It is widely accepted that the use of live crude oil samples provides the most field representative fluids when investigating asphaltenes and paraffin wax problems in laboratory testing. However, this approach is limited by availability of live samples and the potential that samples collected during drilling will be insufficiently representative due to contamination. Rather than going to the significant expense and operational difficulty and risk of collecting and transporting live samples, it is common practice to use ‘dead’ crude oil, i.e., that which has been degassed to ambient pressure. This facilitates the use of larger quantities of test samples. However as many of the light hydrocarbon components have been lost, the ‘dead’ oil is fundamentally different and can display different characteristics to those of live fluids. Asphaltenes deposition occurs as the volume fraction of light ends increases due to depressurisation. Wax solubility is strongly dependent on light end composition, which is significantly different at elevated pressure compared with atmospheric pressure.
We have investigated the use of re-livened oil as an analogue for live oil in flow assurance testing for asphaltenes and waxes. Re-livened oil is composed of dead oil and one or more volatile ends so as to reproduce much of the behaviour of live oil. Where behaviour differs, it does so in a predictable manner that can be readily modelled using an equation of state simulator. Data are presented to compare the behaviour of live oil, dead oil and re-livened oil prepared by adding only gas, only liquid or a mixture of both. We discuss the benefits and drawbacks of each approach as applied to asphaltenes and wax testing with illustrative examples of the behaviour of each fluid using test data from pressurised flow rigs. The test data are also compared with behaviour predicted using the EoS simulator to illustrate that a calibrated model can be used to predict properties and behaviour under a wide range of conditions.
