Study On Reservoir Characteristics And Distribution Prediction Of Xujiahe Formation In Wubaochang Area,Northeast Sichuan

Oil and gas exploration in Northeast Sichuan was mainly concentrated in the marine Triassic Feixianguan Formation and Permian Changxing formation before.There was basically no research on the Late Triassic continental Xujiahe formation.There were few coring data,and only two wells were coring.In recent years,after the Xujiahe formation of well Qian 15 was tested and obtained gas,the oil and gas exploration in Northeast Sichuan began to change from marine conventional gas to continental tight gas.Based on the limited field outcrop,drilling core thin section,physical property data and drilling logging data,this paper studies the petrological characteristics,core physical properties,logging physical properties and main controlling factors of Xujiahe Formation reservoir in Wubaochang area,Northeast Sichuan.On this basis,the sand body distribution and favorable reservoir prediction are carried out according to seismic data.The research shows that:(1)the Xujiahe Formation reservoir in the study area is formed in the braided river delta plain environment,and the sandstone on the field outcrop and core develops trough cross bedding and parallel bedding.The rock types are mainly fine to medium grained lithic sandstone,feldspathic lithic sandstone and a small amount of lithic quartz sandstone.(2)In terms of rock fabric,the content of quartz in particle composition is 30%～ 80%,and that of feldspar is 5% ～ 18%.It is mainly orthoclase,followed by plagioclase,and the content of rock debris is about 36%.It is mainly phyllite rock debris and metamorphic rock debris,followed by sedimentary rock debris;The particle sorting is poor ～ medium,sub angular ～ sub round,the particles are in point line contact,and the local parts are in concave convex contact due to pressure dissolution;(3)Reservoir pores are mainly secondary pores,followed by residual primary intergranular pores;The reservoir has poor physical properties,with an average porosity of 4.05%,an average permeability of 0.0001 md ～ 0.009 md,and an average of 0.0015 md.It is a low porosity and low permeability reservoir;The reservoir of xu2 member is the best,with an average porosity of 4.23%,followed by xu6 member,which is 4.04%,xu4 member and xu3 member are slightly worse,which is about 3.9%,and xu5 member is the worst,which is only 3.04%;(4)The development of reservoir is mainly controlled by sedimentary conditions,diagenesis and structure.The sandstone in the main channel of braided river in delta plain has coarse particle size,large thickness,strong compressive capacity,weak compaction,many original pores preserved,obvious dissolution,good physical properties and high porosity;At the edge of the river,the sandstone has fine grain size,high content of matrix,small thickness,strong compaction,weak dissolution and relatively poor physical properties;Microfractures formed in areas with strong structural compression have greatly improved reservoir permeability.(5)Root mean square amplitude,instantaneous frequency and relative wave impedance in the study area have poor response to sand body,and natural gamma ray can identify sandstone well;The waveform indication inversion results show that the sand body and effective reservoir of xu2 member are the thickest,up to 100 m and 70 m respectively,followed by xu4 member,up to 80 m and 50 m respectively,and the sand body and effective reservoir of xu3 member and xu5 member are thinner.(6)The reservoirs are classified according to the porosity.Porosity < 2% is non reservoir,2%-3.5% is class III reservoir,3.5%-6% is class II reservoir and > 6% is class I reservoir.Xujiahe Formation in the study area is mainly class III reservoir,followed by class II and less class I reservoir.