Kinetic Hydrate Inhibitor Performance Research Articles

The development of high-performance kinetic hydrate inhibitors by introducing N-vinyl caprolactam and vinyl ether homopolymers into PVCap

Low dosage kinetic hydrate inhibitors (KHIs) are a kind of alternative chemical additives to prevent gas hydrate formation in oil & gas production wells and transportation pipelines. In this work, a series of KHIs were experimentally synthesized with N-vinyl caprolactam (N-VCap) and vinyl ether including vinyl ether, vinyl n-butyl ether, vinyl isobutyl ether, triethylene glycol divinyl ether, with the mole ratio ranging from 9:1 to 5:5. The inhibition performance of new-synthesized KHIs on the formation process of methane hydrate were examined and compared with that of commercial N-vinyl caprolactam PVCap. Several ethylenediamine reagents were used as synergists and tested to improve the inhibition capacity of new-synthesized KHIs. The experimental results demonstrate that the introduction of ether groups on PVCap improves the performance of hydrate inhibitors. PVCap-VNBE (N-VCap: vinyl n-butyl ether = 5:5) showed the best inhibition performance for methane hydrate, which could extend the TVO to 1251 min under 6 K subcooling. N,N'-dimethylethylenediamine shows the best synergistic effect for PVCap-VNBE (5:5), and extends the TVO by 2.75 times at 7 K subcooling. Additionally, the relationship between hydrate inhibition performance and interfacial tension of newly-synthesized KHIs under high pressure were studied. It shows that the lower interfacial tension of KHIs would result in longer onset time, exhibiting better inhibition performance.

Determining the critical time points for hydrate formation in the presence of kinetic hydrate inhibitors: A rheological and kinetic study

Kinetic hydrate inhibitors have the characteristics of delaying hydrate nucleation and reducing hydrate growth rate. The utilized of kinetic hydrate inhibitors for hydrate blockage risk management is a promising technology for hydrate prevention in oil and gas industry. In this study, the rheological and kinetic properties of gas–water systems contained pure water, polyvinyl pyrrolidone and newly-synthesized inhibitor during hydrate formation at different subcooling degrees were in situ characterized using a high-pressure rheometer. By analyzing the experimental results, the concept of ‘critical time’ have been proposed to divide the time-varying process of hydrate formation into multiple stages. The three critical times indicated distinct trends in viscosity and pressure changes, as well as varying risks of hydrate blockage in hydrate prevention. The results further compared the differences in determining critical time through pressure and viscosity. The critical time of hydrate nucleation determined by viscosity was earlier than pressure due to the hypothesis of lag in gas consumption. The critical time of rapid hydrate growth determined by viscosity was later than gas consumption, which may be due to that the sharp increase in viscosity requires the aggregation of hydrates. According to the inhibition effect evaluation results determined by three critical times, it was found that the newly-synthesized inhibitor was more effective than polyvinyl pyrrolidone in inhibiting nucleation, delaying rapid hydrate growth time and reaching high viscosity time. This study can provide a comprehensive evaluation method for assessing the performance of kinetic hydrate inhibitors from both kinetic and rheological perspectives.

Comparative study of inhibition mechanism and performance of kinetic hydrate inhibitors: Varying amide group orientation

In this work, the inhibition mechanisms of two kinetic hydrate inhibitors, poly(N-isopropyl acrylamide) (PNIPAM) and poly(N-vinyl isobutyramide) (PNVIBA), were investigated at the molecular level, and the influence of the orientation of the amide group on the inhibition performance was evaluated. The results show that two inhibitors have the similar inhibition behavior, and should have the comparable inhibition performance. However, PNIPAM is slightly better at decreasing the stability of gas clusters to inhibit hydrate nucleation, and PNVIBA is slightly better at disrupting liquid water structure and preventing hydrate nucleus from contacting with the surroundings.

Experimental Investigation of the Weakening Effect of Corrosion Inhibitors on the Performance of Kinetic Hydrate Inhibitors

Experimental Investigation of the Weakening Effect of Corrosion Inhibitors on the Performance of Kinetic Hydrate Inhibitors

Multi-functional Flow Assurance Chemicals: Corrosion and Kinetic Hydrate Inhibition from Maleic Anhydride:N-Vinyl Caprolactam Copolymers and Synergists

Water-based flow assurance issues include corrosion, scale, and gas hydrate formation. Chemical solutions to mitigate these issues usually require separate inhibitors, which sometimes can lead to compatibility difficulties. Herein, we report studies on maleic-based copolymers to combat hydrate and corrosion with a view to optimizing for scale inhibition also. The product of maleic anhydride:N-vinyl caprolactam copolymer reacted with 3-dibutylaminopropylamine (MA:VCap-DBAPA) and its amine oxide derivative (MA:VCap-DBAPA-AO) were the kinetic hydrate inhibitor (KHI) polymers investigated. Due to limited CO2 corrosion inhibition (CI) by the polymers alone, various oxygen-, sulfur-, and nitrogen-based additives were screened for improved CO2 CI and possible KHI synergy. KHI performance screening tests were conducted under high pressure with a structure II-forming natural gas mixture in steel rocking cells using the slow (1 °C/h) constant cooling method. CO2 corrosion inhibition was measured by linear polarization resistance in a stirred 1 L CO2 bubble test apparatus using C1018 steel coupons and 3.6 wt % brine at 20.5 °C. Several sulfur-based additives improved the CI efficiency of the maleic polymers, especially butyl thioglycolate and 2-aminoethanethiol, without a negative effect on the KHI performance. For example, 2500 ppm MA:VCap-DBAPA plus 1000 ppm butyl thioglycolate gave an average hydrate onset temperature (To) of 4.4 °C (12.7 °C below the To for no additive) and 99.7% CI efficiency. In contrast to a classic fatty acid imidazoline surfactant corrosion inhibitor, butyl thioglycolate was also found to greatly enhance the CI efficiency of industrial KHIs, poly(N-vinyl caprolactam) (PVCap) and N-vinyl pyrrolidone:N-vinyl caprolactam copolymer, with no antagonism to the KHI performance of the polymer. In addition, butyl thioglycolate boosted the KHI performance of PVCap. The use of small synergists such as butyl thioglycolate avoids the use of classical surfactant corrosion inhibitors which can lead to tighter emulsions and poor overboard oil-in-water quality.

Elucidating the Impact of Thermodynamic Hydrate Inhibitors and Kinetic Hydrate Inhibitors on a Complex System of Natural Gas Hydrates: Application in Flow Assurance

To alleviate the hydrate blockage risk in oil and gas pipelines/production facilities, thermodynamic hydrate inhibitors (THIs) and kinetic hydrate inhibitors (KHIs) are the frequently used additives/chemicals. While these additives are highly effective, the impact of low dosage of THIs (under inhibited systems) and performance of KHIs at high water cut and/or high subcooling is not well understood. In this work, a high-pressure visual stirred tank reactor was employed to investigate the impact of THIs and KHIs on the kinetics of the complex hydrates of natural gas mixtures (CH4/C2H6/C3H8) and cyclopentane at high water-cut and high subcooling (∼21 °C). Various concentrations of a THI, mono-ethylene glycol (MEG) with a dosage ranging from 0.1 to 25 wt %, and multiple KHIs (polyvinylpyrrolidone (PVP k-30, PVP k-90), caprolactam, butyl glycol ether (BGE), and polyglycerin with 0.1 wt % dosage) were evaluated for hydrate formation kinetics, onset hydrate formation/nucleation temperature, and morphological changes. Gas uptake results reveal that hydrate blockage risk is higher at low MEG content (0.1 to 10 wt %) compared to the baseline, while a significant reduction in gas uptake was observed for the high MEG content trials (20–25 wt %). With 20 and 25 wt % MEG, the hydrate nucleation temperature was reduced by 10–12 °C compared to the baseline. In context to KHIs impact, 0.1 wt % BGE and caprolactam promoted the nucleation temperature and the rate of hydrate formation/gas uptake. However, PVPs not only reduced the gas uptake kinetics but also lessened the hydrate nucleation temperature by 6–8 °C compared to the baseline data. Our results may offer new insights into optimizing hydrate inhibitors dosage to diminish the risk of hydrate blockage in subsea pipelines.

Molecular mechanisms of Poly(N-alkyl methacrylamides)s as Kinetic hydrate inhibitors

Kinetic hydrate inhibitors (KHIs) have been used commercially to inhibit gas hydrate plugging in pipelines due to high efficiency and low dosage, and small changes in their molecular structures can significantly influence the inhibition performance, but the mechanisms by which they function remain unclear. Here, we employ the first principle calculation method to study the molecular mechanisms of poly(N-alkyl methacrylamides)s as KHIs, and to reveal the effect of alkyl pendant groups on their inhibition performance. The results show that the inhibition performance of KHIs correlates well with their reactivity such as energy gap and the charge population. KHIs can slow down the diffusive motion of water molecules, retarding the hydrate formation, but also can adsorb onto the incomplete cages of the hydrate surface, driving methane molecules. These two effects are enhanced by increasing the size of the alkyl pendant chain, leading to the better inhibition performance.

Concentration effect of kinetic hydrate inhibitor on hydrate formation and inhibition

Kinetic hydrate inhibitor (KHI) is an eco-friendly and promising technology for hydrate blockage issue in natural gas pipelines, but it remains unclear of how KHI performance would vary at different subcooling and concentration. In this study, the influence of KHI on the kinetics of methane - propane hydrate formation was evaluated with a wide range of subcooling (5–20 ℃) and concentration (100–51000 ppm) conditions, by characterizing the pressure evolution, average hydrate growth rate and hydrate volume fraction. The results put forward a ‘concentration effect’ concept that represented the nonmonotonic relationship between the performance and concentration of KHI, where KHI obtained higher inhibition performance with either relatively low or high concentration, but became almost ineffective at the intermediate concentration zone. Two hypotheses were then proposed to reveal its internal mechanisms, including the ‘weakened adsorption’ hypothesis and the ‘competition’ hypothesis. Results further demonstrated that the above concentration effect became less obvious when the experimental conditions were more contributory for fast hydrate formation, such as the enhanced subcooling and stirring speed. In addition, the universality of concentration effect was preliminarily verified, which was not restricted by the type of KHI or the selected experimental system. To the best of our knowledge, such concentration effect was for the first time systematically investigated and reported in this study, which highlighted the possibility of flexibly selecting the appropriate KHI concentration based on the practical driving force for hydrate formation.

Boronic and Organic Acids as Synergists for a Poly(N-vinylcaprolactam) Kinetic Hydrate Inhibitor

A range of boronic acids have been investigated as synergists for the kinetic hydrate inhibitor (KHI) polymer, poly(N-vinylcaprolactam) (PVCap, Mw ≈ 10,000 g/mol) using high pressure rocking cells, a natural gas mixture, and a slow constant cooling (1 °C/h) test method from 76 bar. Surprisingly, unlike other classes of synergists such as alcohols and quaternary ammonium salts, the boronic acids that gave the best synergy had an alkyl or cycloalkyl tail with a maximum of a 3 carbon atom distance from the boron atom. The tail-branched iso-butylboronic acid was the best of these, yet it showed a negligible KHI effect when tested alone. However, consistent with the other classes of synergists, tail branching or use of a cyclic alkyl group was beneficial. Interestingly, boronic acids with chains of 5 to 6 carbon atoms, i.e., n-pentyl- and n-hexylboronic acids, were antagonistic to the PVCap KHI performance. For comparison, several organic acids were also investigated as synergists with PVCap. The same trend as for the boronic acids regarding the size and branching of the acid was seen. 3-Methylbutanoic acid gave the best synergy although worse than that of iso-butylboronic acid. The synergistic performance of sodium salts of some organic acids differed markedly to that of the free organic acids. Sodium 3,3-dimethylbutanoate gave the best synergy with PVCap.

Kinetic hydrate inhibitor performance and adsorption characteristics of poly(N-alkyl-N-vinyl acetamide)s: A first-principles study

Kinetic hydrate inhibitors (KHIs) have been developed to prevent hydrate plugging of flow lines due to high efficiency and low dosage, but the intrinsic mechanism remains inconclusive and requires further verification. In this work, the inhibition performance of poly(N-alkyl-N-vinyl acetamide)s having varying alkyl side chain lengths has been investigated by the first-principles calculations and simulations. Further, the adsorption properties of these KHIs on various sites of the hydrate surface are considered. The results show that KHIs can adjust their positions and orientations to fit the empty cages, and that the adsorption strength is enhanced by increasing the alkyl side chain length, which is attributed to both hydrogen bonding and hydrophobic interactions. KHIs can drive CH4 away from the hydrae surface, but also can hold the lattice positions of water cages, which is responsible for reducing gas uptake and inhibiting hydrate growth. The molecular properties of KHIs indicate that the chemical reactivity increases with the increase of the alkyl side chain length, leading to the strong adsorption strength between KHIs and the hydrate surface, and thus improve the inhibition performance of KHIs. These results provide not only an important understanding of the KHI inhibition mechanism but also a basis for designing high efficient KHIs.

Powerful Synergy of Acetylenic Diol Surfactants with Kinetic Hydrate Inhibitor Polymers—Choosing the Correct Synergist Aqueous Solubility

The performance of injected kinetic hydrate inhibitor (KHI) polymer solutions can be boosted considerably by judicious choice of the polymer solvent system. We report the excellent KHI synergism of the low-foaming acetylenic diol gemini surfactant 2,4,7,9-tetramethyl-5-decyne-4,7-diol (TMDD) with poly(N-vinyl caprolactam), N-vinyl caprolactam:N-vinyl pyrrolidone copolymer, and poly(N-isopropylmethacrylamide). High-pressure rocking cell tests, using the slow constant cooling method or the isothermal method, were carried out with a natural gas mixture giving structure II hydrates as the preferred thermodynamically stable phase. Poly(oxyethylene) derivatives of TMDD, which are far more water-soluble than TMDD, gave significantly lower synergetic KHI performance with the same polymers. It is conjectured that the low aqueous solubility of TMDD (1700 ppm at 20 °C) and its two isobutyl groups are key features contributing to the synergism. However, when decane was added to the system as a model liquid hydrocarbon phase, the synergetic performance decreases, probably due to partitioning of TMDD to the hydrocarbon phase. This highlights the need to choose synergist systems which are retained in the aqueous phase for optimal performance when condensate or oil is present in the produced fluids. Optimizing the structure and aqueous solubility of the synergist (solvent or otherwise) can be seen as complementary to the known principle of optimizing the structure and solubility of the KHI polymer.

2-2-1 動的阻害剤の成長阻害効果測定と作用メカニズムの解明

2-2-1 動的阻害剤の成長阻害効果測定と作用メカニズムの解明

Understanding the inhibition performance of kinetic hydrate inhibitors in nanoclay systems

Kinetic hydrate inhibitors are widely used during upstream activities in the oil industry to prevent gas hydrates from clogging pipelines. Yet their performance in the pipelines transporting natural gas from marine environment is largely veiled where clay particles and their adsorbability are generally present. In this study, it was found that the fine clay particles from a hydrate rich area in the South China Sea are majorly composed of layered silicate with a negative surface charge. Consequently, the clay particles would adsorb the inhibitor through Van der Waals attractions and ion–dipole interactions. The resulting weakened surface potential of the particles would trigger an aggregation of the clays together with the inhibitors attached on their surfaces. This will thereby result in less active components in the solution, significantly weakening the inhibition effect. It is therefore suggested that the effects of clay-rich conditions on the performance of the inhibitors should be carefully considered for an efficient dosage in the marine environments.

Preparation of poly(N-vinyl caprolactam) with various end groups using chain transfer agents and evaluation of their effects on kinetic hydrate inhibition

Poly(N-vinylamide) derivatives were synthesized to improve the performance of kinetic hydrate inhibitors (KHIs). In this work, we synthesized poly(N-vinylformamide) (PNVF) and poly(N-vinylcaprolactam) (PVCap) by free radical polymerization with several commercial chain transfer agents (CTAs), which afforded a few thousand Mn. The structures of synthesized PNVF and PVCap were then investigated by 1H NMR and MALDI-TOF/MS spectrograms. KHI properties of the synthesized PNVF and PVCap polymers were also evaluated by the high-pressure slow constant cooling KHI test method. Some of the tested polymers showed a better KHI effect than PVCap.

Investigation of gas hydrate formation and inhibition in oil-water system containing model asphaltene

Gas hydrate and asphaltene are two major flow assurance issues that will cause severe plugging in the subsea transportation pipelines, but the detailed understanding of their interactions remains insufficient. Systematic experiments were performed in the present study to investigate the influence of light oil components and asphaltene on gas hydrate formation, and to evaluate the performance of commercial kinetic hydrate inhibitors (KHIs) in different oil-water systems. Results demonstrated the promotion effect of light oil on initial hydrate growth, and the inhibition effect of asphaltene particularly with the light oil solvent of toluene. The influence mechanisms of asphaltene were based on the weakening mass transfer of methane at the gas-liquid interface, and the adsorption of free methane in the bulk liquid phase, while the degree of inhibition on hydrate formation was not positively related to the total concentration of asphaltene. Results also indicated that light oil components can weaken the performance of KHIs, but the role of asphaltene was closed related to the type of KHIs and light oil solvent. The overall experimental results of gas hydrate formation in the asphaltene system are consistent with our previous molecular dynamics simulations researches. Meanwhile, it provides an implication that asphaltene may have a potential ability to help some KHIs recover their inhibition performance, and emphasizes the necessity in systematically considering the oil composition when attempting to develop and utilize KHIs in oil-water system.

In situ PXRD analysis on the kinetic effect of PVP-K90 and PVCap on methane hydrate dissociation below ice point

Kinetic hydrate inhibitors (KHIs) have been developed as an alternative for the prevention of hydrate plug in natural gas transportations due to economic and environmental factors. To understand the kinetic performance of KHIs comprehensively, dissociations of CH4 hydrates in the presence of PVP-K90 and PVCap were investigated below ice point. Cryo-SEM and in situ PXRD were used to provide a microscopic insight on the dissociation kinetics. Results showed that a typical CH4 hydrate dissociation at 268 K could be divided into 4 stages. The self-preservation effect took place in the second stage accompanied with an rise in the ratio of Ih(002) to Ih(100) peaks from 0.5 to 1.1. About 30% of CH4 hydrates were suggested to dissociate into plate-like ice to form ice coatings on hydrate surface. In the presence of PVP-K90 or PVCap, the self-preservation stage reduced greatly and the initial dissociation rates of CH4 hydrates were found enhanced as the concentrations of the KHIs increased from 0.5 to 2.0 wt%. SEM images revealed that PVP-K90 was suggested to be included in the small ice crystals embedded in hydrate phase and hinder the connections of the plate-like ice crystals on hydrate surface, while PVCap was found to induce a dendritic growth of CH4 hydrate, leading to a surge in the specific surface area of CH4 hydrates which was not beneficial to the formation of ice coatings on hydrate phase. Therefore, both PVP-K90 and PVCap promoted hydrate dissociation below ice point by inhibiting the formation of self-preservation effect.

Correction to Does the Cloud Point Temperature of a Polymer Correlate with Its Kinetic Hydrate Inhibitor Performance?

Correction to Does the Cloud Point Temperature of a Polymer Correlate with Its Kinetic Hydrate Inhibitor Performance?

Investigation of Solvent Synergists for Improved Kinetic Hydrate Inhibitor Performance of Poly(N-isopropyl methacrylamide)

The synergistic effect of a range of solvents on the kinetic hydrate inhibitor (KHI) performance of poly(N-isopropyl methacrylamide) (PNIPMAm) has been investigated in slow (ca. 1 °C/h) constant cooling high-pressure (76 bar) rocking cell experiments using a structure II forming synthetic natural gas mixture. We have tested the synergistic effects of several monoglycol ethers and compared them to those of corresponding diglycol ethers and alcohols. Compounds containing lactate, carboxylate, ammonium, and pyrrolidone headgroups have also been investigated as synergists. In general the monoglycol ethers were found to function best as synergists with PNIPMAm, and the performance improved going from n-butyl to isobutyl, cyclopentyl, and cyclohexyl alkyl substituents. The best performing synergist in this study was found to be 2-(cyclohexyloxy)ethanol (CHexGE). Addition of 5000 ppm CHexGE to 2500 ppm PNIPMAm-II (made in isopropyl alcohol and precipitated out, Mn = 8100 g/mol) dropped To from 6.8 °C for pure po...

Does the Cloud Point Temperature of a Polymer Correlate with Its Kinetic Hydrate Inhibitor Performance?

Most polymers used in commercial kinetic hydrate inhibitor (KHI) formulations show thermoresponsive behavior in aqueous solution. This means that they exhibit a cloud point (or lower critical solut...

Waterborne Polyurethanes as a New and Promising Class of Kinetic Inhibitors for Methane Hydrate Formation

A facile, new and promising technique based on waterborne polymers for designing and synthesizing kinetic hydrate inhibitors (KHIs) has been proposed to prevent methane hydrate formation. This topic is challenging subject in flow assurance problems in gas and oilfields. Proposed technique helps to get KHIs with required number and distance of hydrophilic and hydrophobic groups in molecule and good solubility in water. The performance of these new KHIs was investigated by high pressure micro-differential scanning calorimeter (HP-μDSC) and high-pressure autoclave cell. The results demonstrated the high performance of these inhibitors in delay the induction time (10–20 times) and reduce the hydrate growth rate (3 times). Also they did not increase hydrate dissociation temperature in comparison with pure water and show thermodynamic inhibition as well. Inhibition effect of synthesized polymers is improved with the increase of concentration significantly. Since this is the first report of the use of waterborne polymers as kinetic hydrate inhibitor, we expect that KHIs based on waterborne-based polymers can be a prospective option for preventing methane hydrate formation.