HR: 0800h
AN: C11A-1070    [Abstracts]
TI: Numerical study of hydrate preservation during core recovery
AU: * Moridis, G J
EM: GJmoridis@lbl.gov
AF: Lawrence Berkeley National Laboratory, Earth Sciences Division, Univ. of California, 1 Cyclotron Rd., ESD, MS 90-1116, Berkeley, CA 94720
AU: Kowalsky, M
EM: MBKowalsky@lbl.gov
AF: Lawrence Berkeley National Laboratory, Earth Sciences Division, Univ. of California, 1 Cyclotron Rd., ESD, MS 90-1116, Berkeley, CA 94720
AB: Hydrate preservation during core recovery is of particular importance because no representative (undisturbed) sample of natural gas hydrates has ever been recovered. A representative natural sample can provide answers to questions regarding the occurrence, properties and behavior of hydrates in natural systems, and address the issue of suitability of synthetic hydrate samples (pure and in porous media) as adequate analogs. Recovering undisturbed hydrate-bearing samples is difficult because hydrates occur under a high pressure and low temperature regime, and are unstable at the pressure and temperature conditions at the surface of the earth. Thus, exposure of the relatively warm core (at temperatures ranging between -5 oC to 14 oC) to continuously decreasing pressures during recovery (as the core ascends in the wellbore) prior to storage under controlled pressure and temperature conditions induces significant changes in the recovered sample. In this paper we evaluate methane hydrate preservation during core recovery by means of numerical simulation. We investigate the effect of important operational parameters (i.e., the core dimensions and the drilling mud temperature) and of the initial sample conditions (intrinsic permeability, pressure, temperature, salinity, and hydrate saturation) on the final hydrate recovery. The simulation results indicate that hydrate recovery increases with a higher initial hydrate saturation, a lower mud and initial formation temperature, and a longer and larger-diameter core. Hydrate recovery is also shown to increase when dissociation is treated as a kinetic (vs. equilibrium) process. Pressure appears to be the major factor affecting hydrate preservation because its effect on the core is practically instantaneous. The effect of temperature is demonstrated to be secondary because conduction (the main heat transport mechanism during core recovery) is a slow process compared to the expected rate of core ascent.
DE: 1823 Frozen ground
DE: 4820 Gases
DE: 4840 Microbiology and microbial ecology (0465)
SC: Cryosphere [C]
MN: Fall Meeting 2005