scholarly journals Acoustic Velocity Log Numerical Simulation and Saturation Estimation of Gas Hydrate Reservoir in Shenhu Area, South China Sea

2013 ◽  
Vol 2013 ◽  
pp. 1-13 ◽  
Author(s):  
Kun Xiao ◽  
Changchun Zou ◽  
Biao Xiang ◽  
Jieqiong Liu
Keyword(s):  
Numerical Simulation ◽  
South China Sea ◽  
Wave Velocity ◽  
South China ◽  
Gas Hydrate ◽  
P Wave ◽  
Shenhu Area ◽  
Free Gas ◽  
P Wave Velocity ◽  
Hydrate Saturation

Gas hydrate model and free gas model are established, and two-phase theory (TPT) for numerical simulation of elastic wave velocity is adopted to investigate the unconsolidated deep-water sedimentary strata in Shenhu area, South China Sea. The relationships between compression wave (P wave) velocity and gas hydrate saturation, free gas saturation, and sediment porosity at site SH2 are studied, respectively, and gas hydrate saturation of research area is estimated by gas hydrate model. In depth of 50 to 245 m below seafloor (mbsf), as sediment porosity decreases, P wave velocity increases gradually; as gas hydrate saturation increases, P wave velocity increases gradually; as free gas saturation increases, P wave velocity decreases. This rule is almost consistent with the previous research result. In depth of 195 to 220 mbsf, the actual measurement of P wave velocity increases significantly relative to the P wave velocity of saturated water modeling, and this layer is determined to be rich in gas hydrate. The average value of gas hydrate saturation estimated from the TPT model is 23.2%, and the maximum saturation is 31.5%, which is basically in accordance with simplified three-phase equation (STPE), effective medium theory (EMT), resistivity log (Rt), and chloride anomaly method.

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.

Revision of P-wave velocity and thickness of hydrate layer in Shenhu Area, South China Sea

2014 ◽  
Vol 13 (5) ◽  
pp. 742-746 ◽  
Author(s):  
Jianming Gong ◽  
Xunhua Zhang ◽  
Changchun Zou ◽  
Qiang Chen ◽  
Lichen Wang ◽  
...  
Keyword(s):  
South China Sea ◽  
Wave Velocity ◽  
South China ◽  
P Wave ◽  
Shenhu Area ◽  
China Sea ◽  
Hydrate Layer ◽  
P Wave Velocity

scholarly journals Elevated gas hydrate saturation within silt and silty clay sediments in the Shenhu area, South China Sea

2011 ◽  
Vol 116 (B5) ◽  
Author(s):  
Xiujuan Wang ◽  
Deborah R. Hutchinson ◽  
Shiguo Wu ◽  
Shengxiong Yang ◽  
Yiqun Guo
Keyword(s):  
South China Sea ◽  
South China ◽  
Gas Hydrate ◽  
Silty Clay ◽  
Shenhu Area ◽  
China Sea ◽  
Hydrate Saturation

A case study: travel time inversion for P-wave velocity using OBS data of South China Sea

2012 ◽  
Vol 33 (4) ◽  
pp. 389-396 ◽  
Author(s):  
Xiangchun Wang ◽  
Timothy A. Minshull ◽  
Changliang Xia ◽  
Xuewei Liu
Keyword(s):  
South China Sea ◽  
Travel Time ◽  
Wave Velocity ◽  
South China ◽  
P Wave ◽  
Time Inversion ◽  
P Wave Velocity ◽  
Travel Time Inversion ◽  
Obs Data

Identification of gas hydrate dissociation from wireline-log data in the Shenhu area, South China Sea

Geophysics ◽  
2012 ◽  
Vol 77 (3) ◽  
pp. B125-B134 ◽  
Author(s):  
Xiujuan Wang ◽  
Myung Lee ◽  
Shiguo Wu ◽  
Shengxiong Yang
Keyword(s):  
Wave Velocity ◽  
Gas Hydrate ◽  
Seismic Data ◽  
Pore Space ◽  
P Wave ◽  
Well Log ◽  
Hydrate Dissociation ◽  
Free Gas ◽  
P Wave Velocity

Wireline logs were acquired in eight wells during China’s first gas hydrate drilling expedition (GMGS-1) in April–June of 2007. Well logs obtained from site SH3 indicated gas hydrate was present in the depth range of 195–206 m below seafloor with a maximum pore-space gas hydrate saturation, calculated from pore water freshening, of about 26%. Assuming gas hydrate is uniformly distributed in the sediments, resistivity calculations using Archie’s equation yielded hydrate-saturation trends similar to those from chloride concentrations. However, the measured compressional (P-wave) velocities decreased sharply at the depth between 194 and 199 mbsf, dropping as low as [Formula: see text], indicating the presence of free gas in the pore space, possibly caused by the dissociation of gas hydrate during drilling. Because surface seismic data acquired prior to drilling were not influenced by the in situ gas hydrate dissociation, surface seismic data could be used to identify the cause of the low P-wave velocity observed in the well log. To determine whether the low well-log P-wave velocity was caused by in situ free gas or by gas hydrate dissociation, synthetic seismograms were generated using the measured well-log P-wave velocity along with velocities calculated assuming both gas hydrate and free gas in the pore space. Comparing the surface seismic data with various synthetic seismograms suggested that low P-wave velocities were likely caused by the dissociation of in situ gas hydrate during drilling.

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