Kinematic Analysis of Geomechanical Displacement Fields to Assess Lifetime Integrity of Wellbores

Displacements in geomechanically perturbed formations induce additional stresses on wellbore tubulars. An appropriate well design basis should consider the mechanical response of the tubulars and the associated architectural implications. Traditionally, assessments of well integrity to geomechanical loading states have been conducted with large scale numerical models of reservoir, rock and the wellbore. In this context, we present a method to assess well integrity from a kinematic analysis of the geomechanical displacement field. The crux of the analysis is to regard the displacement field from the viewpoint of an observer on the wellbore centerline. Since the mechanical stiffness of a moving formation greatly exceeds that of a wellbore, the well practically follows the rock, and its shape accords with the equilibrium positions of the surrounding rock. The kinematic analysis identifies the dominant loading mode(s) on all the casings. We then apply specifically developed mechanical limit states to assess the mechanical response of the casings and cement sheaths (when applicable) to the geomechanical displacements. These limit states are used to determine well integrity, times to failure, and architectural options to prolong or optimize well life in an evolving set of geomechanical perturbations. 1. INTRODUCTION Geomechanically induced displacements can severely test the integrity of wells. Regardless of the cause, an arbitrary point in the formation moves to a new location as a function of geomechanical displacements. Reservoir compaction, salt creep, tectonic stresses and fault movements are some of the most common sources of geomechanical loads on wellbores. Traditionally, assessments of well integrity to complex geomechanical loading states have been conducted with large scale integrated numerical models of reservoir, rock and the wellbore (Chia and Bradley, 1989; Bruno and Bovberg, 1992; Fredrich et al. (2001); Ibekwe et al. (2003); Li et al. (2003); Abou-Sayed et al. (2004)). Though these models are technically detailed and accurate, they are time consuming and inflexible, especially when parametric sensitivities are needed. During early stages of field development, when bottom hole locations, surface coordinates, trajectories, casing points and well architectures have not yet been finalized, the impact of geomechanical stresses on well integrity and well lifetimes can determine the success or failure of the project. In this light, our paper presents a method to analyze well integrity by examining the kinematic parameters of the geomechanical displacement field. Since the mechanical stiffness of the formation greatly exceeds the stiffness of the wellbore1, the geomechanical displacements are almost entirely transferred to the wellbore. The displacement deforms the wellbore centerline from its initial shape (defined by the drilling trajectory) into a three-dimensional curve characterized by its kinematic parameters.