Direct Strain Mapping of a Cement Sheath; A New Tool for Understanding and Preventing Cement Failure in Thermal Wells

摘要

The design and application of a new cement integrity validation test apparatus for improving thermal cement integrity will be presented. This novel approach allows direct strain mapping of to-scale cement sheath as it deforms under different wellbore stress scenarios. Not only does this novel technique provide insight into elastic cement deformation but also helps elucidate how cracks form and propagate as the cement sheath deforms. Strain mapping is achieved through Digital Image Correlation (DIC) utilizing dual high speed and resolution camera systems. Reliably capturing crack initiation in the frame of view of the stereo camera system proved to be a significant challenge. After multiple design iterations, the best results were achieved with creating a predefined defect site in the cement sheath. Detailed crack initiation and propagation strain maps were created for thermal cements with and without fiber additives. This testing demonstrated how fibers are able to blunt crack propagation and dissipate energy through a fiber pull out mechanism leading to a more ductile failure. Early results are promising and are consistent with previous tests showing an increase in ultimate failure strength in tensile samples with fiber additives.