Recharacterizing evolving fluid and PVT properties of Weyburn oil–CO2 system

The IEA GHG Weyburn–Midale CO2 Monitoring and Storage Project was a large, multi-year effort involving different research teams, each investigating a key question in a complementary but usually independent manner. This paper discusses the measurement of Weyburn oil physical properties and reservoir oil–CO2 phase behaviour as a means of understanding how these have evolved in the decade since CO2 flooding was started in the Weyburn oilfield. It is well known that in a CO2 miscible/near-miscible flooding process, the injected CO2 is capable of extracting light and intermediate hydrocarbons from the reservoir oil. Therefore, the composition and properties of the reservoir oil are constantly changing over time. After over one decade of CO2 injection into the Weyburn oilfield, it would be expected that the reservoir oil has rather different properties from those studied prior to CO2 flooding. Therefore, it was necessary to resample these reservoir oils in 2010; re-measure their physical properties and phase behaviour under varying pressures and reservoir temperature; and supply the measured data to be used to refine the EOS model for simulation studies. In the experiments, comprehensive PVT and physical property data sets were measured and prepared for the Weyburn oil and oil–CO2 system from a currently producing well that was previously sampled for the same purpose. It was found that the newly sampled Weyburn crude oil exhibited compositional difference so that its physical properties with CO2 were also changed. The resulting data were used by other researchers to further tune EOS parameters; and the previously generated seven-component EOS model could be updated and improved.