scholarly journals Evaluation Method of the Gas Hydrate and Free Gas System and Its Application in the Shenhu Area, South China Sea

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-16
Author(s):  
Pibo Su ◽  
Tingwei Li ◽  
Shurong Liang ◽  
Jinqiang Liang ◽  
Xiaoxue Wang ◽  
...  
Keyword(s):  
Gas Hydrate ◽  
Seismic Reflection ◽  
Effective Porosity ◽  
The Body ◽  
Effective Thickness ◽  
Space Distribution ◽  
Depth Range ◽  
Free Gas ◽  
Gas System ◽  
Reflection Characteristics

As a new alternative energy source, gas hydrate has attracted wide attention all over the world. Since gas hydrate is always associated with free gas, the evaluation of the gas hydrate and free gas system is an important aspect of hydrate reservoir exploration and development. In this study, based on identifying gas hydrate and free gas by well logging, the seismic reflection characteristics of gas hydrate and free gas are determined by an accurate well-to-seismic calibration method. On account of seismic reflection characteristics, AVO attributes are used to identify gas hydrate and free gas qualitatively. Using prestack and poststack inversion to get the ratio of P -wave impedance and P -wave-to- S -wave velocities, we determine the three-dimensional space distribution of gas hydrate and free gas, predict their effective porosity and saturation, and eventually achieve the meticulous depiction of gas hydrate and free gas in the body, which is necessary in subsequent estimation of gas hydrate and free gas resources. Results show that according to logging interpretation, gas hydrate of the B-well is located in the depth range of 1460–1510 mbsl and free gas is in 1510–1542 mbsl. Moreover, gas hydrate of the A-well is located in the depth range of 1425–1512 mbsl, and no obvious free gas is identified. Gas hydrate is located above free gas and distributed continuously. In plane form, gas hydrate and free gas both present subelliptical distribution in the NW-SE direction. Gas hydrate has an effective porosity of 0.30–0.40, an average saturation of 0.33–0.40, and an effective thickness of 3.0–10.5 m, whereas free gas possesses an effective porosity of 0.35–0.40, a saturation of 0.24–0.32, and an effective thickness of 2.0–5.0 m.

scholarly journals Gas origin linked to paleo BSR

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Iván de la Cruz Vargas-Cordero ◽  
Lucia Villar-Muñoz ◽  
Umberta Tinivella ◽  
Michela Giustiniani ◽  
Nathan Bangs ◽  
...  
Keyword(s):  
Gas Hydrate ◽  
Geothermal Gradient ◽  
Last Deglaciation ◽  
Seismic Line ◽  
Central Chile ◽  
Free Gas ◽  
Bottom Simulating Reflector ◽  
South Central ◽  
Gas System ◽  
Central South

AbstractThe Central-South Chile margin is an excellent site to address the changes in the gas hydrate system since the last deglaciation associated with tectonic uplift and great earthquakes. However, the dynamic of the gas hydrate/free gas system along south central Chile is currently not well understood. From geophysical data and modeling analyses, we evaluate gas hydrate/free gas concentrations along a seismic line, derive geothermal gradients, and model past positions of the Bottom Simulating Reflector (BSR; until 13,000 years BP). The results reveal high hydrate/free gas concentrations and local geothermal gradient anomalies related to fluid migration through faults linked to seafloor mud volcanoes. The BSR-derived geothermal gradient, the base of free gas layers, BSR distribution and models of the paleo-BSR form a basis to evaluate the origin of the gas. If paleo-BSR coincides with the base of the free gas, the gas presence can be related to the gas hydrate dissociation due to climate change and geological evolution. Only if the base of free gas reflector is deeper than the paleo-BSR, a deeper gas supply can be invoked.

Characterization of elastic properties of near-surface and subsurface deepwater hydrate-bearing sediments

Geophysics ◽  
2013 ◽  
Vol 78 (3) ◽  
pp. D169-D179 ◽  
Author(s):  
Zijian Zhang ◽  
De-hua Han ◽  
Daniel R. McConnell
Keyword(s):  
Wave Velocity ◽  
Elastic Constants ◽  
Gas Hydrate ◽  
Effective Medium Theory ◽  
Pore Space ◽  
Seismic Interpretation ◽  
P Wave ◽  
Near Surface ◽  
Free Gas ◽  
Hydrate Bearing Sediments

Hydrate-bearing sands and shallow nodular hydrate are potential energy resources and geohazards, and they both need to be better understood and identified. Therefore, it is useful to develop methodologies for modeling and simulating elastic constants of these hydrate-bearing sediments. A gas-hydrate rock-physics model based on the effective medium theory was successfully applied to dry rock, water-saturated rock, and hydrate-bearing rock. The model was used to investigate the seismic interpretation capability of hydrate-bearing sediments in the Gulf of Mexico by computing elastic constants, also known as seismic attributes, in terms of seismic interpretation, including the normal incident reflectivity (NI), Poisson’s ratio (PR), P-wave velocity ([Formula: see text]), S-wave velocity ([Formula: see text]), and density. The study of the model was concerned with the formation of gas hydrate, and, therefore, hydrate-bearing sediments were divided into hydrate-bearing sands, hydrate-bearing sands with free gas in the pore space, and shallow nodular hydrate. Although relations of hydrate saturation versus [Formula: see text] and [Formula: see text] are different between structures I and II gas hydrates, highly concentrated hydrate-bearing sands may be interpreted on poststack seismic amplitude sections because of the high NI present. The computations of elastic constant implied that hydrate-bearing sands with free gas could be detected with the crossplot of NI and PR from prestack amplitude analysis, and density may be a good hydrate indicator for shallow nodular hydrate, if it can be accurately estimated by seismic methods.

Estimation of gas-hydrate concentration and free-gas saturation at the Norwegian-Svalbard continental margin

2005 ◽  
Vol 53 (6) ◽  
pp. 803-810 ◽  
Author(s):  
José M. Carcione ◽  
Davide Gei ◽  
Giuliana Rossi ◽  
Gianni Madrussani
Keyword(s):  
Continental Margin ◽  
Gas Hydrate ◽  
Free Gas ◽  
Gas Saturation

A Developed Numerical Method for Turbulent Unsteady Fluid Flow in Two-Phase Systems with Moving Interface

2017 ◽  
Vol 14 (06) ◽  
pp. 1750063 ◽  
Author(s):  
A. M. Hegab ◽  
S. A. Gutub ◽  
A. Balabel
Keyword(s):  
Numerical Model ◽  
Gas Phase ◽  
Level Set ◽  
The Body ◽  
Phase System ◽  
Computational Domain ◽  
Two Phase ◽  
Moving Interface ◽  
Level Set Function ◽  
Gas System

This paper presents the development of an accurate and robust numerical modeling of instability of an interface separating two-phase system, such as liquid–gas and/or solid–gas systems. The instability of the interface can be refereed to the buoyancy and capillary effects in liquid–gas system. The governing unsteady Navier–Stokes along with the stress balance and kinematic conditions at the interface are solved separately in each fluid using the finite-volume approach for the liquid–gas system and the Hamilton–Jacobi equation for the solid–gas phase. The developed numerical model represents the surface and the body forces as boundary value conditions on the interface. The adapted approaches enable accurate modeling of fluid flows driven by either body or surface forces. The moving interface is tracked and captured using the level set function that initially defined for both fluids in the computational domain. To asses the developed numerical model and its versatility, a selection of different unsteady test cases including oscillation of a capillary wave, sloshing in a rectangular tank, the broken-dam problem involving different density fluids, simulation of air/water flow, and finally the moving interface between the solid and gas phases of solid rocket propellant combustion were examined. The latter case model allowed for the complete coupling between the gas-phase physics, the condensed-phase physics, and the unsteady nonuniform regression of either liquid or the propellant solid surfaces. The propagation of the unsteady nonplanar regression surface is described, using the Essentially-Non-Oscillatory (ENO) scheme with the aid of the level set strategy. The computational results demonstrate a remarkable capability of the developed numerical model to predict the dynamical characteristics of the liquid–gas and solid–gas flows, which is of great importance in many civilian and military industrial and engineering applications.

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