Abstract
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, especially in weakly consolidated sandstone reservoirs. 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 in Xining Basin, China. Then a comprehensive sensitivity analysis of influencing factors was conducted based on the model using a numerical simulation method. 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 due to the migration and precipitation of different types of movable particles. The blockage mainly occurs in the formation within 30 m away from the reinjection well. 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 near the well. The well reinjection capacity can be restored to larger than 70% of the initial. This established mechanism model can be an effective means to investigate the particle movement law in geothermal development.