Low Dosage Hydrate Inhibitors Research Articles

ISOMERS OF 3-CHLORO-N,N,N-TRIS(3-METHYLBUTYL)PROP-2-EN-1-AMMINIUM CHLORIDE AS COMPLEX OIL AND GAS FIELD REAGENTS WITH ANTIHYDRATE, ANTICORROSIVE AND BACTERICIDAL ACTION

One of the most promising classes of low-dosage hydrate inhibitors is anti-agglomerants, which are favorably characterized by high efficacy at very low working concentrations (0.1-0.5%). We have investigated the possibility of creating new anti-agglomerants with enhanced anticorrosive and bactericidal properties based on the quaternization of tris(3-methylbutyl)amine with (E)- and (Z)-1,3-dichloropropene isomers. It is well known that compounds with a 3-chloroprop-2-enyl fragment have a pronounced anticorrosive and bactericidal action. Thus, the presence in the quaternization products of isopentyl groups and 3-chloroprop-2-enyl fragments that are optimal for preventing agglomeration of the gas hydrates can contribute to the complex antihydrate, anticorrosive and bactericidal activity of these compounds. An attempt to conduct the alkylation of tris(3-methylbutyl)amine with (E)-1,3-dichloropropene in standard solvent – boiling ethanol for 3 days leads to a low yield of the target quaternary salt. Using chromatography-mass spectrometry, it was established that there are significant amounts of by-products in the reaction mixture, which are formed as a result of various nucleophilic substitutions and elimination reactions. Alkylation of tris(3-methylbutyl)amine in boiling acetonitrile proceeds faster and more selectively in 80% yield of (E)-3-chloro-N,N,N-tris(3-methylbutyl)prop-2-en-1-amminium chloride in 20 h. A quaternization with (Z)-1,3-dichlopropene under the same conditions gives an isomeric quaternary salt with a similar yield. The alkylation of tris(3-methylbutyl)amine with isomers of 1,3-dichloropropene proceeds without allyl rearrangement and with full retention of the configuration of the chlorovinyl fragment. The structure and purity of the obtained compounds was unambiguously confirmed by NMR spectroscopy data. Tests in rocking cells using tetrahydrofuran-water model systems (forming the structure sII similar to natural gas hydrates), gravimetric and microbiological methods showed high antihydrate, anticorrosive and bactericidal efficiency of the obtained compounds in concentrations of 0.5%.

Review on Application of Quaternary Ammonium Salts for Gas Hydrate Inhibition

Gas hydrate solids occurrence is considered as one of the serious challenges in flow assurance as it affects the hydrocarbon production significantly, especially in deep water gas fields. The most cost-effective method to inhibit the formation of hydrate in pipelines is by injecting a hydrate inhibitor agent. Continuous studies have led to a comprehensive understanding on the use of low dosage hydrate inhibitors such as ionic liquid and quaternary ammonium salts which are also known as dual function gas hydrate inhibitors. This paper covers the latest types of quaternary ammonium salts (2020–2016) and a summary of findings which are essential for future studies. Reviews on the effects of length of ionic liquids alkyl chain, average suppression temperatures, hydrate dissociation enthalpies, and electrical conductivity to the effectiveness of the quaternary ammonium salts as gas hydrate inhibitors are included.

Investigation on the Synergistic Effect of Tetra Butyl Phosphonium Bromide with Poly(N-isopropylacrylamide) Based Kinetic Hydrate Inhibitor

The problem of clathrate hydrate plugging in flow pipes has been the most important issue in the off-shore exploitation since hydrates were found in transport facilities. In recent years, low dosage hydrate inhibitors have attracted much interest among researchers in place of thermodynamic hydrate inhibitors such as methanol and mono ethylene glycol (MEG). Poly-vinyl caprolactam and poly-isopropylacrylamide (PNIPAM) are among the hydrate inhibitors that are typically used for polymers containing amide groups. Furthermore, various kinds of polymer inhibitors containing amide group including tetrabutylphosphonium bromide(TBPB), which is a quaternary salt, were synthesized and studied in a methane gas hydrate environment. In this experiment, the injection of 0.1 wt% inhibitor at 276 K and 5 MPa was followed by stirring the water to induce nucleation. From the result, when PNIPAM alone was used as a single KHI, PNIPAM exhibited worst performance among the KHIs tested in this study. But the mixing of TBPB with PNIPAM further extended the induction time and reduced the CH4 hydrate growth rate. The real-time in situ Raman system used to understand the inhibition principle was recorded during CH4 hydrate formation, as a result, PNIPAM showed that the large hydrate cage affected, while TBPB prevented the CH4 molecule from occupying the small cage. TBPB was excellent synergist in blends with PNIPAM for kinetic hydrate inhibition of structure I forming CH4 hydrate.

Toward a Robust, Universal Predictor of Gas Hydrate Equilibria by Means of a Deep Learning Regression.

Due to offshore reservoirs being developed in ever deeper and colder waters, gas hydrates are increasingly becoming a significant factor when considering the profitability of a reservoir due to flow disruptions, equipment, and safety hazards arising from the hydrate plug formation. Due to low-dosage hydrate inhibitors such as kinetic inhibitors competing with traditional thermodynamic inhibitors such as methanol, accurate information regarding the hydrate equilibrium conditions is required to determine the optimal hydrate control strategy. Existing thermodynamic models can prove inflexible regarding parameter adjustment and the incorporation of new data. Developing a multivariate regression model capable of generalizing hydrate equilibria over a wide range of conditions, with results competing with thermodynamic models is worthwhile. A multilayer perceptron neural network of three hidden layers has undergone supervised training means of a backpropagation to accurately predict uninhibited hydrate equilibrium pressure for a range of gas mixtures with nine input features, excluding hydrogen sulfide and electrolytes, from a dataset of 1209 equilibrium points, 670 of which are multicomponent gases, sampled in a rigorous data sampling campaign from existing experimental studies. Statistical significance of results has been emphasized, with models validated using 10-fold cross-validation and holdout validation, facilitating hyperparameter optimization without overfitting, while stratified holdout ensures testing a wide range of conditions. The developed model has proven to outperform two popular thermodynamic models. Various scoring metrics are used, with an average cross-validated R2 of 0.987 ± (0.003). An R2 of 0.993 and mean absolute percentage error of 5.56% are yielded for holdout validation. Auxiliary models are included to determine the multicomponent prediction capability and dependency on individual data sources. Multicomponent data prediction has proven successful; results prove that the model accurately generalizes hydrate equilibria and is well suited to predicting unseen data. Positive results are largely insensitive to exact model parameters, thus indicating a robust, replicable methodology.

An assessment of hydrates inhibition in deepwater production systems using low-dosage hydrate inhibitor and monoethylene glycol

In this study, a deepwater pipeline-riser system that experienced hydrates was modelled in MAXIMUS 6.20 (an integrated production modelling tool) to understand, predict and mitigate hydrates formation in typical deepwater system. Highlights of the results from this study suggest that the injection of low-dosage hydrate inhibitors (LDHIs) into the hydrate-forming structures within the multiphase flow stream disperses the hydrates particles in an irregular manner and subsequently decreases the nucleation rate of the hydrate and prevents the formation of hydrates. This study found that the cost of using monoethylene glycol was significantly higher than that of LDHI by over $500/day although low-dosage hydrate inhibitors have initial relatively high CAPEX. In the long run, its OPEX is relatively low, making it cost-effective for hydrate inhibition in deepwater scenarios.

Effect of polymer aggregation on the kinetics of hydrate formation

Previous studies have highlighted the importance of low-dosage hydrate inhibitors on the kinetic inhibition of gas hydrates. Here, we investigated the polymers poly(diallyldimethylammonium chloride) (PDADMAC) and poly(acrylic acid) (PAA) as well as their mixtures on the kinetics of hydrate formation. The results show that the polymer mixtures considerably improved the inhibition of hydrate formation. The best inhibition occurred for the mixtures with an excess of PAA2k containing aggregates of around 100 nm in size. The fraction of hydrates formed over time was strongly reduced in the presence of the mixtures, reaching values of accumulated gas consumption of 0.0831 mol for a molar charge ratio Z-/+ = 0.67 compared with 0.6025 mol for water experiments after 15 h. The Johnson–Mehl–Avrami–Kolmogorov (JMAK) phenomenological model was implemented to predict the fraction of transformed hydrate and determine the crystal growth dimensionality. The range of values for the Avrami exponent was 0–1.36, indicating diffusion-controlled one-dimensional growth for methane characterized by the thickening of particles with an appreciable initial volume.

Challenges with gas hydrate formation

Many multiphase flow lines are prone to hydrate formation unless prevention methods are put in place. Chemical management of hydrate formation is traditionally done with thermodynamic hydrate inhibitors but in the last 25 years low dosage hydrate inhibitors (LDHIs) have been developed which can offer economic, environmental and other benefits. LDHIs are divided into two main categories, kinetic inhibitors (KHIs) and anti-agglomerants (AAs), both of which are successfully being used in field applications. This paper briefly reviews the hydrate management tools available to the operator. Then the review focuses on LDHIs, their structure-performance relationships and the various classes that have been designed and tested. The environmental challenges of both AAs and KHIs are also discussed.

Benefits of Low-Dosage Hydrate Inhibitors

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 28905, “Advances in LHDIs and Applications,” by Y.D. Chin and A. Srivastava, Subsea Engineering Technologies, prepared for the 2018 Offshore Technology Conference, Houston, 30 April–3 May. The paper has not been peer reviewed. Copyright 2018 Offshore Technology Conference. Reproduced by permission. This paper summarizes historical advancements in low-dosage hydrate inhibitors (LDHIs) over the past 2 decades, discusses their advantages and limitations, and their selection criteria. Historically, hydrate risk has been managed by keeping fluids warm, removing water, or injecting thermodynamic hydrate inhibitors (THIs), commonly methanol (MeOH) or monoethylene glycol (MEG). THIs require high dosage rates; therefore, that technique can pose limitations to production systems in the form of supply, storage, and umbilical-injection constraints. Additionally, high dosages of MeOH can cause crude contamination for downstream refineries. LDHIs continue to offer significant efficiency and cost benefits over other techniques. Introduction THIs have long been used by the industry because of their ability to shift the hydrate-equilibrium curve toward higher pressures and lower temperatures by changing the activity of water molecules. MeOH and MEG have proved the most popular types of THI because of their low cost and widespread availability. Though THIs are low-cost, the volume requirement per barrel offsets the cost benefit. A group of chemicals developed later, LDHIs, differ from THIs because they do not shift the hydrate curve; rather, they interfere with the process of hydrate formation through different mechanisms. The dosage requirement of these inhibitors is much lower than that required for THIs. LDHIs include two categories, kinetic hydrate inhibitors (KHIs) and antiagglomerants (AAs). KHIs increase the induction time for hydrate formation by interfering with the nucleation process or the crystal-growth process. Special surfactants disperse hydrate particles as they form, reducing the tendency of hydrates to stick to the pipe’s inner surface, reducing the chance of plug formation. AAs modify the agglomeration of hydrate particles, decreasing hydrate-crystal size by affecting hydrate morphology. This leads to a hydrate slurry flow, which decreases the chance of pipeline blockage. Inhibition mechanisms of both KHIs and AAs are discussed in detail in the complete paper, as is the historical development of these LDHIs. LDHI Applications Performance Parameters. The two primary parameters for LDHI performance measurement include the following: Hold Time. This is defined as the time between when a rapidly cooled fluid is at a constant temperature below the hydrate-equilibrium temperature and when hydrates first appear. For KHIs, the hold time decreases steeply with the increase in subcooling. Dosage Rates. To establish actual dosage rates for a LDHI in a specific fluid, technical-feasibility testing would be required with the actual LDHI and fluid under actual pressure and temperature conditions. An approximate range of expected LDHI dosage rates can be given as examples as follows. Gas System. For a gas system operating with condensed water, the dosage-rate guideline is 5 gal LDHI/bbl of condensed water. Breakthrough of formation water with a saline content of at least 3 wt% would reduce the rate to between 0.5 and 1.0 gal LDHI/bbl of formation water, although it should be recognized that this would be a different LDHI from the one used with condensed water.

Locally Sourced, Ecofriendly Hydrate Inhibitor Effective in Simulated Offshore Environment

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 193439, “Gas-Hydrate Inhibition in a Simulated Offshore Environment Using a Local Inhibitor,” by E.V. Urunwo, SPE, S.S. Ikiensikimama, J.A. Ajienka, SPE, O. Akaranta, M.O. Onyekonwu, SPE, T.O. Odutola, SPE, and E.O. Okon, University of Port Harcourt, prepared for the 2018 Nigeria Annual International Conference and Exhibition, Lagos, 6–8 August. The paper has not been peer reviewed. Gas hydrates pose a serious flow-assurance problem in offshore environments where accessibility is restricted. The complete paper investigates gas-hydrate inhibition in a simulated offshore environment using a plant extract (PE) as a local inhibitor. The work aims to identify an effective biodegradable gas-hydrate inhibitor from locally sourced materials and ascertain its effectiveness compared with the conventional hydrate inhibitor monoethylene glycol (MEG). Experiments were conducted using a mini-flow loop, and involved mitigating hydrate formation using varying weight percentages of the inhibitor (1, 2, and 3 wt%) and evaluating their effect on hydrate inhibition in the mini-flow loop. Sensitivity charts for pressure, temperature, and time for both the PE and MEG were made. In 1 and 2 wt% of the PE, better inhibitory capacity than MEG was demonstrated, while 3 wt% of the PE and MEG had a close match. Because of its ecofriendly and biodegradable nature, the PE is therefore recommended for field trial. Introduction Kinetic hydrate inhibitors (KHIs) are water-soluble polymeric compounds that prevent or delay hydrate formation. Antiagglomerants (AAs) function as surfactants and prevent hydrates from sticking together and clumping. The hydrate still forms, but the crystals do not plug and can be transported through pipelines. Unlike thermodynamic hydrate inhibitors (THIs) such as methanol or glycols, low-dosage hydrate inhibitors (LDHIs) do not stop hydrate from forming completely because they do not cause a hydrate-curve shift. Once hydrate forms, it cannot be eliminated by LDHIs because the operating conditions cannot be changed (lowering pressures or raising temperatures); thus, a well is still at risk when LDHIs are used. THIs must still be available on site, especially when shutting in or starting a well. The local inhibitor is a water-soluble PE containing flavonoids, tannins, alkaloids, and saponins. Flavonoids act against inflammation and are anticoagulants. They are polyphenolic compounds found in vegetables, fruits, and beverages, acting as powerful oxidants that protect against reactive oxygen. Tannins are a heterogeneous group of high-molecular-weight polyphenolic compounds with the capacity to form reversible and irreversible complexes. They are also found in fruits, legumes, and grasses. Polyphenolics are a class of chemical compounds consisting of a hydroxyl group bonded directly to an aromatic hydrocarbon group. They are otherwise called polyhydroxylphenols and are phytochemicals. They are a structural class of mainly natural products. Condensed tannins are the most-abundant polyphenols and are found in virtually all families of plants. Alkaloids are natural products that contain heterocyclic nitrogen atoms and are basic in character. They are synthesized naturally by a large number of organisms including animals, plants, bacteria, and fungi. Saponins are a group of secondary metabolites found widely distributed in plant life. They form a stable foam in aqueous solutions such as soap. Chemically, saponins as a group include compounds that are glycosylated steroids, hypernoids, and steroid alkaloids. Saponins also prevent agglomeration and are surface-acting agents with bubbles and foams acting as barriers that provide good stability.

Study Evaluates Hydrate Antiagglomerants

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 28578, “Quantitative Ranking and Development of Hydrate Antiagglomerants,” by Shane A. Morrissy, Temiloluwa O. Kuteyi, Mike L. Johns, Eric F. May, SPE, and Zachary M. Aman, SPE, University of Western Australia, and Stuart F. McKay, SPE, Woodside Energy, prepared for the 2018 Offshore Technology Conference Asia, Kuala Lumpur, 20–23 March. The paper has not been peer reviewed. Copyright 2018 Offshore Technology Conference. Reproduced by permission. A common hydrate-management strategy involves the use of large volumes of thermodynamic inhibitors (THIs) to operate outside the hydrate-stability region. However, this strategy represents significant capital expenditure and operating costs. Low-dosage hydrate inhibitors (LDHIs), in the form of kinetic hydrate inhibitors (KHIs) and antiagglomerants (AAs), present an economical alternative to THIs. In this study, a quantitative micromechanical force (MMF) has been deployed to study the performance of seven industry AAs. The results illustrate that an effective AA is one that lowers the cohesive forces between hydrate particles. Introduction AAs prevent hydrate agglomeration of a steady-state hydrate slurry. Hydratephilic AAs are surfactants that adsorb to the hydrate/oil interface in preference to the water/oil interface. Current operating experience suggests that AAs may be unsuited to the high water cuts that are characteristic of late field life. A successful hydrate AA lowers the cohesive force or surface free energy of hydrate particles to prevent agglomeration. Rocking cells and high-pressure visual autoclaves provide a semiquantitative assessment of hydrate blockage. However, a knowledge gap exists with regard to whether current industry AAs actually lower hydrate interparticle cohesive and surface free energy. Techniques to deconvolute the mechanism of the action of AAs are required to better understand how AAs affect hydrate blockage. Experimental Procedure Micromechanical Hydrate Cohesive Force. A third-generation MMF apparatus was used to measure the cyclopentane hydrate interparticle cohesive force. The MMF uses cyclopentane to create Structure II cyclopentane hydrates, the same hydrate structure present in the field. The cohesive-force-measurement technique was adapted from previous re-search on hydrate cohesion and asphaltene cohesion. Interfacial Tensiometry. An optical interfacial tensiometer was used to measure the interfacial tension (IFT) between water and oil phases at ambient pressure and room temperature. A hooked needle with the AA prepared in paraffin oil was placed in a bulk phase of deionized water. The resolution of this apparatus is typically +- 1 mN/m and the threshold sensitivity is 1 mN/m. Typically, surfactant-free systems will rap-idly reach equilibrium within 1 minute of creating an oil droplet in water. Conversely, the presence of a surfactant may decrease the IFT as a function of time, asymptotically approaching a steady-state value. Because the AAs studied contain surfactant functionality, each IFT was measured for at least 20 minutes, after which point the IFT was not observed to change with time. Each data point represents an average of at least four independent trials.

Functionalized Nanoparticles for the Dispersion of Gas Hydrates in Slurry Flow.

Gas hydrates are crystals that can form in oil and gas production. Their agglomeration in flowlines may disrupt the normal production. One current strategy of hydrate management is to inject an anti-agglomerant, a type of low-dosage hydrate inhibitor that prevents hydrate agglomeration. Concerns in the use of these chemicals include their toxicity, cost, and environmental impacts. In this study, we exploited functionalized nanoparticles in place of anti-agglomerants to produce hydrate slurry, with the potential benefit of nanoparticles to be more environmentally friendly and conveniently recyclable. We coated 256 nm spherical silica nanoparticles with different hydrophobicity and evaluated their performance for the hydrate dispersion at atmospheric and high pressure. Nanoparticles with moderate hydrophobicity stabilized oil-in-water (O/W) or water-in-oil (W/O) emulsions. Direct visualization of the cyclopentane hydrate formation from the nanoparticle-stabilized emulsions revealed different morphologies of hydrate particles depending on whether the nanoparticles prevented agglomeration. We also measured the apparent viscosity of a hydrate–nanoparticle mixture using a high-pressure rheometer. Nanoparticles with moderate hydrophobicity during hydrate formation slowed the viscosification, reduced the maximum viscosity, increased the water conversion, and ultimately helped to maintain a low steady-state viscosity. Increasing nanoparticle or salt concentrations also improved the gas hydrate dispersion. Our study demonstrated the great potential of using nanoparticles in preventing agglomeration of gas hydrates under realistic pipeline flow conditions.

Formation and Dissociation Kinetics of Methane Hydrate in Aqueous Oilfield Polymer Solutions (Polyacrylamide, Xanthan Gum, and Guar Gum) and Their Performance Evaluation as Low-Dosage Kinetic Hydrate Inhibitors (LDHI)

Hydrate formation and deposition during drilling offshore oil and gas wells has been one of the major challenges faced by the oil and gas industry. The use of low-dosage hydrate inhibitor (LDHI), s...

Experimental Investigation of Methane Hydrate Induction Time in the Presence of Cassava Peel as a Hydrate Inhibitor

The oil and gas industry faces numerous problems, from the exploration to the production phase. One of the most common problems faced by the industry is the formation of gas hydrates in the pipeline during the deep-water operation. The advancement of kinetic hydrate inhibitors (KHIs) has been rapid. However, as the natural degradation of conventional KHIs, such as polyvinylpyrrolidone (PVP) and polyvinylcaprolactam (PVCap), is challenging, there is a need to develop environmental-friendly KHIs with enhanced biodegradability to improve possible environmental risks. Thus, green inhibitors have been developed as a new class of KHIs. Research for enhancement of green hydrate inhibitors, as an alternative for existing low dosage hydrate inhibitors (LDHIs), has increased. In this paper, the effect of induction time with presence of cassava peels on the formation of methane hydrate was studied and compared with commercialized inhibitor, PVP. The performance of cassava peels as a kinetic hydrate inhibitor was investigated using high pressure micro differential scanning calorimetry (µ-DSC). For the induction time measurement, linear cooling ramps at a constant cooling rate of 0.5 K/min were used under isobaric conditions. Aqueous solutions of 0.5 wt % and 1.0 wt % of cassava peels were prepared and the induction time of methane hydrate formation in these solutions was measured at pressure ranges from 4.0 to 10.0 MPa. One of the characteristics to be a good kinetic inhibitor is the presence of hydroxyl functional group in inhibitors, which assist to form hydrogen bonds with water molecules, thus preventing hydrates formation. Fourier transform infrared (FTIR) analysis confirms the presence of hydroxyl groups in cassava peels with wavenumber value of 3370.68 cm−1. Cassava peel solution is observed to delay the induction times at all pressure settings and it is better at 1.0 wt % concentration. However, at lower pressures of 4 and 6 MPa, the performance is less effective when compared to a commercial inhibitor, PVP. At high pressures of 8 and 10 MPa, it can be seen that the performance is as effective as PVP. This research paper shows that cassava peels have high potential to be developed as a gas hydrate green kinetic inhibitor that can be applied for industry usage in the future.

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.

Synergy Effect Study of Poly(N-isoacrylamide) with Tetra Butyl Phosphonium Bromide on Methane Hydrate Formation

Natural gas hydrate plugging is one of the costly and challenging problems for the oil and gas industry, especially for subsea fields. One way to prevent gas hydrate formation at low cost is the use of low-dosage hydrate inhibitors (LDHI). Poly(N-isopropylmethacrylamide) (PNIPAM) with amide group have previously been shown to be an outstanding low-dosage hydrate inhibitor (LDHI). PNIPAMs are usually polymerized via radical polymerization, which can allow control over the molecular weight. We have synthesized PNIPAMs using control radical polymerization giving a fairly high degree of polymerization control. Additionally various Kinetic Hydrate Inhibitors (KHIs) were tested as CH4 hydrate inhibitors with polymeric hydrate inhibitor, PNIPAM. Furthermore, to check the synergetic effects of tetra butyl phosphonium bromide (TBPB), PNIPAM and their mixture TBPB-PNIPAM were tested as KHIs for methane gas hydrate formation. In this paper we present results on the performance of various polymeric inhibitors in KHI tests on methane gas in stirred autoclaves and on structure I hydrate formation. When PNIPAM alone was used as a single KHI, PNIPAM exhibited worst performance among the KHIs tested in this study. However the mixing of TBPB with PNIPAM further extended the induction time and reduced the CH4 hydrate growth rate. TBPB was an excellent synergist in blends with PNIPAM for kinetic hydrate inhibition of structure I forming CH4 hydrate. In summary, the mixture TBPB-PNIPAM was proven that great synergist for prevent the CH4 hydrate and good potential in achieving the industrial application of Oil & Gas production technology and therefore was a significantly meaningful discovery in the field of energy production.

Inhibition of structure II hydrates formation by salt-tolerant N-vinyl lactam-based terpolymers

This work presents experimental results on the inhibition performance of low-dosage hydrate inhibitors (LDHIs). The studied LDHIs, namely terpolymers of N-vinylcaprolactam and alkylimidazolium bromide or benzyl ammonium chloride and hydroxyethyl methacrylate or acrylamide derivatives, were synthesized at the Mexican Petroleum Institute with the objective of producing high performance inhibitors with higher cloud points than that exhibited by the poly(N-vinylcaprolactam) homopolymer. Three experimental methods were used to evaluate the hydrate inhibition performance of the synthesized terpolymers: 1) the capacity to inhibit the formation of tetrahydrofuran (THF) hydrates (atmospheric pressure and −0.5 °C); 2) the capacity to inhibit the formation of natural gas hydrates under high pressure and low temperature conditions (∼6 MPa, ∼1 °C, a subcooling of 16 °C for the studied natural gas sample); and 3) the determination of the cloud point temperature of the terpolymers in aqueous systems with varying salinity (atmospheric pressure and temperatures ranging from 2 °C to 81 °C). The inhibition performance and the high solubility (in highly saline aqueous systems) of the synthesized terpolymers indicate that these compounds could be considered promising kinetic hydrate inhibitors or gas-well anti-agglomerants to prevent or delay the formation or agglomeration of clathrate hydrates during the production and transport of hydrocarbons.

Effects of Poly(N-vinylcaprolactam) Molecular Weight and Molecular Weight Distribution on Methane Hydrate Formation

Poly(N-vinylcaprolactam) (PVCap) has previously been shown to be an outstanding low-dosage hydrate inhibitor (LDHI). The inhibition performance of LDHI is known to be influenced by molecular weight (Mw) and molecular weight distribution. In this study, PVCaps were synthesized by two different methods. The first method, reversible addition–fragmentation chain transfer (RAFT) polymerization, was used to prepare PVCap with a narrow molecular weight distribution (about Mw/Mn 1.5). In a semi-batch stirrer reactor, hydrate inhibition performance of PVCap was evaluated. It was found that the inhibition performance was increased when the PVCap molecular weight decreased. PVCap with the narrower molecular weight distribution also showed the better inhibition performance.

Reliable and Repeatable Evaluation of Kinetic Hydrate Inhibitors Using a Method Based on Crystal Growth Inhibition

Low dosage hydrate inhibitors (LDHIs)—antiagglomerants (AAs) and kinetic hydrate inhibitors (KHIs)—are increasingly used as an alternative to the traditional thermodynamic hydrate inhibitors for controlling gas hydrate problems in the petroleum industry. As nucleation inhibitors, KHIs induce an extended induction time (ti) at particular subcoolings before nucleation of hydrate can proceed to growth. However, due to the stochastic nature of nucleation, gaining repeatable and transferrable induction time results can be very challenging and time-consuming. To overcome this problem, study on KHI crystal growth inhibition (CGI) has yielded a KHI evaluation technique which is considerably simpler than induction time measurements. Moreover, this study shows that KHIs create a number of well-defined hydrate CGI regions as a function of subcooling which are completely repeatable and transferrable between different setups. These regions range from complete inhibition (CIR), to slow growth region (SGR), and ultimate...

Competitive Interfacial Effects of Surfactant Chemicals on Clathrate Hydrate Particle Cohesion

In oilfield production conditions, many chemicals are present in the form of natural surfactants that occur in the oil phase as well as additives that are injected to control the properties of the liquid phases. These additives may include low-dosage hydrate inhibitors, such as kinetic hydrate inhibitors or anti-agglomerants, corrosion or scale inhibitors, dispersants, emulsifiers, etc. To achieve slurry flow in subsea oil flowlines, the agglomeration of hydrate particles must be minimized so that small, dispersed hydrate particles are transportable rather than forming larger aggregates that may plug the flowline. While many compounds that are present in flowlines are known to affect the cohesion force between hydrate particles, each chemical is often studied separately, where no other additives are present. This study focuses on classifying the possible interactions of different classes of chemicals from the cohesion force between hydrate particles. A micromechanical force apparatus was used to measure t...

Experimental investigations of clathrate hydrate inhibition in water based drilling fluid using green inhibitor

Formation of hydrate plugs in drilling fluid is a serious problem in oil and gas industries. Recently, interest in the development of green hydrate inhibitors increased which can be used as substitutes for available low dosage hydrate inhibitors (LDHIs). In this research paper the effect of porcine pancreatic lipase on the formation of tetrahydrofuran (THF) clathrate hydrate was studied by determining the time for nucleation of hydrate crystals (induction time). Pancreatic lipase inhibits the formation of clathrate hydrate and its growth by adsorbing to different hydrate crystal faces. The ability of pancreatic lipase to eliminate or extends the “memory effect” was also studied and compared with polyvinylpyrrolidone (PVP). Pancreatic lipase found to be a better inhibitor than PVP and also suppresses the “memory effect” more efficiently. The effect of pancreatic lipase on the rheology of drilling fluid was studied as rheological characteristics of drilling fluid are most crucial for safe drilling operations. It was found that drilling fluid performs satisfactorily in terms of rheology at different concentrations of pancreatic lipase. This research paper shows that pancreatic lipase can be effectively used in drilling fluid as a green hydrate inhibitor.