Discrete Element Simulation of Fracture Conductivity in Hydrate-Bearing Sediments Considering Proppant Embedment

Gas hydrate resources have enormous potential, but their low permeability, weak cementation pose great challenges to economic and efficient development. To improve production efficiency, reservoir stimulation methods such as hydraulic fracturing are usually required to enhance flow conditions, and the effective implementation of these techniques relies on an in-depth understanding of fracture conductivity and its controlling factors. In this study, a flexible triaxial numerical model was first developed using a discrete-continuous coupling approach to calibrate the micromechanical contact parameters of hydrate-bearing sediments. Subsequently, a discrete element model incorporating proppant embedment was constructed to systematically investigate the effects of closure pressure, hydrate saturation, the ratio between proppant and formation median grain sizes (D50/d50), and proppant areal concentration on fracture closure, intrafracture porosity, volume of formation sand invasion, and fracture conductivity. The results show that increasing closure pressure significantly enhances fracture closure and reduces fracture porosity and conductivity; higher hydrate saturation strengthens hydrate-bearing sediments, constraining proppant embedment and formation deformation, thereby markedly enhancing fracture conductivity at low closure pressure, whereas the differences in conductivity among different saturations gradually diminish at high closure pressure. Increasing the proppant size ratio and areal concentration helps create a larger initial fracture width and porosity and maintain relatively high conductivity under high closure pressure, but at the cost of greater sand invasion volume and fracture closure. These findings provide useful guidance for proppant selection and fracture design optimization in hydraulic fracturing treatments of gas hydrate reservoirs.