Online monitoring of wax deposition in sub-sea pipelines

Abstract

This paper describes a new technology (heat pulse wax monitoring) to monitor wax deposition in sub-sea pipelines continuously. The equipment that has been tested in a lab rig consists of a heating element and a temperature sensor which are installed at a fixed point on the oil pipe. By applying a short external heat pulse to the oil pipe, a correlation between the measured transient thermal response and the wax thickness could be derived. If such a system could also be installed in a sub-sea pipeline, it would make continuous measuring of the wax build-up possible. This would in turn allow for a much more efficient use of wax control techniques, by e.g. sending a pig only when a certain thickness threshold has been passed. The equipment in this technology is located outside the pipeline, so that it becomes possible to retrofit it to an existing pipeline. To test the technology, a numerical model was derived to correlate the wax thickness with the thermal readings from the heat pulse wax monitoring. This model was validated using the results from a single-phase flow experimental campaign using a North Sea waxy gas condensate in the Porsgrunn wax deposition test rig. In this experimental campaign, wax deposition experiments were carried out with different flow rates and temperatures. The wax thickness predictions from the heat pulse wax monitoring compared favourably with conventional measurement techniques.