Prediction for Casing Centralization

Abstract

Ensuring an optimal casing centralization is crucial in achieving a high-quality cement bond. One primary goal during the drilling and cementing process is to center the casing in the wellbore. This is done by using centralizers attached to the casing. Centralizer spacing has to be optimized by considering the impact of several factors and forces on the casing [10]. Maintaining the casing centered helps obtain an even and well-distributed cement sheath, which is essential to avoid risks, such as an influx. The increasing prevalence of horizontal well trajectories and dogleg sections introduces several challenges in obtaining the casing sufficiently centered in the wellbore. Precise models are needed to predict the casing centralization for these complex well trajectories, mainly due to the high side forces in these sections. This thesis presents a simple model for predicting casing centralization and, thus, the casing standoff, based on the soft-string model and mathematical equations from the American Petroleum Insitute (API). However, a stiff-string model is becoming more and more used and includes forces of drag and torque, as well as the bending stiffness of the casing. Consequently, the model serves to obtain more realistic results [10]. The code developed is validated with a case study provided by Schlumberger (SLB) and is further applied to a well path from the Ullrigg Test Centre using three different casing types. Several limitations to the developed code are addressed. Results for each case are simulated and compared. As will be observed, with the increasing weight of the casing, the standoff decreases, given that the type of centralizer and spacing between them remain the same. Furthermore, the results are discussed and optimized to achieve an acceptable casing centralization.

Ensuring an optimal casing centralization is crucial in achieving a high-quality cement bond. One primary goal during the drilling and cementing process is to center the casing in the wellbore. This is done by using centralizers attached to the casing. Centralizer spacing has to be optimized by considering the impact of several factors and forces on the casing [10]. Maintaining the casing centered helps obtain an even and well-distributed cement sheath, which is essential to avoid risks, such as an influx. The increasing prevalence of horizontal well trajectories and dogleg sections introduces several challenges in obtaining the casing sufficiently centered in the wellbore. Precise models are needed to predict the casing centralization for these complex well trajectories, mainly due to the high side forces in these sections. This thesis presents a simple model for predicting casing centralization and, thus, the casing standoff, based on the soft-string model and mathematical equations from the American Petroleum Insitute (API). However, a stiff-string model is becoming more and more used and includes forces of drag and torque, as well as the bending stiffness of the casing. Consequently, the model serves to obtain more realistic results [10]. The code developed is validated with a case study provided by Schlumberger (SLB) and is further applied to a well path from the Ullrigg Test Centre using three different casing types. Several limitations to the developed code are addressed. Results for each case are simulated and compared. As will be observed, with the increasing weight of the casing, the standoff decreases, given that the type of centralizer and spacing between them remain the same. Furthermore, the results are discussed and optimized to achieve an acceptable casing centralization.