Hydraulic Well Stimulation in Low-Temperature Geothermal Areas for Direct Use

Abstract

Direct use of hot water through renewable energy resources is globally in demand. Thermal energy stored in fractures and pores within geothermal reservoirs contains natural fluids. At times, extracting natural fluids, or hot water in low-temperature areas, can be a challenge. Hydraulic stimulation is one technique to overcome this challenge. A review of hydraulic stimulation methods is provided based on fluid treatment and well testing in order to see unique trends for low-temperature geothermal applications. In order to predict the effects of hydraulic stimulation before an actual operation, a case study was performed on well HF-1 in Hoffell, Iceland. First, a preliminary lumped parameter model (LPM) was performed using the updated data from completion of testing in 2014. After evaluating the need for stimulation, a fracture model using MFrac software was done in two scenarios with an open-hole packer - injection below the packer and injection above the packer. The packer was placed in a conservative interval of 1070-1110 m depth to isolate the main fracture at 1093 m depth. Injection below the packer failed, therefore results from injection above the packer were only suitable moving forward. Subsequently, MProd software was used to find a production improvement ratio after simulating stimulation above the packer. The improvement ratio of 1.096 was then applied to the original production data of well HF-1 and a LPM was performed yet again. Reservoir properties of storativity (S), transmissivity (T), injectivity index (II), and productivity index (PI) were calculated and compared to original production data. Results indicated the lumpfit model to be very optimistic for the two-tank open scenario and improvement of only 4 l/s flow over a 10 year well lifetime was observed. Therefore, the well is not a good candidate for stimulation. However, the presence of an improvement ratio proves the potential for this methodology to be implemented in other low-temperature geothermal areas.