Acoustic impedance inversion and seismic reflection continuity analysis for delineating gas hydrate resources near the Mallik research sites,Mackenzie Delta, Northwest Territories, Canada

摘要

We combine acoustic impedance inversion of 3D seismic data,log-to-seismic correlation, and seismic attribute analyses to de-lineate gas-hydrate zones at the Mallik site, Mackenzie Delta,Northwest Territories, Canada. Well-log data define three dis-tinct hydrate zones over a depth range of 890-1100 m. Syntheticseismic modeling indicates the base of the two deeper hydratezones are prominent reflectors. The uppermost gas-hydrate zonecorrelates to seismic data with a lower degree of confidence. Theextent and geometry of the two lower hydrate zones suggest thatlocal geology plays a significant role in the lateral and verticaldistribution of gas hydrate at Mallik. The reliability of the hy-drate concentrations calculated from the inverted impedances isqualified by the match between original and synthetic seismicdata to produce confidence maps for the two lower gas-hydrate-bearing intervals. A total in-place volume estimate.of solid gashydrate for an area of 1.44 km2 around well 5L-38 yields a valueof approximately 45 X 106 m3 (equivalently, 6.6 X 109 m3 ofgas). We further qualify our mapping of gas hydrates by someamount of continuous resource, defined as lateral continuitymeasured by seismic attribute similarity and sand-dominatedrock. Using these attributes, the continuous amount of hydrate atMallik is about half the in-place volume (i.e., 25 X 106 m3). Else-where within the 3D seismic cube, the seismic impedance inver-sion yields evidence of potential gas-hydrate deposits near wellsA-06 and P-59 at levels near the predicted base of the hydrate sta-bility zone.