Investigation of Multiphase Flow Behaviour in Horizontal Gas-Condensate Pipelines Under Nigerian Operating Conditions

Multiphase flow in horizontal gas-condensate transmission pipelines presents complex hydrodynamic and thermodynamic challenges that directly affect flow assurance management and pipeline operating efficiency. This study investigates multiphase flow behaviour in horizontal gas-condensate pipelines operating under Nigerian climatic and fluid composition conditions, combining computational simulation with operational data analysis from pipelines in the western Niger Delta corridor. The research employs a combined computational fluid dynamics (CFD) and mechanistic flow modelling methodology, using OLGA transient multiphase flow simulation software calibrated against field pressure drop and liquid holdup measurements from three horizontal pipeline sections. The study systematically characterises flow regime transitions across the range of operational gas-to-condensate ratios, flow rates, and operating pressures encountered in Nigerian gas-condensate pipeline systems, generating flow regime maps specific to the studied fluid properties. A research gap addressed is the inadequacy of existing flow regime correlations, largely developed for North Sea and Gulf of Mexico conditions, in predicting liquid accumulation and terrain slugging in the low-gradient, high-ambient-temperature conditions typical of Nigerian onshore and nearshore pipeline environments. Findings demonstrate that terrain slugging onset occurs at significantly lower gas velocities in hot ambient conditions (greater than 35 degrees Celsius) than predicted by cold climate correlations, with average slug lengths exceeding topside separator design values by 20 to 35 percent. Operational guidance for slug management including minimum production rate thresholds and pigging frequency is derived from the validated simulation models. Recommendations include revision of pipeline slugging design criteria for Nigerian conditions and installation of slug catchers on identified high-risk pipeline segments. Keywords: multiphase flow, gas condensate, pipeline, slugging, OLGA simulation.