Experimental and mechanism study on the synergistic influence of asphaltene and pressure on the flow and rheological characteristics of waxy oil

In underground reservoirs and offshore oilfields, the production and transportation of waxy oil inevitably involve pressure and asphaltene environment. However, the effect of asphaltene on the flow and rheological characteristics of waxy oil under pressure is rarely involved. In this study, asphaltene (Venezuela) was added to waxy oil according to different contents (0, 0.02 wt%, 0.05 wt%, 0.1 wt%, 0.2 wt%), nitrogen (N₂) was provided to form pressure environment (0, 1 MPa, 3 MPa, 5 MPa), and a series of rheological tests were carried out with pressure rheometer. Three main findings were made: 1) With the increase of pressure, the viscosity of waxy oils with the same asphaltene content gradually increases, and the maximum increase can reach about 125 times at 10 °C. Compared with the waxy oils with low asphaltene content, the viscosity of waxy oils with high asphaltene content is more significantly affected by pressure. 2) Both pressure and asphaltene have influence on the yield value of waxy oil. With the increase of pressure, the yield value of waxy oil with the same asphaltene content decreases at first and then increases. When the pressure is the same, the yield value increases at first and then decreases with the increase of asphaltene content. 3) When the pressure is gradually increased, the storage modulus of waxy oils increases gradually, regardless of whether it contains asphaltene or not. On the contrary, the variation of loss modulus is not only related to pressure, but also to the system temperature. This research is expected to provide help for the flow assurance of waxy oil containing asphaltenes in the pressure environment.