Taking the seepage mechanics of porous nano media as the theoretical basis, combining with the experimental data of shale gas desorption in the present field, and considering the initial pore pressure and mud density and other parameters, we use the self-developed shale core gas content calculation program to simulate the whole process of shale core methane degassing, so as to scientifically and accurately evaluate the shale in-situ gas content.
Compared with the USBM method and other calculation models, our proposed calculation method has the following two characteristics:
1、"Zero-moment" correction: Traditionally, we use the moment when the core is lifted to half depth, and the moment when the boundary pressure is equal to the internal pressure of the core during the lifting process is the real "zero-moment";
2、Gas flow mechanism in nanopore: Simple molecular diffusion cannot describe the gas flow in porous nanomedium, and gas slip and Knudsen diffusion are the main control mechanisms of gas flow in shale pore system.
Provide core size parameters, depth, mud density, resolution temperature, initial pressure and porosity, adsorption parameters, the program fits the resolution experimental data, and then calculates the whole process of gas resolution starting from the zero moment, to obtain the gas content under the initial conditions, as well as the descent process of free gas and adsorbed gas within the core during the resolution process.