IMPACT OF CENTRALIZER TYPE AND WELLBORE GEOMETRY ON CASING CENTRALIZATION
DOI:
https://doi.org/10.31471/1993-9868-2026-2(46)-129-148Keywords:
casing, annulus, deflection, radial clearance, casing pipe, stiffness, inclination angle.Abstract
The reliability of oil and gas well casing and cementing largely depends on the degree of casing centralisation. This determines the uniformity of the annular clearance, the efficiency with which the cement slurry displaces the drilling fluid, the formation of a continuous annular cement sheath and the long-term annular sealability. This issue is particularly critical during the construction of directional and horizontal wells, where the placement of the casing eccentrically can significantly impair cementing conditions. This study aims to investigate how centraliser type and wellbore–casing system geometry influence casing standoff. It also seeks to establish the patterns that govern standoff variation depending on centraliser design, centraliser spacing, casing geometry and wellbore profile. Analytical methods were used to calculate the geometric parameters of the wellbore–casing–centraliser system and classical beam bending theory was employed to determine casing deflection between adjacent centralisers. The effects of centraliser spacing, casing diameter, wellbore inclination angle, centraliser outer diameter and borehole enlargement factor (caliper ratio) on radial annular clearance and casing standoff were analysed. It was found that centraliser spacing has the most significant impact on casing deflection, whereas the influence of casing diameter is less pronounced. Casing deflection increases sharply with greater hole inclination and wider centraliser spacing, resulting in poorer centralisation conditions. Increasing the diameter of a rigid centraliser was found to provide a higher degree of centralisation; however, this simultaneously reduces the minimum radial clearance between the casing string and the borehole wall. Furthermore, it has been demonstrated that the standard API Centralization metric cannot serve as a universal criterion for evaluating centralization efficiency, since identical values can correspond to fundamentally different geometric conditions for slurry flow in the annulus. This study's scientific novelty lies in demonstrating the need for a comprehensive assessment of casing centralisation that considers not only the API centralisation ratio, but also the minimum annular clearance, which directly affects mud displacement dynamics and the formation of an impermeable cement sheath. The practical significance of these findings is that they can be applied to select centraliser types and specifications, optimise centraliser spacing and design cementing programmes for casing strings in complex-trajectory wells.
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