Factors Affecting Friction Loss of Hydraulic Fracturing in Ultra-short Radius Radial Wells and the Calculating Equation Thereof

The friction loss testing equipment (composed of friction testing controller, fracturing fluid distributor, speed-controllable screw pump, pipes with varied diameters, high-sensitivity pressure gauge, and electric flow meter) developed by China University of Petroleum (East China) has been used to study the effects of borehole diameters and fracturing parameters on the friction loss of fracturing ultra-short radius radial (URR) wells and to calculate the magnitude of the friction losses of the fracturing fluid. The flow conditions in URR wells were simulated and the friction losses of the fracturing fluids used accurately measured. Analysis of the experiment results shows that factors affecting the friction losses of the fracturing fluids in URR wells are, in the order of decreasing importance, hole diameter, flow rate, viscosity, particle size of proppant, and sand content, and the effects varies in different conditions. An equation for the calculation of friction losses of guar gum fracturing fluid in URR wells has been developed taking into account the aforementioned factors, through the regression fits of 322 sets of data and based on the principle of reducing friction ratios. The standard error of estimate calculated from correlation coefficient testing method is 0.140, indicating that the regression fit equation is valid. It has been found through the experiments that the viscosity of the guar gum fracturing fluid has dual effects on the friction; the viscosity, by increasing the intrinsic shear stress and the shear stress between fluid and the wall of the pipe, increases the friction losses of the fracturing fluid. On the other hand, with an increase in viscosity, a transition delay is being developed in the polymer solution, and the polymer solution has stronger control over the proppants used, thereby decreases the friction losses of the fracturing fluid.