Characterization and Quantification of Gas Hydrates in the California Borderlands

Abstract

Electromagnetic methods are directly sensitive to electrically resistive gas hydrates and can be used to characterize and quantify hydrate deposits. Using a 1 km long deep‐towed marine electromagnetic system, six survey lines were acquired coincident with legacy seismic reflection data in the Santa Cruz Basin in the Outer California Borderlands. While the strongest seismic indicators place hydrate in the central basin, resistors inferred to be hydrate are located predominantly on the flanks of the basin, coincident with gas migration pathways such as faults and steeply dipping strata. Two features consistent with the resistivity profile from previously imaged seafloor methane seeps were also found. Resistivity is related to hydrate saturation through Archie's law, and total hydrate volume of the Santa Cruz Basin is estimated to be 980 × 109 m3 of gas in place.

Laboratory Electrical Conductivity of Marine Gas Hydrate

“…Gas hydrate is electrically resistive, a feature that is exploited in well logging (Collett, 2001; Goldberg et al, 2010), and can be imaged using marine controlled‐source electromagnetic (CSEM) methods (e.g., Constable et al, 2016; Schwalenberg et al, 2010; Wang et al, 2017; Weitemeyer et al, 2006). While CSEM data can be useful as a stand‐alone method, because resistivity and seismic properties sample geology in very different ways, the combination of electrical and seismic methods can be very useful (e.g., Kannberg & Constable, 2020).…”

Electrical Properties of Carbon Dioxide Hydrate: Implications for Monitoring CO2 in the Gas Hydrate Stability Zone

“…Electromagnetic (EM) methods have long been considered an important tool in monitoring CO 2 sequestration where displacement of pore fluid by CO 2 decreases electrical conductivity (Zhdanov et al., 2013), and are also proven to be sensitive to gas hydrate concentration and distribution (Constable et al., 2016; Weitemeyer et al., 2006). Recent advances in controlled‐source EM technology now allows measurement of even small variations in conductivity; for example, Kannberg and Constable (2020) resolved seafloor conductivity by a factor of two. We have previously demonstrated that EM studies in the field can benefit from salinity‐conductivity insights gained from laboratory measurement of σ on pure CH 4 hydrate and hydrate ± variable amounts of ionic impurities, sediments, or brines (Constable et al., 2020; Du Frane et al., 2011, 2015; Lu et al., 2019).…”

Methane Occurrence and Quantification in a Very Shallow Water Environment: A Multidisciplinary Approach

“…Electrical resistivity data can be extremely valuable for analyzing the subsoil gas behavior and its relation to surface emissions. This is valid for hydrocarbon exploration and reservoir monitoring (Jiang et al., 2021; Senger et al., 2021), for gas hydrates studies (Coren et al., 2001; Kannberg & Constable, 2020; Weitemeyer et al., 2011) but also for evaluating other types of gas emissions, as, for example, from landfills (Johansson et al., 2011). Normally, these gas assessment studies are based on well‐logs or CSEM (marine controlled‐source electromagnetic) data.…”