Gas hydrate quantification using sediment cores, marine CSEM, and seismic data coupled by joint elastic-electrical effective medium modeling

We present a rigors quantification of marine gas hydrate deposit, using combined seismic velocity and electrical resistivity data coupled by joint elastic-electrical effective medium modeling. For this purpose, sediment cores, seismic, and controlled-source electromagnetic (CSEM) data were acquired from the CNE03 pockmark, Nyegga region, Offshore Norway. Macro-, meso- and micro- scale analysis of two ?7 m sediment cores reveal significant differences between the CNE03 pockmark and a reference site located ?150 m northwest to CNE03. Hydrate clathrates and methanogenic shells were retrieved from the CNE03 sediments. The seismic velocity and electrical resistivity measured from the CNE03 sediment core are consistent with our P-wave velocity (Vp) and CSEM remote sensing datasets. Comparison between the CSEM electrical resistivity data and effective medium model suggests a gas hydrate saturation of 30%-48% at CNE03, whereas the Vp data indicate 25%-31% of hydrate concentration. This data-dependent discrepancy in hydrate saturation provides evidence to the existence of free gas within the hydrate stability zone beneath CNE03. Our combined Vp-CSEM data compared with the joint elastic-electrical effective medium model infer 28%-35% of gas hydrate saturation at CNE03, for porosity range of 55%-65%, respectively. Thus, at an average porosity of 60%, the CNE03 gas hydrate concentration is 33%. We conclude that a well-constrained gas hydrate quantification can be accomplished by coupling P-wave velocity and CSEM data with joint elastic-electrical effective medium modeling. The approach applied in this study is particularly suitable to quantify disseminated pore-filling hydrate in coarse-grained clay-rich marine sediments.