New method for prediction of shale gas content in continental shale formation using well logs

Shale needs to contain a sufficient amount of gas to make it viable for exploitation. The continental heterogeneous shale formation in the Yan-chang (YC) area is investigated by firstly measuring the shale gas content in a laboratory and then investigating use of a theoretical prediction model. Key factors controlling the shale gas content are determined, and a prediction model for free gas content is established according to the equation of gas state and a new petrophysical volume model. Application of the Langmuir volume constant and pressure constant obtained from results of adsorption isotherms is found to be limited because these constants are greatly affected by experimental temperature and pressures. Therefore, using measurements of adsorption isotherms and thermodynamic theory, the influence of temperature, total organic carbon (TOC), and mineralogy on Langmuir volume constants and pressure constants are investigated in detail. A prediction model for the Langmuir pressure constant with a correction of temperatures is then established, and a prediction model for the Langmuir volume constant with correction of temperature, TOC, and quartz contents is also proposed. Using these corrected Langmuir constants, application of the Langmuir model determined using experimental adsorption isotherms is extrapolated to reservoir temperature, pressure, and lithological conditions, and a method for the prediction of shale gas content using well logs is established. Finally, this method is successfully applied to predict the shale gas content of the continental shale formation in the YC area, and practical application is shown to deliver good results with high precision.