Impact of cleanup additive on methane desorption on Longmaxi shale

After multistage hydraulic fracturing, it is essential to understand the effect of fracturing fluids trapped in shale gas reservoirs on the shale-well. To address the effect of cleanup additive as a major composition of slickwater fracking fluids on methane desorption after hydraulic fracturing, we performed a series of experiments, including X-ray to obtain the mineralogical composition of the gas shale sample, low-pressure nitrogen adsorption to obtain pore size distribution, and series of adsorption and desorption tests. We compared the effect of different methane densities of adsorbed phase on methane absolute adsorption and results demonstrate that the methane adsorption is significantly undervalued. The methane adsorption isotherm and desorption isotherms before and after cleanup additive treatment were well fit by Freundlich model. Furthermore, we compared the desorption isotherms, desorption efficiency, free gas content as well as cumulative gas production before and after treatment. These findings indicate that cleanup additive treatment results in the decrease of adsorption capacity and the increase of adsorption intensity. There exists an intersection between two curves of desorption efficiency before and after treatment. Cleanup additive significantly translates adsorbed phase into free phase to improve free gas content, and increases cumulative gas production. These results can be very helpful for reserves evaluation, knowledge of the role of cleanup additive both increasing slickwater flowback and improving gas recovery.

Automated summary

The experiments demonstrated that cleanup additive treatment decreases adsorption capacity and increases adsorption intensity. There is an intersection between the desorption efficiency curves before and after treatment. Cleanup additive helps translate adsorbed phase into free phase, improving free gas content and increasing cumulative gas production.