| Title | Implications of hydrothermal flow-through experiments on deep geothermal energy utilization |
|---|---|
| Authors | Kong, X-Z; Leal, A M M; Saar, M O |
| Year | 2016 |
| Conference | European Geothermal Congress |
| Keywords | Geothermal, Reactive transport, Fluidrock reaction, Reactive surface area, Dissolution |
| Abstract | Utilization of underground reservoirs for geothermal energy extraction, particularly using CO2 as a working fluid, requires an in-depth understanding of fluid, solute (e.g., dissolved CO2 and minerals), and energy (heat, pressure) transport through geologic formations. Such operations necessarily perturb the chemical, thermal, and/or pressure equilibrium between native fluids and rock minerals, potentially causing mineral dissolution and/or precipitation reactions with often immense consequences for fluid, solute, and energy transport, injectivity, and/or withdrawal in/from such reservoirs. The involved physico-chemico-thermomechanical processes often lead to modifications of permeability, one of the most variable and important parameters in terms of reservoir fluid flow and related advective solute/reactant and heat transport. Importantly, the amount of mineral dissolution/precipitation that can cause orders of magnitude in permeability reduction can be very small, if minerals are removed or deposited in pore throats or narrow fracture apertures. This potentially has detrimental consequences for geothermal energy usage. However, analysing, understanding, and predicting reservoir evolution and flow properties are non-trivial, as they depend on complex chemical, thermodynamic, and fluid-dynamic feedback mechanisms. To achieve these goals, it requires the integration and extrapolation of thermodynamic, kinetic, and hydrologic data from many disparate sources. The validity, consistency, and accuracy of these datamodel combinations are unfortunately often incomparable due to the relative scarcity of appropriate parameterizations in the literature. Here, we present some results of hydrothermal flow-through experiments on rock core samples. During the experiments, we fixed the flow rates, confinement and outlet pore-fluid pressures, and recorded inlet porefluid pressure. We also analysed the outlet fluid chemistry samples throughout the experiments and imaged our rock cores before and after the flowthrough experiments using X-Ray Computed Tomography (XRCT). With all these data, we are able to interpret the changes in permeability, porosity, and (reactive) surface area at the core scale. |