Hydrate Formation In Pipelines Research Articles

Effect of a Terminated PVCap on Methane Gas Hydrate Formation

Polyvinylcaprolactam (PVCap) is an economic kinetic inhibitor for hydrate formation in pipelines during oil and gas transportation. However, its application is limited because of the low inhibition performance under certain conditions. In this work, a modified PVCap on its chain end is proposed. 2-amino-3-propionic acid mercapto-terminated polyvinyl caprolactam (PVCap-NH2-COOH) was synthesized and its performance as a KHI for methane hydrate formation was evaluated under different conditions. Results showed that the performance of PVCap-NH2-COOH as a KHI was better than that of PVCap at the same concentrations. Gas hydrate samples with 1 wt.% PVCap-NH2-COOH were measured using Raman spectroscopy, XRD, and cryo-SEM. PVCap-NH2-COOH had a selective action on a specific crystal surface of the hydrates and could prevent methane molecules from entering large cages. Its inhibition ability increased with the decrease in the occupancy rate of large cages. The morphology of the gas hydrate crystal changed from porous in a pure water system to a chaotic but compact structure state in the system with PVCap-NH2-COOH.

Experimental measurement and model prediction on methane hydrate equilibrium conditions in the presence of organic carboxylic sodium salts

Gas hydrate inhibitors are employed to mitigate gas hydrate formation in pipelines. The effects of thermodynamics inhibition were evaluated by measuring the vapor - liquid aqueous solution - solid hydrate (VLH) equilibrium conditions on methane (CH4) hydrate in the presence of three organic carboxylic sodium salts (sodium formate, sodium acetate, sodium propionate) in this study. The experiments were carried out in the temperature range of 273.65 K to 281.65 K. Compared with deionized water, in the electrolyte solutions of sodium formate, sodium acetate and sodium propionate with mole fraction of 0.010 and 0.020, the VLH equilibrium pressure change (ΔP) increased by 12.93, 27.68 %; 18.78, 38.15 %; 23.51, 49.41 %, respectively. Both of the three organic carboxylic sodium salts have obvious thermodynamic inhibition effect on CH4 hydrate. The strength of hydrate inhibition is related to the carbon chain length of organic carboxylate. The dissociation enthalpy (ΔHdiss) of CH4 hydrate in three organic carboxylic sodium salts solutions remains quite uniform with deionized water, which indicates that three organic carboxylic sodium salts have not been involved in the formation of hydrate nucleus. The Chen-Guo hydrate model and N-NRTL-NRF activity model were employed to predict the VLH equilibrium conditions in electrolyte solutions. In the three organic carboxylic sodium salts solutions, the average absolute relative deviations (AARD) of the VLH equilibrium condition data between the predicted and the experimental were 0.81, 2.17, and 3.02 %, respectively. In the sodium chloride (NaCl) and potassium chloride (KCl) solutions, the AARD between the predicted and literature were 1.44, 1.69 %, respectively. The model has good universality and accuracy. Both sodium acetate and sodium propionate are food grade preservatives. Consequently, these are beneficial for the development of environmental-friendly hydrate inhibitors.

Experimental investigation of the adhesion forces/strengths of cyclopentane hydrate in a gas phase

Hydrate agglomeration in a bulk phase and hydrate deposition on pipe wall are two processes that cause hydrate block in gas pipelines. Hydrate particle–particle/droplet adhesion forces and hydrate deposition-wall adhesion strengths are the essential reasons that determine the hydrate agglomeration and deposition, respectively, which have been rarely studied in the gas phase. In the present work, the interaction behaviors of hydrate particle–particle/droplet and hydrate deposition-pipe wall in the cyclopentane (CyC5) vapor phase were experimentally investigated by using the custom-built micromechanical force (MMF) and shear strength measurement apparatuses, respectively. It has been found that hydrate formation from thawing ice particles in the CyC5 vapor phase is an outward growing process and the formation rate in the vapor phase is much higher than that in liquid CyC5. The particle surface is rougher and thus exhibits strong hydrophilic characteristics. The hydrate particle–particle adhesion forces in the CyC5 vapor phase slightly increase with the temperature, and the value is close to that in the liquid CyC5 phase. Due to the different hydrophilic characteristics of hydrate particles in the oil and gas phases, the corresponding hydrate particle-droplet interaction behaviors are significantly different. With the gradual conversion of water in liquid bridges, the hydrate-droplet adhesion forces first increase, then decrease and finally level off. The early measured adhesion forces in vapor phase are approximately 2–3 times that in the liquid CyC5 phase. In the case of hydrate deposition, the adhesion strengths increase with the substrate roughness and the formation/annealing time and decrease with temperature. This work can provide a further understanding of hydrate plugging in the gas phase, which is important in advancing the management of hydrate formation in pipelines.

Effect of solid dispersants on the formation of hydrates in W/O emulsion systems: Micron and nanoscale

Aiming at the problem of natural gas hydrate blockage in oil and gas pipelines. The key to rationally inhibiting the formation of hydrates in pipelines is to find the factors that lead to the rapid coalescence of hydrates. We studied the effect of 0.2 wt% graphite particles and Fe2O3 particles (20 nm and 1 μm) as solid dispersants on hydrate formation in a W/O emulsion system at 275.15 K and 7 MPa. The results showed that 0.2 wt% solid dispersants could be adsorbed on the interface of Pickering emulsion to inhibit the binding of particles. In addition, solid dispersants improve the mass and heat transfer capacity of the reaction system and increase the final gas consumption. The 20 nm Fe2O3 particle reaction system had the largest gas consumption and the highest reaction rate. A three-dimensional network mechanism was proposed to explain the rapid formation of hydrate particles from the perspective of kinetics. Our experimental results and suggested mechanisms provided a reference for the promotion or inhibition of hydrate growth.

Computational fluid dynamic modeling of methane hydrate formation in a subsea jumper

Gas hydrate in subsea pipelines is a serious flow assurance issue that may impose operational challenges to offshore petroleum production and transportation. The effects of fluid properties on hydrate formation in complex geometries such as jumpers are not fully understood. This study aims to assess hydrate formation in the jumper for the water-methane system using the Eulerian multiphase flow model through employing computational fluid dynamic (CFD) software (STAR CCM+). The numerical model is developed through consideration of transport phenomena equations, including conservation of mass, momentum, and energy in which mass transfer, hydrate reaction kinetics model, and heat of hydrate formation are incorporated in the multiphase flow equations in the form of source terms in the CFD software. In this study, first, the hydrate mass fraction for the fluid velocity of 5 m/s with an inlet temperature of 7 °C and a gas volume fraction of 0.2 is calculated. The sensitivity analysis is then performed considering the influences of changes in the inlet fluid velocity, gas volume fraction, inlet temperature, and subcooling on the hydrate formation. The results reveal that the developed CFD model is capable of predicting hydrate formation behaviors in the jumper with acceptable precision. An increase in the liquid inlet velocity and gas inlet temperature lowers the amount of hydrate formed in the jumper. In contrast, an increase in the subcooling and gas volume fraction leads to more hydrate formation. The proposed CFD model can be successfully used to simulate hydrate formation in pipelines under various process and thermodynamic conditions so that it can help to find reliable/effective methods for hydrate management.

Natural Hydrophilic Amino Acids as Environment-Friendly Gas Hydrate Inhibitors for Carbon Capture and Sequestration

Carbon capture and sequestration using gas hydrates are receiving a great deal of attention as clean processes since hydrates produce water as a major byproduct. The formation of hydrates in pipelines for CO2 transport and oil/gas production systems is also of great importance due to safety and cost issues. The use of chemical additives is necessary to optimize operating temperature and pressure conditions for the proper control and management of hydrate formation. Accordingly, their potential environmental impacts have led to the surging demand for eco-friendly hydrate additives. Amino acids have been recognized as a promising class of hydrate inhibitors as they interact with water via hydrogen-bonding and electrostatic interactions. However, insufficient inhibitory effects of amino acids and low solubility in liquid water have been considered to limit their applications. In this work, we report the effective use of hydrophilic amino acids as promising inhibitors for CO2 hydrates. Superior inhibitory efficiency of l-serine is achieved by its hydroxy group, which lowers the water activity through hydrogen bonding, thus shifting hydrate formation conditions to lower-temperature and higher-pressure regions. When added at 0.1 mol %, l-serine retards hydrate formation kinetics primarily by disrupting the water hydrogen-bond network. The thermodynamic inhibitory effect of l-proline even exceeds that of methanol due to its abnormally high hydrophilicity originating from the unique structural characteristics, and it works at high concentrations as a dual-function inhibitor affecting both phase equilibria and formation kinetics. The use of amino acids is highly preferred as they are natural and biodegradable substances, and therefore the potential environmental risk can be minimized. The corrosion issue often caused by the use of salts can also be neglected. The high solubility of hydrophilic amino acids allows them to be applied for a wide range of temperature and pressure conditions required for carbon capture and sequestration processes using gas hydrates.

Mini review on environmental issues concerning conventional gas hydrate inhibitors

AbstractIn the offshore oil and gas fields, the formation of gas hydrates creates critical issues, and these issues or challenges become more pervasive as productive activities proceed to deep sea waters. Further, a number of chemical additives that are used to prevent gas hydrate formation in pipelines pose toxicity issues and are harmful to the environment. Commercially available inhibitors such as methanol, glycols, polyvinyl caproclatum (PVCap), and polyvinylpyrrolidone (PVP), which are being used for gas hydrate mitigation, have shown toxicity issues such as corrosion and mass loss due to their volatile nature, resulting in their high consumption. Methanol and glycols are identified as thermodynamic hydrate inhibitors (THIs), while PVCap and PVP are classified as low‐dosage hydrate inhibitiors. There has been considerable discussion in the literature on whether to use THIs or low‐dosage gas hydrate inhibitors (LDHIs) but less discussion on their toxicity and harmful effects on the environment. Therefore, in this mini review we intend to throw light on the environmental issues concerning conventional gas hydrate inhibitors used currently.

Application of statistical learning theory for thermodynamic modeling of natural gas hydrates

The gas hydrate formation in pipelines of industries and chemical plants can cause various operational damages and can increase economic risks. Hence, the knowledge of hydrate formation conditions has become a critical research study to overcome the problems arising from the formation of hydrates. In this study, we applied an algorithm to develop an LSSVM model to predict the formation temperature of natural gas hydrate for a comprehensive range of data points. Total 188 experimental data points were applied from the literature for the development of the LSSVM model. The input parameter was finalized based on the structure of hydrates by each gas species. The results obtained by the LSSVM model have good accuracy as compared with empirical correlations available in the literature. This model gave the squared correlation coefficient (R 2 ), and root mean square error of 0.9901 and 0.59974, respectively. The composition of gases may affect the phase equilibrium condition of gas hydrates. The applied algorithm revealed that the developed LSSVM model could become a good alternative for calculating the formation temperature of hydrate for the range of all data sets. The results showed that the proposed LSSVM model could be applicable for the prediction of hydrate formation temperature for all data points.

Quantitative hydrate deposition prediction method and application in deep-water or permafrost gas pipelines

Hydrate formation in pipelines seriously affects the efficiency of energy transmission. Adopting the production process of gas pipelines in deep-water or permafrost regions as the engineering application background, hydrate formation and deposition characteristics at different locations in gas pipelines are analyzed to realize the quantitative prediction of high-risk areas and degree of hydrate plugging in pipelines. A typical deep-water gas pipeline in the South China Sea is selected as an example. The calculation results show that the long-distance pipeline exhibits an obvious hydrate blockage risk area, which occurs 700-3200 m away from the pipeline inlet. The high-risk area of hydrate plugging in the system moves upstream of the pipeline with decreasing ambient temperature. The risk of hydrate blockage increases with decreasing pipeline inner diameter. The established quantitative prediction method for hydrate deposition in deep-water or permafrost gas pipelines accurately locates high-risk areas of hydrate plugging, which could effectively guide hydrate prevention and notably reduce the cost of hydrate control in deep-water or permafrost gas pipelines.

Determination of Methanol Loss Due to Vaporization in Gas Hydrate Inhibition Process Using Intelligent Connectionist Paradigms

The clathrate hydrate formation in pipelines and treatment systems of gas and natural gas liquid (NGL) is an undesirable operating phenomenon. It interrupts the gas flow continuity, reduces safety level, and imposes substantial costs on both gas and NGL processing plants. Therefore, it is necessary to prevent or at least postpone this undesired and high-risk phenomenon. The application of inhibitor agents to shift phase equilibrium of gas hydrate formation to lower temperatures and higher pressures is a mature technology. Methanol (MeOH) is a well-known thermodynamic agent in the hydrate inhibition process that cyclically injects to the gas phase and then recovers and reuses. Significant amounts of methanol vaporize/loss during its recovery in a three-phase separator. An accurate determination of this loss is necessary to estimate the amount of methanol make-up. Therefore, this study tries to determine the methanol loss using six intelligent connectionist approaches, i.e., least-squares support vector machines (LS-SVM), adaptive neuro-fuzzy inference systems, and artificial neural networks. The LS-SVM was finally detected as the most accurate paradigm for the considered purpose. Methanol loss estimation by the LS-SVM model is in excellent agreement with 196 real-field datasets in the literature, i.e., AARD = 0.295% and R2 = 0.9999. An economic study shows that methanol loss may impose more than 132 million US Dollars per year to a gas plant that processes 674 million standard cubic meters of gas per day.

Modelling the Formation of Gas Hydrate in the Pipelines

Water and hydrocarbon are generally found beside each other in nature i.e., hydrocarbons are formed in aqueous environment. Natural gas and crude oil of storage reservoirs and transferring pipes from petroleum wells to industrial processes of oil and gas are in contact with water and they are in equilibrium with each other. Generally, water is considered as an intruder in oil and gas industry from primary production to ultimate consumption. It causes corrosion in pipelines and reduces the heating value of the fuel. High pressure and low temperature could also cause water condensation and liquid water considerably reduces pipelines efficiency. Low temperatures in winter or an adiabatic pressure drop could ultimately lead to hydrate formation in pipelines. Therefore, hydrate formation causes various problems and costs. In order to prevent hydrate formation, there should be comprehensive information about hydrate formation conditions. The available data on hydrate are outdated and might not have enough accuracy. The data are also specified for a single gas component while mixtures of gases are generally observed in pipelines. The current work tries to increase modeling accuracy of hydrate formation condition in pipelines with different compositions. In this research, a program was coded in MATLAB which specifies hydrate formation condition. In this program, the most accurate equations were used to predict the most efficient condition. Results of the program were compared with real data as well as results of PVTsim simulator. The comparisons indicated that this program could predict hydrate formation condition more accurately.

Hydrate bedding modeling in oil-dominated systems

The rapid formation of gas hydrates is one of the major concerns in offshore oil and gas transportation due to the possible plugging of unmanaged hydrate agglomerates. Within the oil and gas industry, hydrate management guidelines have shifted over the last decade from hydrate avoidance to hydrate management. Allowing hydrate formation in pipelines without blockages requires understanding of the hydrate formation and plugging mechanisms under different operational conditions. Furthermore, a predictive tool which can be coupled with the multiphase flow conditions encountered in the field is highly desired in order to ensure successful transportation of hydrate slurries.In the realm of modeling, one such hydrate plugging mechanism that remains unaddressed is the bedding of hydrate particles, which may occur when hydrate particles aggregate within the pipeline. In this work, a bedding model based on force balances has been developed and coupled with a transient multiphase flow simulator. It is proposed that agglomeration controls bedding and bedding is a function of the agglomerate size, which is assumed to follow a log-normal distribution based on an autoclave experimental study. The bedding model has been tested and validated against large-scale flowloop experiments at different water cuts and liquid velocities. Pressure drop comparison between the simulations and experiments shows an improvement after implementing the bedding model for simulations with low liquid velocity. This work may contribute to the understanding of the hydrate plugging mechanisms and be applied to optimize hydrate management guidelines in offshore oil and gas production.

A systematic approach for design and simulation of monoethylene glycol (MEG) recovery in oil and gas industry

Monoethylene glycol (MEG) is a widely used hydrate inhibitor in the oil and gas industry to reduce the risk of hydrate formation in pipelines that could cause a blockage. For flow assurance and hydrate inhibition purposes, large volumes of MEG are required to control the hydrate formation conditions in pipelines. Disposal of rich MEG after separation has considerable costs and poses significant environmental concerns. Therefore, the development of an effective process for MEG recovery has been gaining importance. The current study presents a systematic approach to develop, simulate, and optimize MEG recovery using Aspen Plus and ELEC-NRTL thermodynamic package. Two distinct MEG recovery process (MEG-R-P) designs, namely, the vacuum (design I) and atmospheric (design II) distillation, were tested. Both designs have demonstrated exceptional performance in recovering MEG from salts and water and producing lean MEG at a purity of 90 wt%. Design I operating at vacuum conditions outweighs design II in terms of MEG purity and energy requirements. The addition of MEG-R-P has the advantage of recovering and reusing significant amounts of MEG and removing the burden on the environment.

PC-SAFT/UNIQUAC model assesses formation condition of methane hydrate in the presence of imidazolium-based ionic liquid systems

One of the major problems in flow assurance, especially in the case of deep subsea pipelines, is the accumulation of gas hydrates that leads to significant issues such as pipe plugging and cracking. Utilization of thermodynamic inhibitors is an effective method to prevent hydrate formation in pipelines. Recently, ionic liquids (ILs) have been recognized as new hydrate inhibitors due to their strong electrostatic charges, which form hydrogen bonds with water molecules. In this work, the capability of the PC-SAFT/UNIQUAC model combined with the van der Waals-Platteeuw theory is assessed for estimation of the methane hydrate dissociation temperatures in the presence of various IL solutions. Five pure-component parameters of PC-SAFT EOS for ILs are fitted by using experimental data of liquid density. Furthermore, vapour-liquid and hydrate equilibria experimental data are employed to adjust the binary interaction parameters of the PC-SAFT EOS (kij) and the UNIQUAC model (uij), respectively. Methane hydrate dissociation temperatures are successfully forecasted by using the proposed model for ten (10) IL systems with different concentrations in which the overall average absolute deviation for temperature (AADT %) of the model is lower than 1.5%. The results clearly demonstrate that the developed thermodynamic model is capable of precisely obtaining the methane hydrate dissociation temperatures in the presence of IL solutions, though, for [EMIM][Cl] solutions with a concentration of more than 30 wt%, the model overestimates the methane hydrate conditions. The proposed thermodynamic modeling strategy can assist to screen suitable IL solutions with an optimal composition for hydrate formation inhibition in terms of technical, economic, and environmental prospectives.

Application of hydrophobic particles in the formation kinetics of methane hydrate in water-in-oil emulsion

Aiming at the problem of natural gas hydrate blockage inside oil and gas pipelines, the key to reasonably suppress the formation of hydrates in pipelines is to find the factors that cause the hydrates to coalesce quickly. Since carbonates and silicon-containing substances are the main components of impurities in mining, the formation of methane hydrate has been studied. The emulsion was formulated with Span85 and SDS, and the formation rate and growth morphology of the hydrate were studied by adding nano-calcium carbonate. Experiments were carried out on emulsion systems having a particle content ranging from 0.1 wt% to 6 wt%. The results show that when the particle content in the system is low (less than 0.3 wt%), the hydrate formation rate is accelerated; when the particle content is high (above 2 wt%), the hydrate formation rate is lowered. This phenomenon was confirmed by calculating the moles consumption of methane gas. Moreover, the particles increase the collision probability of the crystal nucleus in the system, and can be used as a nucleation site of the hydrate crystal nucleus. The promotion or inhibition of the system on hydrate growth has reference value for preventing pipeline blockage.

Mechanistic Model To Predict Hydrate Deposition under Stratified Flow Conditions

Gas hydrate formation in pipelines is considered as a serious flow assurance threat to oil and gas production. The severity can be realized from its rapid tendency to form plugs and impede producti...

The Assessment of Potential Hydrate Formation Risk in Well Flow Lines

The problem of increasing the resource base, which today is hampered by significant shortage of funds for exploration under the conditions of a steady decline in oil and gas output in Ukraine is particularly important. The strategy of providing reduction of consumption and increase of production of domestic gas causes the necessity to consider the problem of reserves found in deposits that have been in long-term development, and consequently transportation of quite damp gas. Danger of forming gas hydrates inside a pipeline can cause an emergency situation due to formation of hydrate cork. Thus, our study aims at assessing the potential risks of hydrate formation in pipelines of well flow lines. We selected industrial pipelines of Eastern oil and gas region to be the object of the research. We also analyzed areas of structuring of the types of hydrocarbons. For the characteristic combination of selected indicators defined areas of increased risk of hydrate formation in well flow line corks. We can conclude the highest risk of hydrate formation processes to occur in the fields of Mashivka-Shebelynka, Glynsk-Solokha and of the northern oil-and-gas-bearing-areas. Obviously, the greatest danger is to hydrate in gas fields. For condensate fields such risk is much lower because there hydrate is possible only with the specific terms of condensate. To conclude, we have identified the main reasons for hydrate formation in well flow line and also the structure of the Eastern region for oil and gas fields and areas of structuring of the types of hydrocarbons. Finally, we have defined areas of increased risk of hydrate formation in well flow line corks according to the combination of characteristic parameters.

Synergic Kinetic Inhibition Effect of EMIM-Cl + PVP on CO2 Hydrate Formation

Kinetic hydrate inhibitors (KHIs) are employed to mitigate gas hydrate formation in pipelines at low concentrations. Ionic liquids and conventional available KHIs (polymers) perform poorly at high subcooling and extended shut-in conditions. Thus, it's necessary to understand the inhibition mechanism and performance of mix kinetic inhibitors for gas hydrate mitigation in oil and gas transmission lines. In this work, the synergic kinetic inhibition effect of 1-Ethyl-3-methy-limidazolium chloride (EMIM-Cl) + Polyvinylpyrrolidone (PVP) on the induction time and gas uptake during carbon dioxide (CO2) gas hydrate formation is reported. The study was performed in a high pressure sapphire cell at a pressure and temperature of 36 Bar and 1 oC respectively using an isochoric constant cooling method. Result suggests that, the induction time of deionized water + carbon dioxide hydrate increased over 100% in the presence of pure EMIM-Cl and PVP, with PVP slightly higher than EMIM-Cl comparatively. Surprisingly, a significant reductions in CO2 hydrate inhibition performance is observed in the presence of EMIM-Cl + PVP studied synergic systems compared to their inhibition in pure state.

Testing antifreeze protein from the longhorn beetle Rhagium mordax as a kinetic gas hydrate inhibitor using a high-pressure micro differential scanning calorimeter

Low dosage kinetic hydrate inhibitors are employed as alternatives to expensive thermodynamic inhibitors to manage the risk of hydrate formation inside oil and gas pipelines. These chemicals need to be tested at appropriate conditions in the laboratory before deployment in the field. A high pressure micro differential scanning calorimeter HP-μDSC VII (Setaram Inc.) containing two 50 cc high pressure cells (maximum operating pressure 40 MPa; temperature range –40 to 120 °C) was employed to observe methane hydrate formation and decomposition in the presence of hyperactive antifreeze protein from Rhagium mordax (RmAFP) and biodegradable synthetic kinetic inhibitor Luvicap Bio. A systematic capillary dispersion method was used, and this method enhanced the ability to detect the effect of various inhibitors on hydrate formation with small quantities. The presence of RmAFP and Luvicap Bio influence (inhibit) the hydrate formation phenomena significantly. Luvicap Bio (relative strength compared to buffer: 13.3 °C) is stronger than RmAFP (9.8 °C) as a nucleation inhibitor. However, the presence RmAFP not only delays hydrate nucleation but also reduces the amount of hydrate formed (20%–30%) after nucleation significantly. Unlike RmAFP, Luvicap Bio promoted the amount of hydrate formed after nucleation. The superior hydrate growth inhibition capability and predictable hydrate melting behavior compared to complex, heterogeneous hydrate melting with Luvicap Bio shows that RmAFP can be a potential natural green kinetic inhibitor for hydrate formation in pipelines.

CFD Analysis of Hydrate Formation in Pipelines

Offshore oil and gas exploration and production is increasingly moving further into the deep sea where temperature and pressure conditions favor hydrate. Hydrate formation in gas pipeline is one of the major flow assurance problems, which is enhanced as lower temperature and higher pressure condition. This study explores the CFD analysis of hydrate formation behavior in subsea pipeline by performing sensitivity studies exploring the effects that flow (velocity, diameter) and fluid (viscosity and water fraction) parameters on hydrate formation. The results generated showed that changes in flow conditions or fluid properties have significant effects on the hydrate formation in the pipeline.