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Lee, M. W., T. S. Collett, and W. F. Agena,
Integration of Vertical Seismic, Surface Seismic, and Well-log Data at the Mallik 2L-38 Gas-hydrate Research Well, Mackenzie Delta, Canada
M. W. Lee,1 T. S. Collett,2 W. F. Agena3
1U.S. Geological Survey, Denver, Colorado, U.S.A.
2U.S. Geological Survey, Denver, Colorado, U.S.A.
3U.S. Geological Survey, Denver, Colorado, U.S.A.
Vertical seismic profile (VSP) data acquired at the Japanese Petroleum Exploration Co., Ltd. (JAPEX)/Japanese National Oil Corporation (JNOC)/Geological Survey of Canada (GSC) Mallik 2L-38 gas-hydrate research well, Mackenzie delta, Northwest Territories, Canada, were analyzed and combined with surface seismic and downhole well-log data to (1) estimate gas-hydrate concentration around the well and (2) characterize the arctic gas-hydrate accumulations using different scale lengths ranging from 0.3 (sonic log) to 60 m (197 ft) (surface seismic). The interval compressional (P-)wave velocities derived from VSP data are somewhat slower than those from the well-log data. Furthermore, the shear (S-)wave velocities derived from VSP data within the depth interval 600–900 m (1968–2953 ft) are about 20% slower than the sonic-log-derived velocity, implying seismic anisotropy. The spectral ratio of downgoing waves indicates that the P-wave attenuation quality factor of non-gas-hydrate-bearing sediments is about 65, whereas that of gas-hydrate-bearing sediments is about 170. The seismically determined thickness of gas-hydrate-bearing sediments inside a 2.3 2.4-km (1.42 1.49-mi) area surrounding the Mallik 2L-38 well is about 212 m (695 ft). Porosity obtained from well-log data averages 30%. The average gas-hydrate concentration estimated from the surface seismic data is about 43% of the pore space, and a cubic meter (35 cubic feet) of gas hydrate is 164 m3 (5792 ft3) of free gas. Therefore, the estimated gas content present in the gas-hydrate-bearing sediments is equivalent to 4.5 109 m3/km2 (4.1 1011 ft3/mi2) of gas at the standard conditions (0C and 1 atmosphere).
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