# Presentation: 884830

## DUSEL Experiment Development and Coordination (DEDC)Internal Design ReviewJuly 16-18, 2008Steve Elliott, Derek Elsworth, Daniela Leitner, Larry Murdoch, Tullis C. Onstott and Hank Sobel

## Deep and Ultra-deep Underground Observatory for In Situ Stress, Fluids, and Life

- Working Group Leaders:
- Herb Wang, U. of Wisconsin-Madison, rock mechanics and geohydrology
- David Boutt, University of Massachusetts, geohydrology
- Tom Kieft, New Mexico Institute of Mining and Technology, geomicrobiology
- and a cast of dozens.

## Compelling Research Questions Connecting Geomechanics, Geohydrology, and Geomicrobiology

- Do geomechanical and hydrologic factors control the distribution of life as a function of depth and temperature?
- What patterns in microbial diversity, microbial activity and nutrients are found along this gradient?
- How do state variables (stress, strain, temperature, and pore pressure) and constitutive properties (permeability, porosity, modulus, etc.) vary with scale (space, depth, time) in a large 4D heterogeneous system: core – borehole - drift - whole mine - regional?

**How deeply does life extend into the Earth?**

## Proposed Experiments 

**Ultra-deep Drilling**
- What factors control the distribution of life as a function of depth and temperature?
- What are the patterns in microbial diversity, microbial activity and nutrients along this gradient?
**Scale Effects Experiment (SEE)**
- How are stress state and strength related to geologic heterogeneity, fracture geometry, the presence and flow of fluids, and rock anisotropy?
- How do the fracture network, stress state, and constitutive properties of crystalline rocks affect the stability of tunnels, shafts, wellbores, and large, room-sized excavations?
**Dark Flow**
- How are porosity and permeability maintained with depth?
- What types of fracture networks conduct fluids?
- What are the properties of these networks and how can they be characterized?
- Do patterns of microbial diversity reflect hydrologic connectivity (e.g. can microorganisms be used as a new type of particulate tracer)?
**4-D Hydromechanical Simulator**
- To synthesize observations for site selection of cavern construction, borehole locations, and bioaugmentation/biostimulation experiments.

## Conceptual diagram of deep drilling showing the geothermal gradient

## Conceptual diagram of fiber-optic displacement sensor network

- Distributed Strain and Temperature (DST) measurements can be made over kilometers of distance in the mine.  However, development work must be done to establish clamping techniques to the rock mass and compared with fiber-optic displacement sensors, such as those shown in the figures.

## An Overarching Hypothesis:  Fluid flow in a rock mass can be predicted if both the stress field and the fracture network are characterized at a range of spatial scales.

- Is crust at Homestake critically stressed as at sites in other stable, intraplate areas?
- Do critically-stressed fractures dominate fluid flow?
- How have mining excavations altered the stress field and hydrology?

- How does stress state affect stability of tunnels, shafts, wellbores, and large, room-sized excavations?
*Do the stress and flow environment determine microbial identity, activity, and diversity?*

## Deformation and Fluid-flow can be measured simultaneously as functions of scale

- A 3-D network of extensometers consisting of Distributed Strain and Temperature (DST) chords can monitor large (km-scale)

- Over half the flow comes from just 3 of the 40 intervals and 62% of intervals carried no flow, similar to Stripa where a single sheet of 375 sheets captured 10% of water, 12 captured another 50%, and 2/3 carried no flow

## Expected Microbiology Results  (Hypotheses): 

- Temperature is the primary factor controlling the depth limit of the biosphere.
- Chemoautotrophy increases relative to heterotrophy with depth.
- Diversity declines, but phylogenetic novelty increases with depth.
- Transfer of genetic elements is limited by low cell abundance and low nutrient concentrations.
- Population sizes and/or the low rates of genetic recombination impose more rapid rates of protein evolution, resulting from inability to purge mildly deleterious mutations, as predicted by Neutral Theory and empirical data from surface ecosystems.
- Energy and/or nutrient limitation select for high affinity uptake strategies coupled with motility and chemotaxis or long-term quiescence, maintenance, and passive dispersion strategies.

## Expected Geomechanics and Geohydrology Results

- Observational data sets
- horizontal-to-vertical stress ratio as a function of depth
- rock-mass permeability as a function of depth; occurrences of high-permeability fractures that are typically isolated from the overall low flux through the rock.
- depth and age of fluids which have been isolated in fractures
- Develop predictive capability for 4D rock-mass response to loading over multiple spatial and time scales
- Understand interconnectedness among
- fluid flow
- stress state
- identity, diversity, and activity of microbial life
- Improve understanding of microseismicity, geophysical characterization of rock mass, and large-cavern construction

## Facilities

- Access to one or more boreholes drilled at intermediate depth Access to the 8000L and extensive infrastructure, including electricity, communication, air cooling, and ventilation.
- One or more drill sites with 6-12 m ceiling height and _>_100 m2 area.  Adjacent area for Mobile Underground Laboratory for Experiments (MULE) and other equipment.
- If water from the purification system for a water Cerenkov detector is to be used, then plumbing will have to be provided.  The distance could be 1-2 km.
- Sample processing capabilities at the mid-level campus and/or surface labs.  This will include freezers for storing biological samples.

## Risk Identification

- Most risks are associated with the ultradeep drilling.  Potential problems that could affect successful outcome are the following:
- The 8000 level at Homestake is never dewatered or developed for extended scientific use.
- The deep borehole is unable to produce sufficient water.
- The 2.4 to 5-m depth interval has been geochemically and microbiologically contaminated by mining, drilling/coring, or sampling activities, including the original dewatering and subsequent flooding of the mine.
- The borehole “flashes”, i.e, pressurized water is encountered, releasing hot water and steam.
- Dangerous gases are encountered, e.g., H2S, CH4, H2, CO.
- Drilling problems or even failures occur.
- Drilling/coring activities at the 8000 level negatively affect the physics experiments at the 7400 level.

## E&O

- Opportunity for students and public to experience and understand the deep earth environment where they can be in contact with the crushing weight of thousands of feet of overlying rock and the microbial life it contains, the geothermal gradient, and deep underground fluid flow.
- Partnerships between university, industry, and national laboratory researchers.
- Site research experiences for undergraduates (REUs), embed teachers (RETs) for curriuculum development, and target local Native American STEM students. Example activities:
- Investigate on-line dewatering and climatological data.  Monitor stream flow, e.g., False Creek, USGS borehole pressures, surface GPS measurements
- Create “Hydrologic Science Investigations” (HSI)
- Real and virtual underground tours, LIDAR, etc.  and real-time data stream for classroom and visitor center use.
- DUSEL-Homestake Visitor Center displays

## Schedule

- Oct 2008 Submit S-4 proposal
- Jan 2009 Begin S-4 project.
- Apr 2009 Disciplinary workshops and meetings to make critical decisions about drilling/coring technology and to select and schedule geomechanical, geohydrological, geochemical, and biological technologies.
- Jul 2009 Capstone deep-drilling workshop.
- Dec 2009 Submit Preliminary Design Report
- 2008-2012 Testing drilling technologies, downhole instrumentation, fiber-optic sensor network, and biological characterization methods. PIs will be encouraged to support these activities with funding from various sources, e.g, NSF SGER grants, panel-reviewed NSF grants, and grants from other agencies.
- 2012 Drill pilot hole for initial characterization of the 2.4 to 5-km depth
- interval.
- 2013 Drill and core first full-bore borehole.  Deploy km-scale deformation and hydrologic variable monitoring network.
- 2014 Drill and core second full-bore borehole.
- 2015 Drill and core third full-bore borehole.