CHARACTERISTICS OF MIDDLE-UPPER CAMBRIAN DOLOMITE RESERVOIR IN THE XINGSHAN AREA OF THE SOUTHERN MARGIN OF QINLING AND DABIE OROGENIC BELT

The Middle-Upper Cambrian dolomite reservoirs are well-developed in Xingshan area of the southern margin of Qinling and Dabie orogenic belt.Based on geologic survey on field outcrop profiles,as well as tests on conventional thin sections,SEM,image,petrophysical property,etc.,it has been found out that effective Middle-Upper Cambrian dolomite reservoirs are composed of micritic-crystalline powder dolostones,granular dolostones and kryptomere-mesocrystalline dolostones and so on.Effective reservoir spaces in micritic-crystalline powder dolostones are dominated by intercrystalline pores.Granular dolomites include oolitic dolostones,dolarenites and dolorudites with effective reservoir spaces consisting of intergranular pores and intragranular corrosion pores.Moreover,non-selective corrosion pores and intercrystalline pores develop in kryptomere-mesocrystalline dolomites.Formation and evolution of above-mentioned reservoirs are mainly controlled by effects of sedimentation and diagenesis.Sedimentation is the basis and determines spatial distribution characteristics of reservoir.Flat sedimentary landform and frequent changes of relative sea-level lead to the formation of lithologic interbed.Dolomitization and selective dissolution after burial make granular dolostones and kryptomere-mesocrystalline dolostones with good porosity and permeability come into being.They work as good re-servoirs in the Middle-Upper Cambrian.