Abstract: 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.

Key words: Jia2 Member, gas reservoir forming conditions, main controlling factors of gas reservoir, hydrocarbon source fault, anhydrite rock layers