Pushing the Limits of Ultrasonic Cement Evaluation in Very Large and Heavy-Wall-Thickness Casings

Advancements in offshore drilling technology have enabled operators to construct wells using larger casings, ranging from 22 to 26 inches in diameter, with wall thickness exceeding 1 inch. These configurations present significant challenges for cement evaluation, as traditional ultrasonic tools struggle with signal attenuation and inadequate energy transmission through thick casings. This study presents a case where a 26-inch conductor was installed 120 meters shallower than planned, with no confirmation of cement returns at the seabed. To ensure well integrity and continue drilling, an accurate cement bond log was required to determine the cement height in the annulus. However, conventional ultrasonic evaluation tools were insufficient for this application due to the casing's extreme size and thickness, hardware limitations in tool centralization, and software constraints on data processing. To overcome these obstacles, we deployed new- generation transducers with enhanced signal-to-noise ratio, enabling better signal to noise ratios at lower frequencies. Additionally, a large rotating logging head was utilized to minimize standoff effects, and customized centralizers were employed to optimize tool positioning. These advancements, combined with an improved data processing algorithm, significantly reduced turnaround time from 24–12 hours to just four hours. The results demonstrate the successful cement evaluation log in 26-inch casings with 1.25-inch-thick walls—achieving a groundbreaking first in cement evaluation in such large and thick casing. The cement log confirmed the presence of cement behind the casing and around the shoe, allowing operators to proceed with drilling and blowout preventer (BOP) installation without the need for costly well re-spudding or abandonment. This innovative approach not only enhances cement evaluation capabilities but also improves operational efficiency, reduces rig time, and minimizes environmental impact by lowering carbon emissions.