Shut-in and Restart of Waxy Crude Pipelines: Software Module Development

Waxy oil is commonly found on the Norwegian Continental Shelf and elsewhere. Production through sub-sea pipelines must at times be stopped, and these fluids will then tend to form a gel-like structure. It is thus essential to design and operate the pipeli ne such that restart is possible. It has been observed that when the inlet pressure is increased it can take days for the gel to start moving. No model can accurately predict this process, and it is recognized in the industry that this is a gap in their d esign tools. In order to address this, a major project with a budget of MNOK 20 is jointly initiated by the Ugelstad Laboratory at NTNU and IFE at Kjeller. They are internationally leading centers on properties of complex fluids and on multiphase pipelin e transport, respectively. Detailed rheological measurements will be done on gelled oil properties and on the removal of gelled oil from a pipeline. A model will be developed to encapsulate a physical understanding of the gel-breakage process into a simul ation tool. It will account for chemicals injected to reduce wax formation, and thus enable optimal use of these. This model will finally be condensed to a useful tool for engineers designing production pipelines. It will fit with the industry standard si mulation tool for transport of gas, oil and water in pipelines.