comprehensive evaluation of carbonate reservoir shows that the reservoir of biologic beach is good and the reservoir of micritic beach is poor. Through the study on the factors which affect the reservoir physical properties, sedimentation and diagenesis are main factors...