Analysis on the effect of sample handling on crude oil wax properties

This study investigates the impact of long-term sample handling, preservation, and thermal restoration on the wax properties of crude oils. In upstream developments, samples from the exploration phase are often stored for extended periods prior to laboratory analysis, raising concerns about the representativeness of the measured properties. Three high-wax crude oils from a Southeast Asian field, with wax appearance temperatures (WAT) above 40 °C and pour points exceeding ambient conditions, were evaluated in two testing campaigns conducted in 2018 and 2023. Standard industrial protocols were applied for storage and restoration, including heating the samples to 10 °C above WAT prior to analysis. Comparative testing using liquid composition analysis (LCA), differential scanning calorimetry (DSC), and ASTM D5853 pour point measurements showed significant property deviations after storage. Emphasis was given to ensure that the analysis is using the same testing methodology and conducted by the same team of technicians. The most degraded sample exhibited about 75% loss of light hydrocarbons (C1–C8), resulting in a WAT increase of about 10 °C and a shift in bulk API from 34.6 to 30.8, while heavy fractions remained largely unchanged. In contrast, pour point consistently decreased by approximately 3 °C during initial restoration, though the measurement returned to baseline values following extended heating at higher temperatures. These results indicate that wax properties are strongly influenced by compositional changes and thermal history. Light-end loss increases WAT, whereas insufficient thermal re-homogenization of waxy crude oil that is in a solid state at storage condition can depress measured pour point. The work provides quantitative evidence that these effects are governed by distinct mechanisms, highlighting the need for test-specific restoration protocols and early baseline characterization to ensure data reliability for flow assurance design.