The origin and distribution of dolomite reservoirs in the Permian Maokou Formation,central and eastern Sichuan Basin
Recent exploration has confirmed that the Permian Maokou Formation in Sichuan Basin is rich in oil and gas resources,and is an important natural gas production layer in the basin.Dolomite reservoirs have developed to different degrees in the central and northern Sichuan regions,and determining the dolomite reservoir distribution is crucial for exploration deployment.To clarify the next exploration direction of the Maokou Formation,studies are being conducted based on drilling data,petrography,cathodoluminescence,isotope,and in situ micro-geochemistry results.Via analysis and testing means,in this study research is carried out on the sedimentary evolution law,dolomitization,and dolomite reservoir distribution characteristics of the Permian Maokou Formation in central and eastern Sichuan.The research results show that(1)dolomite in the Permian Maokou Formation is mainly distributed from the lower Maoer Member to the upper Maoer Member.An inner platform,margin-slope sedimentary system has formed in the north;a geomorphic high belt has formed along the platform depression margin;and high-energy shoal facies consisting of grainstone have developed,which have formed a foundation for the development of the dolomite reservoirs.(2)In the sedimentary facies belt,high-energy shoal limestone,consisting of the Mao 2 and Mao 3 Members,has formed,with the characteristics of vertical segmentation and northward zoning.From the depositional period of the Mao 2 Member to the Mao 3 Member,the distribution extends northward from the Moxi-Longnüsi area to the Nanchong-Yuanba area.(3)The dolomite in the Maokou Formation is divided into matrix dolomite and saddle-shaped dolomite.The first type of dolomite is cloudy during the quasi-syngenetic to shallow burial stage,mainly due to the clouding action of syngenetic to quasi-syngenetic marine fluids.The dark red matrix dolomite is superimposed with weaker exogenous hydrothermal dolomitization during the shallow burial stage;The dolomitization time of the second type of dolomite is during the burial period,mainly due to the mixing of hydrothermal fluid with formation brine,which has been strongly modified by exogenous hydrothermal fluids.
central and eastern SichuanPermian Maokou Formationdolomitesedimentary faciessea source fluid
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