Application of distributed fibre-optic sensing to geothermal reservoir characterization and monitoring
Geothermal reservoirs offer unique characterization challenges due to the harsh environment that downhole tools are subject to and the discrete and spatially discontinuous hydrothermal features that make up the reservoir. Enhanced Geothermal Systems (EGS) offer great potential for dramatically expanding the use of geothermal energy by allowing development of traditionally inaccessible thermal resources; thus, offering the possibility to significantly reduce carbon emissions to combat anthropogenically induced climate change. However, EGS development offers an additional set of challenges as reservoir engineers have the burden of not only characterizing the existing reservoir, but to dynamically guide reservoir enhancement in heterogeneous media with a fine degree of resolution and accuracy. Developing EGS resources will require highly advanced and novel characterization and monitoring methods and technologies. Geophysical data can provide some of the most spatially extensive information about the subsurface and has a long and successful exploration role in the oil and gas industry. Continuous monitoring of the subsurface is of great importance especially in operations where the permeability is enhanced during hydro-shearing (expanding existing fractures) and hydraulic tensile fracturing (to create new fractures). Optimization of enhancement processes can be achieved through localization of the geologic structures (e.g. fracture zones), seismic monitoring during stimulation, and characterizing the resultant hydraulic connectivity between injection and production wells. Seismic methods, which utilize elastic waves provide incredibly detailed images of geologic formations and structures play an important role in monitoring changes in the subsurface. Time-lapse (4D) seismic imaging techniques have become commonplace for monitoring the movement of fluids in oil and gas reservoirs and carbon sequestration. They have also been applied to geothermal reservoir characterization. Detection and localization of microseismic events during reservoir stimulation can provide an indication of fracture development to guide stimulation efforts.