Overcoming interpretation problems of gas-contaminated cement using ultrasonic cement logs

Conference · Sun Dec 31 04:00:00 EST 1995

OSTI ID:166628

Butsch, R J

The primary objective of cement sheath evaluation logs is to determine whether the production or injection zones, as well as other critical zones, are hydraulically isolated. Ultrasonic measurements have been used in cement evaluation since the early 1980s. Ultrasonic tools evaluate the cement sheath by measuring the acoustic impedance of the material outside the casing. Cement has a higher acoustic impedance than drilling fluids or water, and gas has an acoustic impedance near zero. Gas-contaminated cement poses the main problem in interpretation of ultrasonic cement tools. To understand the problem, the acoustic impedance of what might be in the casing-to-formation annulus must be considered. The acoustic impedance of cement can range from slightly over 3.0 MRayl to about 7.0 MRayl. Drilling fluids can be 1.5 MRayl to 3.0 MRayl. Water has an acoustic impedance of 1.5, and gas has an acoustic impedance of less than 0.04 MRayl. As long as there is sufficient difference between the acoustic impedance of the cement and the acoustic impedance of the liquid phase, channels in the cement can quickly be identified. In the case of gas-cut cement the texture of the material tends to be that of a honeycomb. This paper proposes a technique for using high-resolution ultrasonic data to identify gas-contaminated cement, while maintaining nearly the same vertical and radial resolution, thus allowing the identification of liquid-and gas-filled channels. The proposed technique allows improved interpretation of the high-resolution ultrasonic data when gas-contaminated cement is encountered. Even when attenuation-type logs are run, this technique will aid the interpretation. The results to date indicate that this technique can be applied to eliminate unnecessary cement squeeze jobs caused by misinterpretation of the ultrasonic data. Examples are shown to compare the technique to other cement log data and cement squeeze results.

• OSTI ID: 166628
• Report Number(s): CONF-951002--
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
03 NATURAL GAS
ACOUSTIC MEASUREMENTS
CEMENTS
CONTAMINATION
NATURAL GAS WELLS
OIL WELLS
ULTRASONIC TESTING
WELL LOGGING