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Subsidence, Wetland Loss, and Hydrocarbon Production in the Mississippi Delta Plain

Subsidence, Wetland Loss, and Hydrocarbon Production in the Mississippi Delta Plain. Robert A. Morton 1 , Julie C. Bernier 2 , John A. Barras 3. 1 U.S. Geological Survey, FISC, Austin, TX 2 U.S. Geological Survey, FISC, St. Petersburg, FL 3 U.S. Geological Survey, NWRC, Baton Rouge, LA.

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Subsidence, Wetland Loss, and Hydrocarbon Production in the Mississippi Delta Plain

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  1. Subsidence, Wetland Loss, and Hydrocarbon Production in the Mississippi Delta Plain Robert A. Morton1, Julie C. Bernier2, John A. Barras3 1U.S. Geological Survey, FISC, Austin, TX 2U.S. Geological Survey, FISC, St. Petersburg, FL 3U.S. Geological Survey, NWRC, Baton Rouge, LA http://coastal.er.usgs.gov/gc-subsidence/

  2. Mississippi delta plain area of detailed investigations ~ 4000 km2 land loss since the 1930s

  3. PRIMARY CAUSES OF WETLAND LOSS CATEGORY PROCESS Delta cycle Construction and destruction Sediment compaction Erosion Biogeochemical Saltwater intrusion Waterlogging Sulfide concentration Herbivory Human activities Levee construction Canal construction Failed reclamation

  4. Before Induced Subsidence Continuous Interior Wetland Subsurface depth meters X103

  5. After Induced Subsidence Fluid Production Subsurface depth meters X103

  6. EVIDENCE OF INDUCED SUBSIDENCE AND FAULT REACTIVATION • Surface changes occur at the same time and place as hydrocarbon production • Large or rapid decreases in subsurface pressure (regional depressurization) • Surface and subsurface fault traces have the same orientation and direction of displacement • Historical subsidence rates were significantly greater than geological subsidence rates • Preservation of marsh sediments beneath open water (historical wetland loss)

  7. Integrated Datasets

  8. Representative Field Production Volumes

  9. Representative Annual Fluid Production Lapeyrouse Field

  10. Representative Pressure Decline Lapeyrouse Field Exposito Reservoir Multiple Wells

  11. DeLarge Field 1968 Continuous wetlands

  12. DeLarge Field 1973 Example of Rapid Interior Wetland Loss

  13. Vibracoring Madison Bay, LA

  14. Madison Bay core

  15. NGS Relevel Lines

  16. NGS Subsidence Rates La 1 1965-1993

  17. Historical Subsidence Rates in Coastal Louisiana

  18. Tide Gauges

  19. Relative sea-level rise mm/yr 1960s -1980s

  20. Grand Isle Annual Mean Sea Level 1947-2006

  21. NGS GPS CORS Subsidence Rates 2002-07 4.4 Boothville 3.5 6.3

  22. Delta Plain Subsidence Rates

  23. Delta Plain Fluid Production vs. Wetland Loss

  24. IMPORTANT CONSIDERATIONS • Subsidence associated with deep-basin processes (salt migration, gravity gliding) should be slow, continuous, and decrease with geologic time • Historical delta-plain subsidence rates accelerated and were greater than geological subsidence rates, then they recently decelerated to near geological rates • Close correlations among regional wetland loss rates, historical subsidence rates, rates of fluid extraction and pressure reduction, and locations of reactivated faults

  25. Prior explanations of regional wetland loss failed to explain the rapid increase and decrease in rates of wetland loss • Marsh sediments are preserved where subsidence was rapid • Interior wetland subsidence rates were substantially higher than subsidence rates measured along the natural levees • Although measured rates of induced subsidence in the Miss. delta are low compared to other areas, they were sufficient enough to cause widespread wetland loss

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