Low-pressure modeling of wax formation in crude oils

Organic deposition in the reservoir and pipelines is responsible for huge losses in profit in petroleum exploration. Among them, wax deposition is of particular concern in offshore and cold climate operation since they are temperature driven. A thermodynamic model able to anticipate the formation of wax in the oil from the knowledge of its properties would be a very valuable help for the design of transport facilities and the operation of reservoirs of potentially problematic oils. A new thermodynamic approach is proposed for the description of wax formation in crude oils at low pressures. This approach is based on the description of the solid-liquid equilibrium of the n-alkanes present in the fluid. It assumes an ideal liquid phase, allowing for the use of any characterization of the fluid, and describes the solid-phase nonideality using a predictive local composition model. The proposed model, unlike previous published models, is purely predictive since it uses only pure compound properties and the fluid composition to describe the wax formation. On the basis of the knowledge of the detailed composition of about 30 crudes from different origins, correlations are proposed to estimate the n-alkane content and distribution for waxy crudes. Using the proposed approach it was possible with very limited information on the composition to produce an excellent description of the experimental data available in the literature for different crudes.