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Gas hydrate stability field in the southwestern Ulleung Basin, East Sea (동해 울릉분지 남서부 해역에서의 가스 하이드레이트 안정영역)

  • Ryu Byong Jae;Don Sun woo;Chang Sung Hyong;Oh Jin yong
    • The Korean Journal of Petroleum Geology
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    • v.7 no.1_2
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    • pp.1-6
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    • 1999
  • 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.

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Hydrocarbon generation and indicator in the western Ulleung Basin (울릉분지 서부에서의 탄화수소 생성 및 지표)

  • Ryu, Byong-Jae;Kim, Ji-Hoon;Lee, Young-Joo;Riedel, M.;Hyndman, R.D.;Kim, Il-Soo
    • 한국신재생에너지학회:학술대회논문집
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    • pp.507-510
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    • 2007
  • Piston cores retrieved from the western Ulleung Basin, East Sea were analyzed to examine the potential for hydrocarbon generation and to determine the hydrocarbon indicators. 2D multi-channel reflection seismic and Chirp data were also investigated for mapping and characterizing the geophysical hydrocarbon indicators such as BSR (bottom simulating reflector), blank zone, pock-mark etc. High organic carbon contents and sedimentation rates that suggest good condition for hydrocarbon generation. High pressure and low temperature condition, and high residual hydrocarbon concentrations are favor the formation of natural gas hydrate. In the piston cores, cracks generally oriented to bedding may indicate the gas expansion. The seismic data show several BSRs that are associated with natural gas hydrates and underlying free gas. A number of vertical to sub-vertical blank zones were well identified in the seismic sections. They often show the seismic pull-up structures, probably indicating the presence of high velocity hydrates. Numerous pockmarks were also observed in the Chirp profiles. They may indicate the presence of free gas below the hydrate stability zone as well.

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Prestack Depth Migration for Gas Hydrate Seismic Data of the East Sea (동해 가스 하이드레이트 탄성파자료의 중합전 심도 구조보정)

  • Jang, Seong-Hyung;Suh, Sang-Yong;Go, Gin-Seok
    • Economic and Environmental Geology
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    • v.39 no.6
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    • pp.711-717
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    • 2006
  • In order to study gas hydrate, potential future energy resources, Korea Institute of Geoscience and Mineral Resources has conducted seismic reflection survey in the East Sea since 1997. one of evidence for presence of gas hydrate in seismic reflection data is a bottom simulating reflector (BSR). The BSR occurs at the interface between overlaying higher velocity, hydrate-bearing sediment and underlying lower velocity, free gas-bearing sediment. That is often characterized by large reflection coefficient and reflection polarity reverse to that of seafloor reflection. In order to apply depth migration to seismic reflection data. we need high performance computers and a parallelizing technique because of huge data volume and computation. Phase shift plus interpolation (PSPI) is a useful method for migration due to less computing time and computational efficiency. PSPI is intrinsically parallelizing characteristic in the frequency domain. We conducted conventional data processing for the gas hydrate data of the Ease Sea and then applied prestack depth migration using message-passing-interface PSPI (MPI_PSPI) that was parallelized by MPI local-area-multi-computer (MPI_LAM). Velocity model was made using the stack velocities after we had picked horizons on the stack image with in-house processing tool, Geobit. We could find the BSRs on the migrated stack section were about at SP 3555-4162 and two way travel time around 2,950 ms in time domain. In depth domain such BSRs appear at 6-17 km distance and 2.1 km depth from the seafloor. Since energy concentrated subsurface was well imaged we have to choose acquisition parameters suited for transmitting seismic energy to target area.

Estimation of gas-hydrate concentrations from amplitude variation with offset (AVO) analysis of gas-hydrate BSRs in the Ulleung Basin, East Sea (동해 울릉분지 해저 모방 반사면의 AVO 분석을 통한 가스하이드레이트 농도 예측)

  • Yi, Bo-Yeon;Lee, Gwang-Hoon;Ryu, Byong-Jae;Yoo, Dong-Geun;Chung, Bu-Heung;Kang, Nyeon-Keon
    • 한국신재생에너지학회:학술대회논문집
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    • pp.676-679
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    • 2009
  • The bottom-simulating reflector (BSR) is the most commonly observed seismic indicator of gas hydrate in the Ulleung Basin, East Sea. We processed ten representative seismic reflection profiles, selected from a large data set, for amplitude variation with offset (AVO) analysis of the BSR to estimate gas-hydrate concentrations. First, BSRs were divided into five groups based on their seismic amplitudes and associated sediment types: (1) very high-amplitude BSRs in turbidite/hemipelagic sediments, (2) high-amplitude BSRs in debris-flow deposits, (3) moderate-amplitude BSRs in turbidite/hemipelagic sediments, (4) very low-amplitude BSRs in debris-flow deposits, and (5) very low-amplitude BSRs in seismic chimneys. The AVO responses of the group 1 and 3 BSRs are characterized by a rapid decrease and a relatively slow decrease in magnitude with offset, respectively. The AVO response of the group 2 BSR is characterized by a relatively slow increase in magnitude with offset. The AVO responses of the groups 4 and 5 BSRs are characterized by a flat AVO with very small zero-offset amplitude. Theoretical AVO curves, based on the three-phase Biot theory, suggest that the group 1 and 3 BSRs may be related to high (> 40%) concentrations of gas hydrate whereas the group 2 BSRs may indicate low (< 20%) concentrations of gas hydrate. The AVO responses of the group 4 and 5 BSRs cannot be compared with the theoretical models because of their very small zero-offset amplitudes. The comparison of the AVO response of the BSR at the UBGH-04 well with theoretical models suggests about 10% gas-hydrate concentration above the gas-hydrate stability zone.

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Seismic Evidence and Characteristics of Gas Hydrate in the Ulleung Basin (탄성파 자료에서 나타난 울릉분지내 가스수화물의 증거와 특성)

  • Kim, Han-Joon;Jou, Hyeong-Tae;Koo, Nam-Hyeong;Yoo, Dong-G.;Suk, Bong-Chool;Yoo, Hai-Soo;Lee, Ho-Young;Park, Keun-Pil
    • Geophysics and Geophysical Exploration
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    • v.11 no.2
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    • pp.148-152
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    • 2008
  • Multichannel seismic profiles reveal a strong bottom simulating reflector (BSR) occurring below the seafloor in the plain of the Ulleung Basin, East Sea (Japan Sea). The essential characteristics of the BSR include its cross-cutting relationship to strata, strong amplitude, and reverse polarity with respect to the seafloor reflection, representing the base of the gas hydrate stability zone (BHSZ). The BSR reflection coefficient ranging from -0.23 to -0.26 is 1.5${\sim}$1.7 times that of the seafloor reflection and interval velocities decrease to less than 700 m/s below the BSR. These features indicate the existence of free gas beneath the GHSZ. Heat flow, estimated from the BSR depth as $95{\sim}98mW/m^2$, is in good agreement with measured values. Therefore, the BSR can be efficiently used to estimate regional distribution of heat flow in the Ulleung Basin.

Seismic Attribute Analysis of the Indicators for the Occurrence of Gas Hydrate in the Northwestern Area of the Ulleung Basin, East Sea (동해 울릉분지 북서지역 가스하이드레이트 부존 지시자의 탄성파 속성 분석)

  • Kim, Kyoung Jin;Yi, Bo Yeon;Kang, Nyeon Keon;Yoo, Dong Geun;Shin, Kook Sun;Cho, Young Ho
    • Geophysics and Geophysical Exploration
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    • v.17 no.4
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    • pp.216-230
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    • 2014
  • Based on the interpretation of 3D seismic profiles acquired in the northwestern area of the Ulleung Basin, East Sea, the shallow sediments consist of five seismic units separated by regional reflectors. An anticline is present in the study area that documents activity of many faults. Bottom simulating reflectors are characterized by high RMS amplitude. Acoustic blanking with low RMS amplitude is distinctively recognized in the gas hydrate stability zone. Seismic attribute analysis shows that if gas hydrates are underlain by free gas, the high reflection strength and the low instantaneous frequency are displayed below the boundary between them. Whereas, if not, the reflection strength is low and instantaneous frequency is high continuously below the gas hydrate zone. Based on the spectral decomposition of the bottom simulating reflector, the high envelope at the specific high frequency range indicates the generation of the tuning effect due to the lower free gas content. Four models for the occurrence of the gas hydrate are suggested considering the slope of sedimentary layers as well as the presence of gas hydrate or free gas.

Seismic Properties Study of Gas Hydrate in Deep Sea using Numerical Modeling Technique (수치 모델링 기술을 이용한 심해 가스 하이드레이트의 탄성파 특성 연구)

  • Shin, Sung-Ryul;Yeo, Eun-Min;Kim, Chan-Su;Park, Keun-Pil;Lee, Ho-Young;Kim, Young-Jun
    • Geophysics and Geophysical Exploration
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    • v.9 no.2
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    • pp.139-147
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    • 2006
  • We had conducted a numerical modeling to investigate seismic properties of gas hydrate with field parameters acquired over the East sea in 1998. We used a 2-D staggered grid finite difference method to generate synthetic elastic seismograms for multi-channel seismic survey, OBC (Ocean Bottom Cable) survey and VCS (Vertical Cable Seismic) survey. The results of this study showed that the method using staggered grid yielded stable results and could be used to seismic imaging. We could find out the high amplitude anomaly and the phase reversal phenomenon of reflection wave at interface between the gas hydrate layer and free gas layer such a BSR (Bottom Simulating Reflector) which is the evidence for existence of gas hydrate in seismic reflection data. And we computed the reflection coefficients at the incident angles corresponding to offset distance with the synthetic seismograms. The reflection coefficients acquired from the numerical modeling were nearly consistent with the reflection coefficient computed by Shuey's equation.

Geophysical study about gas hydrate formation in the Ulleung Basin, East Sea (동해 울릉분지 가스하이드레이트 형성에 관한 지구물리해석)

  • Kang, Dong-Hyo;Ryu, Byong-Jae;Yoo, Dong-Geun;Bahk, Jang-Jun;Koo, Nam-Hyung;Kim, Won-Sik
    • 한국신재생에너지학회:학술대회논문집
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    • pp.680-681
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    • 2009
  • On the basis of seismic interpretation, seismic indicators of gas hydrate and associated gas such as bottom simulating reflector (BSR), acoustic blanking, column structure, gas seepage, enhanced reflection were identified in the Ulleung Basin. Fractures, faults, sandy layer could be the migration pathways transporting fluid and gas to stability zone. The formation of gas hydrate in the Ulleung Basin include: (1) nodules, veins, layers in muddy sediments and disseminated forms in sandy layer within localized column structure, (2) disseminated forms in sandy layer, and (3) disseminated forms in sandy layer just above BSR.

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Parameter analysis for gas hydrate data of East sea using Geobit (지오빗을 이용한 동해 가스하이드레이트 탄성파 자료처리 매개변수 분석)

  • Kim, Young-Wan;Jang, Seong-Hyung;Kim, Hyun-Tae;Yoon, Wang-Joong
    • 한국신재생에너지학회:학술대회논문집
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    • pp.377-381
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    • 2006
  • A seismic survey for gas hydrate have performed over the East sea by the KIGAM since 1997. General indicator of gas hydrate in seismic data is commonly inferred from the BSR(Bottom Simulating Reflector) that occurred parallel to the sea floor, amplitude decrease at the top of the BSR, amplitude blanking at the bottom of the BSR, decrease of the interval velocity and the reflection phase reversal at the BSR. In this paper we had analyzed optimum parameters of the field data to detect the 9as hydrate. Shot delay correction is applied 95ms, spherical divergence correction is applied velocity library 3, bandpass filter is applied 25-30-115-120Hz deconvolution operator length is applied 60ms, lag is 6ms and accurate velocity analysis NMO correction, stack is performed. Geobit 2.11.0 developed by the KIGAM was used for all data processing. Processing results say that the BSR occurred parallel to the sea floor were shown at 3,150m/s of two way travel time from the sea floor through shot point 5,000-5,610, and identified the interval velocity decrease around BSR and the reflection phase reversal corresponding to the reflection at the sea floor.

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Potential of gas generation and/or natural gas hydrate formation, and evidences of their presence in near seafloor sediments of the southwestern Ulleung Basin, East Sea (동해 울릉분지 남서부 천부 퇴적층에서의 가스 생성 및 천연가스 하이드레이트 형성 잠재력과 이들의 부존 증거)

  • Ryu, Byong-Jae;Lee, Young-Joo;Kim, Ji-Hoon;Riedel, M.;Hyndman, R.D.;Kim, Il-Soo
    • 한국신재생에너지학회:학술대회논문집
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    • pp.50-53
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    • 2006
  • Regional geophysical surveys and geological cal studies on natural gas hydrate (NGH) in the East Sea were carried out by the Korea Institute of Geoscience and Mineral Resources (KIGAM) from 2000 to 2004. 16 piston cores, 2270 L-km of multi-channel reflection seismic (MCRS) data and 730 L-km of 3.5kHz Chirp data obtained from the southwestern part of the deep-water Ulleung Basin were analyzed in this study. In piston cores, cracks generally developed parallel to bedding suggest significant gas content. The core analyses showed high total organic carbon (TOC) content, sedimentation rate and heat flow of sediments. These are in favor of the general ion of substantial biogenic methane, which can form the NGH within the stability zone of the near seafloor sediments in the study area. The cores generally show also high residual hydrocarbon gas concentrations for the formation of natural gas hydrates The geophysical indicators of the presence of gas and/or NGH such as bottom simulating reflectors (BSRs), seismic blank Bones, pockmarks and gas seeping features were well defined on the MCRS and Chirp data.

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