Natural-gas-hydrate deposits: a review of in-situ properties

• Main Authors: Halleck, P.M., Pearson, C., McGuire, P.L., Hermes, R., Mathews, M.
• Language: unknown
• Published: 2021
• Subjects: 03 NATURAL GAS; NATURAL GAS HYDRATE DEPOSITS; ELECTRIC CONDUCTIVITY; RESISTIVITY LOGGING; SONIC LOGGING; PERMAFROST; SEDIMENTS; VELOCITY; ELECTRIC LOGGING; ELECTRICAL PROPERTIES; GEOLOGIC DEPOSITS; PHYSICAL PROPERTIES; WELL LOGGING; Ice; permafrost
• Online Access: http://www.osti.gov/servlets/purl/6917373; https://www.osti.gov/biblio/6917373

The Los Alamos hydrate project has concentrated on: evaluating techniques to produce gas from hydrate deposits to determine critical reservoir and production variables; predicting physical properties of hydrate-containing sediments both for their effects on production models and to allow us to develop geophysical exploration and reservoir characterization techniques; and measuring properties of synthetic hydrate cores in the laboratory. Exploration techniques can help assess the size of potential hydrate deposits and determine which production techniques are appropriate for particular deposits. So little is known about the physical properties of hydrate deposits that it is difficult to develop geophysical techniques to locate or characterize them; but, because of the strong similarity between hydrates and ice, empirical relationships between ice composition and seismic velocity, electrical resistivity, density, and heat capacity that have been established for frozen rocks may be used to estimate the physical properties of hydrate deposits. Resistivities of laboratory permafrost samples are shown to follow a variation of Archie's equation. Both the resistivities and seismic velocities are functions of the unfrozen water content (Sw); however, resistivities are more sensitive to changes in Sw, varying by as much as three orders of magnitude, which may allow the use of electrical resistivity measurements to estimte the amount of hydrate in place. We estimated Sw, assuming that the dissolved salt in the pore water is concentrated as a brine phase as the hydrates form, and the brine content as a function of depth, assuming several temperature gradients and pore water salinities. Hydrate-bearing zones are characterized by high seismic velocities and electrical resistivities compared to unfrozen sediments or permafrost zones.