Estimating the heat transfer in fractured geothermal reservoirs

Geothermal systems in fractured rock are a promising energy resource due to the increased temperatures at depth. To enable wide-spread implementation of such systems, modeling tools that are faster and require less input data than discrete fracture network models, yet cover site-specific characteristics, are needed. Heat flow in fractures poses a challenge for the physical/numerical description due to the small water volumes flowing through the fractures. A novel heat transfer model was developed to assess the feasibility of fractured reservoirs for geothermal heat extraction and seasonal storage. The model is based on an innovative approach to determine the heat transferred between rock and flowing fluid in a fractured reservoir considering fracture spacing, fracture aperture, and production/injection rate as main model parameters. Such parameters are often available through borehole logging of a prospective well or outcrop data. The model is compared to laboratory tests, analytical solutions, field data, and complex numerical models proving its suitability and flexibility. The model was successfully demonstrated on hot dry rock and hydrothermal systems, as well as seasonal aquifer thermal energy storage. This makes it an ideal tool for feasibility studies based on early prospection results, minimizing economic risks, and studying possible operational procedures.