Abstract
The formation of natural gas hydrates during processing and transport of natural has historically been one of the motivations for research on hydrates. In recent years, there has been much focus on the use of hydrate as a phase for compact transport of natural gas, as well as many other applications such as desalination of seawater and the use of hydrate phase in heat pumps. The huge amounts of energy in the form of hydrates distributed in various ways in sediments is a hot topic many places around the world. Common to all these situations of hydrates in nature or industry is that temperature and pressure are both defined. Mathematically, this does not balance the number of independent variables minus conservation of mass and minus equilibrium conditions. There is a need for thermodynamic models for hydrates that can be used for non-equilibrium systems and hydrate formation from different phase, as well as different routes for hydrate dissociation. In this work we first discuss a residual thermodynamic model scheme with the more commonly used reference method for pressure temperature stability limits. However, the residual thermodynamic method stretches far beyond that to other routes for hydrate formation, such as hydrate formation from dissolved hydrate formers. More important, the residual thermodynamic method can be utilized for many thermodynamic properties involved in real hydrate systems. Consistent free energies and enthalpies are only two of these properties. In non-equilibrium systems, a consistent thermodynamic reference system (ideal gas) makes it easier to evaluate most likely distribution of phases and compositions.
Highlights
The problems of hydrate formation in pipelines during transport of hydrocarbons and other hydrate forming components is as old as the modern oil industry itself
As we demonstrate in this study there is a lower limit of all hydrate formers and former in surrounding water in all co-existing phases are additional independent thermodynamic variables
The that natural sediments never can reach but reside in a dynamic stationary incoming fluxesbalance of hydrate formers from below andof thermodynamic equilibrium, butbalance reside between in a dynamic stationary between incoming fluxes dissociation through fracture systems bringing in water from above that dissociates hydrate should hydrate formers from below and dissociation through fracture systems bringing in water from motivate a transition over to the useshould of residual thermodynamics alsoover for hydrate will above that dissociates hydrate motivate a transition to the phases
Summary
The problems of hydrate formation in pipelines during transport of hydrocarbons and other hydrate forming components is as old as the modern oil industry itself. The need for calculations of hydrate formation conditions in order to design appropriate measures to counteract problems of pipeline blockings is a continuous effort. During the last three decades there has been a substantial increase in the interest of natural gas hydrates as an energy source, which requires calculation of phase transition conditions and phase transition kinetics. Energies 2020, 13, 4135 fluxes of methane to the oceans and potentially to air. All these dynamics processes may lead to geo mechanical instability and landslides
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