Mechanical Degradation Kinetics of Polymeric DRAs

The addition of a small amount of flexible organic polymers in a turbulent flow can strongly decrease friction pressure drop, allowing thereby substantial increase in crude export pipeline capacity. This effect, known as "Drag Reduction", is widely implemented on various industrial sectors: petroleum, medicine, hydrodynamics, etc. Only a few tens of parts per million by weight of Drag Reducing Agents (DRA) are required, making these additives economically attractive. These long-chain polymers are known to be very sensitive to high shear and are for example completely destroyed through boosting pressure pumps in place throughout long export crude pipelines (> 300 km), requiring the installation of new DRA injection skids at the downstream of each pump station. However these long-chain polymers have been shown to be sensitive to mechanical degradation occurring during the transport within the pipeline, phenomenon which progressively reduces the overall DRA efficiency. An original experimental study, combining two experimental apparatus, a classical rheometer and a specially designed laboratory turbulent flow loop, was carried out to monitor such degradation phenomenon. Different commercial oil soluble DRAs have been tested on various fluids including crude oil and model kerosene, under a large range of experimental conditions in terms of geometrical configuration, temperature and flow rates. The experimental results highlight a clear link between degradation kinetics and flow dissipated energy and led to a patented law allowing the evaluation of DRA efficiency as a function of the dissipated energy, which is directly correlated to pipeline length. This new law is aimed at optimising polymer initial concentrations in order to achieve the desired DRA efficiency by covering the degradation which will occur during transport. Such model will allow better implementation of DRA usage in crude export pipes at the design development stage and not just using them for flow de-bottlenecking cases.