Ultrasonic Log Response in Lightweight Cement Conditions

Abstract

Abstract Lightweight cement can present unique challenges to efficient and accurate evaluation of cement sheath integrity. Standard bond log tools require strong compressional bonding to casing to observe an attenuation of the sonic signal that is set up inside the casing. Lightweight cement often experiences less cohesion to casing because of its lowered fluid density when pumped and lower compressive strength after being set up. These properties can negatively affect measurement. Definition of the cement sheath must still be determined using a method that is both valid and repeatable. The industry has demonstrated the ability to accomplish this task using ultrasonic logging tools. These devices allow very precise definition of the cement sheath using 360° examination of the data, but still require innovative interpretation techniques to derive useful solutions regarding the isolation capability of the cement. Additional complication is introduced when consolidated efficiency fluid material is pumped as an isolation fluid. This fluid material is lighter weight and has lower compressive strength than even the lightest cements. However, isolation of the reservoirs from surface water and the ability to fracture treat wells with restrained fluid mobility must still be determined. This paper demonstrates the application of ultrasonic cement evaluation tools under these difficult conditions. Examples of conventional cement, lightweight cement, and consolidated efficiency fluid isolation fluids are considered. The processed logs highlight the confidence in the reservoir isolation identified using these tools and evaluation techniques.