Qu Haizhou, Yang Xiangtong, Wang Xi, Wang Zhenyu, Liu Hongtao, Zhou Pengyao, Zhu Bo, Wang Yu
Based on the measured physical properties, thin slices, cores and well logging data, this paper researched the characters and genesis of reservoir in the Lianglitage formation of Upper Ordovician in Tazhong area. The average buried depth of the formation was 4868m.There developed four high porosity layers vertically. The average porosity and the thickness of these layers decreased as the depth increases. The reservoir had the features that macro reservoir space layers coincide with the higher matrix porosity layer. The polycyclic thick reef-bank complex which deposited in the suitable deposition environment in Late Ordovician was favorable material basis for developing reservoir, and the reef limb, reef core and bioclast bank were the favorable sedimentary micro-facies. A lot of selective dissolution pores formed by syngenetic karst in the upper part of each reef-bank cycle. The early digenetic stage karst formed lots of non-selective dissolution pores within 100m from the top, so that the reef-bank complex developed lots of pores with the superimposition, which was the key factor for the quasi-layered reservoir in the upper part of Lianglitage formation. Fractures formed by tectonic disruption communicated the pre-pores during burial stage, and provided migration pathway for multiple fluids. These fluids dissolved the surrounding rock or inhibit the cementation, so that insured the reservoir capacity in the deep buried carbonate rock. The space-time configuration of oil and gas migration and porosity development was preferable�?¯�?¼�?ŽThese factors formed the large condensate gas deep reservoir in Lianglitage formation of the Upper Ordovician in Tazhong area.
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