Comparing asphaltenes: Deposit versus crude oil

• Deposit solubility fractionation reveals solubility distribution of deposit.
• Heptane extracted asphaltenes do not represent asphaltenes deposited during production.
• Deposit asphaltenes are less soluble and more aromatic than heptane extracted asphaltenes.

Changes in operating conditions such as pressure, temperature and composition of the oil can trigger asphaltene deposition during oil recovery operations. In the present work, an asphaltene deposit obtained during cleaning of a submersible pump was analyzed. The oilfield was under CO2 flooding as secondary EOR process. The deposit was separated into solubility fractions that were characterized in terms of composition and solubility properties. A comparison with heptane asphaltenes extracted from the crude oil that produced the deposit was carried out and the results indicated that these extracted asphaltenes do not represent the type of asphaltenes present in the solid. Asphaltenes present in the deposit are less soluble and more aromatic than those found in the heptane extracted asphaltenes coming from the original crude oil. Plausible explanations for this observation are discussed based on current knowledge.