Energy & Fuels, Vol.35, No.2, 1422-1432, 2021
Modeling Temporary Plugging Agent Transport in the Wellbore and Fracture with a Coupled Computational Fluid Dynamics-Discrete Element Method Approach
As the consumption of oil and gas resources is increasing, secondary exploitation in old wells and unconventional oil and gas exploitation methods are becoming increasingly important. As a result of complex reservoir environments and the reservoir properties, such as ultralow porosity and permeability, hydraulic fracturing is an important means to achieve effective recovery. Temporary plugging fracturing is currently an efficient fracturing technology and is suitable for refracturing of old wells and multistage fracturing in unconventional reservoirs, which is conducive to constructing complex fracture networks and increasing production. Recently, in the field of temporary plugging fracturing, how to design the operation parameters of temporary plugging fracturing still remains ambiguous and empirical. In this paper, a numerical simulation study of the liquid-solid two-phase flow of the temporary plugging agents and the fracturing fluid was conducted using two physical models: a wellbore flow model and a wellbore-fracture temporary plugging model. The transport processes of the temporary plugging agents along with fracturing fluid in a vertical wellbore, in a horizontal wellbore, and at a fracture position were simulated. Simulations that coupled computational fluid dynamics and the discrete element method were used in the simulation process. The effects of the temporary plugging agent concentration, particle size, particle size ratio, fracturing fluid rate, and fracturing fluid viscosity on the migration process of the temporary plugging agent were investigated. The simulation results show that a higher concentration and viscosity of a temporary plugging agent help to sustain the flow stability in the vertical wellbore, while the viscosity and flow rate of the fracturing fluid have an impact on whether sedimentation of the temporary plugging agent occurred in the horizontal wellbore. In addition, the particle size ratio and concentration of the temporary plugging agent are the key factors for a successful bridging and plugging. For a specific field application in Longmaxi Formation, Sichuan Province, the operation parameters of temporary plugging fracturing have been designed and achieved a successful refracturing treatment.