Thermal disturbance analysis in rock-soil induced by heat extraction from the abandoned well

Abstract

Medium-deep geothermal energy has obvious advantages in building heating in cold regions. The abandoned oil well can be retrofitted into a closed-loop coaxial borehole heat exchanger to save costs. However, continuous heat extraction and recovery in long-term operation can cause potential deformation, and the thermal disturbance scope in the surrounding formation should be determined. In this study, the thermal process and disturbance induced by heat extraction are analyzed. The effects of heat load, flow rate, rock-soil thermal conductivity, outer pipe thermal conductivity, rock-soil density and depth for a single borehole are discussed. And the effects of distance for two boreholes on the thermal disturbance were evaluated. The results demonstrate that heat conduction between the circulating fluid and the formation is opposite at the shallow and deep depth, and the thermal process is enhanced at the bottom borehole. The thermal disturbance scope at the depth of 2000 m can exceed 40 m following 20 years of operation. The superimposed thermal process of the two boreholes induces more thermal disturbance. The thermal disturbance scope of each borehole was able to 75 m for the layout of the two boreholes. The results can provide a basis for layout of the coaxial borehole heat exchanger.