Reservoir Characteristics Of Middle Triassic Leikoupo Formation In The Southern Part Of Central Sichuan Basin

Middle Triassic Leikoupo Formation is one of the main oil-gas bearing formations of the central Sichuan Basin. The total gas production in central Sichuan basin is 10×108m3 per year, but 4×108m3 gas production each year is from Leikoupo formation, and Moxi structural area is the key place of gas production.On the basis of detailed observation of cores and thin-sections, this present paper has divided the types of sedimentary facies and microfacies, analyzed distribution of sedimentary facies, and divided diagenetic stages. The main types of diagenesis and pore are studied. The paper has summarized the diagenetic sequence and history of pore evolution, divided reservoir types according to the pore genesis, finally evaluated the reservoir quality and pointed out the advantaged oil-gas exploration area.During Leikoupo phase, the depositional environment of the research area is predominantly restricted platform, partly evaporative platform and open-platform. Dolostone is the major rock type, secondly is limestone and anhydrock. Dolostone is interbedded with salt rock in some wells. Mudstone is rare. The green-bean rock is the boundary between Leikoupo Formation and Jialingjiang Formation.The diagenesis of Leikoupo formation is complicated. The dolomization and dissolution are the main constructive diagenesis for the formation of porosity, but compaction, pressure solution, packing action is the destructive ones.According to the observation of thin-sections, the pore types of carbonate rocks of Leikoupo formation are intercrystal pore, intraparticle and interparticle dissolution pore, intercrystal solution openings, stylolite and so on. The intercrystal pore, intraparticle and interparticle dissolution pore are the main reservoir pores.The reservoir of Leikoupo formation can be divided to five types based on the pore genesis. They are dissolution pore types, mix-water dolomization pore type, deep burial dissolution pore type, structural dissolution pore type and polygenetic pore type. The controlling factors of reservoir formation are sedimentary facies and diagenesis. The reservoir of Leikoupo Formation is chiefly distributed in the first lower-submember , and ClassⅡand classⅢare the main reservoir types.