Journal of Natural Gas Science and Engineering最新文献

Changes in the physical and mechanical characteristics of the natural gas hydrate reservoir during depressurization production can affect safe and efficient production. In order to reveal the evolution law of reservoir physical and mechanical characteristics, based on the establishment of thermo-hydro-mechanical-chemical (THMC) multi-field coupling theoretical model, taking SH2 drilling platform in Shenhu sea area of the South China Sea as an example, COMSOL multiphysics is used to simulate the processes of depressurization production with a single horizontal well. The results show that, after the bottom hole pressure began to decrease, the gas and water production rates immediately increased from zero to their respective peaks, and then decreased rapidly. The decomposition of hydrate is an endothermic process. The changes of temperature and pressure conditions have a significant impact on the decomposition of hydrate. Effective stress and Mises stress appear to be concentrated in the area of complete hydrate decomposition. Mises stress rises sharply at the location of the leading edge of decomposition, which needs to be alert to the risk of landslide. In the process of depressurization production, the top of the reservoir gradually appears settlement behavior. The upper area of the horizontal well has a large amount of subsidence, and reservoir modification can be implemented during production to improve the mechanical stability of the reservoir. The results are an important guide to achieve stable and continuous gas production.

The solid phase swelling of the clay sediment is related to water from gas hydrate dissociation. Therefore, the relationships among decomposed water content, porosity and effective gas permeability in clay sediment are derived in this paper. A formula for predicting the evolution of effective gas permeability in sediments during clay particle expansion caused by decomposed water content is proposed, which is in good agreement with experimental data. The model of gas production from clay sediments by depressurization is established for the first time, which is verified by gas production rate obtained by gas production experiment. The results show that the porosity and gas phase permeability of clay sediments decrease with the increase of decomposed water content. Then, with the decrease of hydrate saturation, the effect of clay expansion caused by decomposed water content on porosity and gas phase permeability decreases. The amount of decomposed water needed for montmorillonite to expand is less than that of illite. After the gas production rate drops suddenly at 3000s, it could be considered that clay swelling affected by decomposed water basically ends.

Propane is utilised primarily for industrial sector and domestic applications. However, propane is considered a hydrate former. Thus, it is necessary to establish pressure and temperature conditions that ensure a hydrate-free zone. This requires determining the minimum amount of water required for the formation of hydrates and providing a thermodynamic model capable of determining the water content and predicting pressure and temperature conditions for hydrate dissociation. Consequently this study investigated the water content of liquid propane in equilibrium with liquid water or hydrates at pressures up to 8.274 MPa and temperatures between 211.15 K and 313.15 K. Using three different methods: a quartz crystal microbalance (QCM), a silicon oxide-based hygrometer and the new method developed by Burgass et al. (2021). In general, water content measurements determined from the new method and QCM were found to be in good agreement. The fluid phase behaviour of the system (propane + water) was modelled using the simplified Cubic-Plus-Association (sCPA-SRK) and the Soave-Redlich-Kwong (SRK) equation of state combined with the van der Waals classical and non-density-dependent (NDD) mixing rules, respectively. Both models provided similar results, although the sCPA-SRK model used only one adjustable parameter in contrast with the SRK model, which used three adjustable parameters. The experimental measurements from the new method and QCM to the sCPA-SRK and SRK-NDD models presented 4.5% and 4.5% deviation, respectively over temperature range of 276.15–313.15 K. In all cases, the hydrate-forming conditions were modelled using the van der Waals and Platteeuw's solid solution theory. Additionally, the sCPA-SRK + van der Waals and Platteeuw model calculations were compared against hydrate dissociation conditions, using used two adjustable Kihara parameters and showed overall good agreement when compared to data from the literature.

Liquid CO₂ has the synergistic effect of low-temperature damage and displacing CH₄ after injecting into the coal seam, which can effectively improve coalbed permeability and promptly promote the adsorbed CH₄ to desorption state for preventing the coal and gas outburst disasters. The injected CO₂ gets adsorbed at the surface of the coal pores, which causes the coal swelling. In this work, we developed a triaxial experimental platform to explore the features of CO₂ displacing CH₄ under different temperatures. The variation of coal swelling and segmentation features of the displacing concentration was elucidated. The seepage ability and mechanism of gas mitigation in the coal seam during LCO₂-ECBM were revealed. The results showed that the coal samples displayed swelling deformation in the CH₄ adsorption and CH₄ displacement stages, and the strain curves can be divided into rapid and slow deformation phases. The strain in the CO₂ displacing CH₄ stage is notably larger than that in the CH₄ adsorption stage. Three dominant results were obtained during the CH₄ displacement: Free CH₄ driving by CO₂ injection, CH₄ self-desorption, and CO₂–CH₄ competitive adsorption. The displacing flow rate increased swiftly in the initial stage, and then decreased to a stable tendency. The cumulative displacement volume of CH₄ in different stages exhibited distinct functional relationships. The integrated contribution of the coal matrix shrinkage and thermal stress damage to gas seepage improvement was more prominent than that of the adsorption swelling to seepage inhibition in the coal seam.

Continuous flaring of natural gas remains a great environmental threatening practice going on in most upstream hydrocarbon production industry across the globe. About 150 billion m³ of natural gas are flared annually, producing approximately 400 million tons of carbon dioxide alone among other greenhouse gases. A search into a viable method for natural gas conversion to methanol becomes imperative not only to save the soul of the ever-changing climate but also to bring an end to wastage of valuable resources by converting hitherto wasted natural gas to wealth. Currently the technologies of conversion of natural gas to methanol could be categorized into the conventional and the innovative technologies. The conventional technology is sub-divided into the indirect method also called the Fischer-Tropsch Synthesis (FTS) method and the direct method. The major commercial technology currently in use for production of methanol from methane is the FTS method which involves basically two steps which are the steam reforming and the syngas hydrogenation steps. The FTS method is highly energy intensive and this is a factor responsible for its low energetic efficiency. The direct conversion of methane to methanol is a one-step partial oxidation and lower temperature method having higher energetic efficiency advantage over the FTS method. The direct method occurs at temperature range of 380–470 °C and pressure range of 1–5 MPa while the FTS occurs at temperature range of 700–1100 °C and atmospheric pressure. Both methods are carried out under effect of metallic oxide catalysts such as Mo, V, Cr, Bi, Cu, Zn, etc. The innovative methods which include electrochemical, solar and plasma irradiation methods can be described as an approach to either of the two conventional methods in an innovative way while the biological method is a natural process driven by methane monooxygenase (MMO) enzyme released by methanotrophic bacteria. The aim of this study is to review the current state of the technology for conversion of methane to methanol so as to make abreast the recent advances and challenges in the area.

There are many applications with the two-phase flow of gas (hydrocarbon, non-hydrocarbon, and their mixture) and water in different courses of gas recovery from natural gas resources and gas storage/sequestration programs. As the interface of gas-water is crucial in such systems, precise prediction of gas-water interfacial tension (IFT) can aid in the simulation and development of such processes. Artificial intelligence techniques (AIT) are being used to estimate IFT. In this paper, the IFT of the gas and water system was estimated based on models built using a comprehensive data set comprised of 2658 experimental data points. These cover a wide range of input parameters, i.e., specific gravity (0.5539–1.5225), temperature (278.1–477.5944 K), pressure (0.01–280 MPa), and water salinity (0–200,000 ppm). The intelligent models include Least-Squares Boosting (LS-Boost), Multilayer perceptron (MLP), Least Square Support Vector Machine (LSSVM), and Committee machine intelligent system (CMIS). The models reproduce the IFT data in 7.4–81.69 mN/m. The modeling approaches contain new hybrid forms in which Imperialist Competitive Algorithm (ICA), Grey Wolf Optimizer (GWO), Whale Optimization Algorithm (WOA), Levenberg-Marquardt algorithm (LM), Bayesian regularization algorithm (BR), Scaled conjugate gradient algorithm (SCG), and Coupled Simulated Annealing (CSA) were used for optimization and learning purposes. Statistical and graphical analyses were implemented to check the agreement between the prediction and evaluation data. The results show a reasonable coherence for most models, among which the CMIS approach exhibited a promising performance. CMIS was accurate even in conditions of varying specific gravity, pressure, temperature, and salinity. The findings were also compared with available models in the literature and demonstrated superior predictions of the CMIS model. Also, outlier detection by the Leverage approach demonstrates the validity of the gathered dataset and, subsequently, the CMIS model.

Gas production from hydrate-bearing sediments requires methane dissociation, which induces two-phase gas flow, mobilizing fine clay particles from within saturated pores. Fines migration within sandy sediments results in subsequent pore clogging, reducing reservoir connectivity. Sediments complex pore morphology, require direct 3D microscopic pore-scale imaging to investigate fines' influence on the porous media. The work uses synchrotron microcomputed tomography, to understand how fines migration due to gas injection, affects pore morphology and gas connectivity within sandy sediments. The goal is to study the impact of fines type and content at different gas injection stages, on gas flow regime and sediments rearrangement.

Six saturated samples of sand and fines mixtures (Kaolinite and Montmorillonite at different contents) underwent four stages of gas injection during in-situ 3D scanning. X-ray images were segmented for direct visualization, as well to quantify gas ganglia distribution, also to extract pore networks to statistically measure changes in pore and throats distributions, and to simulate single-phase and relative permeability.

Findings reveal that the extent of deformation to pore morphology increases with fines content and gas injection regardless of fines type. High kaolinite content (equal to or larger than 6%) results in fractured porous media, while high montmorillonite content (equal to or larger than 5%) results in disconnected vuggy media. Lower contents cause a gradual reduction in pore and throat sizes during gas injection. As fines content increases, clogging intensifies, thus gas connectivity and flow regime changes from connected capillary to disconnected vugs and microfractures. Both hydrophobic and hydrophilic fines reduced throat sizes, due to dislocations in sand grains. A unique pattern is discovered using pore networks, which describe pore-size fluctuations during fractures and vugs formation, due to fines migration.

Shale rocks have become an indispensable natural gas and oil source. Hence, the knowledge of the mechanical properties of shales is critical for field applications. In this work, we selected three types of shales (argillaceous, kerogen-rich, and bituminous) and conducted detailed chemical and microstructural characterization along with mechanical property measurements by nanoindentation. The three shale samples have highly distinct mineral compositions. The argillaceous and kerogen-rich shales have soft matrix phases - muscovite and kerogen, respectively. The bituminous shale, on the contrary, has no distinct matrix phase and is rich in carbonates. Young's modulus and hardness were observed to be predominantly affected by the mineral composition. The kerogen-rich shale has the lowest Young's modulus and hardness, followed by the argillaceous shale, while the bituminous shale is the stiffest and hardest. Young's modulus is anisotropic for all shales, but hardness does not follow this trend. The three shale samples also show varied fracture behavior. Apparent cracking and spallation were noted in the argillaceous and bituminous shale, but not in the kerogen-rich shale. Cracks, when activated, tend to propagate along the bedding plane-parallel direction, regardless of the loading direction. We anticipate the new information and knowledge generated from this work has a significant contribution to applications such as drilling and hydraulic fracturing.

The use of fuels produced with renewable electricity from wind and solar energy and with CO${}_2$ from unavoidable sources or directly captured form the air (so called e-Fuels) is of great interest as a proposition for further limiting the climate impact of road transportation. One of the most efficiently producible e-fuels is e-methane. Feeding methane from renewable sources into the gas grid is one of the most promising pathways to achieve carbon neutral road transportation on a well-to-wheel (WTW) basis. Currently, the use of odorants is mandatory in the gas grid. It is common that sulfur compounds are used as odorants, which can lead to sulfur poisoning of the catalytic converters if an internal combustion engine is operated with it. Consequently, desulfurization will be necessary to maintain high catalyst efficiency over lifetime, which will increase the tank-to-wheel (TTW) CO${}_2$ emissions through increased fuel consumption. For desulfurization, it is necessary to increase the catalyst brick temperature to levels above 800 °C. This paper investigates how such high temperatures can be realized and derive implications on engine operation and gas grid regulation. To this end, experimental studies were conducted with a 1-liter 3-cylinder prototype engine from Ford-Werke GmbH featuring variable intake valve timing, a compression ratio of 14 and a turbocharger with variable turbine geometry (VTG). The engine was operated with gas direct injection at up to 16 bar pressure. The ECU software allowed to apply deliberate oscillations of the lambda signal (“wobbling” of the air/fuel ratio) and cylinder individual air/fuel ratios to achieve a sufficient exhaust aftertreatment. The three-way-catalyst for the investigations were particularly suitable for methane operation due to a high palladium loading and increased oxygen storage capacity of the washcoat. Different load points were used for the investigations, ranging from near idle to medium engine speed and load. The catalyst brick temperature was increased considerably by splitting the mean air/fuel ratio between lean and rich operation on different cylinders (so called “lambda spli”), which is limited by the ignition limits of air/methane charges. Furthermore, too extreme lambda split leads to unstable engine operation. Sufficient hydrocarbon reduction can be achieved at a catalyst brick temperature above 500 °C, which cannot be achieved for near idle load points without additional measures (e.g. electrically heated catalyst). Desulfurization of the catalyst requires brick temperatures above 800 °C and is accordingly not achievable with stable engine operation in a significantly large area of the low load operation conditions. In this case additional he