Heat Extraction from Fractured Hydrothermal Reservoirs

Abstract

Initial results are available from the experiment to calibrate the heat extraction history of a physically simulated fractured hydrothermal reservoir using a rock loading of large, shaped granite blocks. Thermocouples embedded in a set of the rock blocks and in water at various locations in the model provide heat extraction data. The data are also used to evaluate the effects of thermal stress in g on heat transfer properties. A finite element heat transfer computer model has been developed to assist in the analysis of these experiments. The results of the first experiment a surprisingly unif cross-sectional water temperature throughout the physical model indicating effective cross mixing between fracture channels. The temp e r ature difference between rock centers and surrounding fluid reached during the cooling process, decreasing to smaller values by the end of the experiment, indicating that the rock energy extraction was relatively complete, with a high, constant temperature of the produced water. Additional experiments are planned with increased rates of cold water injection to result in heatt ransfer-limited reservoir conditions, and to extend the magnitude of thermal stress.