Low Dosage Hydrate Inhibitors Research Articles

Biodegradable MAM-based amphiphilic block copolymers: Toward efficient and eco-friendly kinetic inhibitors for methane hydrate formation

The development of low dosage hydrate inhibitors holds significant implications for the oil and gas industry. Some commercially available inhibitors, such as Luvicap EG, are derived from the lactam-containing polymer PVCap, which exhibit limited biodegradability and possess low cloud point (30-40℃), thereby constraining their practical utility. The present study successfully synthesized a series of novel amphiphilic block copolymers based on methacrylamide (MAM) by introducing biodegradable hydrophobic esters (ε-caprolactone (CL), δ-valerolactone (VL), and glycolide (GA)) onto the main chain of poly (methyl acrylamide) (PMAM), serving as KHIs. The synthesized MAM-based polymers maintain water solubility within the range of 0–98 ℃ without thermal responsiveness, effectively preventing deposition issues associated with traditional KHIs. Additionally, all MAM-based polymers demonstrated good biodegradability. The dynamics experiments have shown that PMAM homopolymers did not possess KHI effect, while the MAM-based block copolymers, especially PMAM-b-PVL, exhibited excellent performance in inhibiting hydrate nucleation. At low concentrations, the KHI effect of PMAM-b-PVL was comparable to that of the commercial KHI Luvicap EG. The in-situ Raman spectroscopy experiment further revealed the inhibition mechanism of the amphiphilic polymers, which was achieved by forming effective arrangements at the gas–liquid interface and disrupting the water structure in the interfacial region, thereby impeding the formation of hydrate cages, especially large cages. The findings provided a promising and environmentally friendly solution for the management of hydrates in the oil and gas industry

The effect of PVP and PVA on hydrate formation kinetics of ethane and propane mixture in the presence of kaolin nanoparticles

AbstractThe blockage of gas transmission pipelines due to gas hydrates poses a significant challenge for the gas industry. Low‐dosage hydrate inhibitors (LDHI) are utilized to influence the kinetics of hydrate formation, including nucleation, growth, and/or agglomeration. In the current study, a series of batch, isochoric, and isothermal tests were carried out to investigate the impacts of two LDHIs, poly N‐vinylpyrrolidone (PVP) and polyvinyl alcohols (PVA). This study examined the influence of these inhibitors on nucleation and growth of ethane+propane mixture in the presence of kaolin nanoparticles. In laboratory studies and using pure constituents, the rate of hydrate formation is low to investigate the inhibitors effect. To enhance the rate of hydrate formation, kaolin nanoparticles were utilized as they serve as a suitable representative for solid minerals commonly found in pipelines. The gas phase's compositional change were measured using a gas chromatograph. The results revealed that the growth stage of mixed‐gas exhibited two distinct steps, attributed to the formation of two different structures known as structure II and structure I. During the first step, structure II was formed, and the cavities were occupied by both gas components. In the second stage, structure I was formed by ethane. The effect of temperature on the induction time (nucleation rate) and the growth rate during the second stage was lower than that at the first stage. The increase in PVA concentration resulted in an increase in the induction time and a decrease in the rate of growth during the first stage. The performance of PVA was found to be affected by temperature. Lower temperatures resulted in the formation of less foam, providing improved performance for PVA at −0.5°C. PVP had a stronger impact on induction time and both growth steps compared to PVA, indicating stronger inhibitory impact of PVP on nucleation of hydrates initiated by propane and the growth of both propane and ethane hydrates.

Development and evaluation of aloe vera dry extract quantum dots as novel hydrate inhibitor for the control of flow assurance problems in the oilfields

Application of quantum dots in the oil and gas field operations is an emerging area, especially in tracer application and as hydrate inhibitors. This study involves development and evaluation of a novel low-dosage hydrate inhibitor aloe vera dry extract quantum dots, prepared by hydrothermal method, to prevent the formation of clathrate hydrates. Experimental studies were performed for THF model hydrate system in crude oil-water emulsion to evaluate the effect of wax content on hydrate formation. Quantum dots were tested for varying concentrations from 0.1 wt% to 1.0 wt% and the best result was obtained at 1.0 wt% in the experimental solutions. The quantum dots have shown the ability of anti-agglomerants, which allowed the tiny hydrate particles formed to remain dispersed in the experimental solution for a longer duration of time and also increased the induction time with increasing concentration of quantum dots. The study also revealed that presence of wax delayed the induction time of hydrate formation, but once hydrate formation occurred, the wax particles acted as nucleation sites for the agglomeration of more hydrate particles.

Isolation and Performance Test of Green Low Dosage Hydrate Inhibitors from Local Materials for Improving Flow Assurance in Oil and Gas Industry

The formation of gas hydrates in oil and gas industry can be minimized or prevented by the use of inhibitors. This paper reports on hemicellulose and modified lignin as low dosage gas hydrate inhibitors (LDGHIs). LDGHIs were isolated from sugarcane bagasse (SCB), plant gum exudates (PGE) of Acacia trees, and coconut coir, and further characterized by Attenuated Total Reflectance - Fourier Transform Infrared (ATR-FTIR) spectrometer, porosimeter and thermogravimetric analyzer (TGA). The PGE and SCB yielded 77.75% and 12.38% of hemicellulose, respectively, while coconut coir yielded 35.59% of lignin which was modified to sodium lignosulfonate (SLS) to improve its solubility in water. The inhibition performance of the isolated hemicellulose and modified lignin on gas hydrate was evaluated in terms of percentages of water converted into gas hydrate. In the absence of inhibitors, a large percentage of water (75.20%) was converted to gas hydrates while in the presence of the hemicellulose, the minimum amount of water converted into gas hydrates was 43.37%. The inhibition ability of hemicellulose from PGE and SCB increased with an increase in concentration. The statistical test indicated no significant difference between the percentage of water that formed gas hydrates in the presence of hemicellulose from PGE and SCB (n =4, p = 0.06 at CI = 95%). On the other hand, SLS promoted gas hydrates growth. In the presence of SLS, all liquid in the reactor was converted to gas hydrates. Thus, SLS may be used as a promoter for gas hydrates in natural gas storage and carbon dioxide sequestration while hemicellulose from both PGE and SCB as low dosage hydrate inhibitors.

Effect of Divalent Cations and Other Ions on the Tetrahydrofuran Crystal Inhibition of Quaternary Ammonium Salts-Relevance to the Efficiency of Gas Hydrate Quaternary Anti-agglomerants.

Gas hydrate anti-agglomerants (AAs) are a class of low-dosage hydrate inhibitor that are used to prevent plugging of gas hydrates in oil and condensate upstream flow lines. Industrial AAs are mostly cationic surfactants which are "hydrate-philic", i.e., they are designed to interact with and modify gas hydrate crystal growth. Tetrahydrofuran (THF) hydrate crystal growth studies have been used for many years to determine useful functional groups to incorporate into AA surfactants. In particular, quaternary ammonium and phosphonium salts with optimized alkyl groups show good THF crystal growth inhibition, which is a key property for AAs. AAs are often screened and tested in model brines containing sodium chloride despite the produced water containing various divalent cations. Recent studies have shown that AAs performed better when tested in brines containing both sodium and calcium ions rather than just sodium ions. Here, we present THF hydrate crystal growth studies on quaternary ammonium and phosphonium salts and other related molecules including guanidinium salts and amine oxides. Tests were carried out with a variety of cations including sodium, calcium, magnesium, and lithium at identical pre-determined subcooling, in order to investigate the effect of the ion size and charge density on the crystal growth inhibition. We also investigate the effect of using the more polarizable iodide ions compared to chloride ions. Our results show that crystal growth inhibition in solutions with calcium ions is somewhat greater than that with sodium ions, in agreement with past studies on the effect of AA performance with mono- and divalent cations. However, the variation does not seem to be primarily related to the charge density and polarizing ability of the cations. This study therefore provides evidence that AAs should be tested in brines containing all the ions present in the produced water and not just sodium chloride brine.

Experimental investigation to elucidate the hydrate Anti-Agglomerating characteristics of 2-Butoxyethanol

To alleviate the severity of hydrate formation in subsea oil and gas pipelines, the injection of anti-agglomerants (AAs) is one of the promising approaches. In this work, we investigate the hydrate anti-agglomerating characteristics of 2-butoxyethanol, also called butyl glycol ether (BGE), which has been reported in the literature as an effective synergist for kinetic hydrate inhibitors (KHIs), and a solvent for low dosage hydrate inhibitors (LDHIs). In view of its hydrophobic and hydrophilic moieties, we evaluate the adsorption affinity of BGE for the oil–water interface employing the interfacial tensiometer (IFT) apparatus. Moreover, a micromechanical force (MMF) apparatus was used to probe the interfacial behavior of hydrate particles, wherein we measured the cohesive forces between cyclopentane hydrate particles in the presence of BGE at atmospheric pressure and 274.2 K. The kinetics of methane hydrate formation and resistance-to-flow were assessed while measuring the dynamic pressure–temperature data and motor torque signals alongside with visual observations, respectively, employing a high-pressure visual autoclave (HPVA). IFT results reveal the strong surface active properties of BGE with a substantial reduction in oil–water interfacial tension at ambient conditions. However, no considerable change in the cohesive forces between cyclopentane hydrate particles was observed through MMF measurements. In contrast, HPVA results reveal that the addition of BGE enhanced the kinetics of methane hydrate formation; however, the corresponding torque pattern/visual interpretations indicated an anti-agglomerating action of BGE. While synergistically combining the BGE with under-inhibited dosages of mono-ethylene glycol, we further demonstrated a significant improvement in the hydrate transportability, wherein this synergism led to a non-plugging scenario (flowable hydrate slurry). Our findings will offer new insights into the development of new anti-agglomerant chemistries.

Evaluation of the Xanthan Gum, Gum Acacia, and Their Graft Copolymers with Acrylamide as Low-Dosage Hydrate Inhibitors for Their Application in the Drilling of Gas Hydrate Reservoirs

Hydrate formation is a significant issue while drilling into deep-water reservoirs containing gas hydrates. They may form in the drilling fluid flowlines, wellbore annulus, and ram cavities of blowout preventers. The natural gums, i.e., xanthan gum (XG) and gum acacia (GA), and their two graft copolymers with acrylamide (AAm), i.e., XG-g-PAAm and GA-g-PAAm, have been synthesized and tested as low-dosage hydrate inhibitors using THF hydrate systems via temperature-augmented visual method. XG-g-PAAm and GA-g-PAAm have shown better inhibition efficiencies and higher induction times than XG and GA. All of these inhibitors are then tested as drilling fluid additives to the formulated water-based drilling fluid systems (WBDFs). The formulated WBDFs contained 0.4 w/v % of each carboxymethyl cellulose (CMC), polyanionic cellulose (PAC), and 5 w/v % of potassium chloride (KCl). The rheology of the formulated WBDFs has been tested at an ambient temperature (293 K) and low temperature (275 K). The rheological parameters of WBDFs obtained from the experiments are within permissible limits with an inhibitor concentration of 0.5 w/v %. The rheological data are then fitted to the Bingham–Plastic (B–P) model and Herschel–Bulkley (H–B) model. The coefficient of determination’s (R2) upper and lower limits for the B–P model is 0.9715–0.9969 for 0.5 w/v % GA- and 0.5 w/v % XG-g-PAAm-containing WBDF systems. Again, for the H–B model, the range for R2 is from 0.9891 to 0.9980 for 0.5 w/v % GA- and 0.5 w/v % XG-containing WBDFs. Hence, the R2 showed a better agreement with the H–B model than with the B–P model. These observations suggest that XG, GA, XG-g-PAAm, and GA-g-PAAm may be used as hydrate inhibitors in the formulated WBDFs while drilling into gas hydrate reservoirs.

Application of metal organic frameworks for the inhibition of CO2 hydrates in gas dominated pipelines

The flow assurance problem caused due to the hydrate blockage is a major challenge in gas dominated pipeline flow (natural gas pipelines and CO2 sequestration pipelines). To make the hydrate inhibition economical during the pipeline flow, the use of effective low dosage hydrate inhibitor is the most crucial factor. To prevent the CO2 hydrate formation and blockage in the gas dominated pipelines the use of metal organic frameworks (MOFs) UiO-66 and UiO-66-NH2 is presented in this research work. The UiO-66 and UiO-66-NH2 were synthesized using hydrothermal synthesis method and characterized using scanning electron microscopic (SEM) images, powder X-Ray diffraction (PXRD), Brunauer-Emmett-Teller (BET) analysis, Fourier transform infrared spectroscopy (FTIR) and Thermogravimetric analysis (TGA). The synthesized MOFs were tested for CO2 hydrate inhibition in sapphire rocking cell. Both the MOFs were tested at concentrations of 0.25% w/v and 0.5% w/v. The increase in concentration of UiO-66-NH2 showed enhanced CO2 hydrate inhibition efficiency. UiO-66-NH2 was found to be much more effective in CO2 hydrate inhibition in comparison to UiO-66 during the tests.

Towards Gas Hydrate-Free Pipelines: A Comprehensive Review of Gas Hydrate Inhibition Techniques

Gas hydrate blockage is a major issue that the production and transportation processes in the oil/gas industry faces. The formation of gas hydrates in pipelines results in significant financial losses and serious safety risks. To tackle the flow assurance issues caused by gas hydrate formation in the pipelines, some physical methods and chemical inhibitors are applied by the oil/gas industry. The physical techniques involve subjecting the gas hydrates to thermal heating and depressurization. The alternative method, on the other hand, relies on injecting chemical inhibitors into the pipelines, which affects gas hydrate formation. Chemical inhibitors are classified into high dosage hydrate inhibitors (thermodynamic hydrate inhibitors (THI)) and low dosage hydrate inhibitors (kinetic hydrate inhibitors (KHI) and anti-agglomerates (AAs)). Each chemical inhibitor affects the gas hydrate from a different perspective. The use of physical techniques (thermal heating and depressurization) to inhibit hydrate formation is studied briefly in this review paper. Furthermore, the application of various THIs (alcohols and electrolytes), KHIs (polymeric compounds), and dual function hydrate inhibitors (amino acids, ionic liquids, and nanoparticles) are discussed thoroughly in this study. This review paper aims to provide a complete and comprehensive outlook on the fundamental principles of gas hydrates, and the recent mitigation techniques used by the oil/gas industry to tackle the gas hydrate formation issue. It hopes to provide the chemical engineering platform with ultimate and effective techniques for gas hydrate inhibition.

Evaluation of L-ascorbic acid as a green low dosage hydrate inhibitor in water-based drilling fluid for the drilling of gas hydrate reservoirs

Hydrate plug formation in the drilling fluid flow line is a significant issue in the oil and gas industry. Green hydrate inhibitors have recently gained much interest in flow assurance problems as they are being used as alternatives for existing hydrate inhibitors. The present study described that L-ascorbic acid (LA), a natural organic compound, has been identified as a Low Dosage Hydrate Inhibitor and has exhibited better results than Polyvinylcaprolactum (PVCap) and Polyvinylpyrrolidone (PVP). The temperature-augmented visual method and a self-fabricated set-up have been used to determine the first hydrate crystal formation in the tetrahydrofuran (THF)-water hydrate system. LA has shown a better inhibition effect in terms of induction time (i.e., >1440 min) than PVCap (119.67–180.67 min) and PVP (85.33–240.67 min). Carboxymethyl cellulose (CMC), polyanionic cellulose (PAC), xanthan gum (XG), and potassium chloride (KCl) are mixed with water to make the water-based drilling fluids used in this study. The R2 values showed a good agreement with the Herschel-Bulkley Model (R2 ranges from 0.993 to 0.999 for 0.5 w/v% PVCap and 0.1 w/v% PVP-containing fluids) than Bingham Plastic Model (R2 ranges from 0.836 to 0.952 for 0.1 w/v% PVP and base fluids). The MPE values are less for Herschel-Bulkley Model (From 1.418 to 6.015 for 0.5 w/v% PVCap and 0.1 w/v% PVP) than for Bingham Plastic (From 9.985 to 29.718 for 1.0 w/v% PVP and 0.1 w/v% PVP). Cross Model is also used to determine the zero and infinite shear viscosities for the formulated fluid system, which showed the viscosities are in the permissible range. These observations suggest that L-ascorbic acid (LA) may be an effective hydrate inhibitor in drilling fluids.

Assessment of a Biocompatible Additive for Hydrate Formation Kinetics along with Morphological Observations and Model Predictions

Innovative gas hydrate-based applications and hydrate flow assurance problems of oil & gas pipelines have enabled new opportunities to develop and deploy biocompatible or green low-dosage hydrate promoters and inhibitors, respectively. In this context, we evaluate the performance of a biocompatible additive, lecithin (extracted from egg yolk), for the formation kinetics of binary cyclopentane (CP)-carbon dioxide (CO2) hydrates simulating to the structure-II hydrate of natural gas. A high-pressure visual autoclave is employed in this study to map the morphological observations with the gas hydrate kinetic data. Multiple experiments are performed to examine the inhibition or promotional effect of lecithin in saline (3.0 wt % NaCl) and non-saline water systems at low pressure of 1.0 MPa while utilizing the various CP content (1.5, 3.0, and 6.0 mol%) and 500 to 5000 ppm of lecithin. Moreover, we evaluate the effect of salinity and lecithin on the thermodynamic hydrate equilibrium conditions. The results imply that the presence of lecithin retards the hydrate formation kinetics. However, no shift in the equilibrium frontier is observed. Importantly, we propose a chemical potential based kinetic model by accounting the influence of additives, vapor-liquid interfacial area, temperature and pressure on gas hydrate formation. This model has closely interpreted the experimental data of hydrate former uptake during binary hydrate formation in the presence and absence of lecithin. Our findings highlight the potential of engaging lecithin for hydrate inhibition to mitigate the flow assurance issues and also offer comprehensive insights toward integrated hydrate-based carbon capture and seawater desalination approach.

Polysaccharides from Tamarindus indica L. as natural kinetic hydrates inhibitor at high subcooling environment

In an offshore system, hydrocarbon fluids are produced at deeper depths in the oceans, and extended pipelines delivering fluids over long distances are common. Subsequently, these practices increase the tendency of unprocessed water-containing hydrocarbon fluid to be exposed to lower temperatures and higher pressures conditions where hydrate formation is favourable. One of the solutions to resolve this problem is by introducing hydrate inhibitors preferably low dosage hydrate inhibitors (LDHIs). The more versatile LDHIs; Kinetic Hydrate Inhibitors (KHIs) could further be optimised in cost and its biodegradation properties. The current study used an ionic, neutral, hydrophilic, mucoadhesive and highly branched Tamarindus indica L. polysaccharide (TSP). TSP as a new natural kinetic hydrate inhibitor due to its high methoxyl content. In this study, the polysaccharides were extracted using water-based extraction method which resulted in 61.3% yield. The performance of TSP in delaying the clathrate hydrates formation was evaluated based on the induction time recorded from the thermogram generated by a high pressure micro-differential scanning calorimeter device (HP-μDSC) at pressure of 5 MPa with subcooling degree of 17.3 °C. Three TSP concentrations (0.10 wt%, 0.25 wt%, and 0.50 wt%) were tested to determine the optimal concentration used to increase the delay time at the prescribed conditions while comparing it to a condition when there is no addition of TSP. The outcomes shows that TSP is able to delay hydrates formation at high degree of subcooling. The TSP works well at low concentration at high degree of subcooling while remain relatively economical and biodegradable.

Study on the Formation Characteristics of CO2 Hydrate and the Rheological Properties of Slurry in a Flow System Containing Surfactants.

Adding low dosage hydrate inhibitors to the hydrate systems makes the generated hydrate particles more uniformly dispersed in the liquid phase, which can significantly reduce the hydrate accumulation and blockage in oil and gas pipelines. The effect of surfactant hydrophile–lipophilic balance (HLB) values on hydrate flow characteristics was studied with a flow loop. The experimental results showed that there was a critical HLB value. When the HLB value was 4.3–9.2, it had an inhibitory effect on the hydrate induction time, and when the HLB value was greater than 10.2, it had a promoting effect. The hydrate volume fraction increased gradually with the increase in the HLB value, while the slurry apparent viscosity decreased with the increase in the HLB value. It was also found that different types of surfactants all showed the effects of anti-agglomerant and dispersion, which can obviously improve the flow of the hydrate slurry. Finally, the analyzed results showed that the hydrate slurry exhibited shear-thinning behaviors that can be identified as a pseudoplastic fluid based on the Herschel–Bulkley rheological model, and the functional relationship between the rheological index and the solid phase hydrate volume fraction was obtained using the fitting method. This study can provide a reference for the preparation of high-efficiency hydrate anti-agglomerants.

Regeneration and Reclamation of Mono-Ethylene Glycol (MEG) Used as a Hydrate Inhibitor: A Review

The use of Mono-Ethylene Glycol (MEG) as a hydrate inhibitor in wet gas pipelines is increasingly becoming widespread, especially in deep-water long-tie back pipelines where the use of low dosage hydrate inhibitor (LDHI) is not practical. MEG is a commonly used thermodynamic hydrate inhibitor (THI), and it prevents hydrate formation by lowering hydrate formation temperature. One significant advantage of MEG over other THIs is that MEG can be regenerated and reused, which minimises the cost of chemicals as large volumes of THIs are usually required. Over the years, significant research advances have been made in MEG recovery and the MEG Recovery Unit (MRU) design. This paper presents a comprehensive review of the evolution of MEG regeneration systems over the years and introduces recent developments, particularly on energy conservation. The entire MEG recycle and regeneration process is reviewed as well as the various sections and their functions. The different MRU configuration are discussed and factors that affect the performance of the MRU as well as Corrosion and corrosion mitigation in the MRU. This review shows that there are a number of new improvements in the MRU application that are yet to be fully explored as well as some technical challenges that are yet to be fully understood.

Experimental Measurement of Multiple Hydrate Structure Formation in Binary and Ternary Natural Gas Analogue Systems by Isochoric Equilibrium Methods

Traditionally, it is commonly assumed that a single gas hydrate (or clathrate hydrate) structure/phase is formed in natural gas systems—e.g., “s-II natural gas (NG) hydrates” or “s-I methane hydrates”—based on that which is understood to be the most thermodynamically stable at incipient phase boundary conditions. This applies with respect to both studies of hydrates in natural sediments, and in the case of hydrocarbon production operations, including the testing of low-dosage hydrate inhibitors (LDHIs). Here, we present the results of experimental studies of simple propane (C₃), binary methane–propane (C₁–C₃), and ternary methane–ethane–propane (C₁–C₂–C₃) hydrate systems, aimed at investigating phase behavior at higher subcoolings where significant water conversions to clathrates—and associated gas fractionation—might be expected to result in the formation of more than one hydrate structure. Measurements were made by means of established, reliable, isochoric equilibrium step-heating/cooling approaches. In the single guest propane system, pressure–temperature (PT) conditions follow the gas hydrate phase boundary, in agreement with the univariant hydrate + gas + water (H + G + W) equilibrium. By contrast, binary and ternary mixes clearly show PT behavior consistent with the growth of at least two and four hydrate phases, respectively, with these forming sequentially on cooling, and dissociating in the corresponding reverse order upon heating. In-house hydrate model (HydraFLASH) predictions support experimental observations, pointing to processes being gas fractionation driven; the mixed C₃–C₁ or C₃–C₂–C₁ s-II type hydrates formed first close to the phase boundary preferentially incorporating the most strongly clathrate cage (5¹²6⁴) stabilizing propane, making the remaining gas leaner. Once C₃ is largely consumed, trends agree with less stable C₂–C₁ structures (s-II followed by s-I) then growing (where ethane is present), with this, like C₃ uptake, making remaining free gas increasingly of almost pure C₁. This ultimately drives systems toward the final simple, single guest C₁ s-I clathrate formation as the well-established univariant phase boundary for this structure is reached. As observed phase behavior arises because of gas fractionation, it can be expected to occur during hydrate formation in all mixed gas systems of relatively fixed composition (at constant volume or pressure). The findings highlight that care should be taken in the application of isochoric methods to multicomponent gas systems, given the potential for numerous (rather than just one) clear changes in heating curve slopes as different hydrate structures form/dissociate. In addition, results show that extending equilibrium steps well into the hydrate region can reveal important information on clathrate phase behavior with potentially significant implications for issues such as gas production from hydrates in sediments, hydrate technologies for gas capture/separation/storage in the energy industry, and flow assurance in hydrocarbon production operations.

A systematic molecular investigation on Sodium Dodecyl Benzene Sulphonate (SDBS) as a Low Dosage Hydrate Inhibitor (LDHI) and the role of Benzene Ring in the structure

Thermodynamic hydrate inhibitors (THIs) are water-loving additives that in an aqueous phase preferentially interact with water and inhibit hydrate nucleation at given temperature and pressure conditions. Hydrate inhibition is one of the flow assurance challenges in oil and gas facilities, primarily for the production and transmission pipelines. In this era of a shift towards offshore production of oil and gas that is usually accompanied by large water cuts in production pipelines, the use of THIs requires a huge onboard inventory (of these additives); further, associated higher recovery costs and environmental issues has resulted in the identification and use of low dosage hydrate inhibitors (LDHIs). Thus, as the name suggests they are used in lower concentrations and do not present any space/storage problem on the offshore platforms. However, LDHI works differently, it primarily inhibits the growth and agglomeration of hydrate crystals thus ensuring flow assurance for a given period of time. Hence, an effective LDHI, may or may not delay hydrate nucleation, however, it should certainly reduce the kinetics of hydrate growth and should act as an anti-agglomerant. This work comparatively investigates the effect of three such additives on methane gas hydrate formation kinetics at very low concentrations. Sodium Dodecyl Sulphonate (SDS) is a well-studied molecule for gas hydrate formation kinetics, while SDS is a good anti-agglomerant (and has been used as anti-agglomerant in multiple gas hydrate studies), it is also a well-known hydrate promoter. In this work, additives having some similar molecular fragments to that of SDS were tested for better gas hydrate inhibition insights at molecular level. Sodium Benzene Sulphonate (SBS), Sodium Dodecyl Benzene Sulphonate (SDBS) and SDS was screened for methane gas hydrate formation experiments. A comparative kinetic study with these additives at two different concentrations (0.05 M and 0.1 M) has been presented for methane gas hydrate formation at 5 MPa (at the beginning of the experiments) and 274.15 K in n-heptane with 50% water cut, in a stirred tank isothermal reactor. The presence of a benzene ring in the molecular structure of the additive along with varying lipophilic tail and hydrophilic head on the methane gas hydrate formation kinetics are thoroughly investigated.

Advancing Laboratory Characterization and Qualification of Additives for Hydrate Slurry Flow in Multiphase Systems

In the flowlines of oil/gas production systems, the formation of gas hydrates, icelike crystalline compounds of water and gas that form at low temperature and high pressure, can disrupt stable flow, often resulting in solid blockages that necessitate remediation and pose safety issues. Low dosage hydrate inhibitor antiagglomerants (LDHI-AAs) are chemical additives used to manage the hydrate slurry flow at relatively low dosage (∼1% of water content) by dispersing hydrates in the continuous liquid hydrocarbon phase. A reliable assessment of LDHI-AA performance is thus required for their optimal use under a given field condition. Rocking cells have been extensively used in the oil/gas industry for LDHI-AA qualifications as it is easy to build and allows full visualization of the cell interior. However, a solid rolling ball, which is put into the conventional rocking cell for mixing, brings significant disturbances to the flow and dispersion of the phases and, in particular, by breaking up the hydrates formed and pushing them to accumulate at the end of the cell, giving a very conservative (worst-case) evaluation of LDHI-AAs. There is a large gap between the testing conditions of rocking cells and the actual field conditions. The recently developed rock-flow cell can provide a much closer representation of the shear, phase dispersion and thus the flow regime in flowlines. Here, we demonstrate the capability of the rock-flow cell as a more robust testing tool for LDHI-AA qualification. The impact of the cooling mode, degree of subcooling, and salinity are well characterized in terms of hydrate aggregation, deposition, and bedding. The test results demonstrate the advantages of the rock-flow cell over the conventional rocking cell to characterize the hydrate slurry by visualization and quantification of the hydrate formation and accumulation. As such, the rock-flow cell can be used as an effective testing tool for LDHI-AA qualification, which can also be applied to many other phase precipitation problems encountered in flow assurance.

Understanding the inhibition performance of polyvinylcaprolactam and interactions with water molecules

The inhibition performance of a typical low-dosage hydrate inhibitor, polyvinylcaprolactam (PVCap), has been investigated by a combination method of density functional theory calculation and ab initio molecular dynamics simulation. The results show that PVCap can attract its neighboring planar water rings and destroy them, making the precursors of the cage-like structures disappear. Further, PVCap is likely to adsorb on the face of the water cage, attributing to both hydrophobic and hydrogen bonding interactions. The adsorption of PVCap can effectively inhibit the aggregation of water cages, and this phenomenon is more significant for 51262 cages than 512 cages.

Effect of dodecyl dimethyl benzyl ammonium chloride on CH4 hydrate growth and agglomeration in oil-water systems

Low dosage hydrate inhibitor (LDHI) is an effective choice to prevent hydrate formation and blockage in petroleum and natural gas processing industry. This study investigated the effect of dodecyl dimethyl benzyl ammonium chloride (DDBAC) on CH4 hydrate growth and agglomeration in oil-water systems. Hydrate formation kinetics and torque changes were determined with the isothermal-isochoric method. The kinetic experimental results revealed that 0.35 wt% DDBAC exerted a strong and stable inhibition effect on CH4 hydrate growth, represented by long induction time and low gas uptake amount. The chemical affinity modeling calculation results showed that DDBAC decreased normalized hydrate formation rate and increased the kinetic equilibrium time. The torque changes demonstrated that anti-agglomeration effect strengthened with the increase of DDBAC mass fraction. In addition, the mechanism of CH4 hydrate formation in studied system was proposed combining the experimental results, hydrate morphology and DDBAC’s properties. It showed that DDBAC could hinder gas dissolution in oil phase, separate hydrate particles from each other and make hydrate surface soft. These results are of fundamental value in developing LDHI and understanding the mechanism of hydrate formation, which are essential in preventing hydrate blockage and ensuring safety production of oil and gas.

Flow-Assurance Strategy Manages Subsea Asset Without Continuous MEG Injection

This article, written by JPT Technology Editor Judy Feder, contains highlights of paper SPE 195784, “A New Flow-Assurance Strategy for the Vega Asset: Managing Hydrate and Integrity Risks on a Long Multiphase Flowline of a Norwegian Subsea Asset,” by Stephan Hatscher, SPE, and Luis Ugueto, Wintershall Norge, prepared for the 2019 SPE Offshore Europe Conference and Exhibition, Aberdeen, 3-6 September. The paper has not been peer reviewed. The Vega field on the Norwegian Continental Shelf has been producing successfully using continuous monoethylene glycol (MEG) injection, topped with means of corrosion inhibition. A topside reclamation process allows reuse of MEG but limits the possibilities of producing saline water. The complete paper presents a discussion of a feasibility study of a new flow-assurance and -integrity philosophy to manage wells without continuous MEG injection. The paper describes options for hydrate and integrity management and the required modifications to both subsea and topside facilities to enable an operational philosophy change. Current Subsea Flow-Assurance Approaches Gas-hydrate formation in wet gas flowlines is considered one of the primary challenges seen in subsea assets. Its mitigation requires considerable capital expense and often significant operating expense (OPEX) over field life. Although the thermodynamic stability of the ice-like structures is well understood, the same is not the case for the kinetics of their formation or the dispersion in multiphase systems, which might be a crucial aspect in hydrate plug formation. Traditionally, the approach to hydrate mitigation has been to keep the system outside the hydrate-formation region by various means, including the following: Insulation of flowlines or direct heating possibilities Depressurization on shutdown Hydrate inhibition by thermodynamic or low-dosage hydrate inhibitors Subsea separation and drying of gas For long multiphase flowlines, options are limited. Insulation or direct heating often is uneconomical. Depressurization on shutdown requires significant storage space on a host facility for liquids and leads to massive volumes of flared gas. Subsea separation and gas drying are not yet fully mature, so use of hydrate inhibitors is common. Hydrate inhibitors can be classified as either thermodynamic or kinetic inhibitors. The latter are also called low-dosage hydrate inhibitors (LDHI) because of the lower concentration required. The main advantage of thermodynamic inhibitors is that they shift the hydrate curve to fully protect the system, whereas the kinetic inhibitors tend to wear off after time, leaving the systems un- or underprotected. However, their use often allows for infrastructure reduction and simplified production operations. The most typical thermodynamic inhibitors are based on salts (as from the formation water) or alcohols such as methanol, ethanol, or glycols. The advantage of the latter is that their separation from water is technically viable, so they can be used in a recycle, or closed-loop, system, which can only function well in systems free of salinity or with limited saline formation water ingress.