Numerical study of response behaviors of natural gas hydrate reservoir around wellbore induced by water jet slotting

The trial production of natural gas hydrate reservoirs remains poor. Reasonable reservoir reconstruction, which can improve formation permeability, is an important approach to increasing the efficiency and enhancing production. In this work, water jet slotting is proposed to reconstruct an natural gas hydrate reservoir near a wellbore. The spatial slots formed by water jet slotting not only directly constitute high-permeability channels, but also generate disturbances to the surrounding in-situ sediment. Water jet slotting disturbances to nearby sediment was investigated using a three dimensional flow-structure coupling model to evaluate the proposed reconstruction method. The reservoir at the SH2 site in the Shenhu area of the South China Sea was used as the reference. A horizontal slotting arrangement along the vertical well was adopted. The results demonstrate that water jet slotting can change the primary stress state of the sediment around the wellbore, and generate a dominant stress relaxation zone and small stress concentration zone. Within the stress relaxation zone, the in-situ compressive stress was remarkably reduced or even transformed into tensile stress, accompanied by sediment displacement and volumetric expansion strain. This is conducive to loosening the sediment around the wellbore and improving the permeability characteristics. In addition, the influence of the water jet slotting parameters including slot radius, spacing, and number on disturbances to the nearby sediment was studied. Reservoir responses to water jet slotting under balanced and unbalanced bottom-hole pressures were compared and analyzed. This study provides a reference for natural gas hydrate reservoir reconstruction using water jet slotting. Cited as: Huang, M., Su, D., Zhao, Z., Wu, L., Fang B., Ning, F.  Numerical study of response behaviors of natural gas hydrate reservoir around wellbore induced by water jet slotting. Advances in Geo-Energy Research, 2023, 7(2): 75-89. https://doi.org/10.46690/ager.2023.02.0

Assessing public perception and willingness to pay for renewable energy in Pakistan through the theory of planned behavior

With growing urbanization and increasing world population, energy demand also increases. A significant portion of the world’s energy comes from fossil fuels, and these sources of energy are declining rapidly at the current consumption rate. There are also growing environmental concerns on the use of fossil fuels increasing greenhouse gas emissions. In this regard, renewable energy (RE) shows promising solutions which are both sustainable and environmentally friendly. Developed countries and leading organizations are investing heavily in the RE sector. However, the developing world has anxieties over social acceptability and people’s willingness to pay for renewable energy. This study is conducted in Pakistan to understand the public perception and willingness to pay. The Theory of Planned Behavior (TPB) was utilized with background factors such as awareness, perceived advantages, perceived challenges, and moral obligations to examine its influence on people’s willingness to pay. In addition to this, the study also assessed the indirect effects of background factors (awareness, perceived advantages, and perceived challenges) on willingness to pay through public attitude. Furthermore, the indirect relationship between background factors (awareness and moral obligation) and willingness to pay through subjective norms was also examined. A total of 512 samples were gathered from participants and were analyzed through partial least square–structural equation modeling (PLS-SEM) and SPSS. The study findings are very interesting and back up our hypotheses that the background factors (awareness, perceived advantages, and perceived challenges) are positively associated with public attitude and have an indirect effect on willingness to pay through public attitude. Similarly, variables such as awareness and moral obligation are negatively and positively associated with subjective norms, respectively. However, the variables, awareness and moral obligation, have no indirect relationship with willingness to pay through subjective norms. Additionally, the study reveals that the components (attitude and perceived behavior control) of TPB have a significantly positive effect on willingness to pay. The study also concludes that the participants having formal education and knowledge about climate change and renewable energy are inclined toward green energy and are willing to pay, and they are hardly influenced by others' opinions. Furthermore, the study also provides insights for policymakers, suggestions, and recommendations for the future

A Method to Use Solar Energy for the Production of Gas from Marine Hydrate-Bearing Sediments: A Case Study on the Shenhu Area

A method is proposed that uses renewable solar energy to supply energy for the exploitation of marine gas hydrates using thermal stimulation. The system includes solar cells, which are installed on the platform and a distributor with electric heaters. The solar module is connected with electric heaters via an insulated cable, and provides power to the heaters. Simplified equations are given for the calculation of the power of the electric heaters and the solar battery array. Also, a case study for the Shenhu area is provided to illustrate the calculation of the capacity of electric power and the solar cell system under ideal conditions. It is shown that the exploitation of marine gas hydrates by solar energy is technically and economically feasible in typical marine areas and hydrate reservoirs such as the Shenhu area. This method may also be used as a good assistance for depressurization exploitation of marine gas hydrates in the future

COMPREHENSIVE UTILIZATION OF GEOTHERMAL AND SOLAR ENERGY TO EXPLOIT GAS HYDRATES BURIED IN OCEANIC SEDIMENTS

How to exploit and make use of natural gas hydrates in oceans will weigh much in the future researches. Unlike the oil or gas reservoirs, the distributions of natural gas hydrate are very complicated and don’t congregate massively in oceanic sediments. Besides, factors such as seafloor geohazards and climate must be taken into account, which makes it much more difficult and complicated to exploit oceanic gas hydrates than conventional oil or gas. Nowadays neither of such methods as thermal stimulation, depressurization, inhibitor injection, carbon dioxide replacement and mixing exploitation etc. is applied to exploit gas hydrates in marine sediments because of their disadvantages. This paper introduces a conception of combining solar and geothermal energy for gas hydrates exploitation. The model mainly includes five parts: solar energy transferring module, sea water circulating module, underground boiler module, platform and gas-liquid separating module. Solar cells and electric heaters are used to heat the formations containing hydrates. Because they become relatively more mature and cheaper, it’s the key of how to utilize the geothermy to exchange heat in developing this conception, which needs solution of fluid leakage, circulating passages and heat-exchange interface problems in building underground boiler. Probably it’s a feasible measure to use an effective hydraulic control system and hydraulic fracturing. The idea should be a good choice to exploit marine gas hydrates by combining solar and geothermal energy since this method has a great advantage either in terms of efficiency or cost.Non UBCUnreviewe

Molecular insights into CO2 hydrate formation in the presence of hydrophilic and hydrophobic solid surfaces

Microsecond molecular simulations have been performed on CO2 hydrate formation in the slit-nanopores of graphite and hydroxylated-silica surfaces. The simulation results show that different hydrophilic/hydrophobic properties of graphite and silica surfaces exert substantially different effects on CO2 hydrate formation. It is found that hydrate nucleation requires high aqueous CO2 concentration, and the solid surface affects hydrate nucleation mainly by changing the aqueous CO2 concentration in the systems. The hydrophobic graphite surfaces could adsorb CO2 molecules so strongly that the surfaces are almost covered by CO2 molecules, thus, the aqueous CO2 concentration is lowered. On the contrary, a partially cylindrical CO2 nanobubble is adsorbed at the hydrophilic silica surface and results in a high aqueous CO2 concentration. In the slit-nanopores of graphite and silica surfaces, hydrate nucleation starts from the bulk region and then grows towards the surfaces. CO2 hydrate solids interact with the silica surfaces mainly via semi-cages, which are constituted by the strong hydrogen bonds formed between silanols and interfacial water. At the end of the simulation, the hydrophobic graphite surfaces are still covered by the strongly adsorbed CO2 molecules, preventing the formation of ordered interfacial water on the surfaces, which is previously reported to play a critical role in promoting hydrate formation. These molecular insights into the effects of solid surfaces on CO2 hydrate formation are beneficial to CO2 hydrate-based technologies, such as geological CO2 sequestration. (C) 2021 Elsevier Ltd. All rights reserved

The Effect of Thermal Properties of Sediments on the Gas Production from Hydrate Reservoirs by Depressurization and Thermal Stimulation

AbstractThermal property is one of the most important properties of gas hydrate-bearing sediments (GHBS). In order to investigate the effect of hydrate formation thermal properties of GHBS on the gas production by depressurization with constant bottom-hole pressure and thermal stimulation, we estimated gas production from hydrates at the SH7 drilling site of the Shenhu Area. The hydrate accumulations in the Shenhu Area are similar to Class 3 deposits (involving only one layer of GHBS), and the overburden and underburden layers are assumed to be permeable. In this paper, a single vertical well, extending through the entire GHBS thickness, was designed for the numerical simulation by means of depressurization with constant bottom-hole pressure (3Mpa) and thermal stimulation (80°C) method. The simulation results indicate that hydrate dissociation has low sensitivity to rock grain specific heat and dry thermal conductivity of GHBS under this condition

Mechanical Instability of Methane Hydrate–Mineral Interface Systems

Massive methane hydrates occur on sediment matrices in nature. Therefore, sediment-based methane hydrate systems play an essential role in the society and hydrate community, including energy resources, global climate changes, and geohazards. However, a fundamental understanding of mechanical properties of methane hydrate–mineral interface systems is largely limited due to insufficient experimental techniques. Herein, by using large-scale molecular simulations, we show that the mechanical properties of methane hydrate–mineral (silica, kaolinite, and Wyoming-type montmorillonite) interface systems are strongly dictated by the chemical components of sedimentary minerals that determine interfacial microstructures between methane hydrates and minerals. The tensile strengths of hydrate–mineral systems are found to decrease following the order of Wyoming-type montmorillonite- > silica- > kaolinite-based methane hydrate systems, all of which show a brittle failure at the interface between methane hydrates and minerals under tension. In contrast, upon compression, methane hydrates decompose into water and methane molecules, resulting from a large strain-induced mechanical instability. In particular, the failure of Wyoming-type montmorillonite-based methane hydrate systems under compression is characterized by a sudden decrease in the compressive stress at a strain of around 0.23, distinguishing it from those of silica- and kaolinite-based methane hydrate systems under compression. Our findings thus provide a molecular insight into the potential mechanisms of mechanical instability of gas hydrate-bearing sediment systems on Earth

Research advances on the dissociation dynamics of natural gas hydrates

Natural gas hydrate is a kind of clean energy with great development potential but is still not commercially developed due to the bottlenecks such as exploitation technology, economical efficiency, and environmental effects.In recent years, people have explored the application of hydrate technology in the field of CO2 capture, seawater desalination, energy storage, gas separation, etc. One of the most challenging and critical problems is how the hydrates are formed and decomposed at any time. This paper summarizes the fundamental research on hydrate decomposition dynamics, including hydrate decomposition properties, influencing factors, and dissociation mechanisms. Moreover, the paper reviews the development of hydrate dissociation dynamics models. The existing models are divided into four categories according to dissociation mechanisms: Thermal dissociation models, intrinsic dynamics models, mass transfer dissociation models and integrated models, and their assumptions, main understanding and limitations are highlighted. Future directions for improving hydrate dissociation dynamics research are foreseen to deepen the understanding of hydrate dissociation dynamics and promote the development and utilization of hydrates

Molecular Dynamics Study on the Spontaneous Adsorption of Aromatic Carboxylic Acids to Methane Hydrate Surfaces: Implications for Hydrate Antiagglomeration

Spontaneous adsorption of aromatic carboxylic acids (phenylacetic acid, 2-napthylacetic acid, and 1-pyreneacetic acid) to the CH4 hydrate surface in both liquid hydrocarbon and aqueous phases has been investigated using molecular dynamics simulations, aiming to provide implications for hydrate antiagglomeration. Simulation results indicate that the liquid-phase environment, that is, the liquid hydrocarbon phase or aqueous phase, especially its hydrophilic/hydrophobic property, could profoundly affect the interfacial structures of CH4 hydrate and the adsorption behavior of aromatic carboxylic acids. In the hydrophobic hydrocarbon phase, with many CH4 molecules dissolved, more interfacial hydrate structures decompose and form a thin quasiliquid water film on the hydrate surface; aromatic carboxylic acids act as surfactants, that is, strongly adsorb to the hydrate/hydrocarbon interface and significantly lower the interfacial tension. Moreover, they adsorb to the interfacial water film on the hydrate surface with their carboxylic groups, which may destabilize the capillary liquid bridges formed among hydrate particles and then prevent hydrate coalescence. By contrast, fewer interfacial hydrate structures decompose in the aqueous phase, as CH4 molecules rarely dissolve in water but stay at the hydrate/water interface and stabilize the hydrate solid; only a few aromatic carboxylic acids adsorb to the hydrate/water interface by inserting their aromatic rings into the semicages on the hydrate surface, which may kinetically disturb the hydrate growth. Such adsorption is not very strong and mainly depends on the size matching between aromatic rings and semicages. Consequently, many more aromatic carboxylic acid molecules strongly adsorb to the hydrate surface in the hydrocarbon phase than in the aqueous phase, which can explain why antiagglomerants generally show a higher performance in the hydrocarbon phase and easily lose efficacy at high watercuts. Additionally, the molecular structures could also affect the adsorption behavior of aromatic carboxylic acids: with more aromatic rings, acid molecules can form stable aggregates via the pi-pi stacking interactions of the aromatic rings, adversely affecting the adsorption in the aqueous phase