Research Of The Gas Accumulation Conditions Of The Xujiahe Formation In Northwestern Sichuan Basin

There are abundant gas resources in northwestern Sichuan Basin.And in recent years, it has achieved a major breakthrough in Xujiahe Formation there, confirming that Xujiahe sandstone has a large exploration prospects. It,however, has complex structures and diverse types of reservoir.Main controlling factors and distribution of reservoir and gas accumulation conditions are also not clear.It caused difficulties on further exploration.This paper focuses on the basic research.Through core description,field research, drilling data,thin sections observation,scanning electron microscopy,X ray diffraction,and the characteristic of source rock and gas geochemistry, the gas accumulation conditions of Xujiahe Formation have been systematically studied.The Xujiahe Formation in northwestern Sichuan Basin includes five parts,named X1, X2, X3, X4 and X5,.The X1 and X2 are marine sedimentation,and the X3,X4 and X5 are continental sedimentation.It was warm,moist tropical and subtropical climate during the deposition of Xujiahe Formation.Sand bodies are widespread.Sedimentary facies types are primarily the reef flat and delta in X1, the tidal delta in X2 and the alluvial fan,fan delta and lacustrine facies in X3,X4 and X5.The reservoir in northwestern Sichuan Basin is of the characteristics of low porosity and permeability and diverse reservoir interspace types.The main reservoir interspace types are remained primary intergranular pores,intragranular pores and microfissure.Lithic quartz sandstone is the main rock style.Reservoir of higher porosity develops in deep Xujiahe Formation.The porosity is between 8% and 11%,up to 13.5%.Reservoir of high quality is controlled by rock and mineral composition,chlorite lining, granularity,sorting characteristics,microfissure.Hydrocarbon source rocks are widespread in Xujiahe Formation.The main formation producing gas in research area is X3 and X4,and gas there is mainly coal corruption plant gas.The high Ro shows that the hydrocarbon source Rocks of Xujiahe is currently at a high maturity stage.Reservoir and Hydrocarbon source rocks here are interbedded so that Hydrocarbon source rocks can provide gas efficiently and in large area.