Feasibility of monitoring gas hydrate production with time-lapse VSP Page: 3 of 35
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made possible by recent advances in the ability to model the complex processes which occur
in such systems and which inevitably involve the nonisothermal transport of fluids and gases.
Simulation of Gas Production from Hydrate Accumulation
Numerical Simulator. We used the TOUGH+HYDRATE code (Moridis et al., 2008-
hereafter referred to as T+H) to simulate gas production from the HBS we investigated in this
study. T+H models the non-isothermal hydration reaction, phase behavior and flow of fluids
and heat under conditions typical of natural methane-hydrate deposits in complex geological
formations. It includes both equilibrium and kinetic models of hydrate formation and
dissociation, and can handle any combination of hydrate dissociation mechanisms, such as
depressurization, thermal stimulation and the use of inhibitors. It accounts for heat and up to
four mass components (i.e., water, CH4, hydrate, and water-soluble inhibitors such as salts or
alcohols) that are partitioned among four possible phases (gas, liquid, ice or hydrate phases,
existing individually or in any of 15 possible states, i.e., phase combinations). The numerical
code we used to simulate seismic surveys in a hydrate accumulation before and during
production is described in a subsequent section.
Geological System. The geological system we consider is similar to that described by
Moridis and Reagan (2007). It is based on data collected in the Tigershark exploratory well
(Smith et al., 2006) in the Alaminos Canyon Block 818 of the Gulf of Mexico, where log data
indicate the presence of a sandy hydrate-bearing layer (HBL) of 18.25 m thickness, ranging
from depths below the seafloor of 466 m to 485 m, with the seafloor being 2750 m below the
ocean surface. The porosity 0 is approximately 0.3, and intrinsic permeability k is on the
order of 1 Darcy. The initial estimates of gas hydrate saturation Sh within the HBL, derived
using resistivity and P-wave velocity data (Collett and Lee, 2006), range from 0.6 to 0.8. The
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Kowalsky, M.B.; Nakagawa, S. & Moridis, G.J. Feasibility of monitoring gas hydrate production with time-lapse VSP, article, November 1, 2009; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc1014155/m1/3/: accessed May 24, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.