Experimental study of friction reducer flows in microfracture

• Micro-meter sized fracture models are successfully employed in the study.
• Flow behavior of friction reducer in microfracture is carefully investigated, and compared with that in macro-sized pipeline.
• We analyzed the friction reducer emulsion particle size.
• Fluid impact on shale matrix during slickwater fracturing is discussed.

Tight formations with extremely low matrix permeabilities, such as gas shale, can produce at economical rates is due to the inborn fissures and fractures introduced during hydraulic stimulation. These microfractures have much more contact area with the matrix and therefore hold the majority of the productivity potential of shale gas. Slickwater fracturing has been proved to be an effective method by which to increase the recovery of shale gas reservoirs. And friction reducer is the primary component of this fluid. However, the flow characteristics of this solution in microfractures are not clear.Micro-sized fluidic chip was used to represent the microfracture. Friction reducer solution is a shear thinning fluid. Rather than reducing flowing friction, with 0.075 vol% of this fluid flowing in a 1000 μm height, 50 μm width and 4.14 cm length microfracture, the injection pressure increased more than 50%. The impact of the solution concentration was found to be more obvious at low velocities. If a flowback additive is considered for slickwater fracturing, its performance at low velocity or low shear rate would be critical. At the same shear rate, the apparent viscosity is higher in large microfractures. At the same velocity, large microfractures display higher residual resistance factors. Through the analysis of fluid emulsion particle size and gas shale matrix pore size, this friction reducer solution will not go into the matrix pores easily, but can block the pore entrance on fracture face to prevent the fluid from leak off and help pressure build up during slickwater fracturing.