This project will develop a preliminary design and work-breakdown-structure for a large-scale subsurface experimental facility to investigate coupled thermal-hydrological-mechanical-chemical-biological processes in fractured rock at depth. The experiment will be part of the proposed Deep Underground Science and Engineering Laboratory (DUSEL) in the Homestake Mine, South Dakota. Many natural and engineered earth systems involve coupling of multiple processes in rocks that vary across a wide range of scales. The most pervasive process in the Earth?s crust that gives rise to strongly coupled phenomena is the flow of fluids (water, CO2, hydrocarbons, magmas) through fractured heated rock under stress. Understanding changes in the reactivity, deformability, life-supporting and transport properties of rocks that fluids infiltrate is important in a broad range of geological engineering and geological science endeavors. Despite this fundamental importance, the interactions remain poorly understood.
The project will: (1) Determine properties of Homestake rocks: geological, geochemical, mechanical, thermal, isotopic, and reactivity. (2) Upscale these data to elucidate transport mechanisms (conductive versus convective), natural reaction rates in fractures, and microbial community evolution. (3) Evaluate monitoring strategies, in-situ probes and sampling methods, and necessary measurements. (4) Select a candidate site for the evaluating coupled processes. (5) Develop a work-breakdown-structure. (6) Develop a coupled numerical model to evaluate potential effects on the rock mass and optimal heater configuration, power, and monitoring borehole orientations.
The models and insight from these experiments will have broad applicability to engineered systems, e.g., enhanced geothermal systems, CO2 sequestration and subsurface contaminant transport. Educational outreach will involve facility tours and a traveling benchscale ?mock-up? demonstration experiment.
This work has focused on developing a preliminary design for a large-scale subsurface experimental facility to investigate coupled Thermal-Hydrological-Mechanical-Chemical-Biological (THMCB) processes in fractured rock at depth. The experiment was to have been part of the proposed Deep Underground Science and Engineering Laboratory (DUSEL) at Homestake, South Dakota. Large-scale underground THMCB experiments have never been attempted under deep in-situ stresses, nor with the goal of understanding natural crustal processes at relevant scales. We were examining the feasibility of such a THMCB experimental facility at DUSEL to study the evolution of reactivity, deformation, biological, and transport properties at intermediate length-scales (~1-10 m) where current data are meager. These experiments were to be designed to (1) evaluate scaling in transport and reaction at intermediate length scales; and (2) define the role of reactive fluids in generating or occluding flow pathways, including the roles of chemical potential, effective stress, and temperature. The proposed activities focused on the experiment’s feasibility and to propose methods for its conduct. Specifically: (1) Determine properties of Homestake rocks: geological, geochemical, mechanical, thermal, isotopic, and reactivity. (2) Upscale these data to elucidate transport mechanisms (conductive versus convective), natural reaction rates in fractures, and microbial community evolution. (3) Evaluate monitoring strategies, in-situ probes and sampling methods, and necessary measurements. (4) Select a candidate site for the THMCB experiment. (5) Develop a work breakdown schedule (WBS). (6) Develop coupled THMCB numerical models to evaluate potential effects on the rock mass and optimal heater configuration, power, and monitoring borehole orientations. However, the future of Earth science and engineering activities at DUSEL-Homestake/SURF developed an uncertain trajectory during this study - and the likelhood of being able to conduct an experment in the nascent underground laboratory at DUSEL-Homestake became unlikely. Absent this receptor site, we explored potential experiments in alternate underground research laboratories. These experiments included examining the role of dynamic stressing on permeability and the potential to conduct in situ experiments on hydraulic fracturing and on the rupture of sorbing media.
