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.
Award Amount: 66,247 36 Months. Starting date: 07/01/09 Nuri Uzunlar 605-394-2494 nuri.uzunlar@sdsmt.edu Project Team: Derek Elsworth and Chris Marone, Pennsylvania State University Bob Lowell Virginia Tech Kate Maher Stanford University Brian Mailloux, Barnard College Eric Sonnenthal PI, UC Berkeley Nuri Uzunlar (SDSM&T The purpose of the DUSEL THMCB experiment is to investigate a range of natural and engineered processes by creating a volume of heated rock and fluid which will be instrumented with sensors (mechanical, thermal, chemical) and ports for collecting fluid samples as a function of space, time, and temperature. It is expected that boreholes will be sited that traverse different regions of the heated rock, which are packed off to isolate a particular fracture or fracture set, into which fluids, gases, or even nutrients (e.g., acetate or lactate) can be injected to perturb the local T, H, M, C and B environment. Monitoring ports will be sited along the same fracture that can be used to set up directed flow along the fracture and the fluids extracted for analyses. In addition to geochemical and isotopic (stable and radiogenic) analyses on sampled fluids, gases and solids, state-of-the-art in-situ sampling and monitoring sensors will be employed. Funding provided by NSF was to select a site withinn the mine to implement this experiment. Past thre years number of workshops, meeting and underground visits took place to accomplish this. As one of the PI's of the project in charge of geology of the site I spent number of days underground mapping geology and structure of several key areas which led to a site selection 4850 level of Homestake mine. Scientific Basis for the project: Most natural and engineered earth system processes involve strong coupling of thermal, mechanical, chemical, and sometimes biological processes in rocks that are heterogeneous at a wide range of spatial scales. One of the most pervasive processes in the Earth’s crust is that of fluids (primarily water, but also CO2, hydrocarbons, volcanic gases, etc.) flowing through fractured heated rock under stress. A preliminary design is being formulated for a large-scale subsurface experimental facility to investigate coupled Thermal-Hydrological-Mechanical-Chemical-Biological (THMCB) processes in fractured rock at depth. The experiment would be part of the proposed Deep Underground Science and Engineering Laboratory (DUSEL) in the Homestake Mine, South Dakota. Fundamental geochemical, isotopic, microbiological, laboratory THMC experiments, and numerical modeling will be used to guide the experimental design and evaluation of the time and spatial scales of the coupled THMCB processes. Although we sometimes analyze rocks and fluids for physical and chemical properties, it is difficult to create quantitative numerical models based on fundamental physics and chemistry that can capture the dynamic changes that have occurred or may yet take place. Initial conditions and history are only known roughly at best, and the boundary conditions have likely varied over time as well. Processes such as multicomponent chemical and thermal diffusion, multiphase flow, advection, and thermal expansion/contraction, are taking place simultaneously in rocks that are structurally and chemically complex—heterogeneous assemblages of mineral grains, pores, and fractures—and visually opaque. The only way to fully understand such processes is to carry out well-controlled experiments at a range of scales (grain/pore-scale to decimeter-scale) that can be interrogated and modeled. The THMCB experimental facility is also intended to be a unique laboratory for testing hypotheses regarding effects of heat and chemical reactions on microbial communities. Will microbial communities and gene assemblages evolve rapidly in response to changes in heat-flow and stimulate changes in subsurface geochemistry? Does hydrothermal circulation alter the availability of nutrients, trace metals, and H2 and control observed microbial responses? In this talk we will discuss some of the scientific questions that may be addressed in such an experiment, potential experimental designs, and fundamental scientific studies being performed to aid in the experimental design. Summary of Outcomes of the Project: During early years of the project geologic and structural investigation of various location within the accessible levels of the mine were examined. Geologic and structural investigation have successfully outlined an area at 4850 level of Homestake mine where described experiment could be carried out. As a result of geologic investigation a geologic map of the area was produced and will be included in the final report.
