Compressional and shear-wave velocities from gas hydrate bearing sediments; examples from the India and Cascadia margins as well as Arctic permafrost regions

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doi: 10.1016/j.marpetgeo.2014.07.028
Author(s): Riedel, Michael; Goldberg, David S.; Guerin, G.
Indian National Gass Hydrate Program Expedition 01 Scientsts
Author Affiliation(s): Primary:
Geological Survey of Canada-Pacific, Sidney, BC, Canada
Lamont-Doherty Earth Observatory, United States
Volume Title: Geologic implications of gas hydrates in the offshore of India; results of the National Gas Hydrate Program Expedition 01
Volume Author(s): Ramana, M. V., editor; Ramprasad, T.; Collett, Timothy S.; Kumar, P.; Boswell, Ray M.; Riedel, Michael; Sathe, Arun Vasant; Lall, M.; Vishwanath, Krishna; Mazumdar, A.; Sain, Kalachand; Cochran, James R.
Source: Geologic implications of gas hydrates in the offshore of India; results of the National Gas Hydrate Program Expedition 01, edited by M. V. Ramana, T. Ramprasad, Timothy S. Collett, P. Kumar, Ray M. Boswell, Michael Riedel, Arun Vasant Sathe, M. Lall, Krishna Vishwanath, A. Mazumdar, Kalachand Sain and James R. Cochran; Indian National Gass Hydrate Program Expedition 01 Scientsts. Marine and Petroleum Geology, 58( Part A), p.292-320. Publisher: Elsevier, Oxford, United Kingdom. ISSN: 0264-8172
Note: In English. 54 refs.; illus., incl. 4 tables, sketch map
Summary: Shear wave velocity data have been acquired at several marine gas hydrate drilling expeditions, including the India National Gas Hydrate Program Expedition 1 (NGHP-01), the Ocean Drilling Program (ODP) Leg 204, and Integrated Ocean Drilling Program (IODP) Expedition 311 (X311). In this study we use data from these marine drilling expeditions to develop an understanding of general grain-size control on the P- and S-wave properties of sediments. A clear difference in the downhole trends of P-wave (Vp) and S-wave (Vs) velocity and the Vp/Vs ratio from all three marine regions was observed: the northern Cascadia margin (IODP X311) shows the highest P-wave and S-wave velocity values overall and those from the India margin (Expedition NGHP-01) are the lowest. The southern Cascadia margin (ODP Leg 204) appears to have similar low P-wave and S-wave velocity values as seen off India. S-wave velocity values increase relative to the sites off India, but they are not as high as those seen on the northern Cascadia margin. Such regional differences can be explained by the amount of silt/sand (or lack thereof) occurring at these sites, with northern Cascadia being the region of the highest silt/sand occurrences. This grain-size control on P-wave and S-wave velocity and associated mineral composition differences is amplified when compared to the Arctic permafrost environments, where gas hydrate predominantly occurs in sand- and silt-dominated formations. Using a cross-plot of gamma ray values versus the Vp/Vs ratio, we compare the marine gas hydrate occurrences in these regions: offshore eastern India margin, offshore Cascadia margin, the Ignik-Sikumi site in Alaska, and the Mallik 5L-38 site in the Mackenzie Delta. The log-data from the Arctic permafrost regions show a strongly linear Vp-Vs relationship, similar to the previously defined empirical relationships by Greenberg and Castagna (1992). P- and S-wave velocity data from the India margin and ODP Leg 204 deviate strongly from these linear trends, whereas data from IODP X311 plot closer to the trend of the Arctic data sets and previously published relationships. Three new linear relationships for different grain size marine sediment hosts are suggested: a) mud-dominated (Mahanadi Basin, ODP Leg 204 & NGHP-01-17): Vs = 1.5854 × Vp - 2.1649 b) silty-mud (KG Basin): Vs = 0.8105 × Vp - 1.0223 c) silty-sand (IODP X311): Vs = 0.5316 × Vp - 0.4916 We investigate the relationship of gas hydrate saturation determined from electrical resistivity on the Vp/Vs ratio and found that the sand-dominated Arctic hosts show a clearly decreasing trend of Vp/Vs ratio with gas hydrate saturation. Though limited due to lower overall GH saturations, a similar trend is seen for sites from IODP X311 and at the ash-dominated NGHP-01-17 sediment in the Andaman Sea. Gas hydrate that occurs predominantly in fractured clay hosts show a different trend where the Vp/Vs ratio is much higher than at sand-dominated sites and remains constant or increases slightly with increasing gas hydrate saturation. This trend may be the result of anisotropy in fracture-dominated systems, where P- and S-wave velocities appear higher and Archie-based saturations of gas hydrate are overestimated. Gas hydrate concentrations were also estimated in these three marine settings and at Arctic sites using an effective medium model, combining P- and S-wave velocities as equally weighted constraints on the calculation. The effective medium approach generally overestimates S-wave velocity in high-porosity, clay-dominated sediments, but can be accurately used in sand-rich formations. Abstract Copyright (2014) Elsevier, B.V.
Year of Publication: 2014
Research Program: IODP Integrated Ocean Drilling Program
ODP Ocean Drilling Program
Key Words: 29 Economic Geology, Energy Sources; Alaska; Arctic Ocean; Arctic region; Bay of Bengal; Body waves; Bulk modulus; Canada; Cascadia subduction zone; Case studies; Cores; East Pacific; Elastic constants; Elastic waves; Expedition 311; Gas hydrates; Indian National Gas Hydrate Program; Indian Ocean; Integrated Ocean Drilling Program; Leg 204; Marine sediments; Models; Natural gas; North Pacific; North Slope; Northeast Pacific; Northwest Territories; Ocean Drilling Program; P-waves; Pacific Ocean; Permafrost; Petroleum; S-waves; Sediments; Seismic waves; Shear modulus; United States; Velocity; Velocity structure; Well logs; Western Canada
Coordinates: N150000 N173000 E0840000 E0783000
N443400 N443500 W1250400 W1250900
N483700 N484800 W1264000 W1270400
Record ID: 2016097429
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands