Numerical study on formation blockage and back-pumping during geothermal water reinjection in weakly consolidated heterogeneous reservoirs using a novel mechanism model

For the utilization of low-medium temperature geothermal water, the well injection capacity for tail water disposal is often reduced due to the migration of self-generated particles and the invasion of suspended particles. In this paper, a novel mechanism model of formation blockage and recovery by back-pumping during geothermal water reinjection was established based on the classification and bridging principle of movable particles in porous media. The model validity was confirmed by fitting the field tests of geothermal reinjection and back-pumping in Xining Basin, China. Then a comprehensive sensitivity analysis of influencing factors was conducted based on the model by numerical simulation method to explore the formation blockage laws during water reinjection and the blockage removal performance of the back-pumping operation. The results show that in a weakly consolidated heterogeneous reservoir, a series of preferential seepage channels and low-permeability zones will be formed between reinjection and production wells. The self-generated and invasive coarse particles are the dominant factor to cause blockage.Back-pumping is an effective method to relieve the blockage in the formation within 20m around the well. This established mechanism model can be an effective means to investigate the particle movement law in geothermal development.