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In the present study, the displacement of waxy crude oils is numerically/theoretically investigated in the water-flooding operation. The oil was assumed to obey the Houska model-a robust thixotropic fluid model which is often realized to well describe the rheology of waxy oils in different parts of the world. Based on the concept of effective viscosity, a modified version of the Darcy's law was developed for this particular fluid model in order to describe its flow through a homogenous porous medium. Use was made of numerical and theoretical methods to study the displacement of Houska fluid by water in two benchmark problems: (i) the Buckley-Leverett problem, and (ii) the five-spot problem. It was found that the yield stress of the Houska fluid being variable (i.e., shear-and time-dependent) has a retarding effect on the water breakthrough phenomenon. The breakdown-to-rebuild ratio in the Houska model was shown to play a key role in the water breakthrough phenomenon provided that it is very large. At this extreme, however, the effect was attributed mostly to the shear-thinning behavior of the Houska fluid rather than its thixotropic behavior. In fact, at sufficiently low breakdown-to-rebuild ratios (i.e., when fluid's thixotropy becomes progressively more important) it had no significant effect on the water breakthrough phenomenon. Therefore, it is concluded that in competition with shear-thinning, the thixotropic behavior of Houska fluid plays a secondary role, if any, in the water-flooding operation.

In this paper the unsteady helical flow of Giesekus fluid between two concentric cylinders is investigated numerically. The flow is impressed by inner cylinder's rotation and the outer cylinder's sliding or oscillating movement along its axial direction. The effects of Weissenberg number, the mobility parameter of Giesekus model, and frequency of oscillations on velocity field and shear stresses are studied. These results affirm the shear thinning behavior of Giesekus fluid. Also it was found that tangential shear stress at inner cylinder's surface, axial shear stress at outer cylinder's surface, and first normal stress difference decrease by increasing the mobility parameter and the approach of axial velocity or shear stresses to their steady periodic state values is postponed by decreasing the Reynolds number.

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No abstract