Development of and validation of small volume multi-tasking flow assurance tool

Wax and asphaltenes are well known to cause problems through adhesion and build-up on pipeline walls, restricting flow. Deployment of chemical inhibitors is commonly used in subsea pipelines. Measurement techniques for both asphaltenes and waxes commonly show widespread data scatter. Selection of inhibitor chemicals for both wax and asphaltenes are commonly based upon simple tests conducted on stabilised oil samples. This commonly leads to higher dose rates being used than actually required in the pipeline to successfully reduce or eliminate surface build-up.

We have developed a small volume testing facility for measuring wax and asphaltene phase equilibria and optimising inhibitor deployment. The developed device is based on Quartz Crystal Microbalance (QCM) technology. The QCM is locally cooled to create a temperature gradient between bulk fluid and the surface of the QCM, simulating wall cooling effect. Different temperature gradients could be simulated. The developed device needs 35 ml of fluid and can work at high pressure conditions, simulating effect of pressure and dissolved gas on wax phase behaviour and adhesion tendencies. For wax evaluation, the device can closely simulate a typical "Cold Finger" test with many extra benefits, including: small size of the sample, being non-destructive, real time deposition rate, using live samples (as well as dead/stabilised samples).

In this communication we present some of the results generated using QCM Technology including Wax Appearance Temperatures (WAT) and Wax Disappearance Temperatures (WDT), wax inhibitor screening and results on asphaltene onset determination and inhibitor assessment. Results using the first prototype comparing with "Cold Finger" wax inhibitor screening and showing the effects of temperature gradient and pressure on wax build up for a live oil are presented. The results show that the device and techique proposed in this communication can provide a robust, reliable method for evaluating solid formation and deposition risks using very small sample volumes.