Routes to hydrate formation from water dissolved in gas and impact of mineral surfaces

Abstract

Mineral surfaces adsorb water to extreme densities and corresponding low chemical potentials. This results in a dual effect in terms of hydrate. Water and slightly polar components adsorb directly on mineral surfaces and generate efficient conditions for hydrate nucleation. But due to the extremely low chemical potential of adsorbed water the hydrate nuclei formed towards mineral surfaces have to either detach from the vicinity of mineral surfaces, or be bridged by structured water in a dynamic attachment of hydrate cores some few nm outside mineral surfaces. During transport of gas (CH4, gas mixtures, CO2) the conventional water dew-point analysis will typically result in a substantially higher acceptable water concentration as compared to the concentration for adsorption of water from gas to rust surface. Direct formation of hydrate from water dissolved in gas is thermodynamically feasible, as discussed in open literature. In this work we demonstrate that it is also feasible in terms of mass transport. A new theory for enthalpy of hydrate dissociation has been extended to also direct hydrate formation from water dissolved in gas. The remaining question is whether direct hydrate formation from gas is also feasible in terms of transporting the hydrate formation heat away through a heat insulating medium. We propose further research strategies to enlighten this issue. Addition of glycols to critical points in processing of gas or transport is already in use by companies like for instance EQUINOR. There is, however, a need for more work on how efficient it is and if it can also be used for multiphase transport of hydrocarbons with significant water cut. Some research activities are in progress and briefly outlined here.

Keywords

• Hydrate
• Thermodynamics
• Risk
• Inhibitors