Prediction Of Hydrate Formation Conditions Research Articles

Modelling the hydrate formation condition in consideration of hydrates structure transformation

Accurate prediction of hydrate formation conditions is the basis of hydrate related research. The Chen-Guo hydrate model could accurately predict the formation conditions of hydrates. However, the misjudgment of basic hydrates structure makes it unsatisfactory to calculate the system with sI and sII hydrates coexisting. Consequently, we proposed that sI and sII basic hydrates will be formed simultaneously under specific conditions. The structure composition of basic hydrates is influenced by three factors: structure induction, driving force of hydrate independent nucleation and composition of gas mixture. On this basis, we improved the Chen-Guo hydrate model by introducing new parameters and adjusted the true structure composition of basic hydrates. The calculation results show that the average absolute deviation of 201 sets of data can be reduced from 9.33% to 2.74%. The calculation precision of modified method is better than that of the original Chen-Guo hydrate model.

Prediction of Gas Hydrate Formation in Industries

Natural gas and crude oil in natural underground reservoirs are in contact with water. Stability of these compounds at the presence of both components and complete dependence on the host molecules by forming holes in their guest molecules are replaced. There are many gases such as methane, ethane, propane, carbon dioxide, hydrogen sulphides that can play the role of guest molecules. The natural gas hydrate formation in different sectors of the oil and gas industry in downstream processes causes the production to stop or decrease. Therefore, the need to know the causes and conditions of hydrate formation is strongly felt. In this study, Van der Waals and Platteeuw model was used to predict hydrate formation conditions. The prediction of hydrate formation conditions needs equilibrium fugacity of gaseous components, and for the equilibrium molar component of water.

The SAFT for prediction of hydrate formation conditions of gas mixtures in the presence of methane, glycerol, ethylene glycol, and triethylene glycol

The statistical associating fluid theory (SAFT) equation of state is employed to calculate the fugacities of all components in the vapor and liquid phases in equilibrium with the coexisting hydrate phase. Since the SAFT takes into account the interactions of hard-sphere repulsion, hard chain formation, dispersion and association between molecules, it can successfully predict the inhibiting effect of methanol, glycerol, ethylene glycol, and triethylene glycol on the hydrate formation of gas mixtures containing methane, ethane, propane and carbon dioxide. The predictions were in excellent agreement with experimental data. However, the traditional cubic equations of state fail for systems containing water, alcohols and hydrocarbons in general.

An Examination of the Prediction of Hydrate Formation Conditions in the Presence of Thermodynamic Inhibitors

Abstract Gas hydrates are crystalline compounds, solid structures where water traps small guest molecules, typically light gases, in cages formed by hydrogen bonds. They are notorious for causing problems in oil and gas production, transportation and processing. Gas hydrates may form at pressures and temperatures commonly found in natural gas and oil production pipelines, thus causing partial or complete pipe blockages. In order to inhibit hydrate formation, chemicals such as alcohols (e.g., ethanol, methanol, mono-ethylene glycol) and salts (sodium, magnesium or potassium chloride) are injected into the produced stream. The purpose of this work is to briefly review the literature on hydrate formation in mixtures containing light gases (hydrocarbons and carbon dioxide) and water in the presence of thermodynamic inhibitors. Four calculation methods to predict hydrate formation in those systems were examined and compared. Three commercial packages (Multiflash®, PVTSim® and CSMGem) and a hydrate prediction routine in Fortran90 using the van der Waals and Platteeuw theory and the Peng-Robinson equation of state were tested. Predictions given by the four methods were compared to independent experimental data from the literature. In general, the four methods were found to be reasonably accurate. CSMGem and Multiflash® showed the best results.

A new empirical correlation for prediction of carbon dioxide separation from different gas mixtures

ABSTRACTCarbon dioxide (CO2) emission from different systems such as fuel gas (H2+CO2), flue gas (N2+CO2), and biogas gas (CH4+CO2) is one of the main factors of global warming and environmental problems. So, CO2 separation from different systems is essential. Low energy consumption, environmental friendliness, and low operational cost of hydrate-based gas separation (HBGS) process show the high potential of this approach in separation of some gases such as CO2. Hydrate phase equilibrium data are required for designing the separation process. So far numerous models has been proposed for prediction of hydrate formation/dissociation conditions in various systems with/without promoters or inhibitors. This study attempts to present a simple and comprehensive model for fast prediction of hydrate formation conditions to separate CO2 from biogas, fuel gas, and flue gas systems in the presence of promoters such as tetra-n-butylammonium bromide, tetra-n-butylammonium chloride, tetra-n-butylammonium fluoride, tetra-n-butyl ammonium nitrate, and tetra-n-butylphosphonium bromide. According to the error analysis results, this point can reach the new proposed correlation has better estimation capability in comparison with Sayyad Amin et al. model. On the other hand, hydrate formation temperature can be predicted in the presented correlation with high accuracy.

Prediction of hydrate formation conditions to separate carbon dioxide from fuel gas mixture in the presence of various promoters

ABSTRACTIn this study estimation of hydrate formation conditions to separate carbon dioxide (CO2) from fuel gas mixture (CO2+H2) was investigated in the presence of promoters such as tetra-n-butylammonium bromide (TBAB), tetra-n-butylammonium fluoride (TBAF), and tetra-n-butyl ammonium nitrate (TBANO3). The emission of CO2 from the combustion of fuels has been considered as the dominant contributor to global warming and environmental problems. Separation of CO2 from fuel gas can be an effective factor to prevent many of environmental impacts. Gas hydrate process is a novel method to separate and storage some gasses. In this communication, a feed-forward artificial neural network algorithm has been developed. To develop this algorithm, the experimental data reported in the literature for hydrate formation conditions in the fuel gas system with different concentrations of promoters in aqueous phase have been used. Finally, experimental data compared with estimated data and with calculation of efficiency coefficient, mean squared error, and mean absolute error show that the experimental data and predicted data are in acceptable agreement which demonstrate the reliability of this algorithm as a predictive tool.

Software Development for the Prediction of Hydrate Formation Conditions

Software Development for the Prediction of Hydrate Formation Conditions

Wilson Non-random Factor Reference State Based Model for Prediction of Gas Hydrate Formation Conditions in the Presence of Electrolyte and/or Alcohol in Solution

In this study, a new thermodynamic model is presented for prediction of hydrate formation conditions of different hydrate formers in solutions containing an electrolyte, alcohol and their mixtures. The developed model is based on the γ–φ approach for modeling the phase behavior. The theory of van der Waals–Platteeuw and the Valderama–Patel–Teja equation of state coupled with non-density dependent mixing rules were used to describe the hydrate and vapor phase, respectively. Also, the nonelectrolyte Wilson, non-random factor local composition model and Margules equation were adopted to determine the water activity in solutions containing electrolyte and alcohol, respectively. The effects of solubility of the components in the liquid and vapor phases were considered for prediction of hydrate formation conditions. The model was applied to a number of hydrate forming compounds and mixtures in different electrolyte and methanol solutions, including NaCl, KCl and CaCl2 and their mixtures, and results are compared with experimental data and/or existing models. It was found that hydrate formation conditions are better predicted by this model compared to existing models, especially for ethane and propane in electrolyte solutions, and C1/CO2/C3 gas mixture in solutions containing electrolyte and alcohol. The solubility of components in the liquid and vapor phases was found to have a considerable effect on the model predictions.

Prediction of hydrate formation conditions using GE-EOS and UNIQUAC models for pure and mixed-gas systems

The aim of this study is to predict hydrate formation pressure and temperature through the three-phase (hydrate–liquid water–gas) equilibrium calculation using the GE-EOS and UNIQUAC activity coefficient models. Calculation of the hydrate formation conditions is carried out for pure gases such as CH4, C2H6, C3H8, iC4H10, CO2, H2S and N2, the gas binaries and ternaries; and some synthetic natural gas systems. Also calculations of the gas hydrate formation pressures are performed in the presence of methanol as inhibitor for the different gas hydrate systems. In this work, the Chen–Guo model is used for the hydrate phase and the UNIQUAC activity coefficient is applied for nonideality of the liquid phase. The SRK equation of state coupled with Huran-Vidal (HV) mixing rule is applied for the vapor phase. The UNIQUAC function is used not only for calculation of the activity coefficient of water in aqueous phase, but also is applied in the HV mixing rules. The UNIQUAC binary interaction parameters are adjusted through the hydrate experimental data directly so that there is no need to use the various vapor–liquid experimental data to obtain the parameters. To achieve more accurate results, the solubility of the gases in the aqueous phase is also taken into account using Henry's law. Finally, the present results are compared with the other available works and a very good agreement is observed with the experiment. The percent of Absolute Average Deviation (AAD%) for the calculated hydrate formation pressures and temperatures are considerably less than those results given by the other previous works.

Prediction of hydrate formation conditions in the solutions containing electrolyte and alcohol inhibitors and their mixtures using UNIQUAC-NRF models

In this work, the prediction of hydrate formation conditions in the presence of the thermodynamic inhibitors is presented. Using the van der Waals–Platteeuw model, computation of the L–S–G equilibrium is carried out for hydrate formation conditions in the presence of methanol and electrolytes using the local composition models of the UNIQUAC-NRF and Electrolyte-UNIQUAC-NRF for nonelectrolyte and electrolyte systems, respectively. The model is applied to calculate water activity coefficient for prediction of the hydrate formation pressure of methane, ethane, H2S in the absence and presence of the electrolytes. The results of the present model are compared with the experiment and UNIFAC group contribution model. Also both UNIQUAC-NRF and UNIFAC activity coefficient models are used to predict the hydrate formation conditions in the presence of alcohols. The results show very good agreement with the experiment.

Experimental study of natural gas hydrates and a novel use of neural network to predict hydrate formation conditions

A novel high-pressure apparatus with various abilities in hydrate investigation fields has been designed, constructed and fully described in the present paper. In order to achieve an appropriate understanding of the gas hydrate behavior in formation and destabilization, series of laboratory experiments with six different gas mixtures were done and more than 130 hydrate equilibrium points in the pressure range of about 450–3000psia were recorded. Different methods of hydrate formation prediction were discussed and finally the new promising neural networks method was used. Because of the previous works defects in accurate hydrate formation prediction via neural networks, a new use of neural networks was introduced. Testing and validation of the new neural networks method indicates that it is a reliable technique for the accurate prediction of hydrate formation conditions for generalized gas systems and can be used in future automatic inhibitor dosing devices.

Application of PHSC equation of state in prediction of gas hydrate formation condition

In this work the modified perturbed hard sphere chain equation of state (PHSC), coupled with Van der waals Platteuw model, has been used for prediction of gas hydrate formation (dissociation) conditions. The PHSC EOS has been modified using association and electrostatic contributions. In order to evaluate the capability of the PHSC EOS, the hydrate formation conditions of various pure as well as mixed gases in the presence and absence of the thermodynamic inhibitors such as methanol, ethanol, mono ethylene glycol(MEG), NaCl, KCl and CaCl2 have been studied. In the absence of inhibitors, the pure gas hydrate formation conditions have been predicted within 3.4% absolute average relative deviation. The hydrate formation condition of gas mixtures have been predicted within AARD 4.6%. In the presence of organic inhibitors and single electrolyte 6.1% and 5.8% AARD has been observed respectively. A total of 102 systems have been studied; our results showed that the PHSC EOS is capable of prediction of hydrate formation condition with reasonable absolute average relative deviation (AARD) from experimental data.

Prediction of hydrate formation conditions based on the vdWP‐type models at high pressures

AbstractPrediction of phase boundaries of gas hydrates has been done for several decades based on the vdWP (van der Waals and Platteeuw) hydrate equation and the classical thermodynamic equations for describing the water fugacities in water or ice phase. This procedure gives a reasonable prediction at low pressures, but when the pressure increases, above 105 kPa, it shows a significant error. In the conventional vdWP‐type models it has been assumed that the volume difference between the empty hydrate lattice and pure liquid water is independent of the system pressure and temperature. In this work, different approaches for describing the volume dependency of pure liquid water and the empty hydrate lattice on the system pressure have been used to predict the hydrate equilibria based on the vdWP‐type model. Also, an expression is introduced to estimate the volume of methane hydrate lattice as a function of pressure and temperature. Finally, this method is extended to other hydrate formers, that is, ethane, carbon dioxide, xenon, and nitrogen. The predicted values are in good agreement with the experimental data both for Lw–H–V and Lw–H–Lhf phase boundaries.

A novel correlation for estimation of hydrate forming condition of natural gases

An inherent problem with natural gas production or transmission is the formation of gas hydrates, which can lead to safety hazards to production/transportation systems and to substantial economic risks. Therefore, an understanding of conditions where hydrates form is necessary to overcome hydrate related issues. Over the years, several models requiring more complicated and longer computations have been proposed for the prediction of hydrate formation conditions of natural gases. For these reasons, it is essential to develop a reliable and simple-to-use method for oil and gas practitioners. The purpose of this study is to formulate a novel empirical correlation for rapid estimation of hydrate formation condition of sweet natural gases. The developed correlation holds for wide range of temperatures (265–298 K), pressures (1200 to 40000 kPa) and molecular weights (16–29). New proposed correlation shows consistently accurate results across proposed pressure, temperature and molecular weight ranges. This consistency could not be matched by any of the widely accepted existing correlations within the investigated range. For all conditions, new correlation showed average absolute deviation to be less than 0.2% and provided much better results than the widely accepted existing correlations.

Prediction of VLE and VLLE of Systems Containing Hydrocarbon Reservoir Fluids and Aqueous Methanol Solutions With a Cubic EOS

Abstract With the purpose of accurately representing the phase equilibria of hydrocarbon reservoir fluids, water, and methanol, the revised modified Patel-Teja model (MPT2 model) has been extended to predict the vapour-liquid (VL) and vapour-liquidliquid (VLL) equilibria of hydrocarbon/water/methanol systems. The prominent feature of the work presented in this paper is the minimum usage of binary interaction parameters (BIPs) in the prediction of VLE and VLLE data. The accuracy and reliability of the extended MPT2 model has been demonstrated by extensively testing against diverse experimental data on VLE and VLLE of ternary, quaternary, five component, natural gas, and reservoir oil systems containing water and methanol. The extended MPT2 model can be easily applied to production schemes of natural gases from hydrate formations, hydrocarbon flowlines, and processing units. Introduction The production of natural gases from hydrate formations can be potentially accomplished by shifting the hydrate equilibrium curve through heating, pressure reduction, or by injection of an inhibitor. Water-soluble compounds such as methanol, ethanol, ethylene glycol, diethylene glycol, and triethylene glycol are commonly used as hydrate inhibitors. The other applications of hydrate inhibitors include production and transportation of hydrocarbon streams that also contain water, where there is always a risk of pipeline or processing equipment plugging owing to hydrate formation, particularly when such operations are carried out at low temperature conditions. However, one of the most worrisome problems associated with the application of hydrate inhibitors is the partial dissolution of usually lighter hydrocarbon and other components from natural gas and oil streams in, for instance, the aqueous methanol phase, thereby reducing its effectiveness as a hydrate inhibitor. Moreover, the solubility of such lighter hydrocarbon components in the aqueous inhibitor phase also has a significant effect on the thermodynamic prediction of hydrate formation conditions. Also, from a thermodynamic perspective, the complexity of phase behaviour of hydrocarbon/water systems is even more pronounced when methanol is added as the most widely accepted hydrate inhibitor. Therefore, a thermodynamic model capable of representing the phase behaviour of all phases in a consistent manner for simultaneous phase equilibrium calculations on mixtures of hydrocarbon, water, and methanol is vital for evaluating its application as a hydrate inhibitor. Herein lies the purpose of this work. Cubic equations of state (EOS) with quadratic mixing rules have been successfully applied to hydrocarbon fluids in a wide range of thermodynamic conditions. However, the application of cubic EOS in their basic form to polar-nonpolar systems, i.e., hydrocarbon- water or hydrocarbon-aqueous methanol solutions, is inadequate. Traditionally, the so-called activity coefficient models, such as UNIQUAC and NRTL equations, have handled polar systems. These activity models are not applicable to vapour phase and are unreliable at higher pressures. Therefore, polar-nonpolar systems are generally handled by incorporating unconventional mixing rules in the cubic EOS to improve their performance for such systems.