gas hydrate - CCOP

trends depending on the following fluid system in the sediment samples; 'gas hydrate-free gasbrine'
system and 'gas hydrate-brine' system. In the former case, there is no distinct relation
between gas hydrate saturation and electrical resistance. This may be due to 'Ion-exclusion
phenomena' causing the reduction of electrical resistance of the sediment samples. In case of
'gas hydrate-brine' system, we observed electrical resistance increases with increasing gas
hydrate saturation. The derivation of empirical correlation between gas hydrate saturation
and electrical resistance is possible, if we have enough data.
For the measurement of wave velocity in gas hydrate bearing sediments, the experimental
apparatus has been constructed and test runs were carried out. Among special petrophysical
properties of sediments, we estimated relative permeability in gas hydrate bearing sediment
samples using CT scanner and inversion simulation techniques. This technique to derive the
relative permeability function in gas hydrate-bearing sediments is the first attempt to date.
The hydrate distribution revealed by X-ray CT images was not uniform even with relatively
uniform water saturation and porosity distribution. As basic steps for study on the stability of
gas hydrate bearing sediments, we built experimental apparatus which can simulate stress
conditions of the sediment sample and measure its axial deformation up to 1µm.
In order to study conventional production methods, experimental apparatus has been built to
accommodate porous media simulating geological formation and tested for their validity from
the measurement of related properties. Two dimensional high pressure cells have been built
for the experiments of heat stimulation method that can monitor and control pressure and
temperature at various locations. From the results of the comparison of literature values of
hydrate equilibrium condition with measured ones, we can assure the validity of the
experimental system. As a preliminary study of hot brine injection method, the patterns of two
phase flow in porous media have been analyzed from the relative permeability measurements
using one dimensional high pressure cell. The unsteady state method has been adapted to
measure relative permeability in gas hydrate bearing sediments.
Replacement of gas hydrate by carbon dioxide has been studied as a new emerging
production method. To understand replacement mechanism of CH 4 by CO 2 , gas hydrate was
contacted with liquefied CO 2 and N 2 (80%) + CO 2 (20%) mixed gas, respectively. Total
amount of produced CH 4 was 64% in gas hydrate in case of contacting liquefied CO 2 . In case
of contacting N 2 +CO 2 mixed gas, CH 4 is produced 62% in large cage and 23% in small cage
of gas hydrate, respectively. This means that the replacement of N 2 +CO 2 mixed gas shows
better production efficiency than pure CO 2 replacement.
We have investigated the characteristics of available numerical models for the gas hydrate
simulation. Among them, the most popular model, TOUGH-Fx/Hydrate, was used to apply
depressurization method in virtual system. Although it can not predict or simulate all the
complex phenomena regarding gas hydrate formation and dissociation, the results were
satisfactory. Numerical model can be used to build a production plan and manage gas
hydrate reservoir by applying to the more complicated system and comparison with
laboratory data.
22
New Energy Resources in the CCOP Region - Gas Hydrates and Coalbed Methane