Study On Reservoir Microscopic Characteristics Of Silurian Xiaoheba Formation In Southeastern Sichuan

The study area is located in the northeast Sichuan high-steep tectonic belt and the southern Sichuan low-lying tectonic belt,clastic reservoirs developed in Xiaoheba Formation.Although oil and gas exploration has great potential,there has been no major breakthrough,one of the reasons is that basic research is weak,the formation mechanism,influencing factors and planar characteristics of the reservoir are still unclear.Through research on rock structure,diagenesis,diagenetic evolution,diagenetic facies,reservoir physical properties,the reservoir development characteristics can be clarified,and the distribution of favorable reservoirs on the plane can be predicted.The Xiaoheba Formation sandstone in the study area is mainly feldspar quartz sandstone,followed by lithic quartz sandstone with the least amount of lithic sandstone.The sandstone has a fine overall grain size,mainly very fine sand-coarse silt,medium-good sorting,and most of the debris particles are in line contact.The Xiaoheba Formation in the study area is in the late diagenetic stage and experienced a complex diagenesis.Among them,compaction and cementation are destructive diagenesis,the dissolution produces partial dissolution pores,plays a positive role in the secondary transformation of reservoir pores and the improvement of reservoir physical properties.Combined with the division of diagenesis intensity,the target interval of the study area can be divided into five diagenetic facies types: Strong compaction facies,medium-strong compacted carbonate cemented diagenetic facies,Medium-strong compacted clay heterogeneous filling diagenetic facies.Combined with the division of diagenesis intensity,the target interval of the study area can be divided into five diagenetic facies types: strong compaction facies,medium-strong compacted carbonate cemented diagenetic facies,mediumstrong compacted clay heteroge-neous filling diagenetic facies,medium-strong compaction dissolution diagenetic facies,and weak-medium compaction calcite cementation-clay heterogeneous filling diagenetic facies.medium-strong compaction dissolution diagenetic facies develops a large number of dissolved pores,corresponding to the best physical properties of the reservoir;strong compaction facies withstand strong compaction,and the medium-strong compacted carbonate cemented diagenetic facies are affected by the strong carbonate cementation,both porosity and permeability are low,the corresponding reservoir properties are poor.The physical properties of the sandstone reservoirs of the Xiaoheba Formation in the study area are generally poor.The main distribution of porosity ranges from 0.35% to 8.23%,and the average porosity is about 1.97%,and the permeability is distributed between 0.0029 and 9.88 m D with an average of 0.197 m D.The pore type of the reservoir is dominated by secondary pores,the type of reservoir space is mainly intergranular dissolution pores,followed by intragranular dissolution pores,cracks and intercrystalline micropores.The effective pore radius averages about 10.15?m,and the pore throat radius averages about 0.167?m,the overall performance is micron-nano-scale pore throat combination.Combined with sedimentary characteristics,diagenetic characteristics,physical characteristics and other factors,divide the reservoirs in the study area into four types.Type I reservoirs are the best,type II reservoirs have good physical properties,type III reservoirs are medium in physical properties,type IV reservoirs are inferior in physical properties.The relatively high-quality reservoirs in the study area are mainly type II and III reservoirs,the proportion is close to 50%,mainly distributed in the Shuangliuba and Lengshuixi sections,wells JY7 to JY1 mainly develop type IV reservoirs.