Influence of the Abandoned Oil Layer on Heat Mining Performance of U-shape Well Geothermal System

Regarding the current situation that there are large amounts of high water-cut oil and gas reservoirs, the switching of geothermal development using the available well pattern has become the effective way to control carbon emission. However, the influence of the abandoned oil layer features on geothermal development performance are still unclear. This study combines the exploration of U-shape well geothermal system with the CO2 geological storage using the oil-extracted layer. Considering the fluid natural convection in porous medium induced by temperature gradients in thermal reservoir, the heat and mass transfer in wellbore and thermal reservoir and the heat transfer between pipes and reservoir are coupled, then the effect of oil layer features on heat mining of the U-shape well geothermal system are discussed. The results show that heat mining performance of closed-well geothermal system can be enhanced by the increase of rock permeability around the well (include the oil and cover layer) due to the strengthen of natural convection. In CO2 buried oil layer due to the low viscosity of ScCO2 and the sensitivity temperature-independent density, the natural convection of ScCO2 drives the vertical migration of high temperature heat flow. Comparing the water-flooded abandon layer with the ScCO2-flooded abandon layer, the outlet temperature of geothermal system with ScCO2 storage increased by 11.23% and the heat mining rate increased by 17.9% after 10-year exploitation. The increase of the oil layer number and oil layer thickness will enhance the natural convection, which can raise the heat mining performance of U-shape well geothermal development. This research will provide technical support for the site selection and stimulation scheme design for geothermal development and the CO2 geological storage scheme in abandoned oil reservoirs, and contribute to the carbon reduction in oil and gas field.