Characteristics of the Cambrian Dolomite Reservoirs and Their Facies-Controlling in Eastern Tarim Basin

Based on data from core samples,thin section,and physical property,we have investigated petrological characteristics and reservoir properties of dolomite reserviors in the Cambrian of the eastern Tarim Basin.The dolomites in eastern Tarim basin can be subdivided into two categories,replacement dolomite and crack-cavity-filled dolomite.The replacement dolomite can be further subdivided into mud-silt-sized dolomite,fine and midium crystal dolomite,coarse crystal dolomite,and breccia dolomite.The reservoir space in dolomites is predominated by inter-crystal pore,dissolved pore,stylolite pore and cracks and fractures.Cracks and fractures mainly play the role of connecting the pores.The most common reservoir space is mainly the overlapped complex of cracks and cavities.The replacement dolomites show an obvious facies-controlled feature,with the dolomite of the Yingdong-Luoxi region being developed in the marginal shoal,and tidal flat facies belts of the inner ramp setting,and the dolomite in the vicinity of Well Gucheng 4 being developed in the fore-reef slope facies belt of the rimmed shelf setting.Thin section identification and geochemical analysis indicate that the genesis of dolomite in the study area includes the seepage-reflux,burial,and hydrothermal dolomitization.The distribution of the dolomite reservoirs were controlled by the sedimentary facies,diagenesis(dolomitization,cementation,disolution),and fractures.Higher quality reservoirs are those shaol-facies dolomite overprinted with interaction of seepage-reflux dolomitization,burial dolomitization and/or hydrothermal dolomitization.