Thermodynamics of hydrate systems using a uniform reference state

Kvamme, Bjørn; Zhao, Jinzhou; Li, Qingping; Saeidi, Navid; Sun, Wantong; Zarifi, Mojdeh

doi:10.1002/apj.2706

Cited by 3 publications

(2 citation statements)

References 39 publications

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“…The stability of the formed hydrates is slightly different, and hydrates formed from water with ethanol added are slightly more stable than hydrates formed from water with the same mole fraction methanol, as can be seen from Figures b and b. Note that the methanol activity model for methane has been verified elsewhere. − …”

Section: Heterogeneous Hydrate Formation In Systems Containing Alcoholsmentioning

confidence: 63%

Small Alcohols as Hydrate Promoters

Kvamme

2021

Energy Fuels

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Many methods for the production of natural gas from hydrate reservoirs have been proposed during the latest 3 decades. Reducing pressure, thermal stimulation, or injection of thermodynamic hydrate inhibitors are three examples. A typical problem is, however, that different methods for producing hydrates are not evaluated thermodynamically prior to planning expensive experiments or even more expensive pilot tests. This can be due to the lack of a thermodynamic toolbox for the purpose. On a macroscopic level, there are two criteria that need to be met: the Gibbs free energy change has to be favorable and sufficient heat must be supplied in order to fulfill the first law of thermodynamics. Another challenge is the lack of focus on the limitations of the hydrate phase transition itself. The interface between the hydrate and liquid water is a kinetic bottleneck that requires efficient breaking of water hydrogen bonds. Reducing pressure does not address this problem. Injection of CO2, however, will lead to the formation of a new CO2 hydrate. This released heat from this hydrate formation is an efficient heat source for dissociating the in situ CH4 hydrate. Adding limited amounts of N2 increases the permeability for the injection gas. Addition of a surfactant increases the gas/water interface dynamics and promotes heterogeneous hydrate formation. In this work, we demonstrate a residual thermodynamic scheme that opens up for detailed thermodynamic analysis of different routes to hydrate formation and dissociation. It is demonstrated that addition of 20 mol % N2 to CO2 is thermodynamically feasible for generating a new hydrate in the pores. The available hydrate formation enthalpy when adding N2 is reduced as compared to pure CO2 but still considered as sufficient. Up to 3 mol % ethanol in the free pore water is also thermodynamically feasible. The addition of alcohol will not significantly disturb the ability to form a new hydrate from the injection gas. The released enthalpy from the formation of the new hydrate is also considered as sufficient compared to what is needed for dissociation of the in situ CH4 hydrate. Homogeneous hydrate formation from dissolved CH4 and/or CO2 is limited in amount and is not important. However, the hydrate stability limits related to the concentration of the hydrate former in the surrounding water are important. Mineral surfaces can act as hydrate promoters through direct adsorption, or adsorption in water, which is structured by the mineral surface charges. Examples from theoretical studies are discussed.

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Section: Heterogeneous Hydrate Formation In Systems Containing Alcoholsmentioning

confidence: 63%

Small Alcohols as Hydrate Promoters

Kvamme

2021

Energy Fuels

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“…Equation (7) enters into Equation (6). The free energy change of inclusion for methane in small and large cavity is given elsewhere [9,13,26,[44][45][46]. With Equation (5) in Equation ( 2) and solving Equation (2) equal to Equation (3) for the same chemical potential of water in liquid water as in the hydrate.…”

Section: Hydrate Phase Transition and Free Energy Changesmentioning

confidence: 99%

Small Alcohols as Surfactants and Hydrate Promotors

Kvamme

2021

Fluids

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Many methods to produce hydrate reservoirs have been proposed in the last three decades. Thermal stimulation and injection of thermodynamic hydrate inhibitors are just two examples of methods which have seen reduced attention due to their high cost. However, different methods for producing hydrates are not evaluated thermodynamically prior to planning expensive experiments or pilot tests. This can be due to lack of a thermodynamic toolbox for the purpose. Another challenge is the lack of focus on the limitations of the hydrate phase transition itself. The interface between hydrate and liquid water is a kinetic bottle neck. Reducing pressure does not address this problem. An injection of CO2 will lead to the formation of a new CO2 hydrate. This hydrate formation is an efficient heat source for dissociating hydrate since heating breaks the hydrogen bonds, directly addressing the problem of nano scale kinetic limitation. Adding limited amounts of N2 increases the permeability of the injection gas. The addition of surfactant increases gas/water interface dynamics and promotes heterogeneous hydrate formation. In this work we demonstrate a residual thermodynamic scheme that allows thermodynamic analysis of different routes for hydrate formation and dissociation. We demonstrate that 20 moles per N2 added to the CO2 is thermodynamically feasible for generating a new hydrate into the pores. When N2 is added, the available hydrate formation enthalpy is reduced as compared to pure CO2, but is still considered sufficient. Up to 3 mole percent ethanol in the free pore water is also thermodynamically feasible. The addition of alcohol will not greatly disturb the ability to form new hydrate from the injection gas. Homogeneous hydrate formation from dissolved CH4 and/or CO2 is limited in amount and not important. However, the hydrate stability limits related to concentration of hydrate former in surrounding water are important. Mineral surfaces can act as hydrate promotors through direct adsorption, or adsorption in water that is structured by mineral surface charges. These aspects will be quantified in a follow-up paper, along with kinetic modelling based on thermodynamic modelling in this work.

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Evaluating the impact of sodium chloride and iron carbonate ions on gas hydrate formation in Monoethylene Glycol‐enhanced aqueous solutions

Bloomfield,

Phan,

Mohammed

et al. 2024

Asia-Pacific J Chem Eng

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The management and prevention of hydrates are crucial for the gas industry. This study delves into the intricate challenges associated with gas hydrate formation, with a specific focus on investigating the impact of corrosion by‐products on prevention strategies. Employing a distinctive methodology, the sapphire pressure–volume temperature (PVT) cell was utilized. Experimental tests were conducted using sodium chloride (NaCl) concentrations of 1% and 3% to simulate brine solution levels at the wellhead, incorporating 3% filtrate and unfiltered iron carbonate (FeCO3) as corrosion products associated with the production process. The 1% and 3% salt concentrations were chosen to encompass a broad range of temperature depressions, reflecting common industry standards for simulating realistic environmental conditions. PVT cell test conditions ranged from 80 to 200 bar, with increments of 40 bar. The experiments investigate the effects of common pipeline salts on a monoethylene glycol (MEG)/water mixture in the presence of methane gas at typical industry high‐pressure conditions. The investigation uncovers that the introduction of salts to water, methane, and MEG solutions serves as a hydrate inhibitor, with inhibitory effects directly correlated to salt concentration. While generally hydrate growth inhibition is beneficial in natural gas pipelines, the findings indicate that elevated salt concentrations and lower pressure conditions contribute to the formation of larger hydrates, heightening the risk of surface adhesion and potentially introducing complications in piping equipment, despite the decreased temperature at which these hydrates form due to the inhibitory effects of the salts. In particular, the mixed condition of 3% NaCl and 3% FeCO3 (filtered) has the strongest effect. Examination of hydrate formation temperature and macroscopic observations suggests that the existence of substantial precipitates, as evidenced in the unfiltered FeCO3 sapphire cell experiment, may have the potential to enhance hydrate growth.

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Thermodynamics of hydrate systems using a uniform reference state

Cited by 3 publications

References 39 publications

Small Alcohols as Hydrate Promoters

Small Alcohols as Hydrate Promoters

Small Alcohols as Surfactants and Hydrate Promotors

Evaluating the impact of sodium chloride and iron carbonate ions on gas hydrate formation in Monoethylene Glycol‐enhanced aqueous solutions

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