Wax appearance and prevention in two-phase flow using the multi-solid and drift-flux model

Wax precipitation may lead to obstruction of pipelines generating significant economic losses. Oil reservoirs, especially in the deepwater sea, are found in extreme conditions of pressure and, during the fluid flow inside the pipelines, the fluid temperature may decrease due to heat transfer to the surrounding (seawater) and phase change, tending to deposit solid particles on the pipeline walls. Within this context, it is important to develop a model that calculates the WAT (wax appearance temperature) of a fluid with known composition and then determine the point where the first paraffin crystal will appear inside a pipeline. The objective here is to provide a two-phase flow model coupled with paraffin precipitation model to calculate WAT inside the pipeline. We used the Drift-Flux Model to describe the two-phase flow in steady state and the Multi-Solid Theory to calculate the WAT. The results for a paraffinic mixture of four components show that the effect of the pressure can be considered negligible on WAT calculation for low pressure systems (< 10 MPa). Analyzing the effect of the fluid composition, the larger the number of light compounds in the mixture, the smaller will be the WAT, at constant pressure. For two different cases, it was determined the point inside the pipeline where the solid particles may deposit. We proposed an algorithm to find the minimum inlet temperature such that does not occur wax precipitation along the pipeline. The algorithm was successfully applied to a case study and may be useful for defining operational conditions to prevent solid blockage of pipelines.