Guidelines for ultrasonic cement-sheath evaluation

Abstract

The primary objective of cement-sheath evaluation devices is to define the presence of set cement in the annulus, regardless of its density, compressive strength, or quality. Accepting the premise that any set cement in the annulus with a compressive strength greater than 0 psi cannot be replaced by squeeze cementing emphasizes that necessity of recognizing ultralow-compressive-strength cement ({lt}100 psi) from cement-sheath evaluation devices. Typically, most bond logging instruments cannot define satisfactorily the presence of these generally low-density, low-compressive-strength cements (such as foamed cement, cements filled with sponge-like microspheres, cements containing hydrogen for control of annular influx, or any cement contaminated with gas percolation). The ultrasonic cement evaluation instruments can define these gas contaminated, unset, or low-quality cements, provided the computing parameters are set and the tools calibrated correctly. This paper provides the mechanisms and data required to calibrate the ultrasonic cement evaluation devices correctly and the correct computing parameters for cement-sheath evaluation. Correct interpretation of the cement quality and quantity in the annulus permits the formulation of intelligent annular squeeze decisions.