The Groups’ longest running Joint Industry Project (JIP) addresses mainly thermodynamic issues associated with gas hydrates. In previous phases of this JIP, gas hydrate phase equilibria for various fluid systems (i.e., single, double and multi-component systems; synthetic and real gas, condensate and oil systems) have been studied, resulting in the generation of a large quantity of novel experimental data on hydrate dissociation conditions and the amount and composition of various phases under equilibrium conditions.
The investigation has covered the inhibition characteristics of various alcohols, salts, and combinations of salts and alcohols. A new technique for the optimisation of Kihara potential parameters was developed, with the resulting predictions validated against in-house and literature experimental data. In further phases of the project, the hydrate inhibition characteristics of various salts and organic inhibitors used in drilling and completion fluids were investigated, including salt solubility and salting-out problems. Again, large quantities of new experimental data were generated, and further improvements were made in thermodynamic modelling, with salts being treated as pseudo-components in the Equation of State, enabling salt precipitation prediction. An integrated wax-hydrate model was also developed.
Accompanying studies of wax experimental data and modelling approaches revealed a widespread dependence on Wax Appearance Temperature (WAT) data, which do not necessarily represent equilibrium conditions. To combat this problem, in-house step-heating techniques were extended to wax measurements using Quartz Crystal Microbalance (QCM) technology, and large quantities of experimental data on equilibrium Wax Disappearance Temperatures (WDT) were generated for various real and synthetic systems. A new thermodynamic approach for wax modelling was also developed, with promising results. The current phase of the project, which began in December 2005, covers various topics, including:
- Gas hydrates in low water content gases
- Transportability of water/oil mixtures and natural hydrate inhibition
- Hydrate equilibrium measurements for multi-component systems, including oil systems at very high pressure conditions (up to 2000 bar)
- Inhibitor distribution in water and hydrocarbon phases
- Wax equilibria and wax inhibitors
- Gas hydrates in water-flooded oil reservoirs
- Hydrates and associated phase equilibria database