Experimental study of friction reducer effect on dynamic and isotherm of methane desorption on Longmaxi shale

Abstract After hydraulic fracturing, the fluid-shale interaction has a significant impact on the shale gas desorption and thus on gas production. By providing high viscosity, friction reducer is widely used to decrease the energy loss and carry the proppant. To investigate the effect of friction reducer on the shale gas desorption on the shale, experiments are conducted using a newly designed experimental apparatus. We fit the dynamics and isotherms of methane adsorption/ desorption using the pseudo-second-order adsorption/ desorption dynamic model and Freundlich isotherm model respectively. Results show that the dynamics and isotherms of methane adsorption and desorption before and after friction reducer treatment can be good fitting by pseudo-second-order dynamic model and Freundlich isotherm model respectively. Moreover, we analyze the effect of friction reducer on the desorption efficiency and cumulative gas production. The results show that a higher desorption efficiency after friction reducer treatment can be observed when the pressure is more than 3.85 MPa. Meanwhile, the cumulative gas production before and after friction reducer treatment all nearly linearly increases with the decrease of equilibrium pressure. The curve of cumulative gas production after friction reducer treatment is clearly higher than that before, indicating the negative effect of friction reducer solution on methane desorption and the role to optimize flowing bottomhole pressure during the process of gas well production and the friction reducer during slickwater design.