Develop seismic tools for detecting hydrates and predicting seafloor stability.
The University of Texas at Austin, Bureau of Economic Geology
Austin, TX 78713
This project tested the use of 3-dimensional multi-component seismic (MCS) data recorded with 4-component ocean bottom cables (OBC) as a method for improving the industry's ability to detect and characterize gas hydrates, assess the gas hydrate resource, and predict the stability of hydrate-containing sediments.
The methodologies developed by this project can serve as a road map for interpreters attempting to avoid shallow hazard zones in the northern Gulf of Mexico, and identify potential areas for commercial exploitation of gas hydrates.
A multi-component system is superior to a single-component seismic system for evaluating gas hydrate reservoirs and their surrounding environment because the depositional system can be imaged with both compressional waves (sound waves that pulse through the bottom sediments, called P-waves) and shear seismic waves (waves that move at various crossing angles, called S-waves). Integrating seismic wave types can provide more information about sediment relationships, rock-type distributions, and pore-filler material. In addition, the P-wave velocity (Vp) and S-wave velocity (Vs) can be used to calculate elastic constants and to infer the shear modulus and mechanical strength of the sediments, important factors relating to seafloor stability. In general, a more detailed characterization of marine gas hydrate systems can be obtained if gas hydrate target intervals are described in terms of integrated P and S seismic data rather than P-wave data alone, as is typical in marine seismic investigations.
The principal barrier to overcome when imaging marine gas hydrate sediments, with both P and S-waves, is that S waves do not propagate in fluids. This problem may be overcome if four-component ocean-bottom sensor cable (4-C OBC) is utilized to acquire seismic data at the sea floor.
The initial objectives of the project were to see if P-wave reflection quality could be improved by combining hydrophone and vertical-geophone data, improving structural interpretation in areas with P-wave data "wipeouts". Additional objectives were to evaluate Vp/Vs velocity ratios and seismically derived Poisson's ratios for characterizing near-seabed sediments and to develop practical post-stack 3-D data interpretation methodologies that capitalize on the unique characteristics of the multi-component OBC data.
The research concluded that developing robust 3D interpretation-based methodologies would in fact allow geoscientists to exploit the unique characteristics of multi-component data. Time-dependent attributes like Vp/Vs and Poisson's ratios strongly depend on accurate depth registration between seismic events. Depth registration of wave images should rely on correlating map-based images (either time slices or horizon slices), and correlation between section (2D) views should be done sparingly. Quality control mechanisms are vital to ensure robust correlation and to produce valid MCS-based attributes for shallow marine characterization.
This project has been completed and the final report is available.
In addition to the information provided here, a full listing of project related publications and presentations as well as a listing of funded students can be found in the Methane Hydrate Program Bibliography [PDF].
A final report is available by request. Contact Gary Sames - Gary.Sames@netl.doe.gov or 412-386-5067
Sava, D., and B. Hardage, in review, Rock-physics models for gas-hydrate systems associated with unconsolidated marine sediments, in Collett, T., A. Johnson, C. Knapp and R. Boswell, eds., Natural Gas Hydrates: Energy Resource and Associated Geologic Hazards, The American Association of Petroleum Geologists Hedberg Special Publication.
Hardage, B., M. Backus, M. DeAngelo, S. Fomel, R. Graebner, P. Murray, and L. Wood, 2002, Characterizing Marine Gas-Hydrate Reservoirs and Determining Mechanical Properties of Marine Gas-Hydrate Strata with 4-Component Ocean-Bottom-Cable Seismic Data, Final Report, DOE Contract No. DE-FC26-00NT41024.
Backus, M., P. Murray, B. Hardage, and R. Graebner, 2006, High-resolution multi-component seismic imaging of deepwater gas hydrate systems, The Leading Edge, Volume 25, n. 5, p. 578-596.
DeAngelo, M., M. Backus, B. Hardage, P. Murray, and S. Knapp, 2003, Depth registration of P-wave and C-wave seismic data for shallow marine sediment characterization, Gulf of Mexico, The Leading Edge, Volume 22, n. 2, p. 96-105.
Hardage, B., and P. Murray, 2006, Detailed imaging of deepwater hydrate geology with horizontal arrays of seafloor sensors, Proceedings of the Offshore Technology Conference, paper 17929.
Hardage, B., and P. Murray, 2006, High-resolution P-P imaging of deepwater near-seafloor geology, The American Association of Petroleum Geologists Explorer, Geophysical Corner, Volume 27, n. 7, p. 30.
Hardage, B., and P. Murray, 2006, P-SV data most impressive image, The American Association of Petroleum Geologists Explorer, Geophysical Corner, Volume 27, n. 8, p. 30.
Hardage, B., R. Remington, and H. Roberts, 2006, Gas hydrate--a source of shallow water flow?, The Leading Edge, Volume 25, n. 5, p. 634–636.
Hardage, B., and H. Roberts, 2006, Gas hydrate in the Gulf of Mexico: what and where is the seismic target, The Leading Edge, Volume 25, n. 5, p. 566-571.
Hardage, B., and H. Roberts, 2006, Evaluation of deepwater gas-hydrate systems, The Leading Edge, Volume 25, n. 5, p. 572-577.
McGee, T., and B. Hardage, 2006, Hydrate system to be monitored, The American Association of Petroleum Geologists Explorer, Geophysical Corner, Volume 27, n. 5, p. 24.
Roberts, H., B. Hardage, W. Shedd, and J. Hunt Jr., 2006, Seafloor reflectivity–an important seismic property for interpreting fluid/gas expulsion geology and the presence of gas hydrate, The Leading Edge, Volume 25, n. 5, p. 620–628.
Sava, D., and B. Hardage, 2006, Rock physics characterization of hydrate-bearing deepwater sediments, The Leading Edge, Volume 25, n. 5, p. 616-619.
Backus, M., P. Murray, B. Hardage, and R. Graebner, 2005, Enhanced PS-wave images of deep-water, near-seafloor geology from 2-D 4-C OBC data in the Gulf of Mexico, 75th Annual International Meeting of the SEG, Houston, TX, November 6-11.
Hardage, B., and D. Sava, 2006, Seismic estimation of Gas Hydrate Concentrations in Deepwater Environments: Assumptions and Limitations, Houston, TX, The American Association of Petroleum Geologists Annual Meeting, April 9-12. (Winner of President’s Certificate for Excellence)
Hardage, B., 2006, Detailed imaging of deepwater hydrate geology with horizontal arrays of seafloor sensors, Houston, TX, Offshore Technology Conference, May 3.
Hardage, B., 2005, Assessing deep water gas hydrate systems and seafloor stability, invited lecture, New Orleans, LA, AGU, NABS, SEG, SPD/AAS Joint Assembly, May 23–27.
Hardage, B., and P. Murray, 2006, Detailed imaging of deepwater hydrate geology with horizontal arrays of seafloor sensors, paper 17929, 2006 Offshore Technology Conference, Houston, TX, May 1-4.
Murray, P., M. DeAngelo, B. Hardage, M. Backus, R. Graebner, and S. Fomel, 2005, Interpreting multicomponent seismic data in the Gulf of Mexico for shallow sedimentary properties: methodology and case history, Houston, TX, 2005 Offshore Technology Conference, May 2-5.
Sava, D., and B. Hardage, 2006, Rock physics models of gas hydrates from deep water, unconsolidated sediments, 76th Annual Meeting of the Society of Exploration Geophysicists, New Orleans, Louisiana, October 1-6.