Buoyant Miscible Flows in Axially Rotating Pipes: the Effects of Pipe Rotation and Viscosity

The primary cementing operations of oil and gas wells involve pumping a sequence of fluids into the well (initially within a circular casing and eventually within an annular region) to displace in-situ drilling mud. The fluids involved can be miscible, and they can also have different density and viscosity ratios. It is believed that a casing rotation can generally improve the displacement process, within both the circular casing and the annulus. However, there have not been a lot of laboratory studies to prove that such rotation is indeed effective for the displacement within the casing. In fact, due to the lack of knowledge, the casing axial rotation may not be still among the top recommendations to enhance the displacement occurring within the casing. This is in spite of the fact such a rotation would be feasible using various types of casing heads and special adaptors. In this work, we conduct simulations to understand the fluid mechanics behind buoyant displacement flows that occur within the casing (pipe). Our focus is to analyze the effects of the axial rotation speed of the pipe, the viscosity of the fluids and the viscosity ratio between the two fluids on the flow behaviours. Other flow parameters are also present: the fluids are miscible, and they have a density difference; the pipe inclination angle is considered to be near-horizontal (i.e. the most challenging case in terms of creating efficient displacements). We investigate important flow features, such as the behaviours of the interface between the fluids, the mixing between the fluids, the fluid front velocities, etc. Our results help develop a deep understanding of how casing rotation can be used to enhance displacement flows in the primary cementing operations of oil and gas wells.