A consistent thermodynamic model for predicting combined wax-hydrate in petroleum reservoir fluids

Low oil prices and the competitive nature of the oil industry world-wide demand more cost-effective techniques in the development and operation of offshore reservoirs. Extended-reach gathering networks and transportation of unprocessed well streams by subsea pipelines are two attractive options that could have significant impact in the development of marginal oil/gas fields. These subsea pipelines are prone to wax and/or hydrate formation that can potentially block the pipelines and lead to serious safety and operational problems. Wax and hydrate formation are both examples of solid deposition. They are modelled conventionally and are studied independently. In this work we describe a wax model that has been developed based on regular solution theory. The wax model was successfully coupled with an existing hydrate model. The integrated wax-hydrate model is capable of predicting five phase equilibria (i.e., water, liquid hydrocarbon, vapor, wax, and hydrate) as well as predicting the effect of wax formation on the hydrate phase boundary and vice versa. The results show that a reliable wax-hydrate model can minimize the risks involved in the transportation of fluids prone to wax and hydrate formation. The model can be used as a powerful tool in the design and operation of subsea and arctic pipelines and production facilities.