Measurement of Wax Appearance Temperature of an Offshore Live Crude Oil using Laboratory Light Transmission Method

Abstract

Abstract In subsea completions and transportation of crude oils where flowlines are on the ocean floor at less than about 5°C, knowledge of wax phase behavior of the crude is essential. Benchmark tests such as wax appearance temperature (WAT), pour point and paraffin content can be viable indicators of wax problems as the fluid may flow some considerable distance from the reservoir to the surface through cold seabed and tubing. Wax precipitation and wax related problems such as increased viscosity and pressure drops at temperatures below the cloud point must therefore be clearly identified and eliminated at the initial stages of engineering and facility design to optimize production and transportation of the crude. In this work, a mercury-free, fully visual PVT cell equipped with a laser light transmitted solid detection system, a floating piston and a magnetically coupled impeller mixer was used to investigate WAT of an offshore Niger Delta live oil. The tests were performed at the initial reservoir conditions and at stock tank conditions. Evidence of wax precipitation of the live oil and the STO were observed. We also observed that for this particular sample that was used for the investigation, the live oil WAT was reduced by about 4°C by solution gas. This shows that for a more realistic indication of wax problems for offshore fields and subsea transportation where the sea temperature could generally be lower than STO WAT and pour point, only the STO tests may not provide realistic estimates for making live oil flow assurance related decisions. In addition, other aspects such as the amount and type of wax precipitated need to be considered before making a final decision.