• Proceedings of the KSEEG Conference
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• 2007.04a
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• pp.264-266
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• 2007

• Economic and Environmental Geology
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• v.38 no.2 s.171
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• pp.165-176
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• 2005

Natural gas in deep sediment may occur in three phases based on the physical and chemical conditions. If the concentration of gas in pore water is less than the solubility, gas is dissolved. If the concentration of gas is greater than its solubility (water is saturated or supersaturated with gas), gas occurs as a fee gas below the gas hydrate stability Lone (GHSZ) and is present as solid hydrate within the GHSZ. The knowledge of gas concentration in deep sediment appears critical to determine the phase of natural gases and to understand the formation and distribution of gas hydrate. However, reliable data on gas concentration are usually available only from the upper section of marine sediment by the headspace gas technique, which is widely used for sampling of gases from the sediments. The headspace gas technique represents only a fraction of gases present in situ because sediments release most of the gases during recovery and sampling. The PCS (Pressure Core Sampler) is a downhole tool developed to recover a nominal $1{\cal}m$ long, $4.32{\cal}cm$ diameter core containing $1,465cm^3$ of sediment, pore water and gas at in situ pressure up to 68.9 MPa. During Leg 204, the PCS was deployed at 6 Sites. In situ methane gas concentration and distribution of gas hydrate was measured by using PCS tool. Characteristics of methane concentration and distribution is different from site to site. Distribution of gas hydrate in the study area is closely related to characteristics of in situ gas concentration measured by PCS.

• Economic and Environmental Geology
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• v.47 no.1
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• pp.71-85
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• 2014

To study biogeochemical characteristics and origin organic matter, sediment samples were taken from Site of 1249C and Stie 1251B of ODP Leg 204. Data of Rock-Eval, isotope, and element analysis generally indicate dominance of marine organic matter in sediments deposited under marine sedimentary environment. Only Rock-Eval data are somewhat different from those of others owing to under-maturation of organic matter. Samples of Site 1249C show high content of gas hydrate, whereas Site 1251B low content of gas hydrate in some intervals of the core. This result may be accounted to different location of two cores and presence of transportation passage (Horizon A, BSR 2) of thermogenic gas in the core, 1249 C. However, Site 1251B Located in the basin of low accumulation of gas hydrate is presumed to be limited in the gas hydrate production. Because not only transportation passage is limited to move thermogenic gas from the core, but also gas supply was not enough. Therefore, the biogenic gas that resulted from diagenesis of there sediment is superior.