Equilibrium Conditions For Hydrate Formation Research Articles

Prediction of Phase Equilibrium Conditions and Thermodynamic Stability of CO2-CH4 Gas Hydrate

With the large-scale promotion and application of CO2 flooding, more and more engineering problems have emerged. Due to the high CO2 mole fraction, the associated gas of CO2 flooding very easily forms solid hydrates, compared to conventional natural gas. This has resulted in production decline or shutdown. Understanding the phase equilibrium conditions for hydrate formation in production fluids is crucial for hydrate prevention and control. In this study, accurate predictions of CO2-CH4 mixed gas hydrate formation conditions were performed using theoretical models. The temperature and pressure ranges for hydrate formation were calculated for different CO2 mole fraction, ranging from −11.5 °C to 20.85 °C and from 0.81 MPa to −28.1 MPa, respectively. Based on the calculated phase equilibrium data, a multi-parameter empirical model was developed using polynomial fitting. The calculation errors for the multi-parameter empirical model were 3.09%. The multi-parameter empirical model established in this study can avoid complex thermodynamic equilibrium calculations and has the advantages of simplicity, high accuracy, and wide coverage of downhole conditions. Based on the calculated phase equilibrium data, the dissociation enthalpy of CO2-CH4 hydrate below and above the freezing point of water was calculated. The results showed that an increase in CO2 mole fraction led to an increase in hydrate dissociation enthalpy and enhanced thermodynamic stability, making hydrate prevention more challenging. Our work can contribute to the optimization of CO2 production fluid treatment processes and the development of hydrate prevention and control technologies.

ИЗУЧЕНИЕ ВОЗМОЖНОСТИ ГИДРАТООБРАЗОВАНИЯ В ПЛАСТАХ СЕВЕРО-ЗАПАДНОЙ ЧАСТИ ИНДИГИРО-ЗЫРЯНСКОГО ПРОГИБА

The paper gives a brief description of geological section of the Indigirka-Zyryanka trough, promising for oil and gas, and the results of parametric drilling. Possibility study of hydrate formation in reservoir conditions of trough as one of the reasons for obtaining negative well test results was conducted. Performed calculations of the equilibrium conditions of hydrate formation have determined that the hydrate stability zone covers an insignificant interval of deposits 222 m thick below the bottom of permafrost rocks. It is concluded that the main reason for the insignificance of the hydrate formation zone is a relatively high geothermal gradient, which causes sufficiently high reservoir temperatures in the section. It is noted that favorable conditions for the formation of gas hydrates may arise in the presence of heavy differential pressure drawdown on the formation in the vicinity of borehole.

Simulation of Hydrate Plug Formation During Joint Operation of a Gas-Bearing Reservoir and a Well for the Case where the Equilibrium Conditions of Hydrate Formation Depend on Formation Water Composition

Simulation of Hydrate Plug Formation During Joint Operation of a Gas-Bearing Reservoir and a Well for the Case where the Equilibrium Conditions of Hydrate Formation Depend on Formation Water Composition

Hydrate formation in mesoporous materials: Thermodynamic modeling and experimental investigations

Until recently, analysis and interpretation of the equilibrium conditions of hydrate formation from water adsorbed in mesoporous materials have been carried out with the use of the Gibbs-Thomson equation. For this purpose, only the shift of equilibrium conditions due to the small size of hydrate particles formed in the confining pores was taken into account. A distribution of equilibrium temperatures of the hydrate formed in mesoporous materials was interpreted as a consequence of the existence of hydrate particles differing from each other in size. A new equation describing the equilibrium conditions for gas hydrate in thin pores of mesoporous materials is proposed in this work. This equation takes into account the size of hydrate particles together with the chemical potential of pore water in equilibrium with the hydrate. Thus, an increase in the temperature shift from the equilibrium curve causes simultaneous formation of hydrate in smaller and smaller pores, and an increase in the size of gas hydrate particles that have been previously formed in larger pores. The latter occurs due to gradual transformation into hydrate of the layer of bound water, located between the pore wall and hydrate particle being formed in the pore center. Modeling results are compared with the data obtained previously on the equilibrium conditions for the hydrate of carbon dioxide in mesoporous Al2O3 samples. It is demonstrated that experimental results are in reasonable qualitative agreement with the proposed model.

Search for technogenic deposits under the permafrost-hydrate seal within the Vilyui syneclise

The paper considers the possibility of the formation of technogenic gas deposits under the permafrost-hydrate seal. As the most promising object, the upper part of the Mastakh gas condensate field section is justified and considered. By comparing the equilibrium conditions of hydrate formation with the pressure and temperature of the formation, the lower boundary of the permafrost-hydrate seal was determined, which forms a potential trap for the accumulation of gases due to their flows through the well space from deeper horizons of the field section. Based on the results of the conducted studies, maps of the sole of permafrost rocks and the sole of the hydrate formation zone were constructed. The potential volumes of flow gases from the Lower Jurassic deposit to the upper part of the section have been estimated. The necessity of additional study of the upper part of the Khapchagai mega-shaft section is noted both for the search for technogenic gas deposits and for preventing complications and accidents associated with technogenic deposits. Keywords: Khapchagai megashaft of the Vilyui syneclise; behind-thecasing flows; Mastakhskoye field; permafrosthydrate seal; oil and gas potential.

Assessment of the possibility of natural and associated petroleum gases storage in the hydrate state

The purpose of this work is to study the natural gas hydrates formation and decomposition processes. Natural gases from the Otradninsky and Srednevilyuisky gas condensate fields were chosen as models of associated petroleum gases. In this paper, the natural gas hydrates formation in water, in a 2% sodium bicarbonate solution was studied and the kinetic parameters of the hydrates decomposition were determined. It has been established that the hydrate formation of natural gas with a higher relative density begins at lower pressures at the same temperature. The degree of water conversion into hydrate increases with a decrease of the gas relative density. Compared to water, the stability of hydrates obtained in sodium bicarbonate solution is almost 2 times higher. The concentration of C2-C4 methane homologues in hydrates leads to an increase of the gas fat coefficient. The conclusion is made about the possibility of the natural and associated petroleum gases utilization and storage in the hydrate state. Keywords: natural gas; associated petroleum gas; utilization; natural gas hydrates; equilibrium conditions of hydrate formation; bicarbonate-sodium type water; fat coefficient.

Algorithm for optimization of methanol consumption in the «gas inhibitor pipeline-well-gathering system»

The article proposes an algorithm of actions to optimize the consumption of methanol which is used as an inhibitor of hydrate formation in the process chain of oil and gas production. The proposed approach was developed in the process of analyzing the methanol supply system and planning measures to optimize it for the Eastern section of the Orenburg oil and gas condensate field. The algorithm consists of five sections which to a greater extent affect the efficiency of the inhibition system and are closely related to each other. These are data preparation, determination of equilibrium conditions of hydrate formation, calculation of methanol consumption rates, analysis of the inhibition system flexibility, operational control. The proposed solution in the form of an algorithm makes it possible to carry out a complex analysis of the hydrate formation prevention system, to determine the most optimal solutions to reduce the consumption of methanol.

Анализ методик измерения равновесных условий образования газовых гидратов

In this work, we analyze the factors that affect the experimental determination of the gas hydrate equilibrium conditions in various systems using step heating and ramp heating by GHA350 stirred autoclave or RCS6 rocking cells. It has been found that more reliable results are obtained using the GHA350 autoclave, which provides a more intensive mixing of the fluids. Step heatingis a priori a more reliable way to determine the equilibrium conditions of hydrate formation, suitable for any system. However, its application is time-consuming. An alternative heating method at a constant rate of 0.1-1 deg./h can significantly reducethe time of one measurement. However, when using it, to obtain reliable experimental data, it is necessary to select the heating rate considering the mixing efficiency of the setup used, the type of system under study, and other factors. For most systems, the results of measuring the hydrate equilibrium temperatures by step and continuous heating at 0.1 deg./h using GHA350 autoclaveare consistent within the measurement error. A greater discrepancy between the methods is observed for gas hydrates in concentrated salt solutions, which have a high viscosity at low temperatures.

Methanol and sodium chloride inhibitors impact on carbon dioxide hydrate formation

Given the importance of hydrate formation, scientists have studied its nature and dealt with its formation in the operating systems and so far many compounds have been studied and applied in this regard including alcohols and salts. Determining thermodynamic equilibrium conditions for hydrate formation will be the subject of this study and the additives such as methanol, sodium chloride and their mixture within the weight percentages of 5%–20% is used that changes the thermodynamic conditions governing the problem including temperature and pressure and causes the formation pressure of methane and carbon dioxide gas hydrates to be higher than the case without additives.MATLAB and Hydoff software programs are used for solving equations and obtaining the relevant results. The results indicated that the proposed model is capable of anticipating the pure carbon dioxide hydrate formation and also to make sure, the obtained results were compared with the results obtained by the experimental and laboratory in this field and the results indicated that the accuracy of the model is very desirable and could be used in the process and the mentioned conditions with high reliability. Maximum error was 5% and the minimum error with experimental data was 1.55%.

Prediction of hydrate equilibrium conditions using k-nearest neighbor algorithm to CO2 capture

ABSTRACTGas or clathrate hydrates are an important issue when they form in the oil and gas pipelines. Since the determination of the hydrate formation temperature and pressure is very difficult experimentally for every gas system and it is impossible in terms of cost and time approximately, mathematical models can be useful tools to overcome these difficulties. In this study, k-nearest neighbor model was used to predict the equilibrium conditions of hydrate formation in absorption and separation of carbon dioxide from flue gas mixture, containing carbon dioxide and nitrogen. At the training phase, temperature and composition data of nitrogen and carbon dioxide in the flue gas mixture at equilibrium conditions and the equilibrium pressures of hydrate formation were used as input and output, respectively. The error percentage less than 0.38% indicates the high accuracy of the proposed model. In this study, 80%, 85%, and 90% of the training data are examined for three numbers of nearest. For three numbers of used nearest (k = 1, k = 2 and k = 3), the value of k = 1 leads to the lowest error; so, it is selected as the best nearest in the presented model.

Phase diagrams for clathrate hydrates of methane, ethane, and propane from first-principles thermodynamics.

Natural gas hydrates are inclusion compounds composed of major light hydrocarbon gaseous molecules (CH4, C2H6, and C3H8) and a water clathrate framework. Understanding the phase stability and formation conditions of natural gas hydrates is crucial for their future exploitation and applications and requires an accurate description of intermolecular interactions. Previous ab initio calculations on gas hydrates were mainly limited by the cluster models, whereas the phase diagram and equilibrium conditions of hydrate formation were usually investigated using the thermodynamic models or empirical molecular simulations. For the first time, we construct the chemical potential phase diagrams of type II clathrate hydrates encapsulated with methane/ethane/propane guest molecules using first-principles thermodynamics. We find that the partially occupied structures (136H2O·1CH4, 136H2O·16CH4, 136H2O·20CH4, 136H2O·1C2H6, and 136H2O·1C3H8) and fully occupied structures (136H2O·24CH4, 136H2O·8C2H6, and 136H2O·8C3H8) are thermodynamically favorable under given pressure-temperature (p-T) conditions. The theoretically predicted equilibrium pressures for pure CH4, C2H6 and C3H8 hydrates at the phase transition point are consistent with the experimental data. These results provide valuable guidance for establishing the relationship between the accurate description of intermolecular noncovalent interactions and the p-T equilibrium conditions of clathrate hydrates and other molecular crystals.

Dependence of the rate of formation and the P-T stability field of methane hydrate suspensions in crude oils upon oil composition

Equilibrium conditions for hydrates obtained from water emulsions in crude oils of the Yurubcheno-Tokhomskoe, Verkhnechonskoe, Gerasimovskoe, and Usinskoe fields have been studied, as well as the relative rates of hydrate formation in these systems. It has been concluded that the presence of oil does not alter the equilibrium conditions of hydrate formation. An increase in the concentration of resin-asphaltene substances and paraffins in crude oil leads to a decrease in the hydrate formation rate.

Prediction of Equilibrium Conditions for Hydrate Formation in Binary Gaseous Systems Using Artificial Neural Networks

AbstractThe present work attempts to indicate the potential of artificial neural networks (ANN) for the fast and reliable estimation of the equilibrium conditions of single, binary, and multiple hydrocarbon gas hydrates. The ANN used in this study was a network with the tangent‐sigmoid (tansig) propagation transfer function in the hidden layer and a final layer with the linear (purelin) transfer function. The number of hidden neurons has been determined by minimizing the error of the calculation. The obtained results and the ANN model reliability were compared with other predictive methods. Results showed that the ANN method is able to reliably predict the hydrate equilibrium conditions of hydrocarbons, particularly for binary gas systems, using simple input parameters such as the weight fractions and normal boiling points of the components.

Simulation of gas production in the northern regions: the role of thermodynamics

Purpose: Natural gas extraction can involve conditions favoring the formation and deposition of hydrates in wells and bottom holes. At the moment, these processes are considered separately, i.e., the dynamics of hydrate formation in various production modes is modeled within the framework of non-isothermal multiphase filtration, while the dynamics of hydrate formation in wells is studied within the framework of tube hydraulics. In the latter case, the temperature and pressure near the bottom hole are specified and are normally assumed to be equal to their reservoir values. In the present paper the first attempt of partial combining these two approaches is done. Methods: The influence of mathematical model parameters on the dynamics of pressure and temperature fields at non-isothermal gas filtration is investigated in a numerical experiment. A nonlinear system of partial differential equations obtained from the energy and mass conservation laws and the Darcy law are used to describe the process, and physical and caloric equations of state are used as closing relations. Results: The pressure and temperature fields in the reservoir are determined by solving the problem of nonisothermal filtration of an imperfect gas and are compared with equilibrium conditions of hydrate formation. This solution is be further used to determine the temperature and pressure in the bottom hole region. The boundary conditions correspond to a given pressure drop at the bottom hole. It is shown that the influence of the temperature field on such integral characteristics as cumulative gas production is most pronounced at moderate pressure drops. The size of the zone of possible hydrate formation in a gas reservoir is determined in two particular examples. Conclusions: Two important conclusions can be drawn: (1) a zone of hydrate formation during gas production can be identified with the use of some geophysical method, for instance, acoustic logging; (2) such a narrow zone can be easily affected by one of hydrate formation inhibitors (methanol or calcium chloride solution). These results again demonstrate the importance of taking into account thermodynamic processes in mathematical modeling of natural gas production.

Mathematical Modeling and Simulation of Hydrate Formation Conditions in Nigerian Oil and Gas Pipelines

The transportation of production and processing of petroleum fluids in pipelines and other transport lines can be significantly affected by flocculation, deposition and plugging. This problem has tremendously affected Nigerian pipelines for oil and gas transport. In this paper, the flow assurance considered includes the prevention, mitigation and remediation of hydrate. A mathematical model for predicting the equilibrium conditions for hydrate formation is: and simulations carried out to compare with experimental data. This model would be used to predict the hydrate formation temperature for given operating pressure so as to determine the hydrate inhibition requirement for the pipeline.

Phase equilibria for hydrate formation from binary mixtures of ethane, propane and noble gases

Equilibrium conditions for hydrate formation from binary mixtures of C 2H 6, C 3H 8 and noble gases such as Ar, Kr and Xe were experimentally determined at the temperatures of 273.5, 276.5 and 278.5 K. The binary systems of Xe + C 3H 8, Kr + C 3H 8 and Kr + C 2H 6 mixtures have hydrate azeotropes with pressure minimum points in the isothermal pressure-composition diagrams. Hydrate structural transitions were also observed in the binary systems of Xe + C 3H 8 and Kr + C 2H 6 mixtures.

Equilibrium conditions for hydrate formation for a ternary mixture of methane, propane and carbon dioxide, and a natural gas mixture in the presence of electrolytes and methanol

Methanol and electrolytes are often used to inhibit gas hydrate formation in industrial operations. In order to design such equipment it is required to compute the inhibition effects of these additives. Development of methods for calculating the inhibition effects require accurate experimental hydrate equilibria data. In the present work, experimental three phase (aqueous liquid solution, vapor and incipient solid hydrate) equilibrium data for a ternary mixture of methane, propane and CO 2 and a natural gas mixture in the presence of methanol and electrolytes were obtained. The experiments were carried out in the temperature range of 274–291 K and pressure range of 1.5–10.1 MPa. A `full view' variable volume sapphire cell with a movable piston, described earlier by Dholabhai et al. [P.D. Dholabhai, J.S. Parent, P.R. Bishnoi, Equilibrium conditions for hydrate formation from binary mixtures of methane and carbon dioxide in the presence of electrolytes, methanol and ethylene glycol, Fluid Phase Equilibria 141 (1997) 235-246.], was used to gather the data.

Equilibrium conditions for hydrate formation from binary mixtures of methane and carbon dioxide in the presence of electrolytes, methanol and ethylene glycol

Ethylene glycol, methanol and electrolytes inhibit hydrate formation. Computation of the inhibition effects of these additives is necessary for the design of industrial operations where it is desired to avoid hydrate formation. Development of thermodynamic methods to calculate the hydrate equilibria conditions requires accurate experimental data. In the present work experimental three phase (aqueous liquid solution, vapor and incipient solid hydrate) equilibrium data for two mixtures of methane and CO 2 in the presence of methanol, ethylene glycol and electrolytes were obtained. The experiments were carried out in the temperature range of 264–282 K and pressure range of 1.5–10.4 MPa. A ‘full view’ fixed volume sapphire cell used earlier to gather data on CO 2 by the authors was converted into a variable volume cell with the help of a movable piston to perform the experiments.

Inhibition of Gas Hydrates in Water-Based Drilling Muds

Summary A series of thermodynamic experiments were run on 16 simulated drilling muds and associated test fluids to improve the understanding of the equilibrium conditions for hydrate formation in water-based drilling fluids. Results indicated that, to a first approximation, the salt and glycerol contents of water in mud dominated hydrate formation. Other mud additives, such as bentonite, barite, and polymers, collectively promoted hydrate formation to a lesser degree.