Well A, encountered multiple depleted reservoir layers (initial reservoir pressure >10840 psi) with up to 5,000 psi differential pressure across layers due to irregular depletion in thin bedded shale and sand layers. Well was drilled with over 16 ppg mud to limit under balance in any higher pressure layer and overbalance in depleted layers. After drilling 4 lopes of sand body and during the start of drilling the last sand lope, complete loss of circulation was encountered, followed by kick and differential sticking. The original well integrity assurance plan considered the deployment of borehole compensated sonic tool in order to acquire a discriminated cement bond log based on attenuation measurement. Also in the plan, a Cased Hole Dynamic Tester tool was to be run and the selection of pressure points to be based on the results of the cbl-vdl. So to assure the full integrity of the cement and be able to conduct the Cased Hole Dynamic Tester as required and proper decision to be evaluated regarding the Type of GP job, the use of the Ultrasonic Imaging Tool was evaluated to be run under tough and challenging conditions (high mud weight and thick wall thickness).

The Ultrasonic tool for cement to casing bond evaluation is typically limited by the attenuation of the ultrasonic echo caused by the wellbore mud weight and composition. With the cooperation between BP PhPc and Schlumberger, and making use of worldwide expertise, the decision was taken to include the Ultrasonic Tool in the cement evaluation suite despite the well conditions.

The analysis of the log managed to prove the zonal isolation requirements and be a source of development of best practices that can improve cement evaluation even with the presence of heavy SOBM.

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