gas hydrate - CCOP

Experimental Study on the P-wave Velocity
Depending on Artificial Gas Hydrate Saturation in Sediments
Jaeh-Young Lee, Se-Joon Kim, Won-Seok Lee, Hyun-Tae Kim, and Dae-Gee Huh
Korea Institute of Geoscience and Mineral Resources, Daejeon, Korea
ABSTRACT: We measured the P wave velocity of 4 unconsolidated sediment
samples which have different grain size distribution. To quantify the effect of gas
hydrate saturation on P-wave velocity, artificial gas hydrate saturation was
changed in the same sediment sample. We observed the increase of P wave velocity
with increasing gas hydrate saturation and could not find noticeable effect of grain
size on P wave velocity in the samples used in this study.
Keywords: gas hydrate, P wave velocity, grain size
INTRODUCTION
Natural gas hydrate is in the spotlight as a new clean energy source, though a lot of
technological progress should be made to produce gas hydrate safely and economically. The
most popular method, to identify gas hydrate reserves, is related with characterizes the BSR in
seismic survey. The estimation of gas hydrate contents in the survey area has been inferred
from the information of BSR and calculated interval velocity. As mentioned in Priest et al.
(2005), seismic interpretation without detail information of physical properties of gas hydrate
bearing sediments can be problematic to assessing the distribution and concentration of gas
hydrate. Information of wave velocity for methane gas hydrate itself and sediments bearing
gas hydrate can be found elsewhere such as Helgerud et al. (2002) and Priest et al. (2005),
respectively. However, still there have been a few data available in public for supporting
seismic interpretation.
As the first step to aid in the seismic interpretation, we have performed series of P-wave
velocity measurements. The effect of grain size and hydrate saturation on P-wave velocity
was investigated. We manufactured experimental apparatus for this purpose, which can
accommodate sediments in high pressure condition. The saturation of gas hydrate has been
controlled by input gas pressure in batch system. In this article, we present interim result of
the on-going P-wave velocity measurement.
EXPERIMENTAL METHODS
We used 4 artificial sands which have different grain size distribution depending on their
types. Sediment samples were prepared by flushing with de-ionized water and heating at
120. After that, their size distributions have been measured using laser diffraction particle
analyzer. Figure 1 shows the brief results of 4 artificial sand samples. MV, CS, and SD listed
in Figure 1 means the average size in the volume base, coefficient of skewness, and standard
deviation, respectively. Their porosities are around 40% and their detail petrophysical
information can be found at Lee et al. (2005).
New Energy Resources in the CCOP Region - Gas Hydrates and Coalbed Methane 43