Application of population balance equation in modeling of asphaltene particle size distribution and characterization of aggregation mechanisms under miscible gas Injection.

Particle size distribution (PSD) is an important factor that determines how asphaltene instability can damage porous media during natural depletion and enhanced oil recovery processes. In this work, aggregate size distribution under natural depletion and miscible nitrogen injection processes are determined via image analysis techniques and the results are modelled by population balance equation. Unimodal distribution curves in natural depletion show the dominance of particle-particle aggregation mechanism and the clustering is detected only around crude oil bubble point pressure. It is also observed that miscible nitrogen injection considerably increases the number and size of asphaltene flocs and directs the agglomeration process towards cluster-cluster aggregation (i.e. bimodal distribution curves) which can severely damage porous media. Results of population balance modeling characterize dominant aggregation mechanisms providing one optimum collision factor for unimodal curves and two optimum collision factors for bimodal distributions which confirms the alteration of aggregation mechanism due to miscible gas injection. [ABSTRACT FROM AUTHOR]