Two-phase flow and displacement in eccentric annuli: a CFD study

Abstract

Cementing operations are critical in the petroleum industry to isolate formations. Safety, environment impact and the economic success of a project depend on a successful cementing campaign. Cementing involves pumping spacer fluid to displace drilling mud, then cement in order to create the bond between the casing and formation. It is very rare that the casing is concentric in the borehole; therefore, it is almost always offset, usually to an unknown extent. It is for these reasons that a good knowledge of one fluid displacing another is needed, so that cementing operations may be run with greater certainty. The aim of this work is to build a functional 3-dimensional CFD model to capture the effects of non-Newtonian fluid displacements in eccentric annuli. Effects such as eccentricity of the well bore and rotation of the inner cylinder and fluid rheology may have large influences on the displacement efficiencies and flow phenomena. The model was run using ANSYS CFX 13.0 with fluid flow occurring under laminar conditions with negligible mixing between phases. It was found that the model can predict the effects of eccentricity and rotational flows on displacement efficiency and frictional pressure losses. The simulations confirm the experimental observations that rotation of the inner cylinder, even at low speeds, can significantly improve the displacement performance in highly eccentric annuli. Furthermore, for viscoplastic fluids, mild rotational flows lead to decreases in friction losses, which are strongly dependent of the annular eccentricity.