Analysis of Reinjection Tests in a Bedrock Geothermal Reservoir, Tianjin, China

Abstract

By the end of 2008 there were about 245 production wells and 12 reinjection wells operating in Tianjin. The annual production rate is 25 million m3 and the reinjection rate is 4.2 million m3. Reinjection is expected to gradually cool the reservoir and so it is important to carefully design and manage the well fields and this involves estimating the thermal breakthrough time for different well separation distances. This paper describes the 2-D mass and heat transfer in the heterogeneous fractured rocks. Equations that arise for each grid block were linearised and anumerical model of the geothermal system was developed with TOUGH2. This model was then used to analyse the reservoir pressures and temperatures with special emphasis on simulating break-through of cooling at the production well. The tracer test is shown to be important for improving our understanding of the tracer and heat transport processes and reservoir (channel/fractured/karst) porosity, and for enabling the estimation of future reservoir cooling caused by fluid reinjection.