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American Geophysical UnionOS52B-04, 19 December 2014San Francisco, CA
A Cross-hole, Multi-year Tracer Injection Experiment in the Volcanic Ocean Crust
A. T. Fisher1, N. Neira2, C. G. Wheat3, J. Clark2, D. Winslow1, K. Becker4, C.-C. Hsieh5, M. Rappé5
1Earth and Planetary Sciences Department and Center for Dark Energy Biosphere Investigations University of California, Santa Cruz2University of California, Santa Barbara3University of Mississippi4University of Miami, RSMAS5University of Hawaii
modified from Fisher and Wheat (2010)
The upper oceanic crust is a hydro-thermo-chemo-bio reactor
The Hydrogeologic Architecture of Basaltic Oceanic Crust: Hydrogeology, Geochemistry, Microbiology
Focus on active ridge-flank processes to resolve:
• Magnitude and nature (distribution, extent of channeling) of permeability in crustal fluid-rock systems, variations, scaling (temporal, spatial)
• Magnitudes and directions of driving forces, fluid fluxes, flow channeling, and associated solute, heat, and microbial transport and storage
• Relations between fluid flow, compartmentalization, microbiological communities, seismic properties, alteration, and structure
• Nature of distinct fluid reservoirs, fluid residence times and velocities, response to transient perturbations
Scientific Ocean Drilling Experiments
modified from Fisher et al. (2011a)
IODP Expeditions 301 (2004) and 327 (2010), ROV/HOV expeditions (2004-14)
Subseafloor borehole observatories (CORKs)
• Seal reentry hole to prevent hydrologic contamination, allow return to pre-drilling P/T/Chemistry/MBIO conditions
• Allow access to the subseafloor environment over long times, without drillship
• Permit passive monitoring, facilitate active testing
• Isolate multiple depth intervals
Sounds like a lot of work... It is! But it’s worth the effort…
Hu
ndr
ed
s o
f met
ers
modified from Fisher et al. (2011b)
Setting up a Cross-hole Experiment
• New CORKs installed in Holes 1026B, 1301A/B during IODP Expedition 301 (2004)
• New CORKs installed in Holes 1362A/B during IODP Expedition 327 (2010)
• CORK in Hole 1027C rehabilitated with on AT18-07 (2011)
P
P
Basement relief
modified from Fisher et al. (2011a)
• Tracer injected 2010
• Monitor seafloor (2010-14)
• Monitor downhole (2010-14)
Tracer:• Sulfur Hexafluoride (SF6)
• Injected ~23 M in 24 hr
• Injectate [SF6] ~ 48 µM
• Detection limit ~ 1 pM (dilution factor = 5 x 107)
Fisher et al. (2011b)
First controlled measurement of water, solute velocity!
Setting up a Cross-hole Experiment
Inferred flow direction: N20E, based on geochem, heat flow, modeling
Tracer testing concepts
modified from Fisher et al. (2011b)
Tracer Test Configuration and Operations
Hole 1362BOne depth intervalInjection (2010)Wellhead OS (2011, 13, 14)Downhole OS (2014)Free flow ≥2011
100
0 m
Hole 1301A
Hole 1362A
Hole 1026B
Tracer Test Configuration and Operations
Hole 1362B
100
0 m
Hole 1362A
Hole 1026B
Hole 1301AOne depth intervalWellhead OS (2010, 11, 13, 14)Discharging CORK!
Tracer Test Configuration and Operations
Hole 1362B
100
0 m
Hole 1362ATwo depth intervalsWellhead OS (2011, 13, 14)Downhole OS (2014)
Hole 1026B
Hole 1301A
Tracer Test Configuration and Operations
Hole 1362B
100
0 m
Hole 1362A
Hole 1026B
Hole 1301A
One depth intervalWellhead OS (2010-11,13,14)Downhole OS (2014)
Tracer Recovery: Hole 1301A
Hole 1301A(discharging)
Hole 1362B
Hole 1362A
Hole 1026B
1000
m
modified from Neira (2014)
Expedition delayed (2012)
Tracer Recovery: Hole 1301A
modified from Neira (2014)
Expedition delayed (2012)
SF6 peak arrival~1 m/day
Long plume tail, low [SF6]…
Tracer Recovery: Hole 1362B
modified from Neira (2014)
Hole 1301A(discharging)
Hole 1362B
Hole 1362A
Hole 1026B
1000
mRaw
Corrected
Flowmeter attached,
Valve opened, Wellhead sampler deployed
Expedition delayed (2012)
Tracer Recovery: Hole 1362A
modified from Neira (2014)
Hole 1301A
Hole 1362B
Hole 1362A
Hole 1026B
1000
m
Valve opened
(1362B), Wellhead sampler deployed
Expedition delayed (2012)
Tracer Recovery: Hole 1026B
modified from Neira (2014)
Hole 1301A
Hole 1362B
Hole 1362A
Hole 1026B
1000
m
2010-13Wellhead
Tracer Recovery: Hole 1026B
modified from Neira (2014)
2010-13Wellhead
Tracer Recovery: Hole 1026B
modified from Neira (2014)
Hole 1301A
Hole 1362B
Hole 1362A
Hole 1026B
1000
m
2010-13Wellhead
SF6 peak arrival≥1 m/day
The first three-dimensional, coupled fluid-heat flow ridge-flank hydrothermal models
• Field data guide model design, constrain results (hydrogeological, thermal, chemical)
• Small outcrop vents 5-20 kg/s, 1-2 MW power
• No regional mining of crustal heat
• Basement fluids at 65°C, highly altered
modified from Winslow and Fisher (2014)
The first three-dimensional, coupled fluid-heat flow ridge-flank hydrothermal models
Mixed convection and a hydrothermal siphon between outcrops…
modified from Winslow and Fisher (2014)
tThe first three-dimensional, coupled fluid-heat flow ridge-flank hydrothermal models
Mixed convection and a hydrothermal siphon between outcrops…
modified from Winslow and Fisher (2014)
Specific discharge x 10-8 (m/s)0 0.4 0.8 1.2 1.6
Cou
nt
2,000
6,000
10,000
14,000
0.13 0.26 0.38Specific discharge (m/yr)
Flow rates in the upper ocean crust, between outcrops, are about
0.2 m/yr
What do different flow rates imply?
• Tracer tests: vL ~350 m/yr
• Thermal data/models: q ~0.2 m/yr
• Effective porosity (fraction of rock with flowing fluid):
ne = q/vL = (0.2)/350 ~ 0.0005 (0.05%)
• Implications: very heterogeneous flow system, low specific surface
area available for reaction, most pores are dead ends, etc.
Moreno and Tsang, 1994Tsang et al., 1991
What do different flow rates imply?
• Tracer tests: vL ~350 m/yr
• Thermal data/models: q ~0.2 m/yr
• Effective porosity (fraction of rock with flowing fluid):
ne = q/vL = (0.2)/350 ~ 0.0005 (0.05%)
• Implications: very heterogeneous flow system, low specific surface
area available for reaction, most pores are dead ends, etc.
What do different flow rates imply?
• Tracer tests: vL ~350 m/yr
• Thermal data/models: q ~0.2 m/yr
• Effective porosity (fraction of rock with flowing fluid):
ne = q/vL = (0.2)/350 ~ 0.0005 (0.05%)
• Implications: very heterogeneous flow system, low specific surface
area available for reaction, most pores are dead ends, etc.
What do different flow rates imply?
• Tracer tests: vL ~350 m/yr
• Thermal data/models: q ~0.2 m/yr
• Effective porosity (fraction of rock with flowing fluid):
ne = q/vL = (0.2)/350 ~ 0.0005 (0.05%)
• Implications: very heterogeneous flow system, low specific surface
area available for reaction, most pores are dead ends, etc.
Preliminary Interpretations
• We can run tracer injection tests in the ocean crust!
• Dominant flow direction is N20E, as hypothesized.
• Dissolved gas tracer transport rate is ~1 m/day.
• Effective porosity for tracer transport is small <<1%.
• Upper crustal aquifer is highly heterogeneous
“most of the aquifer is not an aquifer”
Preliminary Interpretations
• More data and interpretations from 1000s of samples recovered
(wellhead/downhole) in Summer 2014, ongoing/new modeling, links to
microbiological analyses…
• Data to be analyzed from cross-hole pressure and temperature
response, independent estimates of formation permeability…
• We can run tracer injection tests in the ocean crust!
• Dominant flow direction is N20E, as hypothesized.
• Dissolved gas tracer transport rate is ~1 m/day.
• Effective porosity for tracer transport is small <<1%.
• Upper crustal aquifer is highly heterogeneous
“most of the aquifer is not an aquifer”
Acknowledgements
J. Cowen, E. Davis, K. Edwards, C. Gable, S. Hulme, G. Iturrino, M. Hutnak, W. Kirkwood, T. Pettigrew, V. Spiess, P. Stauffer, T. Tsuji, T. Urabe, H. Villinger, L. Zühlsdorff, and many others…
Collaboration, advice, encouragement:
Funding, leadership, trust:Planning, field support:
IOs for ODP and IODP, crews and technicians of: J. Resolution, Atlantis, Thompson, Alvin, Jason, ROPOS…
Thank you!
Questions?
modified from Fisher (2005)
Thank you!