X-ray CT Observations of Methane Hydrate Distribution Changes over Time in a Natural Sediment Core from the BPX-DOE-USGS Mount Elbert Gas Hydrate Stratigraphic Test Well

• Main Authors: Kneafsey, T.J., Rees, E.V.L.
• Other Authors: Lawrence Berkeley National Laboratory. Earth Sciences Division.
• Format: Report
• Language: English
• Published: Lawrence Berkeley National Laboratory 2010
• Subjects: Computerized Tomography; Saturation; Dissociation; Sediments; Exploratory Wells; Water; Hydrates; 58 Geosciences; Stability; Gas Hydrates; 54 Environmental Sciences; Oscillations; Chemistry; Morphology; Distribution; Methane hydrate
• Online Access: https://doi.org/10.2172/1050726; https://digital.library.unt.edu/ark:/67531/metadc844173/

When maintained under hydrate-stable conditions, methane hydrate in laboratory samples is often considered a stable and immobile solid material. Currently, there do not appear to be any studies in which the long-term redistribution of hydrates in sediments has been investigated in the laboratory. These observations are important because if the location of hydrate in a sample were to change over time (e.g. by dissociating at one location and reforming at another), the properties of the sample that depend on hydrate saturation and pore space occupancy would also change. Observations of hydrate redistribution under stable conditions are also important in understanding natural hydrate deposits, as these may also change over time. The processes by which solid hydrate can move include dissociation, hydrate-former and water migration in the gas and liquid phases, and hydrate formation. Chemical potential gradients induced by temperature, pressure, and pore water or host sediment chemistry can drive these processes. A series of tests were performed on a formerly natural methane-hydrate-bearing core sample from the BPX-DOE-USGS Mount Elbert Gas Hydrate Stratigraphic Test Well, in order to observe hydrate formation and morphology within this natural sediment, and changes over time using X-ray computed tomography (CT). Long-term observations (over several weeks) of methane hydrate in natural sediments were made to investigate spatial changes in hydrate saturation in the core. During the test sequence, mild buffered thermal and pressure oscillations occurred within the sample in response to laboratory temperature changes. These oscillations were small in magnitude, and conditions were maintained well within the hydrate stability zone.