Study On The Middle Triassic Reservoir Rocks In The Front Area Of Northern-central Longmenshan Mountains And Its Adjacent Areas

In this paper, we have studied the sedimentary stratigraphy, sedimenttary facies, the effect of hydrothermal fluids and diagenesis of the Middle Triassic according these theoretical guidances that sedimentology, reservoir geology, structural geology and "Emei taphrogenesis" . And we tried to recover the palaeogeographical environment of Middle Triassic ,tectonic setting and the evolution of porosity , discussed the relationship between the Middle Triassic sediment, activity of the hydrothermal fluids and the tectonic setting in the study area. Finally, we ascertained the controlling factors of the development of the reservoirs.Our study indicates that the Tianjingshan Formation was the sediments from the platform block margin to the trough. The horst and graben structural type of the Longmenshan islands chain and the different sedimentology in the faulting continental margin formed during the beginning of the late Triassic and the end of the middle Triassic were influenced by the Emei Taphrogenesis. In the study district, below the hydrothermal threshold depth(200m),the hydrothermal fluids from the deep layer of Longmenshan fault invaded into the middle Triassic strata and then resulted in widely hydrothermal alteration , dolomitization and gypsification. The diagenesises of middle Triassic in Longmenshan is complicate with kinds up to 26. And it mainly included compaction, pressolution, cementation, gypsification, dissolution, recrystalliz -ation, dolomitization, silication and so on. The grain dolomite is the main reservoir, and the reservoir in Zhongba area is fa??tter than the reservoir in Tiantaishan area. Because differenct tectonic backgrounds , burial -history and evolution of the diagenesis , and the reservoir has strong aeolotropism.Reservoir controling factors are summarized as follows. In microscopic, the grain deposi -tion of beach was the advantage face for the reservoir development ;Early cementation determined the basic style of the reservoir development;Hydrothermal corrosion and surface solution pore constructed and developed the reservoir early. The filling of the hydrocarbon and deeply buried solution controlled the preservation of the reservoir. In macroscopic, during the Middle Triassic,"trough"was widely exist in the block platform under the control of "Emei taphrogenesis" during the Middle Triassic.. And there was slope nearby the trough,where some favorable conditions for early development and construction of reservoir. After the Late Triassic, the Longmenshan orogeny take overed the preservation and reform of the reservoir.