Natural Gas Hydrate Formation Research Articles

Application of four intelligent models for the estimation of formation pressure of natural gas hydrate

Natural gas hydrate is a clean and efficient resource that contains lots of heat energy. The production, processing and transportation of natural gas can be influenced dramatically by natural gas hydrate. Natural gas hydrate will accumulate at the bottom of the pipeline, even block the pipeline and reduce the flow rate of the natural gas. This article presents four intelligent models named GWO-SVM (Grey Wolf Optimizer connected with Support Vector Machine), GWO-LSSVM (Grey Wolf Optimizer connected with Least Squares Support Vector Machine), GA-LSSVM (Genetic Algorithm connected with Least Squares Support Vector Machine), and GWO-RBF (Grey Wolf Optimizer connected with Radial Basis Function) to predict the formation pressure of natural gas hydrate in different systems. In order to determine the degree of influence of each input variable on the formation pressure of natural gas hydrate, this paper uses Spearman correlation analysis method to calculate the correlation coefficients between the formation pressure of natural gas hydrate and various influencing factors. The contradistinction among different intelligent models shows that the GWO-LSSVM model has the exceptional performance of the smallest average absolute relative deviation (AARD=2.89%), the minimum standard deviation (SD=0.05) with all 244 data of natural gas hydrate formation pressure in different systems. When compared to six commonly used empirical models for predicting formation pressure in common natural gas hydrate, the GWO-LSSVM model has the highest prediction accuracy, with an AARD of only 1.82%. Furthermore, when compared to three thermodynamic models employed for predicting formation pressure in sour natural gas hydrate, the GWO-LSSVM model has the highest prediction accuracy, with an AARD of 2.38%. The leverage method demonstrates that four intelligent models have excellent robustness in reflecting the inner relationships among natural gas hydrate formation pressure and influential factors. The four intelligent models for predicting hydrate formation pressure will be helpful to find hydrate formation pressure in different systems.

The pore-structure characteristics of foraminiferal shells and their relations with natural gas hydrate formation in the marine sediments

Many marine hydrate reservoirs exhibit significant foraminifera abundance. These foraminifera alter the original properties of the sediments, potentially affecting the formation and accumulation of hydrates. This present study analyzed the pore-structure characteristics of foraminifera-containing sediments from the South China Sea and their influences on the hydrate formation process by using microscopic imaging techniques. Scanning electron microscopy (SEM) and X-ray computed tomography (X-CT) reveal the unique dual-porosity characteristics of these sediments, characterized by matrix pores and foraminiferal pores. These two types of pores diverge significantly in their size distribution, morphological attributes, connectivity, and other aspects. Further experiments show the formation and occurrences of tetrahydrofuran (THF) hydrate under different sedimentary conditions and solution concentrations. Foraminiferal shells are found to promote the formation of hydrate by increasing the volume fraction of hydrate-favoring pores, which is more pronounced under conditions of low hydrate saturation. These findings obtained may contribute to global hydrate resource assessments and enhance understanding of hydrate reservoirs.

Influence of SDS on the Growth of Natural Gas Hydrates in a Sand Bed Depending on Saturation and Mineralization of Pore Moisture

Introduction:: Evaluate the effect of SDS on induction time and conversion of water to hydrate in a porous medium model depending on the saturation and salinity of pore moisture. Methods:: The work presents data on the formation of natural gas hydrates in sand bed fraction of 200-500 μm. The silica sand was saturated with water, solutions of SDS or NaCl, or a mixture of these. The saturation was 50% or 100%. The experiments were carried out under isochoric conditions at a temperature of 275 K and an initial pressure of 8 MPa. Results:: It was shown that the main hydrate formation occurred in the first 60 minutes. The addition of SDS 0.05-0.2 wt.% in the sand bed does not exhibit a promoting effect, as was previously shown for pure water. The addition of NaCl 3 wt.% reduces the conversion of water to hydrate by 1.6 and 2 times for 50% and 100% saturation of the sand bed. Conclusion:: The optimal concentration of the SDS additive to the salt solution has been found to reduce the inhibitory effect of the salt. The data obtained can be used to develop technologies for storing and transporting natural gas using sand and seawater.

Analysis of Residual Pressure Power Generation in Natural Gas Pressure Regulating Station

Turboexpander, placed parallel to the regulator in natural gas pressure regulating station (PRS), was proposed to utilize the residual pressure by engineers and researchers. However, the relationship between the power generated by the turboexpander and the energy used to preheat the natural gas (NG) needs to be carefully analysed. This article estimated the electric power that could be generated using residual pressure based on an actual PRS in China. An analysis model was established to study the relationship between electric power generated by the turboexpander and energy used to preheat the NG. Pressures both inlet and outlet and inlet temperature of the established power generation model were carefully analysed as well as the natural gas hydrate formation temperature. The results indicate that the electric power generated by the turbine expander and the energy used to preheat natural gas decrease as the pressure difference decreases. Most of the energy needed to preheat NG in the procedure of PRS can be obtained through the established turboexpander. What’s more, residual electric power can be obtained when the difference pressure is less than the critical point in which the energy used to preheat NG is equal to the energy generated by the turboexpander.

Synergistic performance of mixed agro-waste-based amino acids as kinetic hydrate inhibitors for natural gas hydrate control

The formation of plugs and clogs in pipelines caused by low temperatures and high pressures during drilling and production of natural gas hydrates causes difficulties for the oil and gas sector. Different commercially available kinetic hydrate inhibitors (KHIs) are used to manage this problem; however, they have disadvantages such as toxicity, low biodegradability, and high cost. Through the use of microbiological techniques, this study attempted to synthesize mixed amino acids from agricultural waste to prevent the formation of natural gas hydrates. The performance of mixed agro-waste amino acids (MBL4) was compared to single amino acids (glycine, histidine, proline, and alanine that are major components of MBL4) and PVCap as a control group at dosage of 0.1 and 0.5 wt%. The onset temperature and subcooling were used to assess the performance of the inhibitors in this study, which used the constant cooling method in a stirred high-pressure autoclave at 100 bar. The addition of MBL4 at 0.5 wt% retarded the onset of hydrate formation and increased the subcooling significantly when compared to PVCap and the individual single amino acids, with onset temperature and subcooling of 7.20 °C and 11.67 °C, respectively. The performance of MBL4 is observed to increase from 0.1 to 0.5 wt% dosage concentration, and MBL4 outperformed individual amino acids and PVCap. Mixed agro-waste amino acids showed better performance when used as KHI due to synergism, and this finding can offer a long-lasting, cheaper, and more efficient way of controlling gas hydrate formation in the oil and gas industry.

Investigating the Effect of Crown Ether on the Kinetics and Morphology of Natural Gas Hydrate Formation

Investigating the Effect of Crown Ether on the Kinetics and Morphology of Natural Gas Hydrate Formation

Effects of gas to water ratio and nano-Cu dosage on CH4 hydrate growth: A combined molecular simulation and experimental study

Natural gas hydrate (NGH) is a highly promising alternative for gas storage and transportation. Nevertheless, the artificial generation of gas hydrates faces considerable obstacles for large-scale commercial implementation, primarily due to its slow formation rate and inadequate storage density. This study delves into the effects of gas to water ratios and metal nanoparticle dosages on the synthesis of NGH. Molecular dynamics (MD) simulations were employed to examine the formation of CH4 hydrate under varying gas to water ratios and metal nanoparticle concentrations. The investigation assessed critical parameters of the gas–water system, such as radial distribution function, carbon storage ratio, hydrate cages, potential energy, diffusion coefficient, and thermal conductivity. For the first time, Pearson's correlation coefficient analysis was utilized to discern the interrelationships among these factors. The results demonstrated that medium gas to water ratios led to increased carbon storage, a higher number of cages, and augmented energy consumption. The nano-Cu dosage impacted the stability of hydrates and the thermal conductivity of the gas–water system, particularly at elevated gas to water ratios. Drawing on the MD simulation findings, a design factor was introduced to appraise the performance of the multicomponent system, which in turn, informs the development of a high-performance NGH formation system. The effectiveness of the design factor was corroborated through laboratory experiments, revealing its robust potential for designing high-performance NGH systems. This research paves the way for the practical realization of efficient hydrate-based production in real-world applications.

Study of the Formation of Natural Gas Hydrate in a Porous Medium from a Mixture of Polymer Solutions with Oil

Study of the Formation of Natural Gas Hydrate in a Porous Medium from a Mixture of Polymer Solutions with Oil

Experimental Study of Natural Gas Hydrate Formation in a Porous Medium in the Presence of Aqueous Solutions of Sodium Chloride and Sodium Bicarbonate

Experimental Study of Natural Gas Hydrate Formation in a Porous Medium in the Presence of Aqueous Solutions of Sodium Chloride and Sodium Bicarbonate

Application status and prospect of ionic liquids in oilfield chemistry

The ionic liquid, as a new treatment agent, has been increasingly applied in oil fields due to its strong temperature resistance, good solubility and high surface activity. In this paper, we systematically discuss the action mechanism and application effect of ionic liquids in oilfield chemistry. Ionic liquids can inhibit shale hydration expansion and reduce fluid loss through adsorption and intercalation, inhibit the formation of natural gas hydrate through imidazole five-membered ring structure as a space barrier, reduce viscosity of heavy oil by breaking chemical bonds of heavy oil macromolecules and charge transfer, improve oil displacement efficiency by forming ions pairs with carboxyl groups in crude oil, demulsify by forming channels between dispersed water droplets, acidify the formation by reacting with water to produce acid, interacts with organic material through weak hydrogen bonds and extracts it from oilfield wastewater, desulphurize by inserting sulfide molecules into the “stack” structure and form liquid inclusion complex, inhibit corrosion by forming a protective film on the metal surface. Based on the above aspects, the development direction of ionic liquids is proposed. The application of ionic liquids in oilfield chemistry is still in its infancy. It is urgent to fully explore the application performance of ionic liquids in oilfield chemistry, which also provides theoretical and technical supports for efficient reservoir development.

An investigation on the variation of induction process in natural gas hydrate formation influenced by multiphase flow in a visual flow loop

One of the primary issues with natural gas transportation assurance is pipeline obstruction due to the formation and deposition of gas hydrates. Thus it is crucial to study the prevention and control methods of natural gas hydrateformation. A high-pressure visual flow loop was established in this study to investigate the effects of pressure, liquid velocity, and loop inclination angle on the formation of natural gas hydrates, hydrate slurry flow and morphology. For the formation of hydrates, it was demonstrated that the pressure was inversely related to the induction time and formation time. As the initial pressure increases, the conversion rate of water increases, leading to poor fluidity. With the increase of liquid velocity, the conversion rate of water increases and there is a threshold liquid velocity. Compared with horizontal loop, the hydrate particles in the slope were repeatedly deposited and removed off the surface of the sedimentary layer by gravity, and some large hydrate particles in the slope section gathered near the bottom of the pipeline. The induction time shortens and the formation time prolongs as the inclination angle increases. The inclination angle shows little effect on the final conversion rate of water, but it can delay the growth of hydrates obviously.

Growth behavior and resource potential evaluation of gas hydrate in core fractures in Qilian Mountain permafrost area, Qinghai-Tibet Plateau

The Qilian Mountain permafrost area located in the northern of Qinghai-Tibet Plateau is a favorable place for natural gas hydrate formation and enrichment, due to its well-developed fractures and abundant gas sources. Understanding the formation and distribution of multi-component gas hydrates in fractures is crucial in accurately evaluating the hydrate reservoir resources in this area. The hydrate formation experiments were carried out using the core samples drilled from hydrate-bearing sediments in Qilian Mountain permafrost area and the multi-component gas with similar composition to natural gas hydrates in Qilian Mountain permafrost area. The formation and distribution characteristics of multi-component gas hydrates in core samples were observed <em>in situ</em> by X-ray Computed Tomography (X-CT) under high pressure and low temperature conditions. Results show that hydrates are mainly formed and distributed in the fractures with good connectivity. The ratios of volume of hydrates formed in fractures to the volume of fractures are about 96.8% and 60.67% in two different core samples. This indicates that the fracture surface may act as a favorable reaction site for hydrate formation in core samples. Based on the field geological data and the experimental results, it is preliminarily estimated that the inventory of methane stored in the fractured gas hydrate in Qilian Mountain permafrost area is about 8.67×10¹³ m³, with a resource abundance of 8.67×10⁸ m³/km². This study demonstrates the great resource potential of fractured gas hydrate and also provides a new way to further understand the prospect of natural gas hydrate and other oil and gas resources in Qilian Mountain permafrost area.

Experimental Investigation Into Effects of Thermodynamic Hydrate Inhibitors on Natural Gas Hydrate Synthesis in 1D Reactor

Thermodynamic hydrate inhibitors (THIs) are often used in marine gas field operations to prevent the formation of natural gas hydrate (NGH), and it is important to study the effect of THIs on hydrate synthesis characteristics. Herein, the effects of water (H2O), sodium chloride (NaCl), and ethylene glycol (EG) on NGH synthesis characteristics under different initial pressure conditions are tested using the self‐developed 1D NGH production simulation test system. The effects of each THI on the maximum synthesis rate and maximum synthesis amount of NGH are investigated using two physical quantities, peak of temperature increment and maximum gas conversion rate. The results show that the 2.65 wt% salt solution has the minimum inhibition effect on the maximum synthesis rate of NGH, and the solution with a 3:1 mixture of H2O and EG has the maximal inhibition effect on the maximum synthesis rate of NGH. When only H2O and EG or H2O and NaCl are present in the reactor, the higher the concentration of EG or NaCl, the more significant is the inhibition effect on the maximum synthesis amount of NGH.

Ferromagnetic shape memory alloy Ni52.5Mn22.5Ga25: Phase transformation at high pressure and effects on natural gas hydration

Ferromagnetic shape memory alloy NiMnGa was used to prepare the micro/nano fluid which has a potential role during the formation of natural gas hydrate (NGH). In the present work, phase transformations of Ni52.5Mn22.5Ga25 micro/nano particles under various pressures, and the crystal structure before and after participating in the natural gas hydration were investigated. The effect of the micro/nano fluid containing Ni52.5Mn22.5Ga25 particles on the formation heat of NGH was studied. It was worked out that Ni52.5Mn22.5Ga25 particles exhibit a high stability both in phase transformation below 15 MPa pressure and crystal structure after natural gas hydration. The fluid containing Ni52.5Mn22.5Ga25 particles can reduce the hydration reaction temperature and promote the formation of NGH.

Polysaccharides Are Effective Inhibitors of Natural Gas Hydrate Formation.

This review covers the types and applications of chemical inhibitors of gas hydrate formation in the oil and gas industry. The main directions of the development of new types of highly effective and environmentally safe "green" kinetic hydrate inhibitors (KHIs) based on biopolymers are analyzed. The structure, physicochemical properties, efficiency of gas hydrate formation inhibition, and commercial prospects of polysaccharides in preventing and controlling the formation of gas hydrates are considered. The criteria for their selection, current experimental data, and the mechanism of inhibition are presented. Recent research in the development of cost-effective, efficient, and biodegradable KHIs for industrial applications in the oil and gas industry is also presented.

Natural gas hydrate formation and hydrate slurry transportation in a visual pipeline: reciprocal interaction, capacity prediction and potential regulation

Natural gas hydrate formation and hydrate slurry transportation in a visual pipeline: reciprocal interaction, capacity prediction and potential regulation

Numerical simulation of natural gas flow characteristics and hydrate formation risk in deepwater submarine pipelines

The development of flow assurance technology in submarine pipelines affects the safety, efficiency, and economy of deepwater natural gas development. In this study, in order to accurately predict the hydrate formation risk in deepwater submarine pipelines, a novel mathematical prediction model of hydrate formation risk has been established. The model has been applied and sensitivity analysis of typical factors has been carried out. The model prediction results show that: (1) Due to the low temperature of the seabed, hydrate formation region (HFR) often exists in submarine pipelines. (2) When other conditions are constant, hydrate formation region increases with the decrease in seawater temperature. (3) When other conditions are constant, the temperature drop, and the length of hydrate formation region decrease with the increase of gas transmission rate. (4) When other conditions are constant, the temperature drop, and the length of hydrate formation region decreases with the increase of gas transport temperature. (5) Reasonable setting of gas transmission temperature and gas transmission rate can help to reduce the hydrate risk and consumption of inhibitors during submarine natural gas transmission.

Simultaneous inhibition of natural gas hydrate formation and CO2/H2S corrosion for flow assurance inside the oil and gas pipelines

Compatibility problems are observed during the co-injection of corrosion and gas hydrate inhibitors inside oil and gas pipelines, which reduces their performance. In this study, the newly synthesized dual-purpose inhibitors (DPIs) were developed to overcome the compatibility challenge between the inhibitors. A detailed experimental and computational study was performed to investigate the inhibition activity of DPIs. The results of constant cooling experiments showed that the inhibitors significantly prevented natural gas hydrate formation. DPI2 with a propyl pendant group was the best sample by providing a subcooling temperature of 18.1 °C at 5000 ppm. DPI1 and DPI3 decreased gas consumption by 2.6 and 2.4 times, respectively, compared to pure water. In addition, molecular dynamics simulation revealed that the transportation of gas molecules to the growing hydrate cages was disrupted due to DPI2 adsorption on the surface of the hydrate, which partially covered it and acted as a mass transfer barrier. Furthermore, the interaction of the anion part of the inhibitor with the nearest neighbor water molecules lowered the water activity to form the hydrogen-bonding networks for the hydrate formation. According to corrosion measurements, DPIs suppressed the corrosion rate of mild steel in H2S–CO2 saturated oilfield-produced water, and a maximum inhibition efficiency of 96.3% was obtained by adding 1000 ppm of DPI2. Moreover, the estimated adsorption energy of DPI2 were relatively high and matched with experimental data, implying that the inhibitor has a high degree of adsorption on the metal for forming a protective layer on the mild steel surface. These findings signified that DPIs provide a potential hybrid inhibition of corrosion and gas hydrate formation for flow assurance applications and reduce the operation costs.

Investigation of natural gas hydrate formation and slurry viscosity in non-emulsifying oil systems

At a later stage of oilfield development, there will be more free water in the pipeline, which may engender the phase inversion of water-in-oil emulsions, thereby augmenting the risk of hydrate plugging. In a novel 30 L high-pressure autoclave, the effects of wax content, water cut, temperature, initial pressure, and rotation speed on hydrate crystallization nucleation and slurry viscosity were examined. Results demonstrated that in systems with wax content greater than or equal to 2 wt%, at the onset of the swift hydrate growth stage, the aggregation of wax and hydrate will impair the gelling structure of wax-containing oil, inducing an abrupt fall in slurry viscosity. Consideration is given to the solubility fluctuation of the natural gas in oil, and an empirical prediction formula for gas consumption during hydrate formation in wax-containing systems is established. The presence of wax hinders the crystalline nucleation and growth of hydrates. Notwithstanding, the hydrate slurry viscosity of the wax-containing system is greater because the wax-hydrate aggregates have a more conspicuous effect on the slurry viscosity than the hydrate volume fraction. The water cut of 70% is a critical upper limit, above which the viscosity of hydrate slurry would increase dramatically. Higher rotation speed and initial pressure can significantly enhance the viscosity of hydrate slurries, but their effects on the hydrate nucleation induction time are more perplexing.

Molecular dynamics of the spontaneous generation mechanism of natural gas hydrates during methane nanobubble rupture.

Natural gas hydrates have garnered significant attention as a potential new source of alternative energy, and understanding their formation mechanism is of paramount importance for efficient utilization and pipeline transportation. However, there is no consensus among academics on the formation mechanism of natural gas hydrates. In this paper, we propose a method for promoting the rapid formation of natural gas hydrates based on the rupture of methane nanobubbles, which creates local high temperature and pressure to facilitate the mixing of methane and water. The rapid decrease in system temperature and pressure during the process further enhances the formation of gas hydrates. Using molecular dynamics simulations, we theoretically verify the formation of natural gas hydrates. Our results indicate that the instantaneous rupture of methane nanobubbles induced by shock waves leads to a dramatic increase in the local molecular motion velocity around the bubbles. This results in extreme local high temperature and high pressure, leading to complete mixing of methane and water and rapid formation of gas hydrates during the cooling and pressure drop of the mixture. We confirm our findings by analyzing F3-order parameters, F4-order parameters, and water cage statistics.