Institute of Petroleum Engineering

Modelling



Empirical correlations and thermodynamic models are widely used in predicting hydrate stability conditions. Several software groups and research institutions have developed commercial and/or in-house predictive computer models with various capabilities and reliabilities. However, only a few of the above developers have in-house experimental capabilities of generating data for the development and validation of their predictive models.

Our integrated experimental and modelling research over the past 16 years has resulted in a multi-purpose computer model, Heriot-Watt Hydrate (HWHYD). Several comparative studies against commercial hydrate programs and independent experimental data have demonstrated the reliability of our in-house model. The capabilities of the model in simulating various production scenarios are superior to other existing commercial models. HWHYD capabilities include:

  • PVT (Pressure-Volume-Temperature) calculations covering systems both with and without gas hydrates. The library of the model contains a large number of components including conventional hydrate formers, heavy hydrate formers, water soluble hydrate formers, electrolytes and chemical inhibitors
  • In addition to predicting hydrate stability zone for various reservoir fluids, the thermodynamic model is capable of predicting the amount and composition of various phases (including gas hydrates) at any given P & T condition

In addition to the above, our more advanced in-house models are capable of:

  • Hydrate phase equilibria calculations in porous media. This option takes into account the effect of pore size and water saturation on hydrate stability zone calculations
  • Simulation of rate of hydrate formation in a batch reactor. A useful application which can be used to study the effect of kinetic/low dosage hydrate inhibitors on the rate of hydrate formation
  • Reactor design and volume optimisation for full scale continuous hydrate production. This can be used to study issues such as oil-gas separation by formation of hydrates, transportation of natural gas as hydrates, or application of hydrate formation in wastewater treatment
  • Simulation of dissociation of hydrates in pipelines. This model is particularly useful in formulation of best practices for hydrate plug removal in oil/gas wells and subsea transfer lines

Two versions of HWHYD are available; a commercial version with a user graphical interface, and a research version. The commercial version has been purchased by a number of major oil and service companies. The research version is used for conducting specialised modelling studies for various oil and gas companies.