Experiment and Modeling of Hydrate Equilibrium Line in Gas, Gas Condensate, Black Oil, and Drilling Completion Fluids

Conclusions

The new sets of results for the hydrate dissociation line of methane and Green Canyon gases are reported. For black oils, the effects of WOR and GOR on hydrate equilibrium lines are found to be significant. For example, the lowering of GOR from 564 scf/stb (Oil II) to 267 scf/stb (Oil III) affects significantly the hydrate temperature suppression. This magnitude depends on pressure and temperature. In black oil systems the heating rate of 1 °F/hr can be adequate to represent the hydrate equilibrium points within ±1–2 °F uncertainty.

An improved version of the gas hydrate dissociation model is developed. The model can predict the dissociation line of gases and gas condensates well within 1–2 °F uncertainty. The model can describe accurately the hydrate dissociation line of high GOR black Oil I and Oil II with and without the inhibitor NaCl + MeOH. For the lower GOR (< 300) Oil III and Oil IV, discrepancy between the model predictions and experimental data increases as the strength of the inhibitor NaCl + MeOH increases, especially at lower pressures (< 1000 Psia). This may be attributed to the solubility problem and competing effects of the limited amount of the hydrate forming gases to form hydrates and dissolve in the liquid solvent in attaining the equilibrium during the experiment. We note that Oil II and Oil III exhibit the same characteristic properties, but differ in their GOR appreciably. The model predictions have also been verified successfully with other numerous sets of hydrate equilibrium data for gas, gas condensate and completion fluids with mixed inhibitors, those results are not reported here. In general, the various comparisons of model predictions with existing experimental data show that our model can be applied to gas, gas condensate, drilling completion fluid and black oil systems reliably.