Seismic indicators of gas hydrates and associated free gas

2009 ◽  
Author(s):  
Sanjeev Rajput ◽  
Mrinal K. Sen ◽  
Satinder Chopra
Keyword(s):  
Gas Hydrates ◽  
Free Gas

scholarly journals Seismic and seafloor evidence for free gas, gas hydrates, and fluid seeps on the transform margin offshore Cape Mendocino

2003 ◽  
Vol 108 (B5) ◽  
Author(s):  
Anne M. Tréhu ◽  
Debra S. Stakes ◽  
Cindy D. Bartlett ◽  
Johanna Chevallier ◽  
Robert A. Duncan ◽  
...  
Keyword(s):  
Gas Hydrates ◽  
Free Gas ◽  
Transform Margin

scholarly journals Seismic Attenuation and Velocity Dispersion to Discriminate Gas Hydrates and Free Gas Zone, Makran Offshore, Pakistan

2016 ◽  
Vol 07 (08) ◽  
pp. 1020-1028
Author(s):  
Muhammad Irfan Ehsan ◽  
Perveiz Khalid ◽  
Nisar Ahmed ◽  
Jiachun You ◽  
Xuewei Liu ◽  
...  
Keyword(s):  
Gas Hydrates ◽  
Velocity Dispersion ◽  
Seismic Attenuation ◽  
Free Gas ◽  
Makran Offshore

Characterising Gas Hydrate Deposits on New Zealand's Southern Hikurangi Margin using Seismic Reflection Data

2021 ◽  
Author(s):  
◽  
Hanyan Wang
Keyword(s):  
Gas Hydrates ◽  
Gas Hydrate ◽  
Research Area ◽  
Low Velocity ◽  
Seismic Reflection Data ◽  
Free Gas ◽  
Reflection Data ◽  
Geological Conditions ◽  
Gas Hydrate Deposits ◽  
Seismic Lines

<p>Reprocessed Bruin 2D seismic data (recorded in 2006) from New Zealand Hikurangi Margin are presented and analyzed to show the presence of gas hydrates. We choose six seismic lines that each showed bottom-simulating reflections (BSRs) that are important indicators for the presence of gas hydrate. The aim is to obtain a higher resolution image of the shallow subsurface structures and determine the nature of the gas hydrate system in this area.  To further investigate the presence of Gas Hydrates was undertaken. There is a strong correlation between anomalous velocities and the depths of BSRs, which supports the presence of gas hydrates in the research area and is useful for detecting areas of both free gas and gas hydrate along the seismic lines.  The combination of high-resolution seismic imaging and velocity analysis is the key method for showing the distribution of gas hydrates and gas pockets in our research area. The results indicate that the distribution of both free gas and gas hydrate is strongly localized. The Discussion Chapter gives several concentrated gas hydrate deposits in the research area. Idealized scenarios for the formation of the gas hydrates are proposed. In terms of identifying concentrated gas hydrate deposits we propose the identification of the following key seismic attributes: 1) existence of BSRs, 2) strong reflections above BSRs in the gas hydrate stability zone, 3) enhanced reflections related to free gas below BSRs, 4) appropriate velocity anomalies (i.e. low velocity zones beneath BSRs and localized high-velocity zones above BSRs).  This study contributes to the understanding of the geological conditions and processes that drives the deposition of concentrated gas hydrate deposits on this part of the Hikurangi Margin.</p>

Gas hydrates, free gas distribution and fault pattern on the west Svalbard continental margin

2010 ◽  
Vol 180 (2) ◽  
pp. 666-684 ◽  
Author(s):  
Gianni Madrussani ◽  
Giuliana Rossi ◽  
Angelo Camerlenghi
Keyword(s):  
Continental Margin ◽  
Gas Hydrates ◽  
Gas Distribution ◽  
The West ◽  
Free Gas ◽  
Fault Pattern

scholarly journals Free gas and gas hydrates from the Sea of Marmara, Turkey

2009 ◽  
Vol 264 (1-4) ◽  
pp. 197-206 ◽  
Author(s):  
Christophe Bourry ◽  
Bertrand Chazallon ◽  
Jean Luc Charlou ◽  
Jean Pierre Donval ◽  
Livio Ruffine ◽  
...  
Keyword(s):  
Gas Hydrates ◽  
Sea Of Marmara ◽  
Free Gas

Characterization of gas accumulation at a venting gas hydrate system in Shenhu area, south china sea

2021 ◽  
pp. 1-45
Author(s):  
JInqiang Liang ◽  
Zijian Zhang ◽  
Jingan Lu ◽  
Guo Yiqun ◽  
Zhibin Sha ◽  
...  
Keyword(s):  
South China Sea ◽  
Wave Velocity ◽  
South China ◽  
Gas Hydrates ◽  
Gas Hydrate ◽  
Stability Zone ◽  
Shenhu Area ◽  
Free Gas ◽  
Seismic Amplitude ◽  
Hydrate Stability

Bottom-simulating reflections (BSR) in seismic data have been widely accepted to indicate the base of methane gas hydrate stability zone (MGHSZ) and free gas was thought to exist only below it. However, real geologic systems are far more complex. Here, we presented the results of three-dimensional seismic, logging while drilling (LWD), in situ and coring measurements at a venting gas hydrate system in the Shenhu area of the South China Sea. Our studies reveal that free gas has migrated upward through the thermogenic gas hydrate stability zone (TGHSZ) into the MGHSZ and become a part of the gas hydrate system. Seismic amplitude anomalies and core results suggest the presence of free gas above the base of MHSZ at 165 mbsf and the presence of thermogenic gas hydrates below it in the well SC-W01. Analyses of P-wave velocity, S-wave velocity, density, and porosity logs reveal free gas occurs above and below the MGHSZ as well. Integrating log and core analysis with seismic interpretation suggests that the variation in seismic amplitude within chaotic zone is associated with variable gas saturations, and a large amount of methane and thermogenic gases accumulate near the complex BSRs. We propose that relative permeability likely plays a significant role in the free gas distribution and formation of gas hydrates within a venting gas hydrate system, while the effect of dissolved-gas short migration is not ignored. Our results have important implications for understanding the accumulation and distribution of gas hydrates and free gas in the venting gas hydrate system and seeps at the seafloor.

scholarly journals Gas hydrate and free gas detection using seismic quality factor estimates from high-resolution P-cable 3D seismic data

2016 ◽  
Vol 4 (1) ◽  
pp. SA39-SA54 ◽  
Author(s):  
Sunny Singhroha ◽  
Stefan Bünz ◽  
Andreia Plaza-Faverola ◽  
Shyam Chand
Keyword(s):  
High Resolution ◽  
Frequency Shift ◽  
Gas Hydrates ◽  
Gas Hydrate ◽  
Seismic Data ◽  
Seismic Attenuation ◽  
3D Seismic ◽  
Free Gas ◽  
Centroid Frequency ◽  
3D Seismic Data

We have estimated the seismic attenuation in gas hydrate and free-gas-bearing sediments from high-resolution P-cable 3D seismic data from the Vestnesa Ridge on the Arctic continental margin of Svalbard. P-cable data have a broad bandwidth (20–300 Hz), which is extremely advantageous in estimating seismic attenuation in a medium. The seismic quality factor (Q), the inverse of seismic attenuation, is estimated from the seismic data set using the centroid frequency shift and spectral ratio (SR) methods. The centroid frequency shift method establishes a relationship between the change in the centroid frequency of an amplitude spectrum and the Q value of a medium. The SR method estimates the Q value of a medium by studying the differential decay of different frequencies. The broad bandwidth and short offset characteristics of the P-cable data set are useful to continuously map the Q for different layers throughout the 3D seismic volume. The centroid frequency shift method is found to be relatively more stable than the SR method. Q values estimated using these two methods are in concordance with each other. The Q data document attenuation anomalies in the layers in the gas hydrate stability zone above the bottom-simulating reflection (BSR) and in the free gas zone below. Changes in the attenuation anomalies correlate with small-scale fault systems in the Vestnesa Ridge suggesting a strong structural control on the distribution of free gas and gas hydrates in the region. We argued that high and spatially limited Q anomalies in the layer above the BSR indicate the presence of gas hydrates in marine sediments in this setting. Hence, our workflow to analyze Q using high-resolution P-cable 3D seismic data with a large bandwidth could be a potential technique to detect and directly map the distribution of gas hydrates in marine sediments.

Sign in / Sign up

Export Citation Format

Share Document