1. 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 http://coastal.er.usgs.gov/gc-subsidence/

2. Mississippi delta plain area of detailed investigations ~ 4000 km 2 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. Continuous Interior Wetland Subsurface depth meters X10 3 Before Induced Subsidence

5. Fluid Production Subsurface depth meters X10 3 After Induced Subsidence

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. Exposito Reservoir Multiple Wells Representative Pressure Decline

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

16. NGS Relevel Lines

17. NGS Subsidence Rates La 1 1965-1993

18. Historical Subsidence Rates in Coastal Louisiana

19. Tide Gauges

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

21. Grand Isle Annual Mean Sea Level 1947-2006

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

23. Delta Plain Subsidence Rates SourcePeriodRate mm/yr Reference Radiocarbon datesHolocene1-5Penland et al, 1988; Roberts et al, 1994; Morton et al, 2006 Numerical modelHolocene<5Meckel et al, 2006 NGS Relevel La 11965-827.6Shinkle & Dokka, 2004 NGS Relevel La 11982-199312.1Shinkle & Dokka, 2004 NOS GI tide gauge1947-653.3Morton & Bernier NOS GI tide gauge1965-9310.7Morton & Bernier NOS GI tide gauge1993-064.1Morton & Bernier NGS GPS CORS2002-073.5-6.3Dokka et al, 2006

24. Delta Plain Fluid Production vs. Wetland Loss

25. 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 IMPORTANT CONSIDERATIONS

26. 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