• Title, Summary, Keyword: 음향공백대

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Geophysical studies of gas hydrate in the Ulleung Basin, East Sea (동해 울릉분지 가스하이드레이트 지구물리탐사연구)

  • Yoo, Dong-G.;Kim, Gil-Y.;Park, Keun-P.;Lee, Ho-Y.;Ryu, Byong-J.
    • 한국신재생에너지학회:학술대회논문집
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    • pp.672-675
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    • 2009
  • 동해 울릉분지에서 취득된 다중채널 탄성파자료 해석에 의하면 이 지역에는 가스하이드레이트 부존가능성을 지시하는 해저모방반사면, 탄성파침니/칼럼, 음향공백대, 증폭반사면, 가스분출 구조 등을 포함하는 5가지 탄성파 지시자가 존재한다. 가장 대표적인 지시자인 해저모방반사면은 연구지역의 남쪽사면의 경우 연속성이 양호하고 강한 진폭을 갖는 반면, 북쪽 중앙분지에서는 상대적으로 진폭이 약하고 연속성이 불량하다. 반사도 감소 및 속도 풀업 특징을 갖는 탄성파 침니/칼럼구조는 중앙분지와 북동쪽해역에 주로 분포하며 가스하이드레이트 혹은 가스유체의 부존가능성을 시사해준다. 반사강도가 약화되어 나타나는 음향공백대는 저탁류/원양성 퇴적물이 분포하는 중앙분지에 부분적으로 발달하며, 칼럼과 연계된 음향공백대는 북동쪽 사면저부에 주로 분포한다. 해저모방반사면의 하부에 위치하는 증폭반사면은 연구지역의 서쪽 사면에 분포하며 강한 음의 진폭특성으로 보아 자유가스를 함유한 층으로 해석된다. 가스분출구조는 주로 쇄설성 퇴적물이 우세한 조사지역의 남쪽 대륙사면지역에 광범위하게 분포하며 돔구조 혹은 폭마크 등을 수반한다.

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Study on the Characteristics of Gas Hydrate Layers Distributed in the Southern Ulleung Basin, the East Sea (동해 울릉분지 남부해역에 분포하는 가스 하이드레이트층의 특성 연구)

  • Huh Sik;Yoo Hai-Soo;Kim Han-Joon;Han Sang-Joon;Lee Yong-Kuk
    • The Korean Journal of Petroleum Geology
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    • v.10 no.1_2
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    • pp.18-22
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    • 2004
  • To identify and interpret the distribution and the characteristics of the gas hydrate layers in the Ulleung Basin, we have surveyed and gathered the multi-channel seismic data, Chirp sub-bottom profiler, SeaBeam and 12 m piston core samples since 1996. In previous works, high-resolution seismic profiles showed acoustic anomalies such as acoustic void, acoustic turbidity and pock mark which indicate the presence of gas-charged sediments. The patterns of horizontal degassing cracks originated from free methane expansion is the strong indicator of shallow gas-charged sediments in the core samples. The observation of submarine slides and slumps from destabilizing the sediments in the southern part of the Ulleung Basin may also point out that the gas had been released from gas hydrate dissociation during lowstand of sea level. The multi-channel seismic data show BSR, blanking and phase reversal. The gas hydrate layers above which large-scale shallow gases are distributed exist at the depth of about 200 m from the sea-floor with water depth of 2,100 m. From the interpretation of seismic sections in the southern Ulleung Basin, gas hydrate layers occur in the Pleistocene-Holocene sediments. These gas-charged sediments, acoustic anomalies and BSR may be all related to the existence of gas hydrate layers in the study area.

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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.