Estimating saturation of gas hydrates using conventional 3D seismic data,Gulf of Mexico Joint Industry Project Leg II |
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| Institution: | 1. U.S. Geological Survey Central Energy Resources Science Center, Box 25046 MS 939, Denver Federal Center, Denver, CO 80225, USA;2. U.S. Geological Survey Pacific Coastal and Marine Science Center, 2885 Mission Street 999, Santa Cruz, CA 95060, USA;3. Bureau of Ocean Energy Management, 1201 Elmwood Park Blvd, New Orleans, LA 70123, USA;4. Bureau of Ocean Energy Management, 45600 Woodland Road, Sterling, VA 20166, USA;5. University of Colorado at Boulder Department of Geological Sciences, Boulder, CO, UCB 399, Boulder, CO 80309-0399, USA;6. Department of Energy, National Energy Technology Laboratory, Morgantown, WV, USA;1. CSIR-National Institute of Oceanography, Dona Paula, Goa 403004, India;2. Boone Pickens School of Geology, Oklahoma State University, Stillwater, OK 74078, USA;1. The Ohio State University, School of Earth Sciences, OH, USA;2. Battelle Memorial Institute, OH, USA;3. Bureau of Ocean Energy Management, Sterling, VA, USA;4. Bureau of Ocean Energy Management, New Orleans, LA, USA;1. Oil and Natural Gas Corporation, Gas Hydrate Research & Technology Centre, Panvel, Navi Mumbai, India;2. U.S. Geological Survey, Denver, CO, United States;3. U.S. Department of Energy, National Energy Technology Laboratory, Pittsburgh, PA, United States;4. GEOMAR, Helmhotz Center for Ocean Research, Kiel, Germany;5. Directorate General of Hydrocarbon, Noida, UP, India |
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| Abstract: | We present a methodology for generating pre-drill estimations of hydrate saturations using conventional 3D seismic data. These seismic-based estimates will be compared with well log derived saturations from the subsequently drilled wells of the Gulf of Mexico Gas Hydrate Joint Industry Project Leg II (JIP Leg II) expedition.Predicting saturation of gas hydrates (Sh-seismic) combines pre-stack seismic inversion, rock physics modeling and stratigraphic interpretation. Before the wells were drilled, no nearby sonic and density logs were available to define and calibrate the elastic property trends for the shallow target interval containing the gas hydrate stability zone. Therefore, rock property trends were established by applying principles of rock physics and shallow sediment compaction, constrained by known regional geological parameters. Sh-seismic volumes were generated by inverting pre-stack data to acoustic impedance (PI) and shear impedance (SI) volumes, and then analyzing deviations from modeled impedance trends. To enhance the quality of the inversion, the signal-to-noise ratio of the offset data was maximized by conditioning the seismic prior to inversion. Seismic stratigraphic interpretation plays an important role by identifying the more promising strata and structures for the presence of gas hydrates.The pre-drill Sh-seismic results are compared with saturations calculated from log data, Sh-log, of the wells drilled in the JIP Leg II campaign. Due to weaker seismic reflections, predictions may be less accurate for low concentrations, such as saturations less than 40%, and for thin intervals below the vertical resolution of the seismic data (about 15 m). However, the integrated geophysical workflow is very effective for identifying and quantifying significant hydrate concentrations, making the method a promising prospecting technique. |
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