Drilling in progressively deeper water environments requires that even more attention be given to well integrity because of the serious implications to health, safety and environment. Conventional cement evaluation tools have been available for many years and have been useful in most scenarios, but in more complex and challenging deepwater operations, the need exists for advanced cement evaluation techniques to increase confidence in ascertaining wellbore integrity. There are limitations on cement evaluation for light cements and thick casings. Furthermore, there is usually limited information about the "Third Interface" (i.e. between the cement/formation or cement/next casing), which can provide valuable information about wellbore integrity.
An integrated approach to cement evaluation has been adopted. This approach is based on a cement evaluation service that incorporates 360 circumferential information about cement placement, annulus imaging, and petrophysical evaluation of the formation to ascertain zonal isolation and cement quality behind casing. The azimuthal information is used to understand whether the cement placement was affected by the well deviation and if there are changes in cement quality from one part of the borehole to another. Annulus imaging is used to evaluate the annulus material. Petrophysical data is used to determine if the formation rock and fluid properties contributed to the quality of the cement behind casing. The principles of ultrasonic measurements and unique flexural measurements, and how they aid in cement evaluation, are also considered.