Controlling Factors And Quantitative Evaluation Of Continental Shale Gas Of Ziliujing Formation In Northeastern Sichuan Basin

Understanding different geological controlling factors shale gas and evaluating gas quantitative are vital for hydrocarbon exploration.Shale of Ziliujing Formation in northeastern Sichuan Basin is deposited in terrestrial sedimentary environment,which has huge thickness and is widespread.A series of experiments on geochemical features,pore structure are conducted,and the average total organic matter content is 1.2%and the thermal maturity is 1.655%,and micropores and mesopores are developed in shale reservoir and the space includes several types,pores of rigid framework,pores associated with clay flakes,dissolved pores,organic matter host pores.The average porosity is about 2.20%,and surface area averages 11.39m²/g.Occurrence states of Ziliujing Formation shale in Northeastern Sichuan Basin include absorbed state and free state.Based on CH₄isothermal absorption experiment results,Langmuir isothermal adsorption equation and the ideal-gas equation,shale gas content in different occurrence states was obtained.The average maximum absorbed gas in dry condition is 1.90m³/t,and free gas is 1.57m³/t.Controlling factors of different occurrence state gas were analyzed through the systematical aspects of geochemical characters,reservoir features,temperature and pressure,as well as water condition.The results show that the controlling factors of absorbed gas are organic matter content,clay content,porosity,temperature,pressure and water saturation,and the controlling factors of free gas are organic matter content,brittle content,porosity and gas saturation.Accordingly,the main controlling factors are evaluated.Following,multiple regression analysis of absorbed gas and free gas content is carried out by SPSS statistic analysis software,and different state gas prediction models are established.Data on site are used for reliability of these models,and the result showed the low R².The research results show that organic-rich argillaceous shale has the best gas propertions among the four main types of lithofacies in northeastern Sichuan Basin,followed by organic-fair mixed shale,then organic-fair siliceous shale,and organic-poor siliceous shale.The vertical distribution characteristics of continental shale gas present that the gas content of the Da'anzhai Member is silghtely better than the Dongyuemiao Member.The favorable shale gas content areas with the content greater than 2.50 m³/t are mainly developed in the west of Dazhou and the north of Yingshan,where are near the center of Sichuan Basin.