Hydrate Onset Time Research Articles

Thermodynamic evaluation of inhibitors for methane-hydrate formation

The present paper presents an experimental study on the thermodynamic effect of three amines including (3-Aminopropyl)triethoxysilane (APTES), (3-Aminopropyl)triethoxysilane (APTMS), and Triethylenetetramine (TETA) on methane hydrates. Hydrate-Liquid-Vapour Equilibrium (HLwVE) data for methane hydrate were evaluated in the presence of 7 wt% and 20 wt% APTES, APTMS, and TETA, and with pressure ranging from 2.0 to 9.0 MPa. The thermodynamic effect of these amines on methane-hydrate formation has been investigated via measuring the methane-hydrate dissociation temperature, in applying an isochoric pressure-search method. The results reveal that APTES, APTMS, and TETA effectively shift the hydrate equilibrium curve to higher-pressure and lower-temperature regions for the methane + amine + water system. All of these three show thermodynamic-inhibition effects similar to the lower-concentration case (7 wt%), but with increasing concentration to 20 wt% for the thermodynamic-inhibition effect in the order APTES > APTMS > TETA. The average hydrate-suppression temperature (ΔT), as a ‘signature’ of thermodynamic-inhibition effect on methane hydrates measured for 7 wt% APTES, APTMS and TETA was 1.5, 1.5, and 1.3 K, respectively. ΔT increased with increasing amine concentration; these values were 5, 4.3, and 3.2 for 20 wt% APTES, APTMS, and TETA, respectively. Hydrate-onset time was further delayed due to the synergistic inhibition effect of inhibitors. The results show that these amines have a kinetic effect on gas-hydrate formation, such as for methane-hydrate formation in presence of APTMS: here, the hydrate formed after several cycles with the help of the memory effect. Moreover, the inhibition impact of these amines was compared with conventional hydrate thermodynamics, and found to be in the range of some and similar to ethylene glycol at 5 wt%. Furthermore, the addition of 5 wt% APTMS to sea salt not only enhances the thermodynamic inhibition effect, but also inhibits kinetically the formation of methane hydrate. For modelling of methane-hydrate dissociation conditions, the solid-solution theory of van der Waals and Platteeuw was applied for the hydrate phase along with the Peng–Robinson equation of state for the gas phase. Taken together, this study elucidates a novel class of thermodynamic hydrate inhibitors, which can control methane-hydrate formation efficiently.

Experimental and modelling of the impact of quaternary ammonium salts/ionic liquid on the rheological and hydrate inhibition properties of xanthan gum water-based muds for drilling gas hydrate-bearing rocks

In this study, quaternary ammonium salts (QAS) and ionic liquid (IL) were used as additives in xanthan gum water-based muds formulations to investigate their rheological and hydrate inhibitive potentials in drilling gas hydrate sediment. The QAS/IL used were TMABr, TPrABr, TMACl, and EMIMCl. The mud rheological characterisation was performed at a controlled shear rate of 1 s−1 to 200 s−1 at -2 °C–40 °C. The hydrate test was conducted in a high-pressure reactor at 8 MPa and -2 °C. The hydrate nucleation onset time was predicted using the classical nucleation theory (CNT) model. The rheology and hydrate results confirmed the potential application of QAS/IL in drilling mud formulations for drilling hydrate sediments. The presence of QAS/IL in the base mud suitably reduced the mud viscosity and yield stress, which are desired properties for generating turbulent flow to enhance cuttings transport, especially in high angle wellbores. The rheological properties of water-based mud were found to be significantly controlled or affected by the cation, anion, and alkyl chain length type of QAS/IL. However, the anion effect is more dominant and exhibit a critical concentration depending on its respective ionic strength. Further FTIR analysis confirmed the presence of N–O stretching which supports the performance of TMA+ over EMIM+ to reduce the mud yield stress. In addition, the thermal degradation of the base mud was significantly reduced in the presence of QAS/IL. Amongst the studied additives, TMACl and TPrABr WBMs completely prevented hydrate plugs in the mud system. Furthermore, the CNT model accurately predicted the hydrate onset time with APE <2%. The QAS/IL in the WBM systems exhibited minimal to negligible disturbance (<0.5 K shift) on the methane hydrate phase boundary compared with commercial hydrate additives at 3 wt%. This study provides guidelines to design efficient QAS/IL WBMs for drilling gas hydrate rocks.

Kinetic Hydrate Inhibition Performance of Poly(vinyl caprolactam) Modified with Corrosion Inhibitor Groups

Multifunctional polymers were designed and synthesized that contain both a kinetic hydrate inhibitor and corrosion inhibitor groups. This was achieved by modifying a copolymer of vinyl caprolactam and acrylic acid (PVCap-co-AA) where the acid groups were converted to known corrosion inhibitor groups including imidazole (APIM) and quaternary ammonium (ATCH) moieties. Therefore, all of the resulting polymers had the same molecular weight, end groups, and overall composition which allowed for accurate determination of the performance of these inhibitors. Their performance as kinetic hydrate inhibitors was evaluated by determining the hydrate onset time, growth rate, and resistance to flow using a high pressure autoclave. The experimental results show that both PVCap-co-APIM and PVCap-co-ATCH were able to delay hydrate nucleation; however, PVCap-co-APIM was better than PVCap-co-ATCH. The performance of new KHICIs was evaluated and compared with that of a commercial KHI, Luvicap, with three different cooling rates: for high and medium cooling rates, Luvicap delayed hydrate nucleation for a longer time compared to the new KHICIs. At low cooling rate, one of the KHICIs (PVCap-co-APIM) showed better performance than Luvicap. PVCap-co-APIM also performed better than Luvicap and PVCap-co-ATCH in decreasing the hydrate growth rate. Hydrate growth rate and resistance to flow were also studied during the hydrate formation to investigate the effect of the inhibitors on the growth of hydrate particles in the liquid phase. PVCap-co-APIM successfully suppressed hydrate growth in the early stage of hydrate formation, whereas PVCap-co-ATCH resulted in fast growth of the hydrate phase. For all of the studied cooling rates, PVCap-co-APIM showed stable resistance to flow even with increasing hydrate fraction in the liquid phase; however, PVCap-co-ATCH showed a torque surge in the early stage of hydrate formation when a fast cooling rate was used, which suggests that the ATCH group has a negative effect on the hydrate inhibition performance. These results provide a proof-of-concept that the modified PVCap-co-APIM, or related structures, that contain both kinetic hydrate inhibitor and corrosion inhibitor groups can be used as multifunctional inhibitors for offshore oil and gas fields.

Performance of Poly(N-isopropylacrylamide)-Based Kinetic Hydrate Inhibitors for Nucleation and Growth of Natural Gas Hydrates

Hydrate prevention strategies for offshore flowlines are now moving toward hydrate risk management by delaying its nucleation and growth using water-soluble polymers, known as kinetic hydrate inhibitors (KHIs). This study investigates the natural gas hydrate inhibition performance of three poly(N-isopropylacrylamide) (PNIPAM)-based KHIs [poly(N-isopropylacrylamide-co-acrylic acid (PNIPAM-co-AA), poly(N-isopropylacrylamide-co-cyclopentylamine (PNIPAM-co-Cp), and poly(N-isopropylacrylamide-co-tert-butylamine (PNIPAM-co-C4t)] by determining the hydrate onset time, growth rate, and resistance to flow using a high-pressure autoclave. These data are compared to three control groups [water, Luvicap solution, and polyvinylpyrrolidone (PVP)] under various cooling rates (0.25, 0.033, and 0.017 K/min). The results show that the nucleation of hydrate crystals was delayed in the presence of the KHI candidates as assessed using the onset time at different cooling rates. The effect of the KHI candidate on the hydrate gr...

Hydrate risk management with aqueous ethylene glycol and electrolyte solutions in thermodynamically under-inhibition condition

This study investigates the hydrate equilibrium conditions as well as the formation characteristics of monoethylene glycol and NaCl solutions by varying the concentration of NaCl from 3.5 to 20.0wt% in an MEG solution. As predicted by the thermodynamic model, the hydrate equilibrium conditions were shifted toward lower-temperature and higher-pressure conditions. The equilibrium temperature depression data were interpolated linearly with the NaCl concentration in the MEG solution. The addition of NaCl affected the hydrate onset time and subcooling temperature only slightly, but their addition decreases the initial growth rate and hydrate volume fraction in the liquid phase. By increasing the NaCl concentration to 7.0wt% in a MEG 20wt% solution, the initial growth rate reduced to 0.2vol%/min from 2.3vol%/min of pure water, while the hydrate fraction was decreased to 18.7vol% from 78.9vol% of pure water; moreover, the torque change during the hydrate formation shows severe spikes for pure water with a maximum relative torque of 20 for the pure water. The addition of the 7.0wt% NaCl to the MEG 20wt% solution, however, only showed a negligible torque increase. The growth rate starts to decrease when the torque starts to rise for pure water, suggesting that the agglomeration of the hydrate particles may induce a mass-transfer limitation or slow down the particle growth. The presence of NaCl and MEG in the aqueous phase seems to minimize the interaction between the hydrate particles by surrounding the hydrate particle with the NaCl and MEG. These results proved that the NaCl plays a synergist role for the MEG in an under-inhibition condition by further limiting the hydrate fraction and minimizing the resistance-to-flow. This is the first work to present hydrate formation characteristics in the presence of both MEG and NaCl, and its insight will assist flow assurance engineers in the management of the risk of hydrate plug formation in offshore oil and gas fields.

Relationship between the interfacial tension and inhibition performance of hydrate inhibitors

In this study, we tried to establish the relationship between the kinetic inhibition performance of KHIs and their effects on interfacial properties, such as the interfacial tension between hydrate-forming gases and aqueous solutions. The hydrate onset time and gas/liquid interfacial tension for systems composed of the same natural gas and aqueous phases containing different kinetic hydrate inhibitors (KHIs) and KHI synergists were measured in parallel. Five amide class KHIs, PVP-E, PVP-A, PVP-BP developed by our group, as well as PVP and Inhibex 501 were tested. Four familiar alcohols, methanol, ethanol, glycol and triglycol, were used as synergists. All of the experimental results with different types or dosages of KHIs and synergists show that a lower interfacial tension corresponds to a longer onset time, i.e., a better kinetic inhibition performance. We therefore suggested a lowest gas/liquid interfacial tension rule for developing amide class KHIs or KHI synergists as well as for determining their suitable applied dosages. Additionally, triglycol was found to be a good synergist for PVP-BP, and its best applied dosage is 2.3wt% or so. Finally, we proposed new insights into the mechanisms of both the kinetic inhibition of KHIs and the synergistic effect of alcohols.

Performance of Polymer Hydrogels Incorporating Thermodynamic and Kinetic Hydrate Inhibitors

This study investigates the hydrate formation characteristics of hydrogel particles containing thermodynamic or kinetic hydrate inhibitors. Hydrate onset time, hydrate fraction in the liquid phase, and torque changes were determined from the experiments using a high pressure autoclave. To simulate the mixture of water and liquid hydrocarbon encountered in subsea pipelines, decane was added corresponding to an initial 60% water-cut. In the liquid phase a high hydrate fraction was observed in the pure water + decane mixture with a local maximum in torque. For the hydrogel decane mixture, a lower hydrate fraction was observed, and the torque remained stable during the hydrate formation. The addition of 0.5 wt % of a commercial kinetic hydrate inhibitor (Luvicap) to the aqueous phase (with no hydrogel) delayed the hydrate onset time, but several spikes in the torque were observed during the hydrate formation, which suggests that segregation and deposition of hydrate particles is occurring in the liquid phase....

In situ Raman and 13C NMR spectroscopic analysis of gas hydrates formed in confined water: application to natural gas capture

This study investigates the formation characteristics of gas hydrate from bulk water as well as dispersed water in silica gel and dry water particles when they are exposed to natural gas. The inclusion process of methane, ethane, and propane molecules in hydrate cages were observed with in situ Raman spectroscopy, and the resulting cage occupancies were estimated from 13C NMR spectra. A high-pressure autoclave was used to monitor the formation process to determine hydrate onset time, initial growth rate, and conversion ratio. The obtained data from Raman spectra and gas consumption profiles suggested that hydrate formed within less than 20 min when the temperature is sufficiently lower than the hydrate equilibrium condition at a given pressure. Methane molecules started to occupy the small cages of structure II, but about 6 min later ethane and propane were also included in hydrate cages. 13C NMR spectroscopy confirms that only 23% of large cages of structure II are occupied by methane molecules when hydrate formed from dispersed water in silica gel, which was much less than 68% from dry water. These results suggest that the dispersion of water in silica gel and dry water would enhance the formation process by increasing gas-to-water ratio, although the composition of hydrate phase may vary depending on the formation condition. However the formation of hydrate in silica gel and dry water still provide an effective option to capture the natural gas without using complex rotating machineries.

Effect of Hydrate Shell Formation on the Stability of Dry Water

This study investigates the effect of gas hydrate formation on the stability of dry water (DW) particles when they are exposed to high pressure methane at low temperatures. The DW particles are prepared by mixing water with hydrophobic silica nanoparticles at high speed to form a water-in-air inverse foam. A high pressure autoclave was used to determine the hydrate equilibrium conditions and formation characteristics including hydrate onset time, subcooling temperature, and initial growth rate. In comparison to bulk water, the equilibrium conditions for methane hydrate are shifted to higher temperatures and low pressures, suggesting that the silica nanoparticles promote the hydrate equilibrium conditions. The surface-to-volume ratio between the gas and the water encapsulated by the silica nanoparticles is increased in comparison to bulk water which enhances the kinetics of methane hydrate formation without the need for vigorous mixing. However, after multiple cycles of hydrate formation and dissociation, ...

토크 측정과 시차주사열량계를 이용한 수용성 고분자 화합물의 하이드레이트 저해 성능 평가

본 연구에서는 토크 측정과 고압 시차주사 열량계를 이용하여 pyrrolidone, caprolactam, acrylamide 계열 수용성 고분자들의 하이드레이트 저해 성능을 평가하였다. 실험 결과, 세 종류의 고분자가 모두 동역학적인 하이드레이트 생성억제제 효과를 나타내는 것으로 확인되었으며, 특히 0.5 wt% polyvinylcaprolactam (PVCap)의 경우 34.4분의 하이드레이트 유도 시간, 15.9 K의 subcooling 성능을 보이며 12.3 분, 6.0 K의 순수 물 시스템보다 월등한 저해 성능을 나타내었다. 0.5 wt% polyvinylpyrrolidone (PVP)의 경우 중간 정도의 저해 성능을 보였으며, polyacrylamide-co-acrylic acid partial sodium salt (PAM-co-AA)의 경우 각각 0.5 wt%와 5.0 wt%의 농도에서 미미한 하이드레이트 저해 성능을 보였다. 반면에 생성된 하이드레이트 입자의 성장속도와 생성 양에서는 PAM-co-AA가 PVCap과 더불어 가장 월등한 저해 효과를 나타내었다. 또 다른 주요 성능 평가 요소 중 하나인 토크 변화의 경우에는 PVCap이 평균 토크 6.4 N cm로 가장 좋은 성능을 보였으며, 0.5 wt%의 PAM-co-AA 시스템이 평균 7.2 N cm의 값으로 그 뒤를 이었다. 고압 시차주사 열량계를 이용한 수용성 고분자 물질의 저해 성능 평가 실험의 결과는 autoclave 실험의 결과와 유사하였다. PVCap을 첨가한 경우 하이드레이트가 생성되기까지의 유도시간이 가장 길어서 저해성능이 뛰어난 것을 확인하였다. In this work, hydrate inhibition performance of water-soluble polymers including pyrrolidone, caprolactam, acrylamide types were evaluated using torque measurement and high pressure differential scanning calorimeter (HP <TEX>${\mu}$</TEX>-DSC). The obtained experimental results suggest that the studied polymers represent the kinetic hydrate inhibition (KHI) performance. 0.5 wt% polyvinylcaprolactam (PVCap) solution shows the hydrate onset time of 34.4 min and subcooling temperature of 15.9 K, which is better KHI performance than that of pure water - hydrate onset time of 12.3 min and subcooling temperature of 6.0 K. 0.5 wt% polyvinylpyrrolidone (PVP) solution shows the hydrate onset time of 27.6 min and the subcooling temperature of 13.2 K while polyacrylamide-co-acrylic acid partial sodium salt (PAM-co-AA) solution shows less KHI performance than PVP solution at both 0.5 and 5.0 wt%. However, PAM-co-AA solution shows slow growth rate and low hydrate amount than PVCap. In addition to hydrate onset and growth condition, torque change with time was investigated as one of KHI evaluation methods. 0.5 wt% PVCap solution shows the lowest average torque of 6.4 N cm and 0.5 wt% PAM-co-AA solution shows the average torque of 7.2 N cm. For 0.5 wt% PVP solution, it increases 11.5 N cm and 5.0 wt% PAM-co-AA solution shows the maximum average torque of 13.4 N cm, which is similar to the average torque of pure water, 15.2 N cm. Judging from the experimental results obtained by both an autoclave and a HP <TEX>${\mu}$</TEX>-DSC, the PVCap solution shows the best performance among the KHIs in terms of delaying hydrate nucleation. From these results, it can be concluded that the torque change with time is useful to identify the flow ability of tested solution, and the further research on the inhibition of hydrate formation can be approached in various aspects using a HP <TEX>${\mu}$</TEX>-DSC.

Synergistic hydrate inhibition of monoethylene glycol with poly(vinylcaprolactam) in thermodynamically underinhibited system.

This study investigates the hydrate inhibition performance of monoethylene glycol (MEG) with poly(vinylcaprolactam) (PVCap) for retarding the hydrate onset as well as preventing the agglomeration of hydrate particles. A high-pressure autoclave was used to determine the hydrate onset time, subcooling temperature, hydrate fraction in the liquid phase, and torque changes during hydrate formation in pure water, 0.2 wt % PVCap solution, and 20 and 30 wt % MEG solutions. In comparison to water with no inhibitors, the addition of PVCap delays the hydrate onset time but cannot reduce the hydrate fraction, leading to a sharp increase in torque. The 20 and 30 wt % MEG solutions also delay the hydrate onset time slightly and reduce the hydrate fraction to 0.15. The addition of 0.2 wt % PVCap to the 20 wt % MEG solution, however, delays the hydrate onset time substantially, and the hydrate fraction was less than 0.19. The torque changes were negligible during the hydrate formation, suggesting the homogeneous dispersion of hydrate particles in the liquid phase. The well-dispersed hydrate particles do not agglomerate or deposit under stirring. Moreover, when 0.2 wt % PVCap was added to the 30 wt % MEG solution, no hydrate formation was observed for at least 24 h. These results suggest that mixing of MEG with a small amount of PVCap in underinhibited conditions will induce the synergistic inhibition of hydrate by delaying the hydrate onset time as well as preventing the agglomeration and deposition of hydrate particles. Decreasing the hydrate fraction in the liquid phase might be the reason for negligible torque changes during the hydrate formation in the 0.2 wt % PVCap and 20 wt % MEG solution. Simple structure II was confirmed by in situ Raman spectroscopy for the synergistic inhibition system, while coexisting structures I and II are observed in 0.2 wt % PVCap solution.

Preventing Gas Hydrate Agglomeration with Polymer Hydrogels

This study investigates the potential to use hydrogel particles for simultaneously inhibiting the formation of gas hydrates and preventing their agglomeration after they form. The particles were synthesized specifically for this application and swell to a controlled degree in water and remain discrete. A stirred autoclave was used to determine the hydrate onset time, subcooling temperature, initial growth rate, and torque changes during hydrate formation with the water absorbed in the hydrogel particles. The system also included a liquid decane phase which simulates a condensate. In comparison to water (with no particles) + decane mixture, the hydrate onset time was delayed and the subcooling temperature increases. In addition, both the initial growth rate and hydrate fraction were lower for polymer hydrogels. Stable torque is observed for polymer hydrogels while there are sharp increases in torque before the stirrer stops for water + decane mixture, suggesting that the hydrogel particles (and hence hydrate particles) are well-dispersed in the decane phase. Experimental observations show that the hydrates form as a surface shell on the hydrogel particles and grow inward. The hydrate shell-covered hydrogel particles do not agglomerate or deposit under stirring because the particles remain discrete due to the polymer network. In order to further investigate the ability of the hydrogel particles to prevent agglomeration, the stirring was stopped after confirming the formation of hydrate was complete. After 4 h, additional hydrate formation was negligible, and no serious torque increase or stirrer blockage was observed when the stirring was restarted. These results suggest that the synthesized polymer in this work has the potential to prevent hydrate agglomeration without using surfactants, which is a new concept.

Catastrophic Growth of Gas Hydrates in the Presence of Kinetic Hydrate Inhibitors

The effect of the concentration of kinetic hydrate inhibitors, polyvinylpyrrolidone (PVP), and polyvinylcaprolactam (PVCap) on the onset and growth of synthetic natural gas hydrates is investigated by measuring the hydrate onset time and gas consumption rate. Although the hydrate onset time is extended by increasing the concentration from 0.5 to 3.0 wt % for both PVP and PVCap, the growth rate of hydrates shows that the different tendency depends on the type of kinetic hydrate inhibitor and its concentration. For PVCap solution, the hydrate growth was slow for more than 1000 min after the onset at the concentration of 0.5 and 1.5 wt %. However, the growth rate becames almost 8 times faster at the concentration of 3.0 wt %, representing the catastrophic growth of hydrate just after the hydrate onset. (13)C NMR spectra of hydrates formed at 3.0 wt % of PVP and PVCap indicate the existence of both structures I and II. Cage occupancy of methane in large cages of structure II decreases significantly when compared to that for pure water. These results suggest that increasing the concentration of KHI up to 3.0 wt % may induce the earlier appearance of catastrophic hydrate growth and the existence of metastable structure I; thus, there needs to be an upper limit for using KHI to manage the formation of gas hydrates.

Thermodynamic and kinetic hydrate inhibition performance of aqueous ethylene glycol solutions for natural gas

Hydrate formation characteristics have been investigated with synthetic natural gas at different mono-ethylene glycol (MEG) concentrations by measuring hydrate onset time and subcooling temperature. MEG is well known thermodynamic hydrate inhibitor (THI), however there have been little works studying its effect on hydrate formation kinetics. In this paper, we report the hydrate onset is delayed and crystal growth is suppressed significantly at the MEG concentration of 30.0wt%. We also investigate the hydrate formation in the presence of both MEG and poly-vinyl pyrrolidone (PVP). Hydrate onset time is further delayed due to synergistic inhibition effect of two inhibitors. These results suggest that it might be feasible to incorporate the kinetic inhibition performance of MEG into current hydrate inhibition strategy to manage the hydrate risk.