Method to Determine the Wax Solubility Curve in Crude Oil from Centrifugation and High Temperature Gas Chromatography Measurements

Abstract

Wax precipitation and deposition are major flow assurance problem in crude oil production and transportation. Knowledge of the amount of wax that precipitates from the crude oil at different temperatures, delineated by the solubility curve, is necessary for accurate predictions of wax deposition in subsea pipelines. The solubility curve is obtained from the wax precipitation curve, which is determined using centrifugation and high temperature gas chromatography (HTGC). However, previous studies have overestimated the amount of precipitated wax by assuming that all heavy alkanes or heavy n-alkanes exist solely in the solid phase. This work addresses this issue by conducting mass balances on the noncrystallized carbon numbers in the centrifuged cake and in the crude oil. A new equation was developed to obtain the solid fraction of the centrifuged cake and crude oil. The wax precipitation curve developed by this new method was compared with the curves determined using the previous methods and differential scanning calorimetry (DSC). The curve determined by this new method was consistent with the results obtained by DSC, while previous methods overpredicted the amount of precipitated wax.