The investigation into oxidative method to realize zero flowback rate of hydraulic fracturing fluid in shale gas reservoir

Abstract We previously proposed a new strategy for dealing with hydraulic fracturing fluid (HFF) in shale gas reservoirs, known as zero flowback rate (ZFR) of HFF. We concluded that for some shale gas wells, the ZFR strategy appears to be a better option for dealing with injected HFF. However, neither the methods for implementing ZFR nor the benefits of ZFR were quantifiably studied in that work. In the end-face imbibition tests, shale samples from the Lower Silurian Longmaxi formation in the Sichuan basin of China were used. Non-oxidative fluid (5.5% potassium chloride solution) and oxidative fluid were also used in the tests (sodium hypochlorite solution and ammonium persulfate solution with different concentrations of 1.0%, 3.0%, and 5.0%). Based on laboratory observations and the principle of minimum energy, we propose that the number of cracks initiated by the imbibition process increases in direct proportion to the increase in the imbibition volume of the testing fluids. The crack numbers initiated by 5.0% sodium hypochlorite solution and 5.0% ammonium persulfate solution in the Longmaxi shale sample are 1.2 times and 1.4 times greater than those initiated by 5.5% potassium chloride solution, respectively. To achieve ZFR, oxidative HFF increases imbibition volume and thus shortens the shut-in time for a shale gas well. The optimum shut-in time for a 5.0% ammonium persulfate solution could be one-third that of the non-oxidative HFF.