In recent years specialized cements have been developed for use in the oilfield. These cements have ranged from very lightweight to very heavy cements. They have included additives such as glass or ceramic beads to alter their properties. With an increased use of these cements, concerns have risen about the cement evaluation. Quite often the question is asked, "Can we evaluate these cements?" rather than, "How do we evaluate these cements?" This paper will discuss some logging techniques that can be used to evaluate these new cements.
The desire to cement longer casing intervals without exceeding the formation fracture gradient has led to the use of very light weight cements. These cements have low acoustic impedance values that are not much higher than the acoustic impedance values of drilling fluids. The compressive strength of these cements can also vary significantly. Acoustic impedance and compressive strength are the properties that cement evaluation tools use to differentiate between the fluids and the solids in the casing formation annulus. To identify these differences it is critical that the proper logging techniques and input parameters are selected for the sonic and ultrasonic tools. A statistical analysis of acoustic impedance measurements from the ultrasonic tools has also proven to be valuable for the evaluation of these special cements.
Examples from Alaska, and other areas where these types of cements are being used to solve difficult completion problems, will be shown to demonstrate the use of these cement evaluation techniques.