An Experimental Study on the Effects of Heat and Chemical Inhibitors on the Flow Behaviour of Waxy Crude Oils. The Effects of Heat and Chemical Inhibitors on the Rheological Properties of Waxy Crude Oils with regard to Pumping in Pipelines

Abstract

Waxy crude oils (1/3 of oil produced worldwide), pumping through pipelines considered risky operation due to the crude wax content (15-40 wt.%) and to the temperature at which wax supersaturates and precipitates, leading to the danger of pipe blockage, eventually resulting, in multimillion dollars loss in production and maintenance. This research undertaken to develop operational strategy of waxy crude pipelines, considering the crude and crude gel properties and flow conditions. The research problem was approached by characterizing the crude gel with and without additives using chromatography (GC), differential scanning calorimetry (DSC), cross polarised microscopy (CPM), controlled stress and oscillatory shear rheology (CSR and OSR), the principal parameters being the crude temperature and the rate at which the crude was cooled. GC and DSC were useful in establishing wax composition, content and wax appearance temperature (WAT). Control stress rheometer proved to be the most appropriate as it measured the reduction in apparent viscosity at full production (10-50 s-1 shear rate), near shutdown (1 s-1 ) and yielding when the oil was statically cooled. On this basis, it was established that the wax inhibitor was the most effective. CPM revealed that only the wax inhibitor changed the structure of the gel, disrupting its otherwise knitted crystal network. Dilution with the light crude oil merely reduced the wax content and the pour point depressant reduced the gelling temperature. OSR provided a check on CSR and confirmed the gelation temperature measured. CSR provided the yield stress measured, it also provided comprehensive data that can be used for theoretical modelling of this complex flow.