Abstract
In recent years, the focus of the oil and gas industry has shifted toward the production of oil from deep and harsh environments. This has been possible because of advanced technologies coming available to the industry. However, challenges still remain in designing materials to withstand certain harsh environment. To satisfy the ever-increasing demand for oil and gas, the industry is tapping heavy oil, which poses unique challenges.
Steam-assisted gravity drainage (SAGD) technique has made it possible to reduce the viscosity of heavy oil and render it mobile. In this technique, steam is injected through an injector well and down to the reservoir where temperature can be raised to 260°C (500°F). This reduces the viscosity of heavy oil but imposes severe thermal stresses on the cement sheath and casing.
Such stresses could hamper zonal isolation and result in the release of steam to the surface. Designing a cement slurry for such applications is challenging of various aspects, such as mixability, pumpability, placement in the annulus, sheath resiliency, permeability, and compressive and tensile strength, that should be optimized to meet the technical, economical, and operational requirements.
This paper details the designing of cement systems for SAGD application and its rigorous testing by simulating downhole conditions. A fit-for-purpose slurry was designed that is chemically stable at the downhole temperatures and able to withstand the thermal stresses.
The optimized slurry was subjected to thermal cyclic loading in an experimental setup designed to simulate downhole conditions, and the performance was evaluated. The cement sheath was intact after being subjected to several thermal loadings. No cracking or de-bonding was observed.
In this paper, the experimental setup, slurry design, testing procedure, and the results are discussed in detail. The discussions presented in the paper should help the industry in constructing and operating SAGD wells safely and economically.
