Characteristics and main controlling factors of the Ordovician deep dolomite reservoirs in mid-eastern Ordos Basin
YU Zhou1, HU Zijian2, WANG Qianping3, ZHAO Jing4, WU Dongxu1, WU Xingning1, LI Weiling1, LU Huili1, ZHU Wenbo1
1 PetroChina Hangzhou Research Institute of Geology,Hangzhou 310023,China; 2 Exploration Department of PetroChina Changqing Oilfield Company,Xi'an 710018,China; 3 Exploration and Development Research Institute of PetroChina Changqing Oilfield Company,Xi'an 710018,China; 4 Xi'an Changqing Chemical Group Co.,Ltd.,Xi'an 710018,China
Abstract：The deep Ordovician dolomite in the mid-eastern Ordos Basin is an important target for natural gas exploration. There are few studies on this set of dolomite reservoirs,and the reservoir characteristics and genesis are unclear,which restricts the further exploration. Based on outcrops,cores,thin sections,loggings,physical property data and CT scanning data,the dolomite reservoir is systematically studied here. The dolomit reservoir of gypsum-dissolved pore type,granular beach type and bio-turbated type developed in deep Ordovician in the mid-eastern Ordos Basin. The gypsum-dissolved pore type reservoir is characterized by anhydrite nodule bearing micro-crystalline dolomite,and the pore is composed of gypsum molds and micro-fractures with an average porosity of 2.57%. The grain-beach dolomite reservoir is composed of calcarenite-rudite dolomite,oolitic dolomite and crystalline dolomite. The pores include inter-granular pores and micro-fractures,with an average porosity of 4.65%. The bioturbated dolomite reservoir is porphyritic micro-crystalline dolomite and porphyritic calcareous micro-crystall dolomite. The pores are inter-crystalline pores and micro-fractures, and the average porosity is 2.54%. Development of gypsum-solution pore-type and grain-beach type dolomite reservoirs was mainly controlled by sedimentary facies,quasi-synchronous dissolution and rock salt filling. The gypsum bearing dolomitic flat and grain-beach facies provided the basis for development of the two types of dolomite reservoirs. The quasi-synchronous dissolution was the key to development of the reservoir,and the rock salt filling was the main factor for densification of the reservoir. Development of bioturbated dolomite reservoir was mainly controlled by bioturbation and dolomitization. Bioturbation createed basic conditions for development of bio-turbated dolomite reservoir. Quasi-contemporaneous dolomitization was conducive to formation and preservation of inter-crystalline pores. The above results are conducive to the exploration of deep dolomite natural gas in the Ordovician in mid-eastern Ordos Basin,and may provide technical support for the further exploration.
YU Zhou,HU Zijian,WANG Qianping et al. Characteristics and main controlling factors of the Ordovician deep dolomite reservoirs in mid-eastern Ordos Basin[J]. JOPC, 2023, 25(4): 931-944.
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