An Improved Cement Bond Evaluation Approach for Unconventional Development Wells: A Case Study Integrating CBL and Permanent Downhole Gauge Data

The paper describes a case history using an improved cement bond evaluation workflow integrating traditional cement evaluation logs and downhole permanent temperature and pressure data in a tight oil play in southern Oklahoma. A pair of producer and monitor wells were drilled and completed in a field development study project. Comprehensive data collection and analytics were carried out to devise an optimized well placement strategy in a basin with heterogeneous reservoir rocks and stacked pay zones. With the permanent installation of pressure and temperature gauge arrays and fiber-optic sensors in the casing annulus of the monitoring well, it is critical to accurately assess cement quality and well integrity to ensure that satisfactory zonal isolation is achieved. Minimal cross-gauge interference is desired for reliable real-time data acquisition during fracture stimulation and production monitoring. Cement evaluation log interpretation is inherently qualitative and subjective in nature. To this end, a multiphysics data interpretation workflow was used to integrate downhole distributed temperature and pressure data recorded during cementing operations with conventional acoustic cement evaluation log data. A thorough cement evaluation logging program was devised to collect sonic and pulse-echo ultrasonic logs under standard and pressurized wellbore conditions. Also included in the logging program was a time-lapse component comprised of additional logging runs after the hydraulic fracture operation performed in the nearby producer. The comparison of before and after frac data analyses provides valuable insight into the interpretation process to evaluate the growth of fractures originating from the producer and propagating to monitor wellbores. Results from the integrated workflow indicate that zonal isolation has been achieved across the instrumented segment of the monitor wellbore. Shown in Fig. 1 are sonic and ultrasonic cement evaluation logs and ultrasonic casing integrity logs. Although features such as micro-debonding and small-scale liquid-filled voids were observed in certain intervals, these low-impedance features do not appear to be interconnected. No fluid channels and conduits around fiber-optic cables were observed. Shown in Fig. 2 are borehole temperature profiles recorded by 14 temperature gauges before, during, and after a cementing job. Along with pressure gauge data, temperature data illustrate cement slurry flow as well as cement hydration and hardening processes. The ultrasonic pulse-echo log proved to be critical in understanding casing integrity. The time-lapsed cement evaluation logs show signs of cement quality improvement, indicating that a post-completion compaction trend acts upon the wellbore. In summary, although the assessment of cement integrity is a complex task, it is shown that a workflow incorporating multiphysics measurements has a clear advantage of producing much more reliable and consistent results.