An Original Mechanistic Model for Asphaltene Aggregate Growth Kinetics and Deposition Flux in Production Tubing Under Deepwater Temperature-Pressure Profiles, Offshore Nigeria

Asphaltene deposition kinetics in production tubing under the temperature-pressure trajectories characteristic of deepwater Nigerian production wells involve colloidal aggregation processes, surface adhesion mechanisms, and removal by shear that have not been mechanistically integrated into a predictive deposition flux model applicable to the specific fluid compositions and flow conditions of Nigerian deepwater crudes. This study develops an original mechanistic model for asphaltene aggregate growth kinetics and deposition flux in production tubing under deepwater Nigerian temperature-pressure conditions. The theoretical development draws on Population Balance Equation theory for colloidal aggregation, extending the Smoluchowski perikinetic aggregation kernel with a turbulent orthokinetic contribution derived from turbulent dissipation rate profiles computed from computational fluid dynamics simulations of representative deepwater tubing flow conditions. An original surface adhesion model is derived by coupling the DLVO colloidal stability framework with temperature-dependent interfacial tension measurements from six Nigerian deepwater crude samples. A shear removal function expressed in terms of wall shear stress and aggregate fractal dimension provides the deposition flux closure. The complete mechanistic model is implemented in Python and validated against measured deposition profiles from flow loop experiments conducted at simulated deepwater temperature-pressure conditions. Model predictions agree with measured deposition rates within 18 percent across operating conditions spanning 30 to 150 degrees Celsius and 1,000 to 8,000 psia. Keywords: asphaltene deposition kinetics, mechanistic model, population balance equation, deepwater Nigeria, production tubing.