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1

Gas Hydrate Detection Based on High Resolution Seismic Data in the Southeastern Offshore of Vietnam

Mai Thanh Tan, Mai Thanh Ha, Nguyen Quoc Huy, Nguyen Nhu Trung

Inżynieria Mineralna

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2023

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no. 2, vol. 1

137--142

EN

Gas hydrates are the accumulations of methane (natural gas) trapped in ice-like structures with water. Gas hydrates represent an immense energy resource underlying large portions of the world’s marine continental shelves. Vietnam has a large continental shelf area, in the deep water zone with suitable low temperatures and high pressure, which is suitable for the formation and existence of potential energy source of Gas Hydrate (GH). The application of High-Resolution Seismic method (HRS) plays an important role in exploring for Gas Hydrate. The enhancement of HRS research such as optimal short - reception conditions and advanced data processing suitable for Gas Hydrate in shallow layers below the seafloor, allows for determining the geological factors related to Gas Hydrate’s existence in the deep water area. Advancements in data processing technology, such as noise filters (Radon, F-K, SRMA, Tau-P..), seismic attributes analysis, seismic migration, AVO, seismic inversion, pre-stack seismic data and AI technology … allow to identify of the signs of Gas Hydrate presence, such as Bottom Simulated Reflector (BSR), Gas Hydrate Stability Zone (GHSZ), Pockmark, Chimney, etc. This paper presents some of the results obtained from applying High-Resolution Seismic method to predict the distribution of Gas hydrate in the Southeastern offshore of Vietnam.

2

Seismic imaging of a seepage gas hydrate system with a harrow‑like acquisition geometry

Liu Bin, Xu Yunxia, Xue Hua, Wen Pengfei, Meng Dajiang

Acta Geophysica

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2023

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Vol. 71, no. 4

1717--1728

EN

Seepage gas hydrate systems are abundant around the world. However, it is very challenging to characterize this type of gas hydrate because the internal structure of a seepage structure is difficult to image by the conventional seismic exploration method. Here, a novel approach is proposed to achieve high-resolution seismic imaging of a seepage gas hydrate system related to a pipe structure. Raw seismic data with small-size bins are acquired with a harrow-like acquisition geometry that uses one long cable (up to 2000 m) and multiple short cables (less than 1000 m). A high-frequency GI gun is used as a source. During processing, velocity analysis and footprint attenuation are more focused. Seismic imaging resolution has been greatly improved. A small-scale carbonate layer that is hard to identify on the conventional profile is well revealed on the new profile. The new profiles also better depict the boundary and internal structure of the pipe structure. These improve our understanding of seepage gas hydrate systems. Our approach provides an important complement to conventional offshore seismic exploration.

3

The variation of free gas distribution within the seeping seafloor hydrate stability zone and its link to hydrate formations in the Qiongdongnan Basin

Wei Deng, Jinqiang Liang, Zenggui Kuang, Tong Zhong, Yanian Zhang, Yulin He

Acta Geophysica

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2022

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Vol. 70, no 3

1115--1136

EN

China geological survey has conducted two hydrate expeditions for two gas chimney structures (GC1, GC2) in the Qiongdongnan Basin, South China Sea, where the fluid migrations vary significantly. Although massive hydrates were recovered both in the seepage pathways above GC1 and GC2, the free gas distributions in seeping seafloor hydrate stability zone (HSZ) remain controversial. Previous studies confirm that structure I (sI) and structure II (sII) hydrates occur through the whole seepage pathways, and free gas accumulates below the base of methane hydrate stability zone (BHSZ). In fact, free gas and gas hydrates coexist in the whole seepage-gas chimney system. The quantitative estimation of the fluid distribution is significant for studying the heterogeneous fluid migration in the seepages. In this study, Archie formula and three-phase Biot-type equation are modified to invert fluid concentrations for the whole well sections, in which brine, free gas, gas hydrate and matrix are considered as separate phases. The results indicate that the bottom simulating reflector is the boundary of an increasing gas concentration and a decrease hydrate concentration, instead of the interfaces of the hydrate and free gas in most areas. And hydrate occurrence is closely related to the micro-fault in the gas chimney. By comparing the fluid distribution between GC1 and GC2, more free gas associated with gas hydrates is accumulated in the seepage pathways in HSZ in GC1 where less free gas occurred below the BHSZ. Gas-bearing fluids in GC1 are considered to be very active in historic time, but they nearly stop flowing now, and the remaining gas cannot form hydrates in the hydrate-saturated pores, while the fluids in GC2 tend to convert to hydrates till now, and it is an active or younger fluid system. Free gas is the important intermediate medium for revealing this phase transition and exerts a significant control on the timescales associated with phase equilibrium variation processes. It is the first study revealing the relationship between the fluid distribution and the mobility of the seepage-gas chimney system in the study area, which also provide a new insight for estimating hydrate resource.

4

Self-preservation Effect of Gas Hydrates

Pavlenko Anatoliy

Rocznik Ochrona Środowiska

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2021

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Tom 23

346--355

EN

This work was performed to improve the storage and transportation technology of gas hydrates in nonequilibrium conditions. At atmospheric pressure and positive ambient temperature, they gradually dissociate into gas and water. Simulation of the gas hydrate dissociation will determine optimal conditions for their transportation and storage, as well as minimize gas loss. Thermodynamic parameters of adiabatic processes of forced preservation of pre-cooled gas hydrate blocks with ice layer were determined theoretically and experimentally. Physical and mathematical models of these processes were proposed. The scientific novelty is in establishing quantitative characteristics that describe the gas hydrates thermophysical parameters thermophysical characteristics influence on the heat transfer processes intensity on the interphase surface under conditions of gas hydrates dissociation. Based on the results of experimental studies, approximation dependences for determining the temperature in the depths of a dissociating gas hydrate array have been obtained. Gas hydrates dissociation mathematical model is presented.

5

Gas hydrates impact on corrosion of the well flow lines material

Poberezhny L., Hrytsanchyk A., Mandryk O., Poberezhna L., Popovych P., Shevchuk O., Mishchuk B., Rudyak Yu.

Archives of Materials Science and Engineering

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2021

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Vol. 110, nr 1

5--17

EN

Purpose: Determination of regularities of joint action of mechanical stresses, formation water and hydrate formation on corrosion of material of flow pipelines. Design/methodology/approach: According to the analysis of reservoir water of the investigated deposits, it was found that the main corrosive component is soluble chlorides. Proposed for corrosion and corrosion-mechanical tests of 6 model environments. An estimation of the influence of stress concentration, depending on the defects of the inner wall of the pipe, was carried out, and the nominal local stresses in the pipeline was carried. Findings: The basic regularities of influence of stress and hydration formation on corrosion and localization of corrosion processes and on the kinetics of deformation of samples are described. For samples made of steel 20 and 17GS, an increase in the velocity of general and local corrosion for samples sustained in the gas hydrate was observed compared to the control results obtained, the coefficient of influence of the gas hydrate on corrosion was calculated. Research limitations/implications: The obtained results are valid for thermobaric operating conditions of well flow lines. Practical implications: The data obtained in the work on the patterns of corrosion processes and the impact of hydrate formation on them will allow to identify potentially dangerous areas of flow lines and prevent emergencies. Originality/value: Based on the analysis of the geometric dimensions of the defects, the effective stress concentration coefficients are calculated, and it is shown that the stresses in the vicinity of corrosion defects in normal operating modes range from 164 to 545 MPa.

6

Rock physics based estimation of quartz content in the Shenhu area, South China Sea

Deng Wei, Liang Jinqiang, He Yulin, Kuang Zenggui, Meng Miaomiao

Acta Geophysica

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2020

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Vol. 68, no. 6

1619--1641

EN

Estimation of quartz content (QC) is important for gas hydrate production. However, the existing methods pay more attention to estimate saturations of hydrate or free gas instead of QC. QC is difcult to be estimated because of its limited and unclear infuences on velocities in the hydrate-bearing sediments. A workfow was proposed to estimate QC from core to logging to seismic inversion whose core technologies were an unconsolidated anisotropic model (UAM) and an inverse modeling approach. We used the UAM to construct the quantitative relationships between physical properties including QC and velocity. Then, the velocities of the reservoirs were obtained by logging-constrained seismic inversion. Finally, QC can be scaled by the inverse modeling of the UAM. To build the UAM, we analyzed the physical properties of hydrate reservoirs based on the cores and logging while drilling (LWD) data in the Shenhu area, South China Sea, and characterized unconsolidated sediments with horizontally layered hydrates and gas occurrences. The calculated P-velocities and S-velocities from the UAM agreed with the LWD data when the input variables were QC, porosity, hydrate saturation, and gas saturation. Conversely, for a group of P-velocity and S-velocity from seismic inversion, the corresponding QC can be scaled out as well as the other parameters based on the UAM, which was defned as an inverse modeling. Because the signifcant parameters such as hydrate saturation have been considered as independent variables in the model, we can efectively avoid the correlation between QC and the others. Prediction multiplicity can be reduced. The estimated QC was consistent with the drilling and geological understanding in the feld application, indicating that the method proposed is efective and practical.

7

Feasibility of sparker source in marine seismic exploration: data analysis and processing

Wang Xiangchun, Qi Bin, Zhao Qingxian, Wang Weiwei, Yu Kaiben

Acta Geophysica

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2019

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Vol. 67, no. 5

1413--1418

EN

Sparkers are the sound source widely used in marine seismic exploration to provide high-resolution vertical sections. Sparkers are relatively simple, inexpensive, high-frequency sources. In this study, the types of noise occurring in sparker source data were analyzed and attenuated by a processing technique. Frequency-wave number (f-k) filtering is used for attenuating the linear noise. Predictive deconvolution is used for attenuating the ghost waves and bubble efects. A complete processing workflow was designed for processing the data, and the migration section was obtained. The results show that the sparker source data are capable of achieving vertical sections with very high resolution. It is suggested as a necessary technique for high-accuracy gas hydrate exploration in the South China Sea.

8

Prospects for the development of hydrate storage and transportation technology of methane gas

Pavlenko A., Koshlak H., Vytyaz O., Rybicki Cz.

AGH Drilling, Oil, Gas

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2015

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Vol. 32, no. 1

13--21

EN

The gas hydrate tecłmologies can be alternative to the traditional methods of the rational use of hydrocarbon gases. However the known constructions of apparatuses for the production of gas hydrates cannot satisfy the condition of their industrial use fully. Authors offer to carry out the high-quality contact of gas and water at formation of gas hydrate by jet apparatuses with a free falling jet. On their basis a technological chart is offered for realization of continuous cycle of production of gas hydrate. The aim is to develop technical solutions and process parameters of continuous production of gas hydrates, which would satisfy the requirements of industrial application

9

Numerical Simulation of Response Characteristics of Audio-magnetotelluric for Gas Hydrate in the Qilian Mountain Permafrost, China

Xiao K., Zou Ch., Yu Ch., Pi J.

Acta Geophysica

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2015

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Vol. 63, no. 5

1368--1404

EN

Audio-magnetotelluric (AMT) method is a kind of frequencydomain sounding technique, which can be applied to gas hydrate prospecting and assessments in the permafrost region due to its high frequency band. Based on the geological conditions of gas hydrate reservoir in the Qilian Mountain permafrost, by establishing high-resistance abnormal model for gas hydrate and carrying out numerical simulation using finite element method (FEM) and nonlinear conjugate gradient (NLCG) method, this paper analyzed the application range of AMT method and the best acquisition parameters setting scheme. When porosity of gas hydrate reservoir is less than 5%, gas hydrate saturation is greater than 70%, occurrence scale is less than 50 m, or bury depth is greater than 500 m, AMT technique cannot identify and delineate the favorable gas hydrate reservoir. Survey line should be more than twice the length of probable occurrence scale, while tripling the length will make the best result. The number of stations should be no less than 6, and 11 stations are optimal. At the high frequency section (10~1000 Hz), there should be no less than 3 frequency points, 4 being the best number.

10

Development of new technologies for shipping natural gas by sea

Bortnowska M.

Polish Maritime Research

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2009

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nr 3

70-78

EN

In recent years dynamic increase of orders for ships intended for liquified natural gas (LNG) shipping has been observed with simultaneous trend of increasing their transport capability. This results from the fact that natural gas has become today the third energy source worldwide just next to crude oil and coal. The fast growth of demand for natural gas and its limited resources would cause growth of its price, therefore better solutions of natural gas transport technology with respect to economy, ecology and safety should be searched for. This paper presents various technologies for natural gas transport by sea with special attention paid to some alternative methods of transport, namely: CNG and NGH ransport technologies in contrast to LNG one.

11

Full waveform inversion of gas hydrate reflectors in Northern South China Sea

Huo Y., Zhang M.

Acta Geophysica

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2009

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Vol. 57, no. 3

716-727

EN

Bottom Simulating Reflectors (BSRs) are considered to be the bottom of gas hydrate bearing sediments; hence, BSRs are used to identify gas hydrate and free gas. In order to obtain accurate velocity structure of BSRs, this paper presents a full waveform inversion strategy based on Genetic Algorithm. Synthetic seismograms are calculated using the slowness technique. Through numerical experiments made with noisy synthetic data, the inversion algorithm shows stable performance, and genetic operators are defined. This method was applied to field data from the northern South China Sea. Inversion results show that obvious velocity anomaly of BSRs can be detected, which indicates the existence of gas hydrate and free gas.