Cement evaluation with wireline tools across two different casing sizes is cost-effective and time efficient, but also quite challenging. The acquired data quality, especially across the larger casing, is often affected by the tool eccentricity and poor signal-to-noise ratio due to severe attenuation of acoustic signal by the mud. New ultrasonic technology is required to acquire reliable data for cement evaluation, necessary to assure long-term well integrity and guide operational decision-making processes during well execution.
In this paper, authors discussed several case studies, where high quality cement bond data was acquired across both 7-inch liner and 9.875-inch casing in 17.3 ppg oil-based mud in a single wireline descent by using new generation ultrasonic transducers.
Drilling campaign in the Tengiz Field was restarted in 2012 and reached its peak in 2019. The majority of the wells in the new drilling campaign utilized fit-for-purpose (FFP) well design with long production casing section, which consisted of 9.875-inch casing to the top of the Kungurian Salt and a 7-inch × 7.25-inch liner to the top of the reservoir. Both sections required cement evaluation to guide operational decision-making processes and comply with regulatory requirements.
In the past, cement quality evaluation was performed with standard ultrasonic tool, logged across 7-inch liner and 9.875-inch casing in a single descent. However, heavy mud weight (17.3 ppg) required to drill the salt section caused strong attenuation of the acoustic signal, resulting in poor log quality and unreliable cement evaluation.
The new ultrasonic tool with new generation transducers was successfully introduced in several wells. Comparison of results for cement evaluation with standard and new generation ultrasonic tools showed significant improvement in data quality for both 7-inch and 9.875-inch tubulars in wells filled with 17.3 ppg oil-based muds. Acquired data allowed confident evaluation of cement quality, as well as assessment of the cement contamination level and casing centricity. Reliable cement evaluation expedited operational decisions and clearly identified existing issues. The findings from the cement evaluation supported changes in the cementing design, which led to improved well reliability and integrity. Moreover, cement evaluation in two casings in a single descent saves ~12 hours of rig time per well, enabling significant efficiency gain and cost savings from ongoing drilling operations.
This paper summarizes TCO experience with the use of new generation transducers for cement evaluation, compares results between standard and new generation transducers and provides examples how acquired cement evaluation data impacted operational decisions and cementing practices.