Deep Earth Observatory and Laboratory for Life, Fluid Flow and Rock Processes

T. C. Onstott, Princeton U.

H. F. Wang, U. of Wisconsin-Madison

Geoscience Executive Summary for Working Groupson Geobiology, Geochemistry, Geohydrology, Geomechanics,and Geophysics

Executive Summary

• Theme: Coupled Processes in the Earth at Depth• Life at Depth• Fluid Flow and Transport at Depth• Rock Deformation at Depth• Potential for Scientific and Engineering Innovation • Education and Outreach

Executive Summary for Geobiology/Geochemistry/Geology

Kesler, Phelps,Valley, Sherwood-Lollar, Slater, Bang, Ruiz, Duke, Ridley, Campbell and Onstott

Evolution of Geochemical, Hydrological and BiologicalInterfaces in Heterogeneous Environment over Geological Time

USGS Bull. 1857-J (1991)

Time2.0 b.y. Today

Dep

th

PHOTIC-RHIZO ZONE

THERMO BIOZONE

120oC

HYDROTHERMAL ZONE

Process and Interface Evolution

• Characterization– Hydrothermal and Deformation History – Fracture formation, low temperature geochemical alteration and

biofossilization.– Present hydrogeological system and microbial biozones.– Inferred rates of evolution.

• Experimentaion– Rates - fluid mixing and mass transport– Rates microbial and nonmicrobial activity – Rates of subsurface microbial evolution in changing environment

Infrastructure (surface and subsurface labs)

• Clean lab/uncompromised sample repository

• Unique Experimental facilities

• Long term instrumentation of borehole arrays for experiments

• New scientific drilling

Courtesy: URL at Atomic Energy of Canada Ltd

Proposed New Approach:

Develop a US laboratory and observatory underground,inside the earth.

Much like surgery permits a physician to examine internal bones and organs recognized on X-rays or CAT scans, NUSL will be a fully instrumented, dedicated laboratory and observatory for scientists to examine Earth’s interior.

US has not had a basic science underground lab to study geologic processes

Coupled Processes in the Earth at Depth

NUSL offers unique opportunity to study complex geologic processes in situ with 3-D access for continuous observations and controlled experiments in an exceptionally large volume and great depth.

USGS Bull. 1857-J (1991)

Fluid Flow and Transport

Characterization of active flow system• Characterization of fracture network• Verification of well and tracer test

models• Recharge to deep groundwater system• Colloidal and bacterial transport• Paleohydrology

Rationale: fluid flow influences resource recovery, water supply, contaminant transport and remediation

How do we upscale point (space,time) measurements in a complex geologic system

to larger regional processes?

Whole earth - 107 m

Regional scale – 106 m

Whole mine experiments - 104 m

Stope, cavity scale - 102 m

Tunnel, shaft scale - 101

Borehole, “laboratory” scale - 10-1 m

Grain, sub-lab scale - 10-3 m

Permeability vs. Scale

(a) Sampling arrangement in the Stripa 3-D experiment showing placement of plastic sheets for tracer collection.

(b) Tracer distribution in the test site. Arrows indicate positions of injection holes,solid circles indicate sheet with significant water flow, and rectangles indicate sheets where tracers were collected.

[adapted from Abelin et al., 1987]

Fractures are Key to Many Processes

• Fluid Flow• Rock Strength• Heat Flow• Chemical Transport• Ore Formation• Faults & Earthquakes• Biosphere for deep life

to colonize and pathways for nutrient transport. Mauna Loa fissure eruption, D.A. Clague

Understanding Fractures

• What is their 3-D geometry and evolution?• What processes formed fractures?• What are their fluid and mass transport

properties?• How do fractures influence occurrence and

type of microbial life? • How do they govern microbial remediation

methods?• Can we understand empirically observed

scaling effects?• Can we improve geophysical imaging of

fractures?

While fractures are discontinuities, understanding their role in geologic processes is a unifying theme.

State of Stress: How do point measurements relate to regional and global stress picture?

• Is crust at NUSL critically stressed as at sites in other stable, intraplate areas?

• Do critically-stressed faults dominate fluid flow?

• How does stress state affect stability of tunnels, shafts, wellbores, and large, room-sized excavations?

Permeable Fractures and Faults are Critically Stressed

•Permeable faults/fractures are critically-stressed•High permeability maintains hydrostatic pore pressure•Hydrostatic pore pressure results in high crustal strength

Hypothesis Linking Stress State toPermeability to Crustal Strength.

Local Stress Distribution Critical to Rock Engineering

INSTRUMENTATION and MINE MEASUREMENTS of DISPLACEMENTS are ESSENTIAL

Solid- & Fluid-Environment Interaction

– Models of Fracture Development– Coupled Processes

THM CB THMCB

Time (h)

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800C 1200C

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Coupled Thermal-Hydrologic-Mechanical-Chemical-Biological Experiment Opportunities

• Imperatives– Strong scale dependence– THMCB processes incompletely understood– The role of serendipity in scientific advance

• Approach– Run-of-Mine Experiments (HCB)– Experiments Concurrent with Excavation of

the Detector Caverns (THM)– Purpose-Built Experiments (THMCB)

Large Block Tests Mine-By and Drift Structure

Tests Geophysical Monitoring

– Educational Opportunities

Potential for Scientific and Engineering Innovation

• New genetic materials and applications• Analytical technique for geomicrobiology• Natural resource recovery• Drilling and excavation technology• Novel uses of underground space• Mine safety• Subsurface imaging• Environmental remediation

Closing Perspectives

Geoscience discoveries have depended historically on new exposures of subsurface through civil works, e.g., William Smith’s The Map that Changed the World.

Educational and outreach benefits include providing experiential appreciation of earth’s interior.