A Novel Hybrid Wireline Logging System for Downhole Monitoring of Fluid Injection and Production in Deep Reservoirs

During both geological storage of CO2 and extraction of geothermal heat, fluids are injected in and produced from the subsurface. Classic production logging (PL) includes downhole measurement of pressure, temperature, and fluid velocities, e.g. with a spinner flow meter, to estimate flow rates and phase composition within a flowing well. But during production of geothermal fluids, usually larger flow rates than in standard oil and gas wells are necessary. Physical and chemical properties of CO2 lead to a different flow behavior, as well as possible fluid-rock interactions and corrosion of the borehole completion. The method of fiber-optic distributed temperature sensing (DTS) enables instantaneous registration of continuous temperature profiles over distances of 20 kilometers and longer with high temporal resolution. Here we present the design and first field test of a new hybrid wireline logging system, which combines both classic electric wireline logging tools for PL and depth correlation, as well as optical fibers included in the logging cable for acquisition of DTS temperature profiles. The DTS data was calibrated using the wireline temperature data measured under static conditions. Sufficient temperature resolution for detection of small-scale changes during dynamic flow processes can be achieved.