Kinetic Hydrate Inhibitor Polymers Research Articles

Improved Gas Hydrate Kinetic Inhibition for 5-Methyl-3-vinyl-2-oxazolidinone Copolymers and Synergists.

Kinetic hydrate inhibitors (KHIs) are used to prevent deposits and plugging of oil and gas production flow lines by gas hydrates. The key ingredient in a KHI formulation is a water-soluble amphiphilic polymer. Recently, polymers of a new commercially available 5-ring vinylic monomer 5-methyl-3-vinyl-2-oxazolidinone (VMOX) were investigated as KHIs and shown to perform better than some commercial KHI polymers such as poly(N-vinyl pyrrolidone). This initial study using slow constant cooling (SCC) in rocking cells with a synthetic natural gas has now been expanded to further explore low molecular weight PVMOX homopolymers and VMOX copolymers as well as blends with nonpolymeric synergists. A PVMOX homopolymer with improved KHI performance was found using 3-mercaptoacetic acid as a chain transfer agent in the radical polymerization of VMOX. Among a range of copolymers, VMOX:n-butyl acrylate copolymers in particular gave good KHI performance, better than the PVMOX homopolymer. Among the potential synergists, trialkylamine oxides (alkyl = n-butyl or iso-pentyl) and tetra(n-pentyl)ammonium bromide to 2500 ppm were found to be antagonistic with PVMOX at the test concentrations while some alcohols and glycols were synergetic. The best synergist was 2,4,7,9-tetramethyl-5-decyne-4,7-diol (TMDD). For example, a mixture of 2500 ppm TMDD with 2500 ppm PVMOX (Mw 2400 g/mol) performed significantly better than 5000 ppm PVMOX. Addition of 1250 ppm TMDD to 2500 ppm VMOX:n-butyl acrylate 6:4 copolymer lowered the hydrate onset temperature in SCC tests by a further 3 °C compared to the copolymer alone giving hydrate onset at 4.2 °C.

Kinetic Hydrate Inhibition by Lambda-Carrageenan and Its Synergistic Compositions with Ethylene Glycol, 4-Methyl-1-Pentanol, Polyvinylpyrrolidone, and Polyvinylcaprolactam

For the oil and gas industry to function smoothly, it is essential to have a continuous flow of oil and gas in pipelines without interruptions caused by hydrate blockages. Kinetic hydrate inhibitors (KHIs) are becoming popular as they offer safe and effective hydrate inhibition at low dosages (0.5–2 wt % of the water content). The current commercial KHIs are synthetic and poorly biodegradable, which causes disposal concerns for environmental regulators. The lack of natural, sustainable, and biodegradable KHIs opens the scope to develop natural and biodegradable KHI alternatives. This study investigates the use of a natural and biodegradable polysaccharide, lambda carrageenan (λ-crgn), as a standalone KHI and its combinations with biodegradable solvents mono ethylene glycol and 4-methyl-1-pentanol and commercial KHI polymers (PVP and PVCap) for improved biodegradability and performance. λ-crgn is an environmentally friendly polysaccharide derived and cultivated from red seaweeds. Two variants of λ-crgn, one with a smaller mean size and a lower viscosity (LV) and one with a larger mean size and a higher viscosity (HV), are tested for hydrate inhibition. The lower molecular size/viscosity variant, λ-crgn (LV), showed similar induction times and lower hydrate growth rates compared to PVP when used as a standalone KHI. However, the high-viscosity variant did not perform as well as PVP. λ-crgn (HV or LV), when blended with commercial KHIs (PVP and PVCap), synergized and led to an increase in induction times by up to 63% and a decrease in the hydrate growth rates by 73% compared to when only the commercial KHIs were used at the exact total dosages. When λ-crgn (HV or LV) was blended with solvents 4-methyl-1-pentanol or MEG, again a significant synergy was observed, leading to the hydrate inhibition performance that was found to be at par or better than the commercial KHIs (PVP and PVCap) at the exact total dosages.

Can kinetic hydrate inhibitors inhibit the growth of pre-formed gas hydrates?

Low dosage kinetic hydrate inhibitors (KHIs) are one of the most promising techniques for inhibition at the earliest stages of hydrate formation. Although KHI polymers are generally considered to inhibit nucleation, they also show powerful properties in terms of crystal growth inhibition. Some KHIs may even induce anomalous gas hydrate dissociation inside the hydrate stability zone depending on the conditions. While KHIs have been proven for both inhibition of hydrate nucleation and initial crystal growth, their performance when it comes to pre-formed hydrates – i.e. where significant hydrate has already formed prior to KHI injection/contact with the KHI – has yet to be investigated. In this work, the ability of PVCap polymer to inhibit pre-formed hydrates has been evaluated for a methane-water system. Results are consistent with KHIs being able to inhibit further hydrate growth where a considerable volume of hydrate is already present in the system prior to chemical injection. Not only that, but that in the case of the PVCap system studied here, injection can, under certain conditions, directly result in the partial to complete anomalous dissociation of all pre-formed hydrates, even though conditions are inside the hydrate region. It is speculated this behaviour is related to the transition from metastable to stable hydrate structures/phases; PVCap not preventing the dissociation (of unstable phases) step of this process but inhibiting subsequent regrowth of stable equilibrium structures.

N-Vinyl Caprolactam/Maleic-Based Copolymers as Kinetic Hydrate Inhibitors: The Effect of Internal Hydrogen Bonding

Kinetic hydrate inhibitors (KHIs) have been used for over 25 years to prevent gas hydrate formation in oil and gas production flow lines, but they are some of the most expensive oilfield production chemicals. The main component in KHI formulations is a water-soluble polymer with many amphiphilic groups. Usually, in commercial KHI polymers, the hydrophilic part of these groups is the amide group. In addition, KHI polymers are often incompatible with film-forming corrosion inhibitors. Therefore, we sought to find cheaper but effective KHIs that could also act as a flow line corrosion inhibitor. Continuing earlier work from our group with maleic-based polymers, we have now explored maleic acid/N-vinyl caprolactam (MAcid/VCap) copolymers to introduce VCap, a well-known KHI monomer, together with the cheaper MA monomer. 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 test method. Surprisingly, the MAcid/VCap copolymer showed very poor KHI efficacy. GFN2-xTB molecular dynamics simulations revealed that MAcid/VCap exhibits intra-hydrogen bond networks that trap the polymer morphology in the globular form. In this scenario, the caprolactam ring is encapsulated inside the polymer structure due to the intra-hydrogen bonds and the hydrophobic interactions that minimize its ability to interact with the hydrate surfaces, which significantly reduces the MAcid/VCap kinetic inhibition performance. However, the polymer in such globular forms still displays an important amount of its carboxylic groups exposed to water, which explains the water solubility. In contrast to MAcid/VCap copolymers, maleimide derivatives with dibutylamino end groups were effective KHIs and even better with dibutylamine oxide end groups. A terpolymer of MA/VCap reacted with N,N-dibutylaminopropylamine followed by subsequent oxidation of the end groups to dibutylamine oxide and gave the best performance of any maleic-based polymer reported to date. The combination of caprolactam and dibutylamine oxide groups can be thought of as synergism within the same polymer, akin to the excellent synergy of the separate molecules, tributylamine oxide and PVCap.

5-Methyl-3-vinyl-2-oxazolidinone–Investigations of a New Monomer for Kinetic Hydrate Inhibitor Polymers

Kinetic hydrate inhibitors (KHIs) are polymers used in a chemical method to prevent gas hydrate plugging of oil and gas production flow lines. The main ingredient in a KHI formulation is one or more water-soluble amphiphilic polymers. Several classes of KHI polymers contain pendant heterocyclic 5-rings including poly(N-vinylpyrrolidone) (PVP) and poly(2-isopropenyl-2-oxazoline) (PiPOx). Here, we present a KHI performance study on polymers based on the 5-ring vinylic monomer 5-methyl-3-vinyl-2-oxazolidinone (VMOX), which has only recently been manufactured in large quantities. Low molecular weight PVMOX homopolymers were produced in quantitative yield using radical polymerization, with or without a chain transfer agent. For example, PVMOX-2.4k (Mn = 2400 g/mol) had a cloud point at 2500 ppm of 73 °C in deionized water. The polymers were screened for KHI performance using slow constant cooling tests (1.0 °C/h) in high-pressure rocking cells with a synthetic natural gas blend. At 2500 ppm, PVMOX-2.4k gave a better performance than PVP or PiPOx at a similar molecular weight but not as good as poly(N-vinylcaprolactam) (PVCap). Isobutyl glycol ether was shown to enhance the KHI performance of PVMOX. PVMOX gave improved performance with increasing concentration but not as steep of an improvement as some of the best amide-based KHI polymers. A 1:1 copolymer of VMOX with N-vinylcaprolactam gave improved performance compared to the PVMOX homopolymer.

Kinetic Inhibition of Clathrate Hydrate by Copolymers Based on N-Vinylcaprolactam and N-Acryloylpyrrolidine: Optimization Effect of Interfacial Nonfreezable Water of Polymers.

Amphiphilic polymers have now been designed to achieve an icephobic performance and have been used for ice adhesion prevention. They may function by forming a strongly bonded but nonfreezable water shell which serves as a self-lubricating interfacial layer that weakens the adhesion strength between ice and the surface. Here, an analogous concept is built to prevent the formation of clathrate hydrate compounds during oil and natural gas production, in which amphiphilic water-soluble polymers act as efficient kinetic hydrate inhibitors (KHIs). A novel group of copolymers with N-vinylcaprolactam and N-acryloylpyrrolidine structural units are investigated in this study. The relationships among the amphiphilicity, lower critical solution temperature, nonfreezable bound water, and kinetic hydrate inhibition time are analyzed in terms of the copolymer compositions. Low-field NMR relaxometry revealed the crucial interfacial water in tightly bound dynamic states which led to crystal growth rates changing with the copolymer compositions, in accord with the rotational rheometric analysis results. The nonfreezable bound water layer confirmed by a calorimetry analysis also changes with the polymer amphiphilicity. Therefore, in the interface between the KHI polymers and hydrate, water surrounding the polymers plays a critical role by helping to delay the nucleation and growth of embryonic ice/hydrates. Appropriate amphiphilicity of the copolymers can achieve the optimal interfacial properties for slowing down hydrate crystal growth.

Non-Amide Polymers as Kinetic Hydrate Inhibitors-Maleic Acid/Alkyl Acrylate Copolymers and the Effect of pH on Performance.

Kinetic hydrate inhibitors (KHIs) have been used for over 25 years to prevent gas hydrate formation in oil and gas production flow lines. The main component in KHI formulations is a water-soluble polymer with many amphiphilic groups, usually made up of amide groups and adjacent hydrophobic groups with 3–6 carbon atoms. KHI polymers are one of the most expensive oilfield production chemicals. Therefore, methods to make cheaper but effective KHIs could improve the range of applications. Continuing earlier work from our group with maleic-based polymers, here, we explore maleic acid/alkyl acrylate copolymers as potential low-cost KHIs. Performance experiments 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 test method. Under typical pipeline conditions of pH (4–6), the performance of the maleic acid/alkyl acrylate copolymers (alkyl = iso-propyl, iso-butyl, n-butyl, tetrahydrofurfuryl, and cyclohexyl) was poor. However, good performance was observed at very high pH (13–14) due to the thermodynamic effect from added salts in the aqueous phase and the removal of CO2 from the gas phase. A methyl maleamide/n-butyl acrylate copolymer gave very poor performance, giving evidence that direct bonding of the hydrophilic amide and C4 hydrophobic groups is needed for good KHI performance. Reaction of the maleic anhydride (MA) units in MA/alkyl acrylate 1:1 copolymers with dibutylaminopropylamine or dibutylaminoethanol gave polymers with good KHI performance, with MA/tetrahydrofurfuryl methacrylate being the best. Oxidation of the pendant dibutylamino groups to amine oxide groups improved the performance further, better than poly(N-vinyl caprolactam).

A new investigation of polymaleamides as kinetic hydrate inhibitors – Improved performance and compatibility with high salinity brines

Kinetic hydrate inhibitors (KHIs) have been used for over 25 years to prevent gas hydrate formation in oil and gas production flowlines. The main component in KHI formulations is a water-soluble polymer and most of these polymers are amide-based. A few polymaleamides were investigated as KHIs in the 1990 s. Since then, our knowledge of the optimal structural features for KHI polymers has improved. Here we report a more detailed KHI study on this class of polymers, demonstrating significant KHI performance enhancement. KHI experiments were conducted under high pressure with natural gas mixture in steel rocking cells using the slow (1 °C/h) constant cooling test method. The best polymaleamides gave To (av.) values at around 6.1 °C (Ca. ΔT = 14.0 °C) at the concentration of 2500 ppm. In addition, the best polymaleamides were compatible with 15 wt% (150,000 ppm) brines at up to 95 °C.

Reliability and Performance of Vinyl Lactam-Based Kinetic Hydrate Inhibitor Polymers after Treatment under a Range of Conditions

Well-known kinetic hydrate inhibitors (KHIs) such as poly(N-vinylcaprolactam) (PVCap), poly(N-vinylpyrrolidone) (PVP), and 1:1 N-vinylcaprolactam:N-vinylpyrrolidone (VCap:VP) copolymer have been su...

High Cloud Point Polyvinylaminals as Non-Amide-Based Kinetic Gas Hydrate Inhibitors

In recent years, we have explored non-amide-based classes of kinetic hydrate inhibitor (KHI) polymers to determine if the same level of performance can be achieved as commercial KHI polymers, which...

Additives for Kinetic Hydrate Inhibitor Formulations to Avoid Polymer Fouling at High Injection Temperatures: Part 2 - Experimental Studies with Denaturants, Osmolytes, Ionic Liquids, and Surfactants

Injection of kinetic hydrate inhibitor (KHI) polymers can cause fouling problems if the polymer solution has a deposition temperature below the well head temperatures. In part 1 of this three-part series, we reviewed various classes of additives that can raise the cloud (Tcl) and/or deposition temperature (Tdp) of thermoresponsive KHI polymers. Here, we report here our first experimental studies using two well-known KHI polymers, poly(N-vinyl caprolactam) (PVCap) and poly(N-isopropylmethacrylamide) (PNIPMAM), both with Tcl values of about 30–40 °C in deionized water at typical field dosages of 0.1–1.0 wt %. Changes in Tcl and Tdp were investigated for the addition of denaturants, osmolytes, ionic liquids, and surfactants at varying concentrations. Promising additives that raised the Tdp value significantly were tested for their effect on the hydrate inhibition performance of the KHI polymer. In addition, we investigated if the Tcl and Tdp of various KHI polymer solutions were affected when placed under 80 bar pressure of a natural gas mixture due to the higher solubility of the gases in the aqueous phase.

Additives for Kinetic Hydrate Inhibitor Formulations To Avoid Polymer Fouling at High Injection Temperatures: Part 1. A Review of Possible Methods

The main ingredient in kinetic hydrate inhibitor (KHI) formulations is a water-soluble polymer with both hydrophobic and hydrophilic moieties. Many of these KHI polymers have low cloud point (Tcl) ...

Polyvinylsulfonamides as Kinetic Hydrate Inhibitors

Kinetic hydrate inhibitor (KHI) polymers have been used for over 25 years to prevent gas hydrate formation in oil and gas production flow lines. KHI polymers are water-soluble at hydrate formation ...

Anomalous KHI-Induced dissociation of gas hydrates inside the hydrate stability zone: Experimental observations & potential mechanisms

In the past decade, the low dosage hydrate inhibitors (LDHIs) - which include kinetic hydrate inhibitors (KHIs) and anti-agglomerants (AAs) - have seen increasing use for gas hydrate prevention in hydrocarbon production operations, offering significant CAPEX/OPEX advantages over traditional thermodynamic inhibitors (e.g. methanol, glycols). Typically dosed at < 2.5% in produced water, KHIs were historically considered primarily as hydrate nucleation inhibitors, although in recent years focus has shifted towards their powerful crystal growth inhibition properties. Beginning at low aqueous concentrations, KHI polymers induce a number of highly repeatable, well-defined, hydrate crystal growth inhibition (CGI) regions as a function of subcooling, varying from complete inhibition, through long induction times and reduced growth rates, to final failure/uninhibited growth. This behaviour can be used to robustly assess KHIs for field use, as we have previously demonstrated through development of the KHI CGI evaluation method, which is now used as standard by a number of laboratories. During CGI testing, it is not uncommon to observe anomalous (should be stable thermodynamically) hydrate dissociation in the presence of KHIs, although very little is understood regarding this phenomenon. In this work, we present the initial findings of experimental studies aimed at investigating this anomalous dissociation for different commercial base polymers. Results demonstrate that, in addition to inhibiting hydrate growth/nucleation, low dosages (e.g. 0.5% and 0.25%) of KHI polymers can induce partial or complete hydrate dissociation, with this process largely generic to different KHIs. However, some KHI polymers cause catastrophic hydrate growth after nucleation begins and these polymers show no ability to dissociate hydrates, so this hydrate dissociation ability is not universal to all KHI Polymers. The cause of this dissociation is unclear, although it is postulated to result from interactions between the KHI and inherent hydrate morphological and/or structural changes. In addition to improving confidence in KHI field use, findings potentially have novel applications with respect to hydrate plug remediation and gas production from naturally occurring hydrates in oceanic/permafrost sediments.

Evaluation of a Novel Water-Immiscible Kinetic Hydrate Inhibitor Formulation

The application of low dosage kinetic hydrate inhibitors (KHIs) for hydrate mitigation in hydrocarbon production operations can offer considerable practical benefits and cost savings. However, there are still concerns over KHI usage, particularly with respect to fouling problems in produced water handling/disposal. One possible solution to fouling is KHI polymer removal from produced waters by solvent extraction, with fatty alcohols showing particular promise for this purpose, these having a high affinity for common KHI polymers, but very limited miscibility with water. In this study, it is demonstrated that such solvents can also be used to create novel water-immiscible KHI formulations, with these offering potential for KHI recycling/reuse. The fatty alcohol 1-octanol has been successfully used as carrier solvent for PVCap to produce a KHI, which is immiscible with water, yet shows comparable hydrate inhibition performance to aqueous PVCap. Evaluation of this immiscible KHI using a crystal growth inhibi...

First Study of Poly(3-methylene-2-pyrrolidone) as a Kinetic Hydrate Inhibitor

Formation of gas hydrates is a problem in the petroleum industry where the gas hydrates can cause blockage of the flowlines. Kinetic hydrate inhibitors (KHIs) are water-soluble polymers, sometimes used in combination synergistically or with nonpolymeric synergists, that are used to prevent gas hydrate blockages. They have been used in the field successfully since 1995. In this paper, we present the first KHI results for the polymer, poly(3-methylene-2-pyrrolidone) (P(3M2P)), which is structurally similar to poly(N-vinylpyrrolidone) (PVP), one of the first KHIs to be discovered. 3M2P polymers with different molecular weights (5500 and 2500 g/mol) and at different concentrations (2500, 5000, and 7500 ppm) were investigated for their KHI performance on structure II hydrates in high-pressure rocking cells. We also investigated the synergistic effect of P(3M2P) with n-butyl glycol ether (BGE), a known synergist for some KHI polymers. At the lower concentrations, P(3M2P) gives a similar performance to PVP (Mw = 8000–9000 g/mol). However, PVP outperforms both samples of P(3M2P) at 7500 ppm, with and without BGE. We suggest that the reasons for the performance level of P(3M2P) are related to greater resonance stabilization of the amide group in P(3M2P) compared to PVP. Also, the pyrrolidone ring of the PVP repeat unit has a larger hydrophobic sequence of three methylene units compared to the two methylene units in the pyrrolidone ring of P(3M2P). This relates well to previous studies where larger hydrophobic groups are preferable in KHI polymers as long as they are water-soluble at hydrate-forming temperatures.

Designing Kinetic Hydrate Inhibitors—Eight Projects With Only Partial Success, But Some Lessons Learnt

In our quest to develop new and improved kinetic hydrate inhibitors (KHIs) for practical use in the oil and gas industry, we have carried out a number of projects that, in our hands, proved ultimately unsuccessful. However, as with most laboratory research projects, useful data has been obtained and some important lessons have been learned. These lessons can be helpful in several ways. First, to understand the scope and limitations of chemicals that could be used as KHIs. Second, to highlight mechanistic aspects of KHI theory. Finally, the work may help inspire others to develop related but more successful research projects. In this article we present the results of eight partially successful KHI research projects and explain why each of these projects was undertaken and the results obtained. Seven of the projects concern new classes of polymers, and the other project describes what we hoped was a new class of nonpolymeric synergists for KHI polymers, but instead gave the opposite effect. All new KHI prod...

Poly(alkyl ethylene phosphonate)s: A New Class of Non-amide Kinetic Hydrate Inhibitor Polymers

All commercial kinetic hydrate inhibitor (KHI) formulations are based on polymers with amide (or imide) functional groups. In our continuing work to explore non-amide-based KHI polymers, a series of poly(alkyl ethylene phosphonate)s (PPns) has been synthesized. These polymers were investigated for their performance as KHIs in high-pressure rocking cells using a structure-II-forming gas mixture and the slow constant cooling test method over 24 h. All of the PPns gave better KHI activity than tests with no additive. However, despite several of the polymers being designed to have low cloud points, a factor that is often useful for good KHI performance, none of the PPns gave lower onset temperatures than poly(N-vinylcaprolactam), a well-known commercial KHI with a low cloud point. A random PPn copolymer with eight ethyl and eight n-hexyl groups gave a biodegradation of about 31% using the marine OECD 306 test protocol.

Kinetic hydrate inhibitor removal from produced waters by solvent extraction

Kinetic hydrate inhibitors (KHIs) offer an attractive option for the prevention of gas hydrate problems in hydrocarbon production operations, and are seeing increasing use within the industry as an alternative to traditional inhibition methods. However, there are several challenges emerging in the handling/treatment and disposal of produced waters containing KHIs. KHIs typically contain polymers as the active component and these can precipitate as solid/semi-solid deposits at higher temperatures and/or in the presence of saline fluids, potentially causing fouling problems. This can occur during produced water handling, for example where KHI containing waters may mix with higher temperature/higher salinity waters prior to re-injection, fouling storage/pumping facilities. Furthermore, precipitation may occur in response to high temperatures experienced during re-injection into formations, where fouling can potentially result in reduced injection efficiency. In addition, there is increasing interest in reducing levels of thermodynamic inhibitor used for hydrate prevention – particularly in the case of MEG – by combining these with KHIs. In this instance, KHI drop-out could result in fouling of MEG regeneration units, interfering with production operations. Here we report the results of preliminary investigations into a technique for KHI removal from produced waters based on solvent extraction. The method uses small fractions of largely water immiscible solvents with a high affinity for KHI polymers. Contact between the solvent and aqueous KHI results in strong partitioning of the KHI polymer into the solvent. The solvent containing the polymer can then be separated by standard physical methods used to separate water and hydrocarbons (e.g. gravity settling, centrifugal separation, coalescing separation). Results show that it is possible to remove up to 100% (within detection limits) of some common KHI polymers (e.g. poly-n-vinylcaprolactam/PVCap), potentially providing a simple means to eliminate or mitigate fouling problems associated with KHI containing produced water handling/treatment.

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.