Journal of Marine Science and Engineering

Research

29 pages, 12123 KiB

Open AccessArticle

Fine Particle Migration in a Gas Hydrate Sand: Single- and Two-Phase Fluid Using a Device for Observation at the Pore Scale

by Jie He, Xiang Huang and Pei Cao

J. Mar. Sci. Eng. 2024, 12(1), 109; https://doi.org/10.3390/jmse12010109 - 06 Jan 2024

Cited by 1 | Viewed by 755

Abstract

The production of natural gas hydrates will change the cementation strength, porosity, and effective stress in the stratum, which may lead to engineering and geological disasters. Sand production is a phenomenon where sand particles are carried out of the reservoir along with fluids [...] Read more.

The production of natural gas hydrates will change the cementation strength, porosity, and effective stress in the stratum, which may lead to engineering and geological disasters. Sand production is a phenomenon where sand particles are carried out of the reservoir along with fluids during gas extraction, posing challenges to safe and sustainable production. This study explored the mechanism of fine particle migration in multiphase flow by a microscopic visualization test device. The device can inject a gas–liquid–solid phase at the same time and allow real-time observation. Experimental tests on fine particle migration of single- and two-phase fluid flow were carried out considering different conditions, i.e., fine particle concentration, fine particle size, fluid flow rate, and gas–liquid ratio. The results show that in single-phase fluid flow, the original gas will gradually dissolve in the liquid phase, and finally stay in the test device as bubbles, which can change the pore structures, resulting in the accumulation of fine particles at the gas–liquid interface. In two-phase fluid flow with mixed gas–water fluids, there are two flow modes of gas–liquid flow: mixed flow and separated flow. The interfacial tension at the gas–liquid interface can effectively migrate fine particles when the gas–liquid flows alternately and the sand production rate further increases as the gas–liquid ratio increases. In addition, changes in the concentration of fine particles, particle size, fluid flow rate, and the gas–liquid ratio will affect the migration of fine particles, leading to differences in the final sand production. Full article

(This article belongs to the Special Issue Gas Hydrate—Unconventional Geological Energy Development)

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16 pages, 4392 KiB

Open AccessArticle

Application of Dual Horizontal Well Systems in the Shenhu Area of the South China Sea: Analysis of Productivity Improvement

by Xuezhen Wu, Gaoqiang Guo, Hongyu Ye, Yuanbing Miao and Dayong Li

J. Mar. Sci. Eng. 2023, 11(7), 1443; https://doi.org/10.3390/jmse11071443 - 19 Jul 2023

Cited by 2 | Viewed by 748

Abstract

The horizontal well technology was successfully applied in the Chinese second natural gas hydrate (NGH) field test in the Shenhu area of the South China Sea in 2020. However, the results show that the threshold for commercial exploitation has not been broken, judging [...] Read more.

The horizontal well technology was successfully applied in the Chinese second natural gas hydrate (NGH) field test in the Shenhu area of the South China Sea in 2020. However, the results show that the threshold for commercial exploitation has not been broken, judging from daily gas production and cumulative gas production. Consequently, the paper presents the effects of dual horizontal well systems for exploitation in this area. The NGH reservoir model in the Shenhu area was established with CMG software. The influence of various layout options and various spacing of dual horizontal well systems on the production capacity was investigated. Further, we simulated the production effect of dual horizontal well systems joint auxiliary measures, such as well wall heating, heat injection, etc. The results show that the production capacity of dual horizontal well systems increased by about 1.27~2.67 times compared with that of a single horizontal well. The daily gas production will drop significantly, no matter which method was used, when exploitation lasts for about 200 d. Meanwhile, well wall heating and heat injection have limited effects on promoting production capacity. In conclusion, attention was drawn to the fact that the synergistic effect could be fully exerted to accelerate NGH dissociation when dual horizontal well systems are applied. The NGH reservoirs in the Shenhu area may be more suitable for short-term exploitation. The research results of this paper can provide a reference for the exploitation of the Shenhu area. Full article

(This article belongs to the Special Issue Gas Hydrate—Unconventional Geological Energy Development)

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21 pages, 6310 KiB

Open AccessArticle

ABAQUS Numerical Simulation Study on the Shear Instability of a Wellbore Induced by a Slip of the Natural Gas Hydrate Layer

by Yujing Jiang, Baocheng Li, Changsheng Wang, Hengjie Luan, Sunhao Zhang, Qinglin Shan and Xianzhen Cheng

J. Mar. Sci. Eng. 2023, 11(4), 837; https://doi.org/10.3390/jmse11040837 - 15 Apr 2023

Cited by 1 | Viewed by 1530

Abstract

To study the shear deformation and failure characteristics of a wellbore and the interaction mechanism with its surrounding rocks induced by a layer slip during natural gas hydrates (NGHs) extraction, this paper conducted a numerical simulation study of wellbore shear induced by a [...] Read more.

To study the shear deformation and failure characteristics of a wellbore and the interaction mechanism with its surrounding rocks induced by a layer slip during natural gas hydrates (NGHs) extraction, this paper conducted a numerical simulation study of wellbore shear induced by a layer slip using ABAQUS software and carried out a laboratory experiment of wellbore shear to verify the accuracy of the numerical model. The results show that the shear force–displacement curves obtained from the laboratory experiments and numerical simulations are consistent with five stages, including the compaction stage, linear stage, plastic stage, strain-softening stage and residual stage. The wellbore shows a “Z”-shaped deformation characteristic after its shear breakage. The shear force of the wellbore is maximum at the shear surface, and it is distributed in an approximate “M” shape along the shear surface. The axial force of the wellbore is small and uniformly distributed in the initial stage of the shear. The wellbore bending moment is minimum at the shear surface, with a value of 0, and it is distributed in a skew–symmetric wave shape along the shear surface. During the shearing, the evolution of the wellbore axial force and shear force can be classified into the distribution pattern along the radial direction on the shear surface and the pattern along the axial direction. The combination of the wellbore axial force and shear force causes the tensile–shear compound failure of the wellbore. During shearing, the wellbore and rock body gradually enter the plastic state with the increase in the shear displacement. When the entire cross-section of the wellbore is in the plastic state, a “necking” phenomenon of the wellbore begins to appear. During the shearing, the frictional dissipation energy and plastic dissipation energy increase constantly. In addition, the elastic strain energy increases to a peak and then decreases to a certain value, which remains unchanged along with the work conducted by the shear force. Full article

(This article belongs to the Special Issue Gas Hydrate—Unconventional Geological Energy Development)

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16 pages, 5121 KiB

Open AccessArticle

Multifractal Analysis of the Structure of Organic and Inorganic Shale Pores Using Nuclear Magnetic Resonance (NMR) Measurement

by Rui Yang, Weiqun Liu and Lingren Meng

J. Mar. Sci. Eng. 2023, 11(4), 752; https://doi.org/10.3390/jmse11040752 - 30 Mar 2023

Cited by 3 | Viewed by 902

Abstract

The multifractal structure of shale pores significantly affects the occurrence of fluids and the permeability of shale reservoirs. However, there are few studies on the multifractal characteristics of shale pores that distinguish between organic and inorganic pores. In this study, we obtained the [...] Read more.

The multifractal structure of shale pores significantly affects the occurrence of fluids and the permeability of shale reservoirs. However, there are few studies on the multifractal characteristics of shale pores that distinguish between organic and inorganic pores. In this study, we obtained the pore size distribution (PSD) of organic and inorganic shale pores separately by using a new NMR-based method and conducted a multifractal analysis of the structure of organic and inorganic shale pores based on PSD. We then investigated the geological significance of the multifractal characteristics of organic and inorganic shale pores using two multifractal characteristic parameters. The results showed that the structures of both organic and inorganic pores have multifractal characteristics. Inorganic pores have stronger heterogeneity and poorer connectivity compared to organic pores. The multifractal characteristics of inorganic pores significantly affect shale permeability and irreducible water saturation. Greater heterogeneity in the inorganic pore structure results in lower shale permeability and higher irreducible water saturation. Meanwhile, better connectivity leads to higher shale permeability and lower irreducible water saturation. The multifractal characteristics of organic pores significantly affect the shale adsorption capacity and have a weak impact on irreducible water saturation. Greater heterogeneity in the organic pore structure results in the shale having stronger adsorption capacity and higher irreducible water saturation The results also indicate that the multifractal characteristic parameters of inorganic pores can be regarded as an index for estimating the irreducible water saturation and flowback rate of fracturing fluid, and the multifractal characteristic parameters of organic pores can be regarded as an index for evaluating the quality of shale reservoirs. Full article

(This article belongs to the Special Issue Gas Hydrate—Unconventional Geological Energy Development)

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23 pages, 5844 KiB

Open AccessArticle

THMC Fully Coupled Model of Natural Gas Hydrate under Damage Effect and Parameter Sensitivity Analysis

by Yue Qiu, Xiangfu Wang, Zhaofeng Wang, Wei Liang and Tongbin Zhao

J. Mar. Sci. Eng. 2023, 11(3), 612; https://doi.org/10.3390/jmse11030612 - 13 Mar 2023

Viewed by 1425

Abstract

In order to study the influence of damage on the gas production of natural gas hydrate, a multi-physical field theoretical model considering damage effect and coupling thermal-hydraulic-mechanical-chemical (THMC) was established by theoretical analysis and numerical simulation. The THMC model establishes the relationship between [...] Read more.

In order to study the influence of damage on the gas production of natural gas hydrate, a multi-physical field theoretical model considering damage effect and coupling thermal-hydraulic-mechanical-chemical (THMC) was established by theoretical analysis and numerical simulation. The THMC model establishes the relationship between the elastic modulus of hydrate sediment and hydrate saturation during the whole process of hydrate decomposition. The THC (thermal-hydraulic-chemical) and THMC fully coupled models not considering or considering the damage effect were compared and analyzed, and the reliability of the THMC fully coupled model was verified. On this basis, the deformation, permeability and damage of hydrate sediments under different initial hydrate saturations and different depressurization amplitudes, as well as the hydrate gas production rate and cumulative gas production, are analyzed. The results showed that higher initial hydrate saturation inhibited the development of damage, maintained stable gas production and increased cumulative gas production. Larger depressurization promoted damage and increased cumulative gas production, but it was easy to cause stability problems. Full article

(This article belongs to the Special Issue Gas Hydrate—Unconventional Geological Energy Development)

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21 pages, 11745 KiB

Open AccessArticle

Marine Natural Gas Hydrate Self-Entry Exploitation Device: Evaluation of Production Enhancement Measures

by Jianhua Wang, Hongyu Ye, Jingyu Chen, Qichao Huang, Gaoqiang Guo, Xuhong Huang, Mucong Zi, Dayong Li and Xuezhen Wu

J. Mar. Sci. Eng. 2023, 11(3), 543; https://doi.org/10.3390/jmse11030543 - 03 Mar 2023

Cited by 2 | Viewed by 1484

Abstract

Test exploitation equipment and technology have progressed considerably in marine natural gas hydrate (NGH) exploitation, but many critical technical issues still need to be resolved before commercial production. Previous studies have proposed a non-drilling exploitation device—a self-entry exploitation device (SEED)—but reaching the NGH [...] Read more.

Test exploitation equipment and technology have progressed considerably in marine natural gas hydrate (NGH) exploitation, but many critical technical issues still need to be resolved before commercial production. Previous studies have proposed a non-drilling exploitation device—a self-entry exploitation device (SEED)—but reaching the NGH commercial exploitation threshold in its initial state is difficult. Consequently, we verified and evaluated some production enhancement measures to improve the exploitation system of the SEED. In this study, based on the geological data from the SHSC-4 site in the Shenhu sea and the material characteristics of the SEED, we carried out four production enhancement measures by numerical simulation. The results indicate that: (i) open-hole position adjustment can expand the contact areas between the device and NGH reservoirs; (ii) the effect of inner wall heating is limited but sufficient to achieve the goal of preventing clogging; (iii) it is necessary to select a reasonable spacing according to a combination of expected production cycle time and pressure when carrying out clustered depressurization; and (vi) when performing depressurization combined with thermal stimulation exploitation, factors such as permeability and thermal conductivity play a decisive factor in gas production. Full article

(This article belongs to the Special Issue Gas Hydrate—Unconventional Geological Energy Development)

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12 pages, 1668 KiB

Open AccessArticle

Permeability of Hydrate-Bearing Sediment Formed from CO₂-N₂ Mixture

by Nan Li, Ziyang Fan, Haoran Ma, Shuai Jia, Jingyu Kan, Changyu Sun and Shun Liu

J. Mar. Sci. Eng. 2023, 11(2), 376; https://doi.org/10.3390/jmse11020376 - 08 Feb 2023

Cited by 2 | Viewed by 1770

Abstract

CO₂-N₂-mixture injection can be used for the exploitation and reformation of natural gas hydrate reservoirs. The permeability evolution of sediments in the presence of CO₂-N₂ hydrate is very important. In current permeability tests, hydrate-bearing sediment formed [...] Read more.

CO₂-N₂-mixture injection can be used for the exploitation and reformation of natural gas hydrate reservoirs. The permeability evolution of sediments in the presence of CO₂-N₂ hydrate is very important. In current permeability tests, hydrate-bearing sediment formed from CO₂-N₂ gas mixture is rarely involved. In this work, hydrate-bearing sediment was formed from CO₂-N₂ mixtures, and a constant flow method was employed to measure the permeability of the hydrate-bearing sediments. The effects of CO₂ mole fraction and hydrate saturation on the permeability were investigated. The results show that gas composition is the key factor affecting hydrate formation. Hydrate saturation increases with increasing CO₂ mole fraction in the gas mixture. The presence of hydrate formed from a CO₂-N₂ mixture leads to a sharp permeability reduction. The higher the fraction of CO₂ in the injected gas mixture, the lower the sediment’s permeability. Our measured permeability data were also compared with and fitted to prediction models. The pore-filling model underestimates the permeability of hydrate-bearing sediments formed from a CO₂-N₂ gas mixture. The fitted hydrate saturation index in the Masuda model is 15.35, slightly higher than the general values, which means that the formed hydrates tend to occupy the pore center, and even block the pore throat. Full article

(This article belongs to the Special Issue Gas Hydrate—Unconventional Geological Energy Development)

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21 pages, 10223 KiB

Open AccessArticle

Discrete Element Simulation on Macro-Meso Mechanical Characteristics of Natural Gas Hydrate-Bearing Sediments under Shearing

by Meng Li, Hengjie Luan, Yujing Jiang, Sunhao Zhang, Qinglin Shan, Wei Liang and Xianzhuang Ma

J. Mar. Sci. Eng. 2022, 10(12), 2010; https://doi.org/10.3390/jmse10122010 - 16 Dec 2022

Viewed by 1269

Abstract

In order to study the macro-meso shear mechanical characteristics of natural gas hydrate-bearing sediments, the direct shear simulations of natural gas hydrate-bearing sediment specimens with different saturations under different normal stress boundary conditions were carried out using the discrete element simulation program of [...] Read more.

In order to study the macro-meso shear mechanical characteristics of natural gas hydrate-bearing sediments, the direct shear simulations of natural gas hydrate-bearing sediment specimens with different saturations under different normal stress boundary conditions were carried out using the discrete element simulation program of particle flow, and the macro-meso shear mechanical characteristics of the specimens and their evolution laws were obtained, and their shear damage mechanisms were revealed. The results show that the peak intensity of natural gas hydrate-bearing sediments increases with the increase in normal stress and hydrate saturation. Hydrate particles and sand particles jointly participate in the formation and evolution of the force chain, and sand particles account for the majority of the force chain particles and take the main shear resistance role. The number of cracks produced by shear increases with hydrate saturation and normal stress. The average porosity in the shear zone shows an evolutionary pattern of decreasing and then increasing during the shear process. Full article

(This article belongs to the Special Issue Gas Hydrate—Unconventional Geological Energy Development)

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