Experimental Simulation of Proppant Transport in the Process of Sand Carrying Fluid Pumping, Fracture Closure, and Fluid Flowback in Hydraulic Fracturing

Hydraulic fracturing is one of the important processes for production stimulation in low-permeability oil and gas reservoirs. The stages during the hydraulic fracturing operation, such as sand-carrying fluid pumping, fracture closure, and fluid flowback, all affect the final placement profile of the proppant and the fracture productivity after. At present, the experimental and numerical simulation studies about proppant migration usually analyze the migration in a certain stage alone instead of the migration in the whole stages of the hydraulic fracturing operation. Based on the self-developed deformable and visual fracture model, the visual experiment simulation of proppant migration was carried out. The influence of the sand-carrying fluid pumping - fracture closure - flowback stage on the proppant placement profile was analyzed successively. The difference between the proppant migration rule and different densities was compared. The influence of different stages during hydraulic fracturing operation on proppant placement was discussed. The experimental studies show that the migration and placement rules of proppant are different for various proppant densities. The high-density proppant particles settled quickly, which was easy to accumulate at the entrance after settlement, which was not conducive to the migration of proppant to distant places of inner fracture. The low-density proppant was suspended in the carrying fluid for a longer time and created a more uniform sand bank. The extrusion closure of the fracture caused the settled proppant to transport further, forming a tighter support structure inner the fracture to bear the situ stress of formation. The movement of the proppant at the heel and middle of the fracture was more obvious during fracture closure. Blowdown of wellbore pressure and final fracturing fluid flowback affected the proppant migration, presenting as first rising and then falling of inlet-end placement profile and sand inflow problem. Squeezing the proppant tightly during the fracture closure stage was helpful in reducing proppant reflux and improving proppant placement performance. This study was useful in understanding the proppant migration in the whole process of the hydraulic fracturing operation.