Investigation of Slickwater Effect on Permeability of Gas Shale from Longmaxi Formation

Knowing of gas shale permeability reduction is vital for gas production from shale gas reservoirs stimulated by multistage hydraulic fracturing. However, the role of shale matrix permeability reduction is not well addressed for evaluating the contribution on gas well production. In this study, the experiments of slickwater treatment at different injection pressures, injection volumes, and slickwater compositions were conducted by using an experimental apparatus based on the steady-state method. The results show that slickwater flow in the core is seriously affected by microfracture. The cumulative gas volume through the core with microfracture increases nearly linearly with time. Then, we analyzed the effect of injection pressure gradients, injection volume, and slickwater compositions on the permeability reduction and flowback efficiency. The permeability reduction and flowback efficiency both increase slightly at beginning and then nearly linearly in the middle and gradually at last with the increase of injection pressure gradient. Permeability reduction and flowback efficiency both decrease quickly at first and then slightly with the increase of injection volume, indicating only a small proportion of slickwater, which occupied much more small pores, can be displaced and flow back to the entrance piece of core sample. The permeability reduction and flowback efficiency after different chemical solution treatments are in the order from highest to lowest of cleanup additive, slickwater, clay stabilizer, defoamer, and friction reducer, indicating the synergy effect of slickwater compositions on the permeability reduction and flowback efficiency. These results can be helpful for optimizing the slickwater formulation and understanding the damage mechanism of shale formation during hydraulic fracturing.