Paper: Casing Corrosion Evaluation Using Ultrasonic Techniques A Unique Approach For West Texas Wells

Virtually all west Texas wells possess, to varying degrees, conditions of internal and/or external casing corrosion. The majority of the corrosion problems begin when produced (or injected) fluids come in contact with the casing inner wall, or when formation fluids come in contact with the outer wall of the casing in areas not protected by adequate annular cement. Both internal and external casing corrosion problems can become more severe with time, and can, if not addressed, lead to premature demise of the well. In order to ascertain the severity of corrosion problems in any specific well, many wireline logging devices have been developed over the past several years. Basically mechanical/magnetic in makeup, quantitative interpretation from the classic tools depends largely upon assumption of unknowns that, in most cases, are very hard, if not impossible, to accurately identify. A new corrosion evaluation procedure developed by Schlumberger uses a uniquely different approach to the challenge of quantitative casing inspection. The technique uses full ultrasonic casing resonance information recorded with a modified cement evaluation tool. Using the CET* tool, all necessary casing inspection data can be recorded simultaneously with cement evaluation information. The waveforms recorded at each of the eight (8) radially spaced CET ultrasonic transducers can be analyzed to obtain the following information regarding the condition of the casing: - The specific internal geometry of the casing - An internal casing roughness profile. - A casing metal thickness profile. A derivation of the measurements obtained at each CET transducer will be presented followed by discussion of the currently available display presentations and casing imaging techniques. The specific utilities of the ultrasonic casing inspection technique will be highlighted by citing several examples from west Texas wells.