| Yuanba area in northern of Sichuan basin is a key area for shale gas exploration,Jurassic Ziliujing formation in this area has great shale gas exploration potential.A total of 50 exploration wells have been drilled in this area,and many industrial oil and gas have been achieved.Therefore,evaluating the shale gas resources in this area is an important prerequisite for the next exploration.From perspectives of organic geochemical characteristics of source rocks,pore characteristics of shale reservoirs,hydrocarbon generation potential of hydrocarbon source rocks,hydrocarbon generation evolution and shale gas resource prediction,etc.The hydrocarbon generation evolution of hydrocarbon source rocks,the resource potential of shale gas in the Da'anzhai member has been comprehensively evaluated.The organic carbon content(TOC)of the shale in Da'anzhai member of Yuanba area averaged 0.80%,the second Da'anzhai sub-member has the highest TOC content,with an average value of 0.86%,which is significantly higher than the first Da'anzhai sub-member(0.78%)and the third Da'anzhai sub-member(0.41%).The organic matter types of the Da'anzhai member shale in Yuanba area are mostly type III,and a small amount are type II.The source rocks are in high maturity.Most of the organic matter types in the shale of Da'anzhai member in Yuanba area are type III and a few are type II.The pores of Da'anzhai shale are divided into organic pores,intergranular pores,intrgranular pores and microfractures.The total porosity is 5%,and the pore space is mainly mesopore(60%?80%).The Da'anzhai member has a small number of organic pores,most of which are isolated and difficult to connect in three dimensions.The main types of inorganic pores are mineral-based interparticle pores.Intergranular pores are abundant in shallow buried sediments,and usually have good connectivity,forming a permeable pore network.In the Da'anzhai member of the Yuanba area,the planar TOC distribution ranges from 0.7%to 1.2%,the thickness of the planar source rock ranges from 30m to 70m,the vitrinite reflectance ranges from 1.5%to 1.9%,and the hydrocarbon generation intensity ranges between 1.5?4.0×10~8m~3/km~2.Free gas is mainly in the shale of Da'anzhai member in Yuanba area,supplemented by adsorbed gas.The shale entered the maturity period,a lot of hydrocarbons were generated,and the free gas in the porosity increases greatly until it reached the maximum burial depth,and then the free gas decreased during the formation uplift period.The adsorbed gas reached a maximum value of 0.5m~3/t at about 150Ma,and then started to decrease,and reached a minimum value when the maximum burial depth was reached,at which time the free gas reached a maximum value of 1.5m~3/t.During the uplift period,the temperature decreased,which is conducive to shale adsorption.Some free gas is converted into adsorbed gas,and the content of adsorbed gas increases.The shale of Da'anzhai member in Yuanba area has high organic carbon content,good type,high maturity and large amount of hydrocarbon generation.It is located in the weak tectonic deformation zone,with well-developed fractures,and has the conditions of high shale gas production and good preservation.According to the calculation,the shale gas resource quantity of Da'anzhai member in Yuanba area is about 948.318 billion cubic meters,so this area has good resource potential.According to the evaluation,the zone favorable for shale gas exploration in Yuanba area consists of two potential shale gas enrichment zones developed in Da'anzhai member:one weak deformation zone of well Yuanba 21 well,Yuanba 11 well and Yuanba 12 well,and the other weak deformation zone is in the southern of Yuanlu 4 well and Yuanlu 173 well.The two zones develop continuous thick shale with a thickness of70m.The content of TOC was higher,reaching 1.2%.Shale pores and fractures are relatively developed,porosity up to 5%,is a good reservoir.After evaluation,the shale of Da'anzhai member in Yuanba area has high exploration value. |
PDF Full Text Request