Gas hydrate stability field in the southwestern Ulleung Basin, East Sea

동해 울릉분지 남서부 해역에서의 가스 하이드레이트 안정영역

  • Ryu Byong Jae (Petroleum and Marine Research, KIGAM) ;
  • Don Sun woo (Petroleum and Marine Research, KIGAM) ;
  • Chang Sung Hyong (Research Instituteof Basic Science, Chungnam National University) ;
  • Oh Jin yong (Research Instituteof Basic Science, Chungnam National University)
  • 류병재 (한국자원연구소 석유해저연구부) ;
  • 선우돈 (한국자원연구소 석유해저연구부) ;
  • 장성형 (충남대학교 기초과학연구소) ;
  • 오진용 (충남대학교 기초과학연구소)
  • Published : 1999.12.01

Abstract

Natural gas hydrate, a solid compound of natural gas (mainly methane) and water in the low temperature and high pressure, is widely distributed in permafrost region and deep sea sediments. Gas hydrate stability field (GHSF), which corresponds to the conditions of a stable existence of solid gas hydrate without dissociation, depends on temperature, pressure, and composition of gas and interstitial water. Gas hydrate-saturated sediment are easily recognized by the bottom simulating reflector (BSR), a strong-amplitude sea bottom-mimic reflector in seismic profiles. It is known that BSR is associated with the basal boundary of the GHSF, The purpose of this study is to define the GHSF and its occurrence in the southwestern part of Ulleung Basin, East Sea. The hydrothermal gradient is measured using the expandable bathythermograph (XBT) and the geothermal gradient data are utilized from previous drilling results for the adjacent area. By the laboratory work using methane and NaCl $3.0 wt{\%}$ solution, it is shown that the equilibrium pressures of the gas hydrate reach to 2,920.2 kPa at 274.15 K and to 18,090 kPa at 289.95 K for the study area. Consequently, it is interpreted that the lower boundary of the GHSF is about 210 m beneath 400-m-deep sea bottom and about 480 m beneath 1,100-m-deep sea bottom. The resultant boundary is well matched with the depth of the BSR obtained from the seismic data analysis for the study area.