Physical simulation study of proppant settling and migration within deep shale narrow fractures

Abstract

Hydraulic fracturing is an important technology in shale gas reservoir development. Effective improvement of proppant sanding in the “long narrow fracture” in deep shale reservoirs is important. In this study, based on the simulation of long narrow fractures in deep shale reservoirs with a flat plate experimental setup, we conducted comparative experiments with various parameters (e.g., fracturing fluid viscosity, injection pump flow rate, proppant particle size, sand concentration, fracture width, and proppant type) to understand the settlement and migration pattern of the proppant particles in the long narrow fractures in deep shale reservoirs. The results showed that, compared to that in wide fractures, under the same conditions, the sand bed formed by proppant particles in the long narrow fracture in deep shale has a smaller front edge slope and lower height difference between the front and end of the sand bed, resulting in a more even and smooth overall sanding of proppant particles. In the long narrow fractures in deep shale, the percentage of the area of the sand bed at the outlet end to the area of the whole sand bed increases with fracturing fluid viscosity and the injection pump flow rate, while it is less influenced by the sand concentration. The micro-sized proppant particles also promote the placement of the sand bed at the outlet end and are more conducive to the overall uniform placement of the sand bed. The contracting width of the long narrow fracture in deep shale has no significant effect on the placement of the sand bed in the fracture in front of the contraction, but it impedes the proppant particle flow distribution in the fracture behind the contraction. The coverage area and equilibrium height of the sand bed after the contraction decreased, and the overall sanding was more even. However, the amount of settled proppant decreased, increasing the difficulty of effective fracture support in deep shale reservoir fractures. The results of this experimental research provide strong support to the reforming design of fracturing in deep shale reservoirs.