U'S' Department of the Interior

1
Title
Probable Production Induced Subsidence, Fault
Reactivation, and Wetland Loss in the Gulf Coast
Region
R. Morton, N. Buster, D. Krohn, and R. Peterson
U.S. Geological Survey
Center for
Coastal and Watershed Studies
St. Petersburg, FL 33701
http//coastal.er.usgs.gov/gc-subsidence/
U.S. Department of the Interior U.S. Geological
Survey
2
SCIENTIFIC OBJECTIVES

• Investigate timing of subsidence and faulting
• Compare geological and historical rates of
  subsidence
• Evaluate geological and engineering factors that
  may influence induced subsidence and faulting

3
Objectives continued

• Examine mechanisms of subsidence and faulting
• Evaluate methods of regional subsidence detection
  and monitoring
• Develop predictive capabilities
  (subsidence susceptibility)

4
ENVIRONMENTAL APPLICATIONS

• Evaluate potential contributions to historical
  wetland losses
• Incorporate into resource management and coastal
  restoration plans
• Evaluate methods of subsidence mitigation

5
EVIDENCE OF INDUCED SUBSIDENCE AND FAULT
REACTIVATION

• Temporal and spatial correlation of surficial
  changes and hydrocarbon production
• Large or rapid subsurface pressure decline
  (regional depressurization)

6
Evidence continued

• Consistent orientation and displacement of active
  surface and subsurface faults
• Historical subsidence rates significantly greater
  than geological subsidence rates
• Preservation of marsh sediments beneath open
  water (historical wetland loss)

7
Overburden stress
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Fieldwork
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COCODRIE TIDE GAUGE
10
Coring
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Texas location map
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Fields table Port Neches
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Port Neches field map
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Port Neches field graph
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Port Neches diagram
16
Texas location map
17
Bolivar photo
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Caplen Field map
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Caplen Field graph
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Caplen Field diagram
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Texas location map
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Clam Lake map
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Aerial photo
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Clam Lake graph
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Wetlands photo
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Louisiana map
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Well field map
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Fields table Valentine
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Annual Production Valentine
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BHP Valentine
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Annual Production Houma
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Annual production Lirette
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Annual production Lapeyrouse
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BHP Exposito
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Pressure gradient decline
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Core MB 06
37
Houma tide gauge
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Loss lines
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NGS Data 1965 - 1982
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Benchmarks
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NGS Data 1966 - 1993
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Average geological and historical rates of
subsidence for the Terrebonne delta plain region
near Madison Bay.
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Annual Production Lapeyrouse
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DELTA PLAIN WETLAND LOSS
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CONCLUSIONS

• Prior studies attributed regional wetland loss to
  delta plain compaction, canal construction, and
  biogeochemical processes
• Subsidence associated with natural compaction
  should be slow and decrease with geologic time
• Some delta plain subsidence rates accelerated
  recently and are greater than geologic subsidence
  rates

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CONCLUSIONS CONTINUED

• Marsh sediments are preserved where accommodation
  space is created by induced subsidence
• Prior explanations of regional wetland loss fail
  to explain the rapid increase and decrease in
  rates of loss (1950s-1970s)
• Close temperal and spatial correlations among
  regional wetland loss, highest historical
  subsidence rates, maximum rates of fluid
  extraction and pore-pressure reduction, and
  locations of potentially reactivated faults
• Decrease in wetland loss possibly related to
  decreased subsidence associated with decrease oil
  gas production