UBC Theses and Dissertations
Annular displacement flows in primary cementing of horizontal and irregular wellbores Renteria Ruiz, Alondra Perla
Large numbers of oil and gas wells, in Canada and worldwide, allow leakage to surface from the reservoir. One common reason is associated with unsuccessful mud removal during the primary cementing operation. Horizontal wellbores present particular cementing challenges that have not been fully solved. This thesis explores (i) the fundamental mechanisms of fluid displacements in a horizontal narrow eccentric annulus from an experimental and computational perspective; and (ii) cementing horizontal irregular wellbores. We present results of about 300 miscible Newtonian displacement flow experiments carried out in a dimensionally scaled laboratory setup. Annulus eccentricity, density difference and viscosity of the fluids is varied, over a wide range of laminar Reynolds numbers. Comparisons with predictions from the two-dimensional gap averaged model of Carrasco-Teja et al. show excellent agreement in predicting the underlying competition between buoyancy and eccentricity, which results in either top side or slumping flows. The main discrepancy results from a variety of dispersive effects that are not present in the model, e.g. dispersion within the annular gap and due to azimuthal secondary flows. We show that these features are better predicted on computing the flow with a three-dimensional Volume of Fluid model. Regarding cementing irregular wellbores, we present two independent studies. The first one explores the effects of local irregularities (i.e., washouts) on mud removal in strongly inclined wellbores, experimentally and via two-dimensional simulations. The competition between slumping and eccentricity is affected by the washout. In most of the experiments the mud was removed from the washout, but the simulations showed this is not true for muds with higher yield stress than those tested experimentally. The second study deals with the effect of borehole ovalization and large-scale irregularities (e.g., breakouts). We use a two-dimensional gap-averaged model that can compute the displacement within eccentric and elliptic geometries. The irregularities can induce additional azimuthal flow when compared to uniformly circular wellbores. In cases when the displaced mud has a significant yield stress, the displacement can leave patches of residual mud at the top of eccentric horizontal wellbores: not usually found without ellipticity.
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