Numerical simulation of the thermomechanical behavior of cement sheath in wells subjected to steam injection

Abstract

The exposure of oil wells to extreme conditions may lead to numerous problems associated with the loss of integrity of the cement sheath. A damaged cement sheath may result in fluid leakage and in some cases cause significant economic loss and environmental degradation. Thermal recovery processes are common techniques used to enhance oil recovery by submitting the materials to severe temperature gradients. However, this heating process induces thermomechanical stresses in the cement sheath which may lead to its cracking. This paper investigates the effects of cement slurry formulation on the thermomechanical behavior of cement sheath in wells subjected to the first heating phase of steam injection. For this purpose, three types of cement slurry formulations, one standard and two others with latex additions, were designed, mixed and tested in the laboratory to evaluate their mechanical properties. An axisymmetric finite element model was then developed and used to conduct a parametric study to investigate the thermomechanical response of oil wells with cement sheaths made of the various cement slurries, as well as the influence of applied temperature gradients, heating durations and formation stiffness. The results mainly show that issues of cement sheath integrity under steam injection are generally localized in the region near the formation, and that they are closely related to the heating phase of the well. It is also found that combining the use of a more flexible and expansive cement slurry formulation with the slow application of temperature gradient generally improves cement sheath integrity during steam injection. These beneficial effects were shown to be more effective for stiffer rock formation and larger applied temperature gradients.