Finite-Element Studies of Near-Wellbore Region During Cementing Operations: Part I

Abstract

Summary A wellbore cement sheath is expected to provide zonal isolation and borehole integrity during well construction and well life. Mechanical interactions of the cement sheath to existing and operationally induced stresses, along with other elements in proximity to the wellbore, have increasingly large technical, economic, and environmental ramifications. Staged-finite-element procedures during well construction consider sequentially the stress states and displacements at and near the wellbore. The model replicates complicated stress states arising from simultaneous action of far-field stresses, overburden pressure, cement hardening and shrinkage, debonding at the interfaces, and plastic flow of cement sheath and rock formation. At present, temperature, flow, and poroelasticity effects are not included. The technique tracks the time-dependent behavior of cement slurry, curing (with or without shrinkage), and hardened cement during the critical period after slurry placement. Material models for casing, cement, and rock formation and failure criteria for cement, formation, and interface bonds were calibrated using published information and experimental data. Calculations were conducted for various loading and unloading scenarios, geometric configurations, properties of rock formations, and cement-slurry formulations. Results are discussed in terms of field implication;, for example:Interface microchannels may or may not develop, depending upon shrinkage magnitudes; andsimplifying modeling assumptions that are often used, such as 2D stresses and/or deformations, may obscure critical casing, cement, and formation behavior in the wellbore region and in the producing horizon. This paper, part of a series quantifying the interacting physical components and processes at and near the wellbore region, initiates useful comparisons of analytical results and field realities. The series illustrates and compares results and practical implications from simple to increasingly complex, but more realistic, assumptions, such as isotropic/directional-stress states and isotropic/anisotropic casing, cement, and formation-material parameters.

Well integrity for CO2 injection from ships: Simulation of the effect of flow and material parameters on thermal stresses

“…This is a most common assumption in rock-mechanical well models (see e.g. Gray et al (2009)), and it is valid as long as the well is sufficiently long and straight.…”

Nonlinear Stress-Strain Model for Confined Well Cement

“…Consequently, more accurate mechanical strength models and better assessment of cement integrity are necessary to reduce the risk of failure. Numerical simulation is commonly applied to investigate the mechanical integrity of cement [2], also by using some software such as ABAQUS [3,4], ANSYS [5], and ADINA [1]. In all types of applications, an accurate well cement stress–strain model is required.…”

Effect of Dynamic Loading on Wellbore Leakage for the Wabamun Area CO2-Sequestration Project

“…Removing the casing in certain areas is one method of mitigating the leakage caused by a poor bond or debonding between the casing and cement. If wells are plugged and abandoned permanently, both Gray et al (2009) and Carlsen and Abdollahi (2007) suggested removing the casing steel before placing the final cement plugs. This removes the most likely leakage pathway along the casing.…”

“…The advantage of building the model in several steps is the ability to observe and record stress and deformation changes after each loading. Furthermore, knowing previous deformation and loading history will help to specify the initial stress state before final thermal and mechanical loads are applied to the model (Gray et al 2009). …”