Modelling of Acceptable Hole Curvature for Running Casing Strings

Authors: A. J. Lagraca, S. Z. Miska, J. R. Sorem

A mathemetical model is presented to analyze insertion forces for casing strings in high hole curvatures (dogleg severity) and high deviation angles.

This mathematical model allows simulation of forces acting on casing strings in short and long doglegs with constant curvature.

Equations for predicting the acceptable hole curvature are obtained by analyzing the static equilibrium of forces acting on casing string.

Since the resulting differential equation is non-linear, an approximating function, which satisfies the geometrical boundaryconditions, is proposed as a solution.

This approximating function describesthe equilibrium configuration of the casing centerline and provides a method to predict forces acting belowthe neutral point.

The influence of hole curvature on these forces was simulated for some casing strings.

Calculated forces are described and presented in graphical form.