The annular cement sheath is one of the most important well barrier elements, both during production and after well abandonment. It is however well-known that repeated pressure and temperature variations in the wellbore during production and injection can have a detrimental effect on the integrity of the cement sheath. Degradation of cement sheaths result in formation of cracks and microannuli, which leads to loss of zonal isolation and subsequent pressure build-up in the annulus. It is therefore important to study and understand cement sheath failure mechanisms to prevent such barrier failures.
A unique laboratory set-up with downscaled samples of rock, cement and pipe has been constructed to study cement sheath failure mechanisms such as radial crack formation and debonding during pressure cycling. Cement integrity before and after pressure cycling is monitored by X-ray computed tomography (CT), which enables 3D visualization and quantification of radial cracks formed inside the cement sheath as well as debonding towards casing and formation.
This paper describes this laboratory set-up in detail. Furthermore, some preliminary experimental results are also included that demonstrates the applicability and functionality of the new set-up.