Advanced Computational Modeling of Proppant Settling in Water Fractures for Shale Gas Production

This paper shows advances in the numerical simulation of proppant transport in hydraulically stimulated fractures for oil and gas production. Water or commonly known "slickwater" hydraulic-fracture treatments have become increasingly popular in shale gas. This is widely applied in the Haynesville shale in northern Louisiana, but because of the large depths and high pressure, conventional wisdom suggests that intermediate-strength proppants (generally 4,000- to 6,000-psi crush strength) should be used. This strength envelope is in the transition range between ceramics and sand. Sand is lower in cost and has the advantage of having better transport properties in water fractures. In the paper, a 3D computational-fluid-dynamics (CFD) model with Lagrangian solid-particle transport is used to visualize the propagation of sand and other lighter proppants in a simulated fracture. The proppant-settling behavior influenced by proppant density, size, and flow rates is demonstrated. The final proppant-settling patterns can vary dramatically and may result in significant changes in the fracture's conductivity. Model assumptions, simplifications, and numerical details are discussed along with issues regarding validation and simulation strategy. The model geometry is highly idealized (i.e., neglecting fracture tortuosity and expansion during water fracturing, surface roughness, and fluid leakoff). The importance of this work lies in the fact that the model can resolve the interactions between fracturing fluid (water) and proppants within complex 3D geometries, thus providing a better understanding of the fracturing process to allow for possible enhancements to production procedures.