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Advances in Marine Gas Hydrate Exploration and Discovery

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A special issue of Journal of Marine Science and Engineering (ISSN 2077-1312). This special issue belongs to the section "Ocean Engineering".

Deadline for manuscript submissions: closed (31 December 2024) | Viewed by 17537

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Special Issue Editors

Dr. Wei Zhang

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Guest Editor

Sanya Institute of South China Sea Geology, Guangzhou Marine Geological Survey, Sanya, China
Interests: gas hydrate; marine and petroleum geology
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. Pibo Su

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Guest Editor

Sanya Institute of South China Sea Geology, Guangzhou Marine Geological Survey, Sanya, China
Interests: natural gas hydrate; oil and gas; geophysical exploration
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Dr. Jiliang Wang

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Institute of Deep-sea Science and Engineering, Chinese Academy of Sciences, Sanya, Hainan
Interests: marine geophysics; gas hydrate
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. Qianyong Liang

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Guest Editor

National Engineering Research Center of Gas Hydrate Exploration and Development, Guangzhou Marine Geological Survey, China Geological Survey, Guangzhou, China
Interests: gas hydrate; environmental influence; geochemistry
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Natural gas hydrate has been widely accepted as a clean energy with great potential. Some countries, with powerful technology, especially those that have strong demands for fossil fuels, have put extensive efforts into conducting studies on the exploration and development of gas hydrate surrounding continental margins. The academic and industrial communities have also paid enthusiastic attention by conducting studies concerning the mechanism of hydrate accumulation and how it affects resources and the environment. In recent years, breakthroughs in gas hydrate exploration have been made in many regions around the world, showing good prospects in terms of exploration and development. However, the mechanisms of hydrate accumulation, resource evaluation, and environmental impacts have still not been fully answered, which restricts the exploitation and utilization of hydrate resources and necessitates further research.

The aim of this Special Issue is to advance research on gas hydrate exploration and discovery in continental margins, with an emphasis on the mechanism of accumulation and the assessment of marine hydrate's environmental and resource benefits. Papers on the following topics are welcome: gas hydrate exploration, exploration theory and technology, the distribution and occurrence of hydrates in nature, resource appraisal techniques and technology, environmental monitoring, and the relationship between hydrates and climate change. Both review and research papers are welcome to be submitted.

Topics of interest for this Special Issue include, but are not limited to, the following:

Geological, geophysical, and geochemical method for the exploration of gas hydrate;
Dynamic gas hydrate system and methane recycling;
Hydrate occurrence associated with cold seeps;
Resource evaluation and prediction methods;
Environmental monitoring and evaluation of the gas hydrate system;
The interaction between climate change and the gas hydrate system;
New technology and applications in gas hydrate exploration.

Dr. Wei Zhang
Prof. Dr. Pibo Su
Dr. Jiliang Wang
Prof. Dr. Qianyong Liang
Guest Editors

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Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Journal of Marine Science and Engineering is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

gas hydrate system
resource evaluation and prediction
accumulation mechanism
environmental monitoring and evaluation

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Published Papers (13 papers)

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Research

14 pages, 19711 KiB

Open AccessArticle

Shallow Gas Distribution Influenced by the Interface of Sedimentary Facies in the Southwest of the Qiongdongnan Basin

by Taotao Yang, Xiaohan Li, Jiapeng Jin, Jianwei Chen, Zhi Gong, Li Zhao, Wenlong Wang, Bo Liu, Jinzi Hu, Wenlu Wang and Xiujuan Wang

J. Mar. Sci. Eng. 2025, 13(2), 301; https://doi.org/10.3390/jmse13020301 - 6 Feb 2025

Viewed by 765

Abstract

Shallow gas, with huge resources, has been confirmed using three dimensional (3D) seismic data and more than 20 drilling sites in the deep water of the LS36 gas field, the Qiongdongnan Basin, the South China Sea. The interface of sedimentary facies in the southern boundary of the basin controls the distribution within the basin of clastic sediments coming from the north and west of the land uplifted. In this study, seismic data and geophysical attributes were used to investigate the controlling effect of the interface of sedimentary facies on the distribution of shallow gas within the basin. Our study shows that the shallow gas is mainly distributed in the Quaternary Ledong Formation in the southwest of the Qiongdongnan Basin, which was observed from acoustic impedance, amplitude versus offset (AVO), and seismic interpretations. The channelized submarine fans that onlap the interface of the sedimentary facies are distributed in a vertically stacked manner and are the main reservoirs for the shallow gas. Therefore, these sedimentary studies show that the sand-rich sediments are distributed along the interface of the sedimentary facies from the southwest to the northeast and are limited to the shallow gas within the basin. The Central Canyon provides an important deep gas source, while the flank of the canyon, gas chimney, and normal faults related to basement uplift provide pathways for vertical and lateral gas migration to form the shallow gas. This study shows that shallow gas may be widely distributed in other marginal sea basins, and sedimentary systems should be further studied in the future. Full article

(This article belongs to the Special Issue Advances in Marine Gas Hydrate Exploration and Discovery)

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18 pages, 13718 KiB

Open AccessArticle

High-Resolution 3D Geological Modeling of Three-Phase Zone Coexisting Hydrate, Gas, and Brine

by Han Yu, Ju Wang, Wei Deng, Zenggui Kuang, Tingwei Li and Zhangshu Lei

J. Mar. Sci. Eng. 2024, 12(12), 2171; https://doi.org/10.3390/jmse12122171 - 27 Nov 2024

Cited by 1 | Viewed by 1082

Abstract

Three-dimensional geological modeling is essential for simulating natural gas hydrate (NGH) productivity and formulating development strategies. Current approaches primarily concentrate on the single-phase modeling of either hydrate or free gas layers. However, an increasing number of instances suggest that the three-phase coexistence zone, which includes hydrate, gas, and water, is common and has become a focal point of international research, as this type of reservoir may present the most viable opportunities for exploitation. At present, there exists a significant gap in the research regarding modeling techniques for such reservoirs. This study undertakes a comprehensive modeling investigation of the three-phase zone reservoir situated in the sand layer of the Qiongdongnan Basin. By employing deterministic complex geological modeling techniques and integrating existing seismic and logging data, we have developed a three-phase coexistence zone model that precisely characterizes the interactions between geological structures and utilizes them as auxiliary constraints. This approach effectively mitigates the potential impact of complex geological conditions on model accuracy. Through a comprehensive analysis of 105 seismic profiles, we enhanced the model’s accuracy, resulting in the creation of a three-phase coexistence zone model comprising 350,000 grids. A comparison between the modeling results and well data indicates a relatively small error margin, offering valuable insights for future development efforts. Furthermore, this method serves as a reference for modeling hydrates in marine environments characterized by three-phase coexistence on a global scale. Full article

(This article belongs to the Special Issue Advances in Marine Gas Hydrate Exploration and Discovery)

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26 pages, 22159 KiB

Open AccessArticle

Gas–Water–Sand Inflow Patterns and Completion Optimization in Hydrate Wells with Different Sand Control Completions

by Chenfeng Liu, Changyin Dong, Haoxian Shi, Yanjiang Yu and Bin Yin

J. Mar. Sci. Eng. 2024, 12(11), 2071; https://doi.org/10.3390/jmse12112071 - 15 Nov 2024

Viewed by 962

Abstract

Sand production poses a significant problem for marine natural gas hydrate efficient production. However, the bottom hole gas–water–sand inflow pattern remains unclear, hindering the design of standalone screen and gravel packing sand control completions. Therefore, gas–water–sand inflow patterns were studied in horizontal and vertical wells with the two completions. The experimental results showed that gas–water stratification occurred in horizontal and vertical standalone screen wells. The gas–water interface changed dynamically, leading to an uneven screen plugging, with severe plugging at the bottom and high permeability at the top. The high sand production rate and low well deviation angle exacerbated screen plugging, resulting in a faster rising rate of the gas–water interface. The screen plugging degree initially decreased and then increased as the gas–water ratio increased, resulting in the corresponding variation in the gas–water interface rising rate. Conversely, gas–water stratification did not occur in the gravel packing well because of the pore throat formed between the packing gravels. However, the impact of gas and water led to gravel rearrangement and the formation of erosion holes, causing sand control failure. A higher gas–water ratio and lower packing degree could result in more severe destabilization. Therefore, for the standalone screen completion, sand control accuracy should be designed at different levels according to the uneven plugging degree of the screen. For the gravel packing completion, increase the gravel density without destabilizing the hydrate reservoir, and use the coated gravel with a cementing effect to improve the gravel layer stability. In addition, the screen sand control accuracy inside the gravel packing layer should be designed according to the sand size to keep long-term stable hydrate production. Full article

(This article belongs to the Special Issue Advances in Marine Gas Hydrate Exploration and Discovery)

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22 pages, 19366 KiB

Open AccessArticle

Selection Results of Solid Material for Horizontal and Highly-Deviated Well Completion Gravel-Packing: Experiments, Numerical Simulation and Proposal

by Haoxian Shi, Changyin Dong, Xinjie Zhan, Chenfeng Liu, Lixia Li, Jianrong Ji, Yanjiang Yu and Zhendong Li

J. Mar. Sci. Eng. 2024, 12(10), 1690; https://doi.org/10.3390/jmse12101690 - 24 Sep 2024

Viewed by 1262

Abstract

Lightweight and ultra-lightweight solid materials are being used in gravel packing for horizontal wells instead of traditional quartz and ceramsite to decrease the risk of premature plugging and improve packing efficiency. Physical and numerical simulation experiments of gravel packing were conducted to assess the effectiveness of reducing solid material density and investigate its impact on packing and sand control. Packed gravel destabilization experiments highlighted the importance of high-compaction degree packing for effective sand control. Further gravel packing experiments examined the packing performance of different solid materials, revealing that lightweight solids have minimal gravitational deposition effect because their density is similar to the gravel slurry, relying primarily on fluid flow for compaction. The numerical simulation indicated that lightweight ceramsite is unsuitable for horizontal and highly-deviated wells because of its poor compaction degree and sand control, especially with high-viscosity slurry. High-density particles enhance gravitational deposition, improving packing compaction and sand control. Lightweight materials are recommended only when advanced plugging of α wave packing cannot be avoided. In highly-deviated wells, high-density materials significantly improve packing stability and sand control. This study provides clear technical guidelines for selecting solid materials for gravel packing in horizontal and highly-deviated wells. Full article

(This article belongs to the Special Issue Advances in Marine Gas Hydrate Exploration and Discovery)

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16 pages, 24109 KiB

Open AccessArticle

The Effects of Controlling Gas Escape and Bottom Current Activity on the Evolution of Pockmarks in the Northwest of the Xisha Uplift, South China Sea

by Xuelin Li, Xudong Guo, Fei Tian and Xiaochen Fang

J. Mar. Sci. Eng. 2024, 12(9), 1505; https://doi.org/10.3390/jmse12091505 - 1 Sep 2024

Cited by 4 | Viewed by 999

Abstract

Submarine pockmarks are typical indicators of submarine gas escape activity. The deep strata of the Xisha Uplift are rich in biogenic and thermogenic gas, accompanied by strong bottom current activity. Investigating the effects of controlling submarine gas escape and bottom current activity on the formation and development of pockmarks in the Xisha Uplift is significant for understanding the evolution of submarine topography and geomorphology. This study utilized high-resolution multibeam data to identify 261 submarine pockmarks in the northwest of the Xisha Uplift. These pockmarks were categorized based on their morphology into circular, elliptical, elongated, crescent-shaped, and irregular types. The diameters of pockmarks in the study area range from 0.21 to 4.96 km, with maximum depths reaching 30.88 m. Using high-resolution multi-channel seismic data, we conducted a detailed analysis of the subsurface strata characteristics of the pockmarks, identifying chaotic weak reflections, bright spots, and high-angle reflectors. We believe that deep gas in the northwest of the Xisha Uplift escapes to the seafloor through migration pathways, such as faults, fractures, and gas chimneys, resulting in the formation of submarine pockmarks. Bottom current activity has a significant impact on already-formed pockmarks. Crescent-shaped and elongated pockmarks in the Xisha Uplift are largely the result of bottom current modifications of pre-existing pockmarks. Full article

(This article belongs to the Special Issue Advances in Marine Gas Hydrate Exploration and Discovery)

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17 pages, 12049 KiB

Open AccessArticle

The Mesozoic Subduction Zone over the Dongsha Waters of the South China Sea and Its Significance in Gas Hydrate Accumulation

by Pibo Su, Zhongquan Zhao and Kangshou Zhang

J. Mar. Sci. Eng. 2024, 12(8), 1432; https://doi.org/10.3390/jmse12081432 - 19 Aug 2024

Viewed by 1315

Abstract

The Mesozoic subduction zone over the Dongsha Waters (DSWs) of the South China Sea (SCS) is a part of the westward subduction of the ancient Pacific plate. Based on the comprehensive interpretation of deep reflection seismic profile data and polar magnetic anomaly data, and the zircon dating results of igneous rocks drilled from well LF35-1-1, the Mesozoic subduction zone in the northeast SCS is accurately identified, and a Mesozoic subduction model is proposed. The accretion wedges, trenches, and igneous rock zones together form the Mesozoic subduction zone. The evolution of the Mesozoic subduction zone can be divided into two stages: continental subduction during the Late Jurassic and continental collision during the late Cretaceous. The Mesozoic subduction zone controlled the structural pattern and evolution of the Chaoshan depression (CSD) during the Mesozoic and Neogene eras. The gas source of the hydrate comes from thermogenic gas, which is accompanied by mud diapir activity and migrates along the fault. The gas accumulates to form gas hydrates at the bottom of the stable domain; BSR can be seen above the mud diapir structure; that is, hydrate deposits are formed under the influence of mud diapir structures, belonging to a typical leakage type genesis model. Full article

(This article belongs to the Special Issue Advances in Marine Gas Hydrate Exploration and Discovery)

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16 pages, 4898 KiB

Open AccessArticle

Seafloor Subsidence Evaluation Due to Hydrate Depressurization Recovery in the Shenhu Area, South China Sea

by Benjian Song and Qingping Zou

J. Mar. Sci. Eng. 2024, 12(8), 1410; https://doi.org/10.3390/jmse12081410 - 16 Aug 2024

Cited by 2 | Viewed by 1243

Abstract

Submarine hydrate mining can trigger geological disasters, including submarine landslides and seafloor subsidence due to excess pore pressure and weakened layers, which may potentially lead to the reactivation of faults and increased seismic activity. However, current research encounters challenges in assessing geotechnical issues associated with long-term and large-scale production from well grids located in sloped areas. Limited by the complexity of the hydrate sediment, a multifield coupled numerical model of hydrate slope in the Shenhu area was established. Utilizing the modified Mohr–Coulomb model as the constitutive model for hydrate-bearing sediments to track the dynamic reduction in strength and employing the shear strength method to assess submarine slope stability, a series of depressurization strategies are applied to evaluate the risks associated with submarine landslides and seafloor subsidence. Results show that the hydrate dissociation tends to stagnate after a period of mining. The strength of the hydrate decomposed area is severely reduced, and a volume deficit occurs in this area, causing formation displacement. The peripheral region of the decomposed area is compacted by high stress, resulting in a serious decrease in permeability and porosity, which limits the continued decomposition of hydrates. The large-scale submarine landslides with hydrates decomposition will not appear in this block. However, several meters’ seafloor subsidence over a wide range risks engineering safety significantly. The amount of seafloor subsidence in the first 50 days is approximately half of the final settlement. A higher production pressure drop can speed up the recovery rate while resulting in more significant seafloor subsidence and slippage. Therefore, the balance between mining speed and formation stability needs more research work. Full article

(This article belongs to the Special Issue Advances in Marine Gas Hydrate Exploration and Discovery)

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20 pages, 26532 KiB

Open AccessArticle

Numerical Simulation of Gas Production Behavior Using Stepwise Depressurization with a Vertical Well in the Shenhu Sea Area Hydrate Reservoir of the South China Sea

by Tinghui Wan, Zhanzhao Li, Hongfeng Lu, Mingming Wen, Zongheng Chen, Lieyu Tian, Qi Li, Jia Qu and Jingli Wang

J. Mar. Sci. Eng. 2024, 12(7), 1169; https://doi.org/10.3390/jmse12071169 - 12 Jul 2024

Cited by 1 | Viewed by 1159

Abstract

Stepwise depressurization is an important depressurization strategy in the development of natural gas hydrates. This work numerically analyzes the effects of different depressurization gradients and constant pressure durations on gas and water production during stepwise depressurization extraction with a vertical well in the Shenhu Sea area hydrate reservoir of the South China Sea. The results indicate that stepwise depressurization can reduce water production and raise the gas-to-water ratio in the early stages of production while ensuring cumulative gas output. When the vertical well is deployed at the model’s center with a completion length of 70 m and a constant pressure duration of 10 days, a depressurization gradient of 0.5 MPa, stepwise depressurization by 6 MPa, and continuous production for one year is achieved. Compared with direct depressurization, its cumulative gas production is 2.966 × 10⁶ ST m³, which only decreases by 2.94%. However, it maintains a higher gas-to-water ratio in the early stages of production. Considering factors such as engineering operability, cumulative gas output, and gas-to-water ratio, it is recommended to use a small pressure gradient and a medium constant pressure stabilization time for stepwise depressurization Stepwise depressurization can maintain a high gas-to-water ratio while ensuring gas production and reducing water production can alleviate sand production problems and improve economic efficiency. The understanding gained from this work has reference value for the development of similar hydrate reservoirs worldwide. Full article

(This article belongs to the Special Issue Advances in Marine Gas Hydrate Exploration and Discovery)

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15 pages, 12464 KiB

Open AccessArticle

Acid-Extracted Hydrocarbon Anomalies and Significance in the Chaoshan Depression of the Northern South China Sea

by Guangjian Zhong, Jing Zhao, Zhongquan Zhao, Kangshou Zhang, Junhui Yu, Chunjiang Shang, Guanghong Tu and Changmao Feng

J. Mar. Sci. Eng. 2024, 12(6), 909; https://doi.org/10.3390/jmse12060909 - 29 May 2024

Viewed by 902

Abstract

To predict the favorable zones and the types of reservoirs, acid extraction has been used in the Chaoshan depression to detect trace amounts of light hydrocarbons, heavy hydrocarbons, and the δ ¹³C (‰) of methane. As a result, two integration anomalous zones for exploration activity were blocked out in the northeastern and southwestern parts of the Chaoshan Depression, respectively. By analyzing the differentiation law and structural characteristics of hydrocarbon gases, as well as the stable carbon isotope ratio of methane, the underlying reservoirs were predicted to be gas reservoirs, and the seismically interpreted Dongsha-A (DS-A) structure was predicted to be a gas-rich structure. By correlating the seismic profile and geochemical anomalies, it was determined that fault planes and micro-fractures are the main controlling factors for the occurrence of the seabed’s geochemical anomalies. A composite formation mechanism of “lower generation, upper accumulation and micro fractures leaking” is proposed for the control of the underlying petroleum reservoirs, as well as for the micro-fracture control of permeability and surface adsorption control. Acid-extracted hydrocarbon anomalies have favorable indicating significance for exploration activity. Full article

(This article belongs to the Special Issue Advances in Marine Gas Hydrate Exploration and Discovery)

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16 pages, 11721 KiB

Open AccessArticle

Identification of Mass Transport Deposits and Insights into Gas Hydrate Accumulation in the Qiongdongnan Sea Area, Northern South China Sea

by Yuehua Gong, Shengxiong Yang, Jinqiang Liang, Dongmei Tian, Jing’an Lu, Wei Deng and Miaomiao Meng

J. Mar. Sci. Eng. 2024, 12(6), 855; https://doi.org/10.3390/jmse12060855 - 22 May 2024

Cited by 1 | Viewed by 1263

Abstract

Accurately identifying the Bottom Simulating Reflector (BSR) is a crucial and fundamental task in seismic exploration and the interpretation of gas hydrates in marine areas. During our seismic interpretation and inference work on a gas hydrate survey in the Qiongdongnan Sea area, we encountered a phenomenon that closely resembled the seismic reflection characteristics of BSR. By comparing and identifying various geological phenomena, we have determined that this unique seismic reflection phenomenon is, in fact, the reflection of the depositional bottom interface known as “mass transport deposits (MTDs)” as described by previous researchers. The physical properties of the MTDs developed on the shallow surface of the seafloor are similar to those of gas hydrate reservoirs in the seismic exploration of marine areas, particularly in the northern South China Sea’s Qiongdongnan Sea area. Due to the lack of active neotectonic movement in the area, most identified BSR reflection occurrences are parallel to the seafloor. Consequently, during the process of seismic interpretation of BSR in the Qiongdongnan Sea area, it may be confused with the bottom boundary reflection interface of MTDs. Accurately identifying MTDs’ sedimentary bodies in gas hydrate exploration activities in this area would greatly enhance the accurate identification of BSR and support the refined evaluation of gas hydrate resources. In this paper, the structural characteristics of MTDs are compared with the reflection characteristics of seismic profiles, the reflectors are identified as MTDs rather than BSR through analysis and interpretation, and the possible mechanism of hydrate accumulation in this region is discussed. Full article

(This article belongs to the Special Issue Advances in Marine Gas Hydrate Exploration and Discovery)

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18 pages, 9265 KiB

Open AccessArticle

Representative Dynamic Accumulation of Hydrate-Bearing Sediments in Gas Chimney System since 30 Kyr BP in the QiongDongNan Area, Northern South China Sea

by Jinan Guan, Menghe Wang, Wei Zhang, Lihua Wan, Matthias Haeckel and Qi Wu

J. Mar. Sci. Eng. 2024, 12(5), 834; https://doi.org/10.3390/jmse12050834 - 17 May 2024

Cited by 1 | Viewed by 1622

Abstract

A stratigraphic complex composed of mass transport deposits (MTDs), where the gas occurrence allows for the formation of a gas chimney and pipe structure, is identified based on seismic interpretation in the QiongDongNan area of the northern South China Sea. During the Fifth Gas Hydrate Drilling Expedition of the Guangzhou Marine Geological Survey, this type of complex morphology that has close interaction with local gas hydrate (GH) distribution was eventually confirmed. A flow-reaction model is built to explore the spatial–temporal matching evolution process of massive GH reservoirs since 30 kyr before the present (BP). Five time snapshots, including 30, 20, 10, and 5 kyr BP, as well as the present, have been selected to exhibit key strata-evolving information. The results of in situ tensile estimation imply fracturing emergence occurs mostly at 5 kyr BP. Six other environmental scenarios and three cases of paleo-hydrate existence have been compared. The results almost coincide with field GH distribution below the bottom MTD from drilling reports, and state layer fracturing behaviors always feed and probably propagate in shallow sediments. It can be concluded that this complex system with 10% pre-existing hydrates results in the exact distribution and occurrence in local fine-grained silty clay layers adjacent to upper MTDs. Full article

(This article belongs to the Special Issue Advances in Marine Gas Hydrate Exploration and Discovery)

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20 pages, 6752 KiB

Open AccessArticle

Controls on Deep and Shallow Gas Hydrate Reservoirs in the Dongsha Area, South China Sea: Evidence from Sediment Properties

by Chenyang Bai, Hongbin Wang, Qing Li, Yu Zhang and Xiaolei Xu

J. Mar. Sci. Eng. 2024, 12(5), 696; https://doi.org/10.3390/jmse12050696 - 23 Apr 2024

Cited by 1 | Viewed by 1321

Abstract

The Dongsha area, a key region in the northern South China Sea (SCS), features both diffusive deep and seepage shallow gas hydrate reservoirs. Utilizing sediment samples from gas hydrate reservoirs and adjacent layers at sites W08 and W16 in the Dongsha area, this study aims to uncover the sediment property differences between deep and shallow gas hydrate reservoirs and their impact on gas hydrate accumulation through grain size, X-ray diffraction, and specific surface area (SSA) analyses. The findings classify the study intervals into four distinct layers: shallow non-gas hydrate layer (shallow-NGHL), shallow gas hydrate reservoir (shallow-GHR), deep non-gas hydrate layer (deep-NGHL), and deep gas hydrate reservoir (deep-GHR). In the clayey silt sediment reservoirs, grain size has a minor influence on gas hydrate reservoirs. Both shallow and deep NGHLs, characterized by high smectite content and SSA, possess a complex structure that impedes gas and fluid migration and offers limited potential reservoir space. Consequently, both shallow and deep NGHLs function as sealing beds. The deep GHR, having low smectite content and SSA, exhibits a strong capacity for gas and fluid migration and greater potential reservoir space. As a result, sediment properties significantly influence the deep GHR. Seepage primarily controls the shallow GHR. Full article

(This article belongs to the Special Issue Advances in Marine Gas Hydrate Exploration and Discovery)

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16 pages, 8834 KiB

Open AccessArticle

Mechanical Characteristics of Gas Hydrate-Bearing Sediments: An Experimental Study from the South China Sea

by Qingmeng Yuan, Liang Kong, Qianyong Liang, Jinqiang Liang, Lin Yang, Yifei Dong, Zhigang Wang and Xuemin Wu

J. Mar. Sci. Eng. 2024, 12(2), 301; https://doi.org/10.3390/jmse12020301 - 8 Feb 2024

Cited by 6 | Viewed by 2075

Abstract

Clarifying the mechanical characteristics of gas hydrate-bearing sediments (GHBS) from a mechanical perspective is crucial for ensuring the long-term, safe, and efficient extraction of natural gas hydrates. In this study, seabed soft clay from the northern South China Sea was utilized to prepare clayey silt samples, aligning with gradation curves related to hydrate extraction projects in the Shenhu area of the South China Sea. Utilizing the high-pressure low-temperature hydrate triaxial testing system (ETAS), twelve sets of triaxial shear tests were conducted. The results highlight that increases in hydrate saturation and confining pressure significantly enhance GHBS’ strength and stiffness, with more pronounced volume expansion observed during shearing. These tests have elucidated the mechanical responses of GHBS. Subsequently, empirical formulas were developed to characterize their properties under varying conditions. Additionally, based on the experimental data, the micro-mechanisms of GHBS were analyzed, suggesting that hydrates notably contribute to the filling and cementing effects in GHBS, with these effects varying with changes in hydrate saturation and confining pressure. This study contributes to a deeper understanding of the fundamental mechanical properties of GHBS. Full article

(This article belongs to the Special Issue Advances in Marine Gas Hydrate Exploration and Discovery)

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