Improving gas hydrate saturation estimates using P-wave velocity log data by incorporating XRD-data for detailed matrix-mineralogy definition

2013 ◽  
Vol 47 ◽  
pp. 155-167 ◽  
Author(s):  
H.-S. Kim ◽  
M. Riedel ◽  
B.-J. Ryu ◽  
G.-Y. Kim ◽  
J.-J. Bahk
Keyword(s):  
Wave Velocity ◽  
Gas Hydrate ◽  
P Wave ◽  
Log Data ◽  
P Wave Velocity ◽  
Hydrate Saturation

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.

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.

scholarly journals The Acoustic Properties of Sandy and Clayey Hydrate-Bearing Sediments

Energies ◽  
2019 ◽  
Vol 12 (10) ◽  
pp. 1825
Author(s):  
Xiao-Hui Wang ◽  
Qiang Xu ◽  
Ya-Nan He ◽  
Yun-Fei Wang ◽  
Yi-Fei Sun ◽  
...  
Keyword(s):  
Wave Velocity ◽  
Gas Hydrate ◽  
Acoustic Properties ◽  
P Wave ◽  
S Wave ◽  
Hydrate Saturation ◽  
New Apparatus ◽  
Sandy Sediments ◽  
Hydrate Bearing Sediments ◽  
And Control

Natural gas hydrates samples are rare and difficult to store and transport at in situ pressure and temperature conditions, resulting in difficulty to characterize natural hydrate-bearing sediments and to identify hydrate accumulation position and saturation at the field scale. A new apparatus was designed to study the acoustic properties of seafloor recovered cores with and without hydrate. To protect the natural frames of recovered cores and control hydrate distribution, the addition of water into cores was performed by injecting water vapor. The results show that hydrate saturation and types of host sediments are the two most important factors that govern the elastic properties of hydrate-bearing sediments. When gas hydrate saturation adds approximately to 5–25%, the corresponding P-wave velocity (Vp) increases from 1.94 to 3.93 km/s and S-wave velocity (Vs) increases from 1.14 to 2.23 km/s for sandy specimens; Vp and Vs for clayey samples are 1.72–2.13 km/s and 1.10–1.32 km/s, respectively. The acoustic properties of sandy sediments can be significantly changed by the formation/dissociation of gas hydrate, while these only minorly change for clayey specimens.

scholarly journals Rock Physics Model and Seismic Dispersion and Attenuation in Gas Hydrate-Bearing Sediments

2021 ◽  
Vol 9 ◽  
Author(s):  
Zhiqi Guo ◽  
Xueying Wang ◽  
Jian Jiao ◽  
Haifeng Chen
Keyword(s):  
Gas Hydrate ◽  
Rock Physics ◽  
P Wave ◽  
Pore Filling ◽  
P Wave Velocity ◽  
Hydrate Saturation ◽  
Physics Model ◽  
Rock Physics Model ◽  
Hydrate Bearing Sediments ◽  
Dispersion And Attenuation

A rock physics model was established to calculate the P-wave velocity dispersion and attenuation caused by the squirt flow of fluids in gas hydrate-bearing sediments. The critical hydrate saturation parameter was introduced to describe different ways of hydrate concentration, including the mode of pore filling and the co-existence mode of pore filling and particle cementation. Rock physical modeling results indicate that the P-wave velocity is insensitive to the increase in gas hydrate saturation for the mode of pore filling, while it increases rapidly with increasing gas hydrate saturation for the co-existence mode of pore filling and particle cementation. Meanwhile, seismic modeling results show that both the PP and mode-converted PS reflections are insensitive to the gas hydrate saturation that is lower than the critical value, while they tend to change obviously for the hydrate saturation that is higher than the critical value. These can be interpreted that only when gas hydrate begins to be part of solid matrix at high gas hydrate saturation, it represents observable impact on elastic properties of the gas hydrate-bearing sediments. Synthetic seismograms are calculated for a 2D heterogeneous model where the gas hydrate saturation varies vertically and layer thickness of the gas hydrate-bearing sediment varies laterally. Modeling results show that larger thickness of the gas hydrate-bearing layer generally corresponds to stronger reflection amplitudes from the bottom simulating reflector.

scholarly journals Laboratory observations of frequency-dependent ultrasonic P-wave velocity and attenuation during methane hydrate formation in Berea sandstone

2019 ◽  
Vol 219 (1) ◽  
pp. 713-723 ◽  
Author(s):  
Sourav K Sahoo ◽  
Laurence J North ◽  
Hector Marín-Moreno ◽  
Tim A Minshull ◽  
Angus I Best
Keyword(s):  
Aspect Ratio ◽  
Wave Velocity ◽  
Methane Hydrate ◽  
Hydrate Formation ◽  
P Wave ◽  
Gas Bubble ◽  
Berea Sandstone ◽  
Frequency Dependent ◽  
P Wave Velocity ◽  
Hydrate Saturation

SUMMARY Knowledge of the effect of methane hydrate saturation and morphology on elastic wave attenuation could help reduce ambiguity in seafloor hydrate content estimates. These are needed for seafloor resource and geohazard assessment, as well as to improve predictions of greenhouse gas fluxes into the water column. At low hydrate saturations, measuring attenuation can be particularly useful as the seismic velocity of hydrate-bearing sediments is relatively insensitive to hydrate content. Here, we present laboratory ultrasonic (448–782 kHz) measurements of P-wave velocity and attenuation for successive cycles of methane hydrate formation (maximum hydrate saturation of 26 per cent) in Berea sandstone. We observed systematic and repeatable changes in the velocity and attenuation frequency spectra with hydrate saturation. Attenuation generally increases with hydrate saturation, and with measurement frequency at hydrate saturations below 6 per cent. For hydrate saturations greater than 6 per cent, attenuation decreases with frequency. The results support earlier experimental observations of frequency-dependent attenuation peaks at specific hydrate saturations. We used an effective medium rock-physics model which considers attenuation from gas bubble resonance, inertial fluid flow and squirt flow from both fluid inclusions in hydrate and different aspect ratio pores created during hydrate formation. Using this model, we linked the measured attenuation spectral changes to a decrease in coexisting methane gas bubble radius, and creation of different aspect ratio pores during hydrate formation.

Sign in / Sign up

Export Citation Format

Share Document