X-ray Computed Tomography Observation of Methane Hydrate Dissociation

X-ray Computed Tomography Observation of Methane Hydrate Dissociation Liviu Tomutsa; Liviu Tomutsa Lawrence Berkeley National Laboratory Search for other works by this author on: This Site Google Scholar Barry Freifeld; Barry Freifeld Lawrence Berkeley National Laboratory Search for other works by this author on: This Site Google Scholar Timothy J. Kneafsey; Timothy J. Kneafsey Lawrence Berkeley National Laboratory Search for other works by this author on: This Site Google Scholar Laura A. Stern Laura A. Stern United States Geological Survey Search for other works by this author on: This Site Google Scholar Paper presented at the SPE Gas Technology Symposium, Calgary, Alberta, Canada, April 2002. Paper Number: SPE-75533-MS https://doi.org/10.2118/75533-MS Published: April 30 2002 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Get Permissions Search Site Citation Tomutsa, Liviu, Freifeld, Barry, Kneafsey, Timothy J., and Laura A. Stern. "X-ray Computed Tomography Observation of Methane Hydrate Dissociation." Paper presented at the SPE Gas Technology Symposium, Calgary, Alberta, Canada, April 2002. doi: https://doi.org/10.2118/75533-MS Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll ProceedingsSociety of Petroleum Engineers (SPE)SPE Unconventional Resources Conference / Gas Technology Symposium Search Advanced Search AbstractDeposits of naturally occurring methane hydrate have been identified in permafrost and deep oceanic environments with global reserves estimated to be twice the total amount of energy stored in fossil fuels. The fundamental behavior of methane hydrate in natural formations, while poorly understood, is of critical importance if the economic recovery of methane from hydrates is to be accomplished. In this study, computed X-ray tomography (CT) scanning is used to image an advancing dissociation front in a heterogeneous gas hydrate/sand sample at 0.1 MPa. The cylindrical methane hydrate and sand aggregate, 2.54 cm in diameter and 6.3 cm long, was contained in a PVC sample holder that was insulated on all but one end. At the uninsulated end, the dissociated gas was captured and the volume of gas monitored. The sample was initially imaged axially using X-ray CT scanning within the methane hydrate stability zone by keeping the sample temperature at 77°K. Subsequently, as the sample warmed through the methane hydrate dissociation point at 194°K and room pressure, gas was produced and the temperature at the bottom of the sample plug was monitored while CT images were acquired. The experiment showed that CT imaging can resolve the reduction in density (as seen by a reduction in beam attenuation) of the hydrate/sand aggregate due to the dissociation of methane hydrate. In addition, a comparison of CT images with gas flow and temperature measurements reveals that the CT scanner is able to resolve accurately and spatially the advancing dissociation front. Future experiments designed to better understand the thermodynamics of hydrate dissociation are planned to take advantage of the temporal and spatial resolution that the CT scanner provides.IntroductionIn the oil and gas industry, gas hydrate research has traditionally focused on designing improved methods to prevent its formation in conduits where it impedes fluid transport in subsea or permafrost operations (1,2,3). More recently, the interest in hydrates has been directed towards understanding of the vast potential of gas hydrates as a natural gas resource (4). Field, laboratory, and theoretical work have begun to focus on the many aspects of gas hydrates including reserve evaluation, hydrate recovery, gas production, hydrate formation, hydrate properties, dissociation, depressurization modeling, and thermal gas production from hydrates (5). To help refine current models of gas production from natural gas hydrate accumulations (6), a better understanding of the physical processes that occur during methane hydrate dissociation is critically important. Many physical and hydrologic properties of hydrate/sediment aggregates require evaluation to gain a further understanding of the potential for gas recovery from hydrates. These properties include relative permeability, thermal conductivity, heat capacity, and compaction. While various aspects of gas hydrate formation and dissociation have been investigated on both natural (7) and synthetic (8,9) gas hydrate test materials, synthetic hydrates offer the advantage of better sample control and uniformity than natural materials. Furthermore, representative natural hydrate samples have proved to be very difficult to collect.Imaging methods, such as X-ray Computed Tomography (CT), have been used to characterize naturally occurring hydrates (10) or to directly observe their dissociation while reducing the ambient pressure below the stability pressure (11). In this study, we describe CT scanning experiments on an aggregated sample of methane hydrate with quartz sand, and show how this technique can be used successfully to image an advancing dissociation front due to heat influx applied to one end of the sample, at a constant pressure of 0.1 MPa. Keywords: spe 75533, attenuation, ct image, nitrogen, computed tomography observation, attenuation change, sample holder, gas production, liquid nitrogen, methane hydrate dissociation Subjects: Flow Assurance, Hydrates This content is only available via PDF. 2002. Society of Petroleum Engineers You can access this article if you purchase or spend a download.

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