River In North-central Region Leikoupo Deposition, Diagenesis And Its Relationship With The Reservoir

Focus on leikoupo group formation and make T2l43as the main study layer in north-central of Sichuan, guided by the theories of sedimentary petrology.reservoir geology,natural gas geology and other related theories. Through the study of a large number of literature, combination with drilling cores,micro-thin slices, measured logging and a variety of analysis data, we have studied the strara, the types and characteristics of sedimentary facies,diagenesis and reservoir, analyzed the influencing factors of reservoir development, and finally predicted favorable exploration zone.The stratigraphy study have shown that the layers of the top of leikoupo group have contacted with the layers of the bottom of the overlying T3X1as the parallel unconformity, and the bottom have been in contact with the top of the following jialingjiang group as the regional marker layer named mung bean rock. According to the lithology,electrical and sea level fluctuation law,leikoupo group can be diveded into T2l1, T2l2, T2l3and T2l4, which Tol4can be divided into T2l41, T2l42and T2l43.Moverover, T2l43can be divided into the three sub-member thin layer of a, b and c. The formation is thinning from northwest to southeast.Based on a variety of sedimentary facies signs and previous studies research,we can know about that the leikoupo group in the area has been in the epi continental platform environment and can be divided into3subfacies of restricted platform,open platform, table point sand and a plurality of microfacies, which table point sand in T2l43is the favorale microfacies belt.Thanks to the study of diagenesis, we can know about that the study area has been subjected to a variety of destructive diagenesis successively, such as compaction, pressure solution, cementation, mechanical filling, which can hider the development of the reservoir by reducing the connectivity between the pore size and cutting off pore. In addition, the study area has also been subjected to the transformation of mixed water dolomitization, recrystallization and karst constructive diagenesis, which can improve reservoir performance by expanding the porosity and interconnecting the isolated pore.Arenite dolomite and oolotic dolomite is the mainly reservoir rocks in T2l43of the study zarea,secondly is crystal grain dolomite in this formation.The mainly reservoir space is a variety of intergranular pores,intercrystal pores.intergranular dissolved pores etc.The major influent space is the fracture.The reservoir has mainly distributed in a layer of T2l43.such as Ionggangl9-longgang21well area, longgang22-longgang23well zone.In all, the leikoupo group reservoir in study area is subjected to the control of the deposition, diagensis and tectonism. It existed a variety of particle dolomites with all kinds of intergranular pores, intergranular holes, the body cavity hole and algae bonding hole, which is conductive to the development of the reservoir. Through the transformation of the constructive diagenesis and the influence of the indo-China, Yanshan period and Himalayan tectonic movement, it can be formed the favorable reservoir.Summarizing the above analysis,we believe that the Ionggang173-yingshan104well area and longgang22-longgang23well area are the most favorable exploration zone.