The Research On Shale Reservoir Characteristics Of Wufeng-longmaxi Formation In Yongchuan Area Of Southern Sichuan Basin

The potential of shale gas in the Sichuan Basin is huge and breakthroughs have been made in recent years.It has been shown that black organic-rich shales developed in the Upper Ordovician Wufeng Formation and the Lower Silurian Longmaxi Formation in the south of Sichuan Province have the basic conditions for shale gas formation and have good shale gas exploration potential.At present,the Yongchuan block and its periphery is undergoing a large-scale development of shale gas with a good prospect.Based on the above considerations,this paper takes the organic-rich shale of Wufeng Formation and Longmaxi Formation in Yongchuan area of southern Sichuan as the research object,takes the sedimentology and reservoir geology theory as the guide,makes full use of the outcrop profile,observes the drilling core,and measures logging data.As well as test and analysis data,the characteristics of organic-rich shale deposits and reservoir development in the study area were studied,and a classification evaluation of favorable reservoir areas was carried out.The main knowledge gained is as follows:Through profile and drilling data summary,the strata division of the study area was determined.The Wufeng-Longmaxi Formation in Yongchuan area of South Sichuan is widely distributed in the area,with a thickness of about 360⁴70 meters.Its burial depth gradually decreased from the northwest to the southeast,and the burial depth was approximately 3000-4200 meters.The lithology of the lower segment of Wufeng-Longmaxi Formation is mainly composed of black shale,carbonaceous shale,black shale,silty shale with thin layer of gray mudstone,and palaeontology is the most developed.The Wufeng-Longmaxi Formation in the study area is a continental shed environment,according to sedimentary facies markers?sedimentology,palaeontology,geophysics,geochemical markers?,it can be divided into shallow water shelf sediments and deep water shelf sediments.According to lithological differences,it can be subdivided into stucco,argillaceous,shale,siliceous,and carbonaceous shelf micro phase.The Wufeng-Longmaxi shale in the study area has a high content of organic value,ranging from 0.12 to 10.2%,with an average of 2.7%.The kerogen type is dominated by the type I humic rot and the type II₁ supplements,and the thermal evolution is High-over-mature stage.Study shows that the study area Wufeng-Longmaxi Formation shale can be evaluated as a good source rocks.Through the whole rock analysis,it is believed that the Wufeng-Longmaxi Formation shales are mainly composed of quartz,plagioclase and clay minerals,and there are less carbonate minerals and pyrite.Overall,the organic-rich shale of the Wufeng-Longmaxi Formation in the study area is characterized by high quartz,low-clay minerals and carbonate minerals.The average content of brittle minerals in shale reservoirs in the study area is 55%,which is conducive to acid fracturing.The reservoir porosity is 1.8 to 7.9%?average 3.56%?,and the permeability is 0.01 to0.26×10^-3?m²(average 0.028×10^-3?m²).The types of reservoir space are various,and the pores are mainly organic.Cracks develop.A total of 10 parameters including the effective shale thickness,bottom depth,organic carbon content,maturity,reservoir brittle composition,clay mineral content,porosity,permeability,gas content,and fracture development were selected for Yongchuan reservoir In the evaluation,it was considered that the Baofeng-Laisu town and Zhisheng-Yongrong town were the most favorable areas for shale gas exploration in the Wufeng-Longmaxi Formation in the study area.