Reinjection Modeling in Sandstone Geothermal Reservoirs: A Case Study of Dezhou Geothermal Heating Demonstration Project

To ensure the long-term and sustainable development and utilization of geothermal resources, the extracted geothermal water should be reinjected. Considering Guantao Formation in the Dezhou Area, the geothermal reinjection process is analyzed through experimental and numerical modeling. Numerical analysis suggests that the reinjection flow only has a strong influence on the reservoir pressure over a relatively narrow range, whereas the range over which this process has a weak influence exceeds 500 m. Assuming that the reinjection well is full, a reinjection flow rate of 50–100 m3/h can theoretically be achieved without additional pressure. Experimental modeling of geothermal exploitation and reinjection suggests that sandstone reservoirs with good porosity and permeability should be selected to lower the reinjection pressure of geothermal reservoir projects. In real geothermal reinjection processes, the reinjection flow rate should be carefully determined to prevent excessive pressure in sandstone reservoirs and ensure long-term stable and efficient reinjection. The Huaneng Geothermal Project has been operating for 2 years, and there has been no significant change in the outlet temperature and reinjection pressure of the geothermal wells. This is generally consistent with the modeling results, demonstrating the accuracy of the exploitation and reinjection modeling analysis. An efficient reinjection scheme for sandstone geothermal reservoirs is developed based on the Huaneng Dezhou Geothermal Heating Project, in which the total reinjection rate is approximately 99.1 %. Based on our experimental and numerical modeling, no significant temperature and pressure changes will happen for at least 5 years at the present exploitation and reinjection pressure and amount.