gas hydrate - CCOP

lithospheric extension, thinning of the lithosphere causes the asthenospheric mantle to upwell
which in turn causes the temperature to rise. This is the point where the heat flux is the
highest along the basin seafloor. With time as lithosphere cools, the temperature and heat flux
both gradual drops. This process has been explained and modeled by McKenzie (1978). By
examining the heat flux, we can constrain the timing of extension and the amount of extension
(often expressed in terms of stretching factor) that Ulleung Basin accommodated. During this
year, we constructed simple models that can be used later when the actual heat flow
measurement become available.
To identify the potential area of gas hydrates in prospect area I, "2005 Gas Hydrates 2-D
Data Acquisition" survey was conducted in connection with this project, under the contract
with KNOC. Field acquisition project includes the design of pre-plot survey line, 2-D seismic,
gravity and multi-beam survey. Total length of survey lines was 6,600 L-km, composed of 64
survey lines.
The gas hydrates survey was conducted in Block VI-1 and northern area using Tamhae II and
the seismic survey equipment consisted of source, streamer, and navigation system and
recording system. The length of streamer cable was 3 km and the volume of seismic air gun
source was about 1,000 in 3 . Gravity and multi-beam survey was performed with seismic
survey together. Gravity data was acquired using LaCoste-Romberg S-118 marine gravimeter
and multi-beam data was acquired using Simrad EM950/EM12S multi-beam echo sounder.
Seismic data processing is the process of identifying the physical properties and producing the
seismic section to investigate subsurface structure after signal processing. Basic data
processing procedure includes such as the data input, matching of seismic data and geometry,
static and delay time correction, signal enhancement, velocity analysis and stack.
We carried out the refraction seismic survey and derived velocity information of the gas
hydrates bearing sediments to increase the reliability of the gas hydrates reserve estimation.
We introduced ocean bottom seismometer (OBS) and performed the test survey. Field test
survey was carried out using 2 OBS with 10 km interval at the area of about 70 km east of
Pohang. The volume of seismic source was 1,035 in 3 and shooting interval was 50 meters (~
20 sec). Considering the estimated target depth of gas hydrates, one EW line with the length
of 50 km and two NS lines with the lengths of 30 and 20 km were surveyed and 200 data
samples per 1 second were recorded.
BSR, the characteristic phenomenon appearing in gas hydrates bearing sediments, could be
identified on the seismic sections in southern part in the survey area. This phenomenon has
been used as the evidence that gas hydrates exists typically above BSR. Because BSR may not
be the sufficient condition for the existence of gas hydrates, we studied additional analysis of
BSR properties to increase the reliability of BSR. Typical AVO analysis was carried out to
understand the amplitude variation of BSR with offset. We examined the consistence of BSR
and AVO anomaly by displaying the AVO anomaly zone with the seismic section together and
could confirm that AVO anomaly was consistent with BSR.
As the basic research of geophysical exploration to secure the infra technology for the
development of gas hydrates, we carried out the numerical and physical modeling studies and
examined the geophysical characteristics for the various subsurface velocity models. In
numerical modeling, producing the synthetic data similar to the field data by numerical
calculation, staggered grid was introduced to typical finite difference method in order to
New Energy Resources in the CCOP Region - Gas Hydrates and Coalbed Methane 19