Theoretical and Experimental Investigation of Wax Deposition Mechanisms in Nigerian Waxy Gas Condensate Pipelines

Wax deposition in waxy gas condensate pipelines is a critical flow assurance challenge in certain Nigerian offshore and onshore fields, yet the fundamental mechanisms governing wax deposition kinetics under Nigerian fluid and thermal conditions remain insufficiently characterised at the theoretical level. This study conducts a combined theoretical and experimental investigation of wax deposition mechanisms in Nigerian waxy gas condensate systems, developing and validating an original wax deposition prediction model. The theoretical framework is developed from coupled mass and heat transfer equations governing wax crystallisation and diffusion deposition at the pipe wall, incorporating a novel wax crystal structure model specific to the high-wax-content Nigerian gas condensates with cloud points between 25 and 42 degrees Celsius. The experimental programme employs a purpose-built cold finger apparatus and a flow loop system at the University of Port Harcourt petroleum engineering laboratory, using gas condensate fluids from three producing fields in Imo and Rivers states. Wax deposition rates, crystal morphology, and gel strength are characterised under a systematic matrix of temperatures, shear rates, and condensate compositions. The study's theoretical contribution includes: an original wax diffusivity correlation derived from molecular weight distribution data specific to Nigerian paraffinic condensates, a crystal ageing kinetics model validated against experimental data, and a pipeline restart pressure surge model for waxy gel blockage scenarios. The validated model demonstrates prediction accuracy within 15 percent of experimental deposition rates across all test conditions. Recommendations include integration of the wax deposition model into national flow assurance design standards and its adoption by Nigerian field development engineers as a replacement for generic wax models poorly suited to local fluid characteristics. Keywords: wax deposition, gas condensate, flow assurance, Nigeria, deposition kinetics.