Thixotropic Rheological Behavior of Maya Crude Oil

Heavy oil and bitumen exhibit non-Newtonian rheological behaviors at lower,temperatures. Thixotropy is one such behavior. Thixotropy affects the efficiency and length scale of mixing during blending operations and flow behaviors in pipes and pipelines following flow disruption, where it affects the pressure required to reinitiate flow. In the present work, thixotropic behaviors of Maya crude oil are explored systematically using a stress-controlled rheometer. Maya crude oil is shown to be a shear-thinning fluid below 313 K The thixotropic behaviors are identified and explored Using transient stress techniques (hysteresis loops, stepwise change in the shear rate, and startup experiments). The magnitude Of the thixotropy effect is larger at lower temperatures. Relationships are identified between rest times and other thixotropic parameters, such as hysteresis loop area and stress decay, in startup experiments. Stress growth, which occurs as a result of a step-down in the shear rate, is shown to correlate with the temperature. The results also provide a benchmark data set for validation of rheological models for heavy oil that are immerging in the literature.