Effects of clean fracturing fluids on coal microstructure and coalbed gas adsorption

Nowadays, some fracking fluids can enable resourceful extraction of coalbed methane and reduce greenhouse gas emissions. However, their toxicity or corrosiveness will cause harm to downhole workers and pollute groundwater resources. Thus, five kinds of clean composite fracturing fluids were developed in this paper by using starch solution as the matrix and adding various preparations. The change rule of methane adsorption capacity by microstructure changes of coal samples was investigated systematically, and the optimal composite fracturing fluid was determined. The results showed that the new fracturing fluid increased the degree of aromatic ring condensation by 43.3% and the average pore size by 52.1%. Also, the adsorption constants of a value decreased by 11.6% and b value decreased by 23.9%, which can remarkably reduce the methane adsorption. The experimental results provide theoretical support for the clean production of coalbed methane.