A Three-Dimensional Analytical Solution of Stress Field in Casing-Cement-Stratum System Considering Initial Stress State

Abstract

Accurate stress field calculation of the casing-cement-stratum system is crucial for evaluating wellbore integrity. Previous models treated in-situ stress as boundary pressure loads, leading to unrealistic infinite displacements at infinity. This study presents a three-dimensional (3D) analytical solution for the stress field within the casing-cement-stratum system in inclined wells, considering in-situ stress and hydrostatic stress in cement as the initial stress state and taking into account stress components related to the axial direction. Assuming a plane strain condition and superimposing the in-plane plane strain problem, elastic uni-axial stress problem and anti-plane shear problem, a 3D analytical solution is obtained. Comparisons with previous models indicate that the existing model overestimates the absolute values of stress components and failure potential of casing and cement in both 2D and 3D scenarios. The presence of initial stress in cement greatly increases the absolute value of the compressive stress state but decreases the failure potential in cement, which has not been well studied. Additionally, a low Young’s modulus and high initial stress state of the cement benefits the cement’s integrity since the maximum Mises stress significantly decreases. The new 3D analytical solution can provide a benchmark for 3D numerical simulation and quick assessment for wellbore integrity.

Study on Casing Safety Evaluation in High-Temperature Wells with Annular Pressure Buildup

“…Once the temperature distribution of the wellbore and the APB in annuli are obtained, the casing stress can be calculated via Equations (10) and (11). Then the safety factor of the casing at different depths can be found with Equation (15).…”

“…However, the release may not be possible in outer annuli in subsea wells because of the wellhead limits [9]. Therefore, research on casing safety evaluation and APB limit determination has great engineering significance and is favorable for maintaining wellbore integrity and ensuring the efficient development of the heavy oil [10]. Many scholars have researched APB prediction and casing failure.…”