Abstract
Cement is placed in the annulus between the casing(s) and the surrounding formation rock to ensure no migration of fluids form through the barrier. However, during the operational lifetime of a well changes of pressure and / or temperature lead to extra stresses inside the casing. These stresses can lead to expansions and / or contraction of the casing, with subsequent extra stresses on the surrounding cement sheath. These stresses can result in debonding between the materials or the formation of fractures along the material interfaces or through the material itself. Assessment of the cement is crucial in order to sufficiently manage the integrity of the well. The ideal assessment should consist of 1) a proper visualization of both the sample and fracture geometry, 2) comparison with logging and 3) permeability measurements of the sample/specimen.
This paper describes a study where we have used a unique downscale wellbore cell to mimic the behavior of casing-cement-rock specimens. The specimen was exposed to inner casing pressure cyclic changes and the effect of these cyclic changes are measured using pulse-echo and pitch-catch ultrasonic tool to assess the cement-casing debonding. Furthermore, the specimens are visualized using X-ray CT, and finally the changes in permeability are tested.
