In the calculation of shale gas resources/reserves,isothermal adsorption parameters are mainly determined by dry sample data at the laboratory temperature,and the regression effect of total organic carbon content(TOC)...In the calculation of shale gas resources/reserves,isothermal adsorption parameters are mainly determined by dry sample data at the laboratory temperature,and the regression effect of total organic carbon content(TOC)isothermal adsorption parameters is poor.Based on the physical significance of key parameters in Langmuir and Henry adsorption models,the problems in determining the isothermal adsorption parameters in the calculation of shale gas reserves/reserves are analyzed by taking the marine shale in the Upper Ordovician Wufeng FormingeLower Silurian Longmaxi Formation in the Sichuan Basin as an example.Based on a large number of measured isothermal adsorption data,the effects of TOC,temperature and water saturation on the shale gas adsorption parameters are analyzed.The influence model of TOC,temperature and water saturation on isothermal adsorption parameters of shale gas is established,and a novel method for calculating the adsorption parameters of shale gas from under experimental conditions to original reservoir conditions is proposed.The results are obtained as follows.First,there are problems in the calculation of shale gas resources/reserves,such as poor and contradictoryfitting relation between isothermal adsorption parameters and TOC,difficulty in the conversion of Van't Hoff equation,and difficulty in direct application of water saturation(Sw)in resource/reserves calculation.Second,the problem of poor directfitting relation between Langmuir pressure(pL)and TOC is solved by integrating the Langmuir adsorption model with the Henry adsorption model and by establishing a new parameter e Henry constant a for methane adsorption capacity of shale.Third,when Sw<40%,the Langmuir volume(VL)is linearly negatively correlated with Sw;when Sw<20%,a is constant relatively;by establishing the relationship between the normalized absolute adsorption capacity and Sw(<50%)under the pressure exceeding 30 MPa,the effect of Sw on the isothermal adsorption capacity can be calculated.Fourth,the in-situ stress in the Wufeng FormationeLongmaxi Formation shale reservoir affects the adsorption capacity of shale.For shale reservoirs with the same TOC,the higher the in-situ stress,the smaller the VL and a values.Under high pressure(>30 MPa),the effect of Sw on the methane adsorption capacity of shale shows a similar trend,and the effect of water molecules on the adsorption capacity on shale pore surface is constant.It is concluded that the proposed novel method for determining the isothermal adsorption parameters of shale with different TOC,temperature and water saturation conditions provides a technical support for the accurate calculation of shale gas resources/reserves and contributes to the scientific development of shale gas industry.展开更多
基金supported by the Scientific Research and Technol-ogy Development Project of PetroChina Company Limited,"Research on Geological Activity Evaluation Technology of shale gas Development Zone"(No.2022DJ80)"Research on Exploration and Development Technology of Marine shale gas"(No.2021DJ19).
文摘In the calculation of shale gas resources/reserves,isothermal adsorption parameters are mainly determined by dry sample data at the laboratory temperature,and the regression effect of total organic carbon content(TOC)isothermal adsorption parameters is poor.Based on the physical significance of key parameters in Langmuir and Henry adsorption models,the problems in determining the isothermal adsorption parameters in the calculation of shale gas reserves/reserves are analyzed by taking the marine shale in the Upper Ordovician Wufeng FormingeLower Silurian Longmaxi Formation in the Sichuan Basin as an example.Based on a large number of measured isothermal adsorption data,the effects of TOC,temperature and water saturation on the shale gas adsorption parameters are analyzed.The influence model of TOC,temperature and water saturation on isothermal adsorption parameters of shale gas is established,and a novel method for calculating the adsorption parameters of shale gas from under experimental conditions to original reservoir conditions is proposed.The results are obtained as follows.First,there are problems in the calculation of shale gas resources/reserves,such as poor and contradictoryfitting relation between isothermal adsorption parameters and TOC,difficulty in the conversion of Van't Hoff equation,and difficulty in direct application of water saturation(Sw)in resource/reserves calculation.Second,the problem of poor directfitting relation between Langmuir pressure(pL)and TOC is solved by integrating the Langmuir adsorption model with the Henry adsorption model and by establishing a new parameter e Henry constant a for methane adsorption capacity of shale.Third,when Sw<40%,the Langmuir volume(VL)is linearly negatively correlated with Sw;when Sw<20%,a is constant relatively;by establishing the relationship between the normalized absolute adsorption capacity and Sw(<50%)under the pressure exceeding 30 MPa,the effect of Sw on the isothermal adsorption capacity can be calculated.Fourth,the in-situ stress in the Wufeng FormationeLongmaxi Formation shale reservoir affects the adsorption capacity of shale.For shale reservoirs with the same TOC,the higher the in-situ stress,the smaller the VL and a values.Under high pressure(>30 MPa),the effect of Sw on the methane adsorption capacity of shale shows a similar trend,and the effect of water molecules on the adsorption capacity on shale pore surface is constant.It is concluded that the proposed novel method for determining the isothermal adsorption parameters of shale with different TOC,temperature and water saturation conditions provides a technical support for the accurate calculation of shale gas resources/reserves and contributes to the scientific development of shale gas industry.
