Experimental and Numerical Investigations of the Role of Proppant Embedment on Fracture Conductivity in Narrow Fractures

With the advancement of drilling and completion technologies in unconventional reservoirs, more extended reach wells are developed, and narrow-fracture environments are created in these reservoirs. Proppant embedment in monolayer/thin-layer-propped fractures can be significantly different from multilayer-propped fractures. In this study, a comprehensive investigation combining laboratory experiments with numerical simulations was conducted to explore the factors affecting proppant embedment and induced fracture conductivity loss in narrow fractures. The fracture-conductivity experiments were performed using monolayers of sand and ceramic proppant particles sandwiched between Berea Sandstone and Eagle Ford Shale plates under different closure pressures. The experiment study demonstrated that the long-term rock/fluid interaction leads to significant proppant embedment, and the fracture having a rough rock surface has higher fracture conductivity in monolayer-propped fractures. To further quantify the influence of proppant layer number, size, distribution variations, and particle crushing on proppant embedment, a numerical modeling approach that coupled continuum mechanics, discrete element method (DEM), and the lattice Boltzmann (LB) method was developed. In the simulation, the fracture/ proppant system was constructed by filling proppant, modeled by DEM, between two fracture surfaces that were modeled by FLAC3D (Itasca Consulting Group 2012); LB simulation was then performed on the changing proppant pack to compute its time-dependent permeability. The numerical model was validated by comparing numerical results with measured fracture conductivities in the laboratory experiment. The simulation results demonstrated a strong correlation between proppant embedment and rock mechanical properties. When the Young's modulus of the rock plate is less than 5 GPa, large magnitudes of proppant embedment can be expected in fractures supported by monolayers of ceramic proppant particles. Moreover, large-size proppant particles are more sensitive to the variations of Young's modulus of the rock plate. When the rock formation in a narrow fracture environment has a relatively high Young's modulus, the proppant diameter distribution has a lesser effect on the fracture conductivity. The outcome of this study will provide insights into the role of reservoir rock characteristics, proppant properties, and closure pressure on proppant embedment in narrow fractures.