Zonal isolation throughout the life of the well is important to help ensure that health, safety, and environmental (HSE) standards are not compromised and that the well operates economically. The life expectancy of a well is dependent on the protection that the wellbore can receive from primary cementing operations.
A primary cement job design that provides zonal isolation and preserves structural integrity over the life of the well can reduce or eliminate the need for remedial operations. Achieving successful zonal isolation comprises three key mechanisms:
Design and delivery of a reliable cement system that can withstand the effects of the operational loading and cyclical stresses exerted on the well by drilling, completion, and production operations.
An auto-seal feature in the cement sheath itself. In the event that the cement sheath fails and develops cracks and/or micro-annuli because of primary cementing job failure in the presence of a mud filter cake, the sealant sheath can then react and respond in an attempt to automatically seal itself if formation fluid enters the cemented annulus. This is a fail-safe technology mode that can be included in the design of the cement slurry.
Employing a packer element as part of the casing/liner string that can swell and seal the annulus if formation fluid comes in contact with the element. This additional contingency can help prevent flow of the hydrocarbon past the packer element by creating an effective mechanical seal.
By applying these features, it is possible to effectively and successfully perform primary cementing operations with additional protective options and place sealants that will last throughout the life of the well (Fig. 1).