Characterization of gas hydrate systems on the Hikurangi margin (New Zealand) through geostatistical seismic and petrophysical inversion

Abstract

Quantitative characterization of gas hydrate systems on continental margins from seismic data is challenging, especially in regions where no well logs are available. However, probabilistical seismic inversion provides an effective means for constraining the physical properties of subsurface strata in such settings and analyzing the variability related to the results. We apply a workflow for the characterization of two deep-water gas hydrate reservoirs east of New Zealand, where high concentrations of gas hydrate have been inferred previously. We estimate porosity and gas hydrate saturation in the reservoirs from multi-channel seismic data through a two-step procedure based on geostatistical seismic and Bayesian petrophysical inversion built on a rock physics model for gas hydrate-bearing marine sediments. We found that the two reservoirs together host between 2.45 × 105 m3 and 1.72 × 106 m3 of gas hydrate, with the best estimate at 9.68 × 105 m3. This estimate provides a first-order assessment for further gas hydrate evaluations in the region. The two-step statistically based seismic inversion method is an effective approach for characterizing gas hydrate systems from long-offset seismic reflection data.