Effect of Fluid Rheology on Proppant Transport in Hydraulic Fractures in Soft Sands

摘要

We have developed a new frac-pack model to simulate power-law fluid flow coupled with proppant transport inside the fracture. Two empirical correlations of the relative velocity between the fluid and proppant for the vertical direction (settling) and the horizontal direction (retardation) are incorporated in the model. This model can simulate fully 3-D fracture growth in poro-elasto-plastic materials with tensile and shear failure. A cohesive zone model is used for fracture propagation along with a dynamic and adaptive meshing procedure. We investigate the effect of fluid viscosity, injection rate, proppant diameter, and reservoir permeability on proppant placement. Higher apparent viscosity fluid and injection rate results in wider fractures with better proppant placement, when the fracture is expected to be contained within the payzone. In the case of fracpacks, utilizing larger diameter of proppant leads to settling-dominant proppant placement rather than the retardation-dominant due to the relatively wider induced fracture. The effect of fluid leak-off and the pore pressure diffusion in the reservoir is captured. Higher leak-off in the high permeability sands leads to a poroelastic backstress that builds up around the fracture, and results in a shorter fracture due to larger leak-off. This new frac-pack model allows us to design and analyze hydraulic fracturing stimulations in soft, elasto-plastic formations when Theologically complex fracturing fluids are used. Our results also provide guidelines for the selection of fracturing fluid rheology, proppant size, and injection rates.