Casing String Centralization Considering Irregular Wellbores

Abstract This study investigates the performance of casing centralizers in irregular and tortuous wellbores, focusing on the effects of borehole geometry on standoff and mechanical behavior during casing running. Emphasis is placed on bow-spring centralizers in open-hole sections, where diameter variations and tortuosity are pronounced. The objective is to quantify how these irregularities influence the overall standoff ratio and hookload using a detailed three-dimensional modeling approach. A finite element model (FEM) is developed to simulate the full three-dimensional displacement field of the casing and centralizers within a geometrically varying wellbore. In this study the wellbore geometry is generated artificially with one case considering the helix equations and another case considers a stochastic method to introduce realistic spatial variations. The model evaluates the standoff ratio and mechanical interaction forces under various levels of borehole irregularity and tortuosity. Additionally, the hookload during casing running is calculated to assess the influence of tortuosity on casing installation and centralizer placements. The results show that borehole spiraling and irregularities can significantly reduce the local standoff ratio, even when the average standoff across the open-hole section remains relatively high. The presence of irregularities leads to sections where the casing becomes highly eccentric, and in severe cases of tortuosity, direct contact with the borehole wall occurs. The results show that borehole spiraling can increase surface torque significantly due to additional contact points, while having negligible impact on axial hookload as the casing stiffness allows the string to bridge over short-pitch undulations. In contrast, irregular wellbores characterized by washouts force the casing into a state of global tension and high bending energy. However, the associated hole enlargement was found to reduce the average contact friction in this numerical study. These findings demonstrate that wellbore geometry alters the mechanical state of the string in complex ways, separating the effects of geometric locking from pure wall friction. This emphasize the importance of accounting for such effects when designing casing centralizer programs. The novelty of this work lies in the evaluation of casing centralization along the entire casing string in irregular and tortuous wellbores. The developed FEM framework enables assessment of how increasing borehole tortuosity and diameter variations degrade standoff performance and influence casing friction and hookload during running in hole. By capturing the deformation and contact interactions throughout the string, the method provides new insight into how wellbore irregularity directly affects the degree of centralization. Furthermore, wellbore irregularities can be read in directly from high-resolution caliper logs, providing detailed representations of the wellbore geometry. When combined with the real-time FEM solver, this enables new approaches to operational decision-making. Such integration could allow for adjustments to centralizer programs and running strategies during casing operations, increasing reliability and reducing the risk of stuck casing in highly irregular wellbores.