A Comprehensive Model of Fluid Loss in Hydraulic Fracturing

Abstract

Summary This paper presents a comprehensive model of the fluid-loss process that occurs in hydraulic fracturing. The model treats the three flow regions in the leakoff process—the filter cake, the invaded zone and the reservoir zone—as a composite system with a rigorous account of the interface between the last two zones. This allows automatic consideration of the variation in pressure drops across the three zones and the inclusion of many variable physical aspects in each region. For the description of the filter cake behavior, effects of the internal filter cake, core length, shear rate, and non-Newtonian behavior of fluids have been taken into account. In the invaded zone, the non-Newtonian behavior of the filtrate, the permeability damage caused by the filtrate invasion, and rock and fluid compressibility have been simulated. Different boundary conditions, such as no-flow, constant-pressure, finite, and infinite boundaries, have been incorporated into the model, making it applicable for simulating both laboratory tests and the real leakoff process in fracturing treatments under a variety of conditions. The model has been validated against laboratory and published data. Excellent agreement between predicted results and test data has been achieved. The analyses show that the non-Newtonian behavior of the filtrate represented by the model has a significant effect on leakoff. Leakoff would be considerably underestimated if a Newtonian fluid filtrate, as in the classic theory, were assumed instead of the non-Newtonian system. We also show that the variation in pressure drops across the three zones may cause a strong nonlinear relation between leakoff and t½ that cannot be explained by the classic theory because constant pressure drops are assumed.