Research On Natural Gas Enrichment Laws Of Xu-2Gas Reservoir In Yingshan Structure, Central Sichuan, China

Basing on the geology, logging, seismic and retrieval data of the study area.The papercomprehensively researched the features of the reservoir and gas-water distribution and thetrap type.Basing on tectonic evolution with inclusion data,the paper has summarized the gasreservoir accumulation mode and the main controlling factors.The main achievements madein this paper are as follows.（1） Reservoir lithology of T₃x²are main feldspathic quartz sandstone,lithic feldsparsandstone and feldspar lithic sandstone,having a characteristics of the low porosity, ultra-lowpermeability and high water-cut saturation.The reservoir pore space mainly consists ofintergranular pore,residual intergranular pore, solution pore and fracture, dominated byintergranular pore.Pore throat has a characteristics of the smaller slanting degrees and poorlysorting.Reservoir of T₃x²was developed within multiple layer overlaid on each other invertical,distributing steadily between well-to-well.The continuity of reservoir is bad inhorizon.（2）There are three characteristics of gas-water distribution on the profile as follows:a)gasaccumulate differently between the north and south.b)The structural high parts is highabundance of natural gas.c)Thickness of gas and water formation is small.Gas-water samelayer is mainly developmented in whole structure.Natural gas-rich region is concentrated inthe structural highs in the first row structure.Secondly, gas-water in the same layer isdistributed in the second row of the structural.Planar characterization of gas-water distributionis similar to the one of the profile.（3）There is no obvious gas water interface in T₃x²gas pool of Yingshan structure,whichis lithologic or structural-lithologic gas reservoir that corresponds to lithologic and structural-lithologic traps, which can be divided into anticline-lithologic traps and fault/faultedanticline-lithologic traps. （4）The lateral fault seal is an important factor to affect the North-South gas differentialaccumulation in Yingshan structure.Through computing the fault plane pressure andgeochemical characteristics of natural gas,the fault is less damaging to Xujiahe natural gasreservoirs with vertical seal being better.（5）The accumulation process is divided into three phase：early hydrocarbon charging inlate Jurassic，the dominant hydrocarbon charging period in middle-late Cretaceous，and thefinal accumulation of gas pools since the late Cretaceous.（6）The main controlling factors of gas accumulation in T₃x²gas pool of Yingshanstructure are analyzed in the paper.The reservoir physical property control the enrichment ofnatural gas, the structure amplitude control the gas-water distribution in the gas reservoir,thefractures developed locally is a key factor of gas accumulation and high productivity in theT₃x²Formation and the fault sealing control north-south gas differential accumulation.