Factors Governing Asphaltene Deposition under High Pressure and High Temperature Studied by Quartz Crystal Microbalance

Asphaltene deposition from recombined crude oils was studied using a quartz crystal microbalance (QCM) under high-pressure and high-temperature (HPHT) conditions. During depressurization, the deposition rate rises as pressure decreases until reaching the bubble point, after which it declines and becomes negative, indicating redissolution. Deposition is analyzed as a three-step process: destabilization, mass transfer, and attachment (surface reaction). The governing factors include gas-oil ratio (GOR), pressure, and depressurization rate, along with additional factors that depend on the ratio of mass transfer to reaction rate constants (km/kr). An expression was derived to calculate this ratio from measured deposition rate at different mixing rates: kmkr=a(∂ln⁡⁡m˙∂ln⁡Re)−1, where ṁ is the deposition rate, Re is the Reynolds number, and a is the exponent on Re in the mass transfer correlation. When kmkr≫1, as observed for oil B at high mixing rates, deposition is reaction-limited and additionally governed by the steric factor of asphaltene particles. When km/kr ≪ 1, as observed for oil B and oil C at low mixing rates, deposition is mass-transfer-limited and additionally governed by oil viscosity, Reynolds number, and asphaltene particle size. When kmkr∼1, no single step dominates, and multiple additional parameters exert influence. These findings underscore the importance of aligning the slowest step in laboratory testing with that in the field to achieve a reliable lab-to-field correlation. In this regard, the most critical test parameters are solution GOR, pressure, depressurization rate, and Reynolds number.