Development Of Natural Gas Hydrate Research Articles

Estimation on strength parameters of sediments with hydrate layered distribution based on triaxial shearing tests

Proper models for predicting strength parameters of reservoirs are vital to the numerical simulation and risk analysis during gas hydrate exploration. However, unlike homogeneous hydrate reservoirs, strength parameters of interlayered sediments depend on hydrate distribution modes, which remains unclear. Herein, a series of triaxial shearing tests on sediments with hydrate layered distribution are conducted to investigate variations of strength parameters and effects of sublayers. The results indicate that failure strength of whole sediments mainly depends on the high hydrate-saturated sublayer, while the cohesion is more relevant to the low hydrate-saturated layer. Besides, prediction models are proposed to estimate the failure strength through data-fitting, strength-average, and hydrate-average methods. By comparing the accuracy and applicability of these three methods, the hydrate-average method is the best way to estimate failure strength for current use. This study can provide a feasibility reference for strength estimation and risk control during natural gas hydrate development.

Effect of the protrusion of the mining chamber on particle recovery performance in solid-state fluidization mining for natural gas hydrate

Solid-state fluidized mining is a promising method for the development of natural gas hydrate (NGH), in which hydrate recovery is a key technology. Following the water jet, circular protrusions appeared on the inner wall of the mining chamber, having a substantial effect on the recovery of hydrate particle. In order to improve the particle recovery rate, this paper uses experimental and modeling methods to investigate the effects of protrusion height (h) and protrusion spacing (s) on particle recovery performance. The results show that the resistance of protrusion and gravity results in the formation of three types of recovery flow fields, each of which contains circulating flow, supplementary flow, and recycling flow. The third type of flow field is beneficial for particle recovery. When s is 90 mm or more, the recovery flow field changes from the first type of flow field to the third type of flow field as h increases. The particle recovery rate gradually increases as h increases when s is 90 and 120 mm, and the maximum recovery rates can reach 44.6 % and 46.2 %, respectively. When h is 40 mm or more, the recovery flow field gradually transforms into the third type of flow field as s increases. The particle recovery rate gradually rises and then declines with increasing s, with the turning points occurring at s = 110 mm. The results further enrich the mechanism of hydrate recovery and help optimize the design of recovery tools.

Achieving effective and simultaneous consolidation breaking and sand removal in solid fluidization development of natural gas hydrate

Natural gas hydrate (NGH) as the new generation clean energy resource possesses tremendous commercial potential and strategic significance. Solid fluidization is one of the major extraction approaches and shows advantages in reducing safety risks as the reservoir pressure is maintained at native condition. Despite of great promises in this technology, one critical challenge embedded within the extraction process is the deep separation of NGH particles from their weakly consolidated sands. Solving this practical issue requires comprehensive understanding of the interactions between NGH fragments and sands yet seldom systematic studies were available. Herein, we proposed to achieve simultaneous NGH-sand consolidation breaking and sand removal by hydro-cyclone technology. We firstly launched a systematic theoretical analysis on the mechanical forces of NGH fragments within the swirling flow field, and then validated the principle of our method on polyproylene-quartz sand research template. We constructed a dual-chamber cyclone desander (DCCD) apparatus and the results showed polypropylene recovery efficiency was as high as 99.8%. Collectively, our solid fluidization technology pioneers the development of safe NGH extraction by killing consolidation breaking and separation these two birds with one stone.

Experimental investigation on the propagation of hydraulic fractures in massive hydrate-bearing sediments

Hydraulic fracturing is regarded as one of the potential technical means to realize efficient development of natural gas hydrate. Massive-distributed hydrates are widespread around the world, although the solid fluidization method has been proposed to develop this kind of reservoir, the process of this method is complex, and there are still a lot of key problems need to be solved. Meanwhile, when the hydrate decomposed during production, how to maintain formation stability is still an unsolved key problem. Therefore, we consider using hydraulic fracturing technology to exploit this kind of reservoir. On the one hand, the fractures formed by high viscosity fracturing fluid can improve the reservoir permeability. On the other hand, the proppant added during fracturing can play a good supporting role to the formation. In this work, a series of large-size (300 × 300 × 300 mm) hydraulic fracturing physical simulation experiments were conducted under true triaxial stress states to investigate hydraulic fracture propagation law in massive-distributed hydrate-bearing reservoir. The effects of massive hydrate size, approaching angle and fracturing fluid displacement on the fracture propagation were studied. The experimental results indicated that massive hydrate exerts an important influence on hydraulic fracture propagation. Two main massive hydrate-hydraulic fracture interaction modes were observed in our experiments: (a) When the massive hydrate size is small, the hydraulic fractures mainly propagated along the interface between the sediment matrix and the massive hydrate. (b) The hydraulic fractures penetrated the massive hydrate, which usually occurs when hydraulic fracture encountered large-size massive hydrate, and the penetrated position moves from both sides to the central position of the massive hydrate. The approaching angle has a significant effect on the massive hydrate-hydraulic fracture interaction law. Under the condition of high approaching angle, hydraulic fractures easily penetrated the massive hydrate. The influence of fracturing fluid displacement on massive hydrate-hydraulic fracture interaction is closely related to massive hydrate size. When hydraulic fractures encountered the small-size massive hydrate, increasing the displacement has a limited effect on massive hydrate-hydraulic fracture interaction, and the hydraulic fractures still mainly propagated along the interface. When large-size massive hydrates are distributed in the sample, increasing the displacement has a significant effect on the massive hydrate-hydraulic fracture interaction, and hydraulic fractures tend to branch, the complex fracture geometry would be formed. In this study, a new large-size massive hydrate sample preparation method was proposed, and the effects of various factors on the hydraulic fracture propagation law were investigated experimentally, which can provide guidance for the fracturing design of massive hydrate-bearing reservoir.

Numerical simulation of natural gas hydrate development with radial horizontal wells based on thermo-hydro-chemistry coupling

Numerical simulation of natural gas hydrate development with radial horizontal wells based on thermo-hydro-chemistry coupling

A novel permeability model for hydrate-bearing sediments integrating pore morphology evolution based on modified Kozeny-Carman equation

Permeability of hydrate-bearing sediments is the key parameter to determine the gas production performance, which is mainly affected by the pore morphology and hydrate saturation. Existing models of permeability could not well capture the dynamic characteristic of permeability in sediments with changing hydrate saturation and pore morphology. In this paper, a novel normalized permeability model using logistic function linked different hydrate pore morphology evolution was established by modifying tortuosity, surface area and pore shape factor simultaneously in Kozeny-Carman equation. It was verified by different published data and compared with other models. The introduced critical hydrate saturation and transitional intensity of hydrate pore morphology were optimized by genetic algorithm. Results indicated that this model was more powerful than existed models and better captured the permeability evolution in hydrate-bearing sediments at various conditions. The critical hydrate saturation and transitional intensity of hydrate pore morphology dominated the characteristics of permeability evolution. In addition, the effect of porosity would not be ignored especially below the critical hydrate saturation when hydrate pore morphology changed from pore filling to grain coating. The proposed model brings reliable predictions and mechanistic understandings of the permeability evolution in hydrate-bearing sediments, and builds fundamental theory for development of natural gas hydrate in safety and efficiency.

Preface

China is currently the world’s largest producer of wind and solar energy. China has made great efforts in promoting decarbonization in energy and reducing greenhouse gas emissions. In the future, China will accelerate the development of low-carbon and zero-carbon technologies to help promote green development. China has a clear pathway to build a more sustainable, secure and inclusive energy future.Following this concept, the 2022 International Conference on Renewable Energy and Electrical Technology (ICREET 2022) took place held during December 16th-18th, 2022 in Xi’an, China (virtual event). The conference provided a platform of international standards where all the participants discussed and shared persuasive key advances in renewable energy and electrical technology. It also offered a unique venue for renewing professional relationships and for remaining up-to-date variations in the challenging and expanding fields.This volume contains the papers presented at the 2022 International Conference on Renewable Energy and Electrical Technology. The papers covering various topics including Renewable Energy Power Generation, Natural Gas Hydrate Development Technology, Energy Internet Technology, Electric Motors and Drives, Power System Analysis, etc. have been through rigorously reviewed by experts and meet the requirements of publication.The online conference attracted about 60 individuals, and three sophisticated professors performed their keynote speeches during the conference. Among them, Prof. Pierluigi Siano from University of Salerno, Italy, one of our keynote speakers, shared with us his research on Energy Communities in Smart Grids. A novel scalable and privacy-preserving distributed parallel optimization that allows the participation of large-scale aggregation of prosumers with residential PV-battery systems in the market for the ancillary service (ASM) was proposed in this study. To consider both reserve capacity and reserve energy, day-ahead and real-time stages in the ASM were considered. A method, based on hybrid Variable Neighborhood Search (VNS) and distributed parallel optimization was designed for the day ahead and real-time optimization. All the keynote speakers made brilliant speeches combing their own research domains and experiences, and shared unique insights, creating a great platform for academic communication.On behalf of the Conference Organizing Committee, we would like to extend our sincere acknowledgement to all the keynote speakers, peer reviewers, and all the participants. Particularly, our heartfelt thanks and appreciation go to the Editors and Managers, Journal of Physics: Conference Series for their help and kind cooperation during the preparation of the proceedings. Hopefully, all participants and other interested readers can benefit significantly from the proceedings and find it rewarding.The Committee of ICREET 2022List of Committee member is available in this Pdf.

Sensitivity analysis of the main factors controlling the potential volumetric evaluation of natural gas hydrate resources in the South China Sea

The China Geological Survey successfully completed the second trial of natural gas hydrate (NGH) production in 2020, and the daily gas production and total gas production were greater than those in the first trial, but the evaluation of NGH resources in the South China Sea (SCS) is still in the evaluation stage, specifically for the gas content. In 2021, some scholars used different methods to more accurately evaluate NGHs in the SCS to aid in NGH exploration and evaluation in the SCS; some of them analysed the main factors controlling NGH resources, added several factors to the volume method for optimization, studied the sensitivity of the evaluation of resources to each of the main controlling factors (NGH stability zone area, NGH area coefficient, NGH stability zone thickness, NGH thickness coefficient, NGH reservoir porosity, NGH reservoir saturation, NGH volumetric ratio, NGH resource ratio coefficient and NGH recovery coefficient) and found that the effective thickness coefficient, effective thickness and effective area coefficient are the most sensitive; these values are 23.15%, 15.66%, 13.98%, and 13.95%, respectively, while the other values are 0%, 15.66%, 8.42%, 8.41%, 2.50%, and 13.92%; taking into account the influence of the main controlling factors, the range of the water resource potential evaluation results in the SCS is 2.4 × 107 m3–5.9 × 1014 m3, the modal value is 7.25 × 1011 m3, and the confidence level of the modal ±25% interval is 77.8%; these values provide a higher evaluation accuracy and higher resource level, which is consistent with the current results of NGH research in the SCS. Although the development of NGHs in the SCS is progressing rapidly, basic exploration is relatively scarce, and the number of samples of effective thickness obtained through dozens of exploratory wells is too few. It is recommended that China carry out more exploration and research projects in the Shenhu area and the entire SCS to obtain more accurate thickness data.

Numerical simulation of failure properties of interbedded hydrate-bearing sediment and their implications on field exploitation

Marine natural gas hydrate is widely accepted as a promising substitute energy resource, whereas geotechnical responses of hydrate-bearing sediments (HBS) are crucial for the safe development of natural gas hydrate. The hydrate spatial distribution in sediments is multitype and present different coalescence degrees, its distribution pattern significantly influences the failure behavior of HBS, but the mechanics behind this influence is unclear. Numerical simulations are of great importance in revealing such mechanics. In this paper, a series of numerical simulations, using a modified Mohr–Coulomb (MC) model, were performed to analyze the deformation mechanisms of HBS when the hydrate was laminarly distributed in its host sediment. Considering the vertical heterogeneity of the hydrate distribution, the vertical-laminar hydrate distribution samples were simplified as interbedded samples. The interbedded HBS specimens consisted of three layers: the middle layer with relatively lower hydrate saturation; and the upper and lower layers with relatively high hydrate saturation. Interbedded samples with different hydrate saturations, depressurization ratios, and thickness ratios were designed to analyze their mechanical behaviors. The results indicated that in both the hydrate saturation and thickness ratio of the interbedded samples, the plastic yield area first occurred in the lower hydrate saturation layer; the failure mechanism was mainly determined by the strength of the lower hydrate saturation layer. In addition, the shear failure behavior of the HBS was controlled by the hydrate saturation difference between the middle and upper layers. With a smaller hydrate saturation difference between the middle and upper layers, the samples were more likely to experience shear failure. In the thickness ratio samples, the HBS changed from brittle to ductile failure with an increase in the thickness of the lower hydrate saturation layer. Under different depressurization amplitudes, the larger compression and shear yield zones were mainly confined in the upper layer. This study provides a theoretical framework for controlling the strength-weakening mechanism during natural gas development, which can be used to guide reservoirs characterization, the selection of depressurization schemes, and decomposition zones monitoring.

Feasibility Evaluation of a New Approach of Seawater Flooding for Offshore Natural Gas Hydrate Exploitation

In this work, a new approach of seawater flooding was proposed for offshore natural gas hydrate (NGH) exploitation, whose feasibility was numerically evaluated based on a large-scale NGH reservoir situated in the Shenhu Area of the South China Sea. Then, two artificial means of well location rearrangement and hydraulic fracturing, as well as their combination, were proposed to be incorporated with seawater flooding to promote gas production from offshore NGH deposits. Simulation results indicated that seawater flooding had great advantages over depressurization and could substantially promote hydrate dissociation, effectively prevent secondary hydrate formation, and greatly facilitate gas production. Furthermore, a stable gas production period could be achieved for a long duration, which made the most significant contribution to gas production. The two artificial means of well location rearrangement and hydraulic fracturing could both promote hydrate dissociation and enhance gas recovery, but the promotion mechanisms were different. When these two methods were combined, hydrate dissociation in the whole hydrate-bearing layer could be further facilitated, and a favorable gas production rate could be obtained with a low water production and a high gas–water ratio, which demonstrated great superiority of the combined method over these two methods when used alone. Therefore, it is expected that the newly proposed approach of seawater flooding combined with well location rearrangement and hydraulic fracturing can be applied in the future commercial offshore NGH development.

Numerical simulation of gas extraction from marine hydrate sediments using sodium chloride injection

The inhibitor injection method is an important method for natural gas hydrate development and sodium chloride (NaCl) is a cheap and clean inhibitor. In this study, a new three-dimensional three-phase, four-component numerical model is developed to consider the effect of inhibitors. The focus is on the production dynamics of hydrate development by using inhibitor injection method, and the effects of different injection salt mass fraction, temperatures, and pressures are investigated. The results show that the inhibitor injection method has higher gas production rates, higher peak gas production, and shorter extraction development period compared to conventional extraction methods in challenging hydrate reservoirs. In addition, higher inhibitor concentrations increase peak gas production rates and shorten the development period. Injected pressure at 20 MPa is reasonable. The results of the global sensitivity analysis of the production parameters indicate that the mass fraction of salt in the injected water has a significant positive effect on extraction. In summary, the inhibitor injection method can be an effective method for developing challenging hydrate-bearing sediments

Numerical analysis of the geomechanical responses during natural gas hydrate production by multilateral wells

Multilateral wells are acknowledged as a promising well type to achieve the commercial development of natural gas hydrate. Previous studies have validated the efficacy of multilateral wells for hydrate mining without considering the geomechanical responses. However, effective stress increases during hydrate extraction by depressurization, and the reservoir skeleton degrades with hydrate dissociation, which might induce stress concentration, stratum subsidence, seafloor inclination, and other hazards. Understanding the geomechanical responses is thus crucial for the design of hydrate exploitation utilizing multilateral wells. As a continuation of our previous study, a coupled thermal-hydrologic-mechanical model was constructed to investigate the geomechanical responses during hydrate production by multilateral wells. Results reveal that multilateral wells can upgrade geomechanical risks and gas production capacity for hydrate exploitation. Stress concentration and stratum sinks are prevalent around the multilateral well. Increasing production pressure may alleviate stratum subsidence but has a noticeable impact on gas production. Since stratum inclination generated by hydrate mining with multilateral wells is minimal, geological catastrophes are most improbable. For utilizing multilateral wells in hydrate extraction, it is recommended to pay more attention to wellbore and wellhead safety.

Research on methane hydrate formation in porous media with gas–water two-phase flow

The study of hydrate formation in porous media is crucial for the efficient production of natural gas hydrate. Current research on gas hydrate formation in porous media has primarily focused on the static state. A prediction model of hydrate formation under the condition of gas–water two-phase flow was established by combining the heat transfer and gas–water two-phase flow mechanisms in porous media. Methane hydrate formation in quartz sand was experimentally investigated under a gas–water two-phase flow. The results revealed an obvious pressure difference with hydrate formation at different positions; the pressure difference increased with time, which can be used as an important basis to assess the distribution of flow obstacles in porous media. COMSOL Multiphysics was used to solve the proposed model, and the accuracy of the model prediction results was verified using the experimental data. Further, the hydrate formation process and evolution law in the experiment were simulated and inverted. Flow parameters, such as pressure, hydrate saturation, and water saturation, presumably exhibit non-uniform distributions with the formation of hydrates in porous media. The longer the time, the more distinct the non-uniform distribution of the aforementioned parameters and the higher the risk of flow obstacles in porous media. This study provides an important theoretical basis for the efficient development of natural gas hydrate in the future.

A novel model of reaction specific surface area via depressurization and thermal stimulation integrating hydrate pore morphology evolution in porous media

Reaction specific surface area (RSSA) of hydrate is essentially important for hydrate kinetic dissociation and gas production from hydrate-bearing sediment. Models of RSSA available in literatures neglecting hydrate pore morphology evolution and methods induced hydrate dissociation could not capture the characteristic of RSSA evolution accurately. In this study, a novel model using logistic function to link microscale hydrate pore morphology evolution with macroscale RSSA variations was proposed, and verified by different published laboratory data and compared with other models. The introduced critical hydrate saturation and transitional intensity of hydrate pore morphology were optimized by genetic algorithm. Results indicated that the critical hydrate saturation and transitional intensity of hydrate pore morphology dominated the characteristics of RSSA evolution. The RSSA evolution was orderly divided into four stages named ‘high Sh pore wall coating dominated’, ‘high Sh pore filling dominated’, ‘low Sh pore filling dominated’ and ‘low Sh pore filling only’ in both method of hydrate dissociation by depressurization and thermal stimulation. In addition, the RSSA for depressurization was lower than that of thermal stimulation at the same hydrate saturation due to annulus hydrate by thermal stimulation. Grain size and arrangement factor significantly influenced RSSA, which showed a negative correlation. The proposed model brings reliable predictions and mechanistic understandings of the RSSA evolution in hydrate-bearing sediment, and builds fundamental theory for development of natural gas hydrate in safety and efficiency.

Numerical analysis of gas recovery enhancement from natural gas hydrate reservoir by using a large-diameter casing

Multi-well patterns and complex structural wells can enlarge the contact area between the wellbore and natural gas hydrate (NGH) to improve productivity significantly, but the construction cost of drilling is still too high. The previous study has proposed a self-entry exploitation device (SEED) with an enlarged device diameter, allowing more NGHs to dissociate simultaneously. While for conventional wellbore, a large-diameter casing may be applied in NGH development to enlarge the wellbore diameter of the production section. This work continued to study the influences of enlarged device/wellbore diameter on gas production characteristics, temperature-pressure evolutions, and the dissociation front movement pattern. The sensitivity analysis was also carried out by various reservoir and depressurization parameters under different wellbore diameters. Results show that the enlarged wellbore diameter can enlarge the drainage area and increase the dissociation efficiency. The temperature and pressure around the wellbore remain relatively stable, meeting the conditions for long-term production. Also, the dissociation front moves farther away faster as the wellbore diameter enlarges, accelerating NGH dissociation at distant wells. Finally, the sensitivity analysis reveals that the enlarged wellbore diameter enhances gas production significantly in unfavorable production parameters: poor production pressure, low permeability, low NGH saturation, and narrow reservoir thickness.

Visual experimental study on hydrate occurrence patterns and growth habits in porous media

The distribution and morphology of natural gas hydrates in pores have significant impacts on the macroscale physical properties of hydrate-bearing sediments. This paper investigated hydrate morphology characteristics using a micromodel, and the memory effect was used to accelerate the hydrate formation process. It is found that the initial gas and water saturation play a significant role in hydrate occurrence patterns and growth habits. When water is the initial main continuous phase, the hydrate prefers to grow towards the center of pores during hydrate formation. When gas is the initial main continuous phase, hydrates grow towards the center of pores and along the wall, and the mass transfer happens between the water and gas phases. It can be realized that the hydrate occurrence pattern is determined by the growth habit, which is related to mass transfer. These findings provide a theoretical foundation for future natural gas hydrate development.

Numerical simulation of productivity improvement of natural gas hydrate with various well types: Influence of branch parameters

The depressurization method and its modified scheme may be the best way to efficiently recover marine natural gas hydrate (NGH) from the reservoir. However, the capacity of existing engineering tests still poses considerable challenges to the industrial development of NGH. The complex structure wells can effectively promote the NGH contact area to enhance the exploitation efficiency, but the influence of branch parameters on gas production performance is not well sorted out for reference when performing well type optimization. Therefore, a geological model of an ideal hydrate reservoir and 65 wellbore models were established based on the geological data from station AT1 in Nankai Trough to analyze the influence of different branch parameters on the production capacity for various well types. Results indicate that the open hole section length is heavily constrained by the size of the reservoir for a single well. Compared to the corresponding single well, the multi-branch vertical wells can increase productivity by about 2.12%–51.18%, the multi-branch horizontal wells by about 0.99%–29.75%, and the cluster horizontal wells by about 54.36%–250.66% well. Moreover, the correlation coefficients of various branch parameters were analyzed as a reference when optimizing the well type and show that the cluster horizontal well has the highest sensitivity to branch parameters, which can significantly promote gas production efficiency, and is expected to break the threshold of industrial development.

Comparative study of the electrical characteristics of hydrate reservoirs before and after gas hydrate trial production in the Muli permafrost area of the Qilian Mountains, NW China

Natural gas hydrate (NGH) is considered one of the most promising alternative energy sources in the 21st century. The exploitation and decomposition of NGHs could cause geological disasters and eco-environmental problems related to climate warming, seawater blue tides, submarine landslides, drilling platform collapses, slope instability, etc. Thus, an investigation of the eco-environmental effects of NGH exploitation and decomposition has scientific and practical significance. In this paper, the electrical characteristics of NGH reservoirs before and after NGH trial production in the Muli permafrost area of the Qilian Mountains are comparatively examined for the first time. The electrical structure models before and after NGH trial production are obtained through two-dimensional and three-dimensional inversion of the NE audio-magnetotelluric (AMT) sounding profile around production test well SK2. Notably, the electrical structure of the NGH reservoir changes greatly. The research indicates that (1) after NGH trial production, the formation resistivity increases remarkably within 200 m and burial depths in the range of 120– 340 m around the production test well; (2) the main reason for the increasing resistivity after trial production is the Joule-Thomson effect caused by depressurization production and the endothermic effect of NGH decomposition, which lead to the formation of ice-bearing strata; afterwards, we explain the formation process of ice-bearing strata after NGH trial production; and (3) we speculate that the formation stability is not adversely affected after NGH trial production. These findings and research results can provide guidance for subsequent geoenvironmental safety risk assessments of NGH development in permafrost areas.

Study on the marine environment limiting conditions of deepwater drilling for natural gas hydrate

Natural gas hydrate (NGH) is a kind of clean energy which has attracted more and more attention. At present, deepwater drilling engineering is an effective way to develop the NGH in deepwater areas. Ensuring the safe and efficient deepwater drilling engineering is the necessity for exploitation of the NGH resources. If the marine environment is particularly harsh, deepwater drilling operations could be suspended, which will affect the process of NGH development. Normally, the operation safety of the drilling system, including the drilling riser, subsea wellhead and conductor, is the limiting factor of the marine environment. Therefore, it is important to study the mechanics of the drilling system for accurate evaluation the risk of NGH development. In this paper, in order to obtain the marine environment limiting conditions of deepwater drilling operations, the mechanical model of the drilling system is established through taking the drilling riser -subsea wellhead-conductor as a whole research object. The top boundary condition of the conductor is determined by the mechanical response of the drilling riser subjected to marine environmental load, and the interaction between the conductor and the soil is described by the P-y model. In addition, the correctness and accuracy of the model is verified. Then, parameter sensitivity analysis is carried out to present a comprehensive influence of the marine environment on the mechanical behavior of the drilling system. Finally, the marine environment limiting conditions of deepwater drilling engineering for NGH are obtained. This study has guiding significance for the safety of deepwater drilling for NGH development.

Long-Term In-Situ Monitoring and Analysis of Terrain in Gas Hydrate Trial Harvesting Area.

With the increase in global energy demand, the exploration and development of natural gas hydrate in sea has become a research hotspot in recent years. However, the environmental problems that may be brought about by large-scale harvesting are still concerns. The terrain monitoring of the trial harvesting area can effectively prevent the geological disasters that may be caused by the development of hydrates. Therefore, we have developed a new terrain monitoring device, which can work in the deep sea for a long time. Firstly, the structure of the sensor arrays and bus-type control system of the device are introduced. Secondly, an arc model with an interpolation method is used for reconstruction of the monitored terrain. Thirdly, after the accuracy of the sensing arrays are verified in laboratory, the device was placed in the Shenhu area of the South China Sea for more than 6 months of in-situ monitoring. Finally, we analyzed the data and concluded that the terrain of the monitored area was relatively flat, where the maximum subsidence was 12.3 cm and the maximum uplift was 2.75 cm.