Characterisation of the Rheological Properties and Flow Behaviour of Nigerian Waxy Crude Oils for Pipeline Transport Optimisation

Nigerian crude oils from inland and shallow offshore fields of the Niger Delta display high wax content and complex non-Newtonian rheological behaviour at sub-tropical temperatures, creating significant operational challenges for subsea and onshore pipeline transport, including wax deposition, gel formation, and restart pressure surges after shutdown. This study characterises the rheological properties of four waxy crude oils produced from Imo and Delta State fields using rotational and oscillatory rheometry over a temperature range of 10 to 60 degrees Celsius. Measurements include viscosity, yield stress, gel strength, thixotropic recovery index, pour point, wax appearance temperature, and viscoelastic moduli. The Herschel-Bulkley and modified Bingham plastic models were fitted to shear stress-shear rate data to determine rheological parameters. Pour points ranged from 24 to 36 degrees Celsius across the four crude oils, with yield stress values at 10 degrees Celsius ranging from 18 to 74 Pa. Oscillatory rheology revealed that Imo State crude exhibited gel network formation below 27 degrees Celsius, while the Delta State crudes showed liquid-like behaviour down to 22 degrees Celsius. Temperature dependence of viscosity followed an Arrhenius model with flow activation energies of 38 to 62 kJ/mol. Empirical correlations between wax content, pour point, and pipeline restart pressure were developed. The characterisation data directly support pipeline shutdown management procedures, heat tracing design, and pour point depressant selection for waxy crude transport in Nigerian oil fields. Keywords: waxy crude oil, rheology, pour point, pipeline transport, Niger Delta