Research On Reservoir Characteristics And Natural Gas Enrichment Law Of Feixianguan Formation Gas Reservoir In Longhuichang Area

the study of reefs and oolitic reservoir at Permian and Triassic of Sichuan basin has formed some great research achievements these years,and that is also a significant guide for the exploration and development of gas reservoir around Kaijiang-Liangping trough.In this paper,theories of geology,sedimentology,petrology and petroleum geology are used as the guideline.And with the help of the data of seismic,drilling,cores examination,logging and chemical examination,the paper carried out the research on sedimentary evolution,distribution characteristics of reservoir,reservoir formation characteristics and favorable area optimization in Feixianguan Formation,Longhuichang area.The strata thickness of Feixianguan formation changes from 339.5m to 955.9m.This paper divide Feixianguan Formation in Longhuichang into 5 cycles,which are ?,?,?,? and?,based on the rise and fall of the sea level and the characteristics of the electrical and lithological changes.In those 5 cycles,the ? and ? cycles are the main stage of reservoir development,which is mainly distributed in platform-margin facies.Feixianguan formation consist by limited platform facies,open platform facies,platform edge facies,slope facies and trough facies.From ? cycle to V cycle,the thickness difference of every cycle is reduce from 352m to 52m.The lithology of the lower period of Feixianguan Formation is mainly oolitic limestone,but the upper period is mainly oolitic dolomite.The porosity of two periods are almost same,which are 4.5%and 5%.However,because of the more cracks in the upper period,its permeability(2.12mD)is better than the lower one(1.23mD).The logging characteristics of Feixianguan Formation is low nature gamma,middle-low resistivity,low density,high interval transit time and high neutron value.The reservoir of lower period of Feixianguan Formation is mainly distributes near LH002-X1 and LH002-X2,and the upper one is mainly distributes in the syncline at the west side,the attitude of which is controlled by the fault.Longtitudinally,many reservoir overlays,which made Feixianguan formation be heterogeneity.and reservoir of lower period is thicker than the upper,from early to late,oolitic reservoir was transfer to the trough.The source rock of Feixianguan formation reservoir is the coal-bearing source rock of Longtan formation,which has higher maturity and greater hydrocarbon-generating intensity.The upper reservoir has the higher methane content,but the less carbon dioxide and hydrogen sulfide.However,both of the upper and lower reservoir are high sulphur gas reservoir.The direct caprock of these reservoir is the mudstone at the top of Feixianguan formation,and the regional caprock is the plaster layer of Jialingjiang formation.The match between the evolution of source rock and tectonic activity is good.Before the massive hydrocarbon generation,the fracture made by Indosinian movement provided the necessary passway of gas migration.At the same time,the effective trap has already formed,and provided the basic condition of later gas reservoir adjustment.According to the result of strata pressure test,the reservoir of Feixianguan formation in Longhuichang area can be divided into 3 independent gas reservoirs.Because of LH2 well area's biggest gas bearing area(10.4km2),the larger effective thickness(18.8m),the biggest porosity(5.2%)and the biggest gas saturation(79.2%),LH2 well area is the most favorable exploration area.The second is LH006-H2 well area,and the third is LH005-X1 well area.