Integration of Vertical Seismic, Surface Seismic, and Well-log Data at the Mallik 2L-38 Gas-hydrate Research Well, Mackenzie Delta, Canada

Abstract

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).