Effects of Rheological Properties on Primary Cementing of Irregular Horizontal Wells

Abstract Primary cementing is an industrial operation that is used to seal every oil and gas wells, of which there are many millions globally. The process aims to remove the drilling fluid and other residues from the annulus between the casing and the formation, replacing it with a cement slurry, which then hydrates and seals the well to prevent subsurface leakage. Leakage compromises well productivity and can have environmental and health consequences, e.g. polluted aquifers, methane emissions, and subsurface ecosystems. In this work, we focus on fluid displacement mechanics of primary cementing operations. Even in stable boreholes, several geometrical and operational irregularities can be seen while reading caliper data. Washouts, keyseats, and breakouts are examples of irregularities. The other irregularity arises from eccentricity which mainly originates from operational features. Eccentricity of the annulus significantly affects the cement placement flow and longevity of the wellbore. In this work, we study the effect of the rheological properties of fluids involved in the primary cementing on displacement flows in an irregular horizontal section of well. The focus of the work is on irregularities in the shape of enlargements. We use three-dimensional (3D) numerical simulations, using the Volume of Fluid (VoF) method to compute displacement of a drilling mud by a spacer within an annulus with series of enlargements. We use Bingham fluid and Newtonian fluid models for the mud and spacer, respectively. The 3D model allows us to capture the interface between fluids and study the effects of more local irregularities in detail, e.g. secondary flows and residual mud layer on the wall of the well. The rheology of the fluids beside the geometrical properties, irregularity and eccentricity, plays important role in determining the presence of unyielded residual mud layer. In this paper we describe the competition between viscosity ratio and density differences with geometrical properties.