Controlling groundwater infiltration by gas flooding for oil shale in situ pyrolysis exploitation

Abstract

Abstract An inrush of groundwater will absorb the heat injected in oil shale in situ pyrolysis exploitation, which will reduce the pyrolysis efficiency and generate a large amount of oil-containing water. This paper proposed a novel method of water-stopping by gas flooding to solve the problem of groundwater infiltration into the in situ pyrolysis zone of oil shale. In this paper, numerical simulation by TOUGH2/EOS3 and field experiment studies were conducted, with the general aim of this study focused on the establishment of the inflatable area and the long-term water-stopping mechanism. The simulation results showed that the resistance of gas to groundwater flow and the pressure balance of the gas-water interface at the inflatable area front were the main mechanisms of water-stopping. The water yield in the pyrolysis zone decreased significantly from 6\u202fm3/h to nearly 0\u202fm3/h after the inflatable area was established, and the effective water-stopping radius exceeded 50\u202fm around a single well. Furthermore, a field-scale water-stopping by gas flooding experiment was carried out in the National Pilot Project for Oil Shale in situ Exploitation of China (NPOSE), with the results demonstrating that the water yield could be reduced from 6\u202fm3/h to 0.5\u202fm3/h after gas injection, which was basically consistent with the numerical simulation results. Cracked oil (2.85 tons) was successfully obtained at high energy efficiency of approximately 6.1. Consequently, it is verified that the method proposed in this paper has the desired effect of water-stopping and practical application value, which provides technical support for large-scale oil shale in situ pyrolysis exploitation around the world.