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Evaluating Casing Condition Through Integration of Multi-Finger Calipers and Ultrasonic Imaging with Casing Wear Analysis - A Hybrid Approach


 Casing degradation evaluation is of prime importance to ensure well integrity system reliability and sustainability. Multi-finger calipers have been around for more than 50 years and are used to assess internal casing damage. In addition, high resolution ultrasonic imaging, introduced relatively recently, determines casing thickness by transmitting pulse-echo waveforms to initiate thickness-mode of the casing through induction of mechanical resonance. A high-profile exploratory gas well was at stake of being compromised due to fishing and cable sticking incidents in the 7-inch section. In this work, a novel combination of multi-finger caliper and ultrasonic imaging is investigated to accurately determine metal loss with assistance of hybrid threedimensional casing morphological visualizations which is then utilized to validate casing derating models and ensure well integrity.
 In order to evaluate the casing condition, it was decided to run a 24-finger caliper tool and to make up for loss of coverage area, ultrasonic imaging was employed. In order to process caliper data from various fingers, a three-tier process was applied which includes finger calibration, caliper correction due to eccentricity, finger sticking, finger offset, and lastly statistical analysis was conducted to generate corrosion summary report for metal penetration computations. Next, characteristic of the casing resonance was processed to measure thickness and compared with the nominal thickness to determine metal loss percentage. Furthermore, arithmetical analysis of internal casing radius measurements from both the tools was done to ensure data reliability. Ultimately, combining the measurements, 3D descriptions were generated in order to better characterize localized damage.
 A multi-physics approach led to a comprehensive characterization of in-situ casing condition. Consistency between internal radius measured by the calipers and deduced by pulse- echo arrivals was observed, improving confidence on the end-product. In the 7-inch casing section, a 40-meters interval was identified to have medium intensity grooves where the maximum penetration was computed to be in excess of 20% of the nominal pipe thickness This groove can be associated with tripping in / out operations of drill string or BHA. Also, the log results agree with the relatively higher side forces across this interval due to increased dog-leg-severity. In addition, cyclic response in radius measurements identified another zone where potential casing deformation (ovalization) near the surface was observed. Results of torque and drag simulations and well trajectory parameters were integrated with casing degradation analysis from the logs which assisted in qualifying well barrier status for the casing.