川中川南过渡带嘉二段成藏条件及主控因素

JIA-2 MENBER GAS RESERVOIR FORMING CONDITIONS AND THE MAIN CONTROLLING FACTORS IN THE CENTRAL-SOUTH SICHUAN TRANSITIONAL ZONE

研究区嘉二段构造起伏平缓,断裂及裂缝相对较小,碳酸盐岩和蒸发岩发育,基本属于(半)局限-蒸发台地相,部分属于开阔台地相。台内滩、台内雏滩、(半)局限台地泻湖和(半)局限台地潮坪等亚相影响储层的形成和发育;蒸发台地泻湖、蒸发台地潮坪和局限台地泻湖等亚相控制盖层的分布。通过对烃源条件、储盖组合、圈闭类型、天然气运聚特征和保存条件等方面的详细分析,认为川中川南过渡带嘉二气藏成藏条件优越,具有形成中型气藏的潜力,其中天然气的近源垂向运聚和理想的保存条件,是形成嘉二气藏的重要保障。有利的沉积亚相、建设性成岩作用、背斜构造、烃源断层和硬石膏岩层是该气藏的成藏主控因素。烃源断层和硬石膏岩层的分布,为油气聚集层位及有利成藏区块的确定提供了重要信息。

The gentle structure, poor developed faults and fractures and developed carbonate rocks and evaporate can be regarded as obvious characteristics of Jia-2 Member in the study area. The Member basically belongs to restricted platform(semi-restricted platform)-evaporated platform facies except for fewer open platform facies. Bank subfacies, quasi-bank subfacies of inner carbonate platform, lagoon subfacies and tidal-flat subfacies of restricted platform(semi-restricted platform) influence formation and development of the reservoirs in Jia-2 Member. Lagoon subfacies and tidal-flat subfacies on evaporated platform and lagoon subfacies on restricted platform control distribution of cap rocks. Through the detailed analysis of hydrocarbon source conditions, reservoir-cap association, trap types, characteristics of gas migration and accumulation and gas preservation conditions, it is recognized that forming conditions have evident superiority and forming medium-scale gas reservoirs in Jia-2 Member is potential in the zone. Proximal and vertical migration and accumulation of gas as well as perfect conditions of preservation become important guarantees for forming Jia-2 gas reservoirs in the zone. The study shows that favourable subfacies, constructive diagenesis, anticline structure, hydrocarbon source fault and anhydrite rock layers are principally controlling factors of the gas reservoir forming. Distributing laws of hydrocarbon source fault and anhydrite rock layers provide important information for determination of gas-oil accumulation horizons and favourable region of reservoir forming in the zone.