Ultrasonic Evaluation of Clay Behind Casing
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There's an increasing number of oil fields on the Norwegian continental shelf that will go out of production in the coming years, resulting in a big demand for permanent plugging and abandonment (P&A) services. There are huge expenses related to permanent P&A, and the demand for new and cheaper methods has driven the industry to look into new alternatives for plugging the well. Exploiting shales natural creeping properties has proven to be a good alternative for sealing the annulus. Field results has shown that the sealing properties of the creeping shale can be detected by logging tools. The question that follows is if it is possible to detect the contact the shale in lab experiments, and whether or not it is possible to detect micro-annulus and fractures in the shale. In this thesis, some of the ultrasonic evaluation tools used in the oil and gas industry will be presented together with two ultrasonic logging techniques, the pulse-echo and the pitch-catch methods. A set of ultrasonic measurements were performed to test if it is possible to detect, and evaluate shale behind a steel casing. The ultrasonic pulse-echo and pitch-catch experiments in this thesis were conducted on the Behind Casing Logging Set-Up (BeCaLoS) developed by SINTEF Petroleum Research, designed to replicate the steel casing setup in an oil well. The pulse-echo and the pitch-catch technique are performed under various conditions, with air, water and clay behind the steel plate. Both measuring techniques was successfully performed. Pulse-echo wave resonance attenuation measurements prove to be successful in evaluating the physical state of the material behind the casing, and was found to be a good tool for identification of annulus media. There was a good match between experimental and theoretical values. Calculated clay impedance values indicated the presence of a water filled micro-annulus. The pitch-catch lamb wave attenuation measurements prove to be difficult to interpret. The measurements with clay behind the steel plate was only successful to some extent, and prove to be difficult to analyse with unexpected attenuation values. There is a need for further research on the pitch-catch and pulse-echo technique to see if it is possible to detect micro-annulus and fractures in the shale.