First-Time Application of Enhanced Active Cement System to Secure Zonal Isolation in the First Shale Oil Reservoir in Kazakhstan

Abstract

Abstract This paper presents the challenges and solutions associated with implementing an enhanced active cement system (EACS) in Kazakhstan's first horizontal shale oil reservoir. The critical challenge is related to high-pressure fracturing operations that often cause conventional cement sheaths to crack, leading to sustained casing pressure (SCP) and loss of zonal isolation. The study evaluates the system's effectiveness in mitigating SCP through enhanced mechanical strength, fracture resistance, and self-healing capabilities that preserve long-term cement bonding. A comprehensive evaluation was conducted using formation data, casing details, and fracturing stresses up to 10,000 psi, supported by state-of-the-art in-house software for analysis. The analysis identified the optimal mechanical property window to ensure cement integrity while considering potential micro-annulus formation and mud channel retention. The cementing operation was executed using standardized slurry placement practices for conventional wells. Post-job evaluation included real-time monitoring and pressure data analysis to assess field performance and zonal isolation. In addition, design field simulation data were compared with real-time execution of the cementing operation to validate performance accuracy. Based on the technical analysis, conventional cement systems cracked under simulated high-pressure conditions, resulting in fluid migration and compromised well integrity. In contrast, the EACS, which is both flexible and self-healing, was identified as the best solution due to its unique ability to self-heal by swelling in the presence of hydrocarbons to restore and seal cracks. The flexible aspect of the system enables it to withstand fracturing stresses with a reduced Young's modulus compared to a conventional system. Field results confirmed the successful implementation of the flexible and self-healing cement system, which prevented SCP, improved zonal isolation, and ensured safe production without the need for abandonment. No SCP was recorded during pressure testing or production phases, and the well maintained stable pressure conditions without the need for remedial jobs. A comparison of real-time execution data with pre-job simulations showed strong correlation, supporting the predictive accuracy of the design. The EACS, which is flexible and self-healing, has proven to be a key innovation for mitigating SCP in challenging environments in Kazakhstan's shale oil reservoir. Its proven performance showcases its superiority in unconventional reservoirs where fracturing operations can compromise conventional cement integrity. This success provides an established solution for the industry moving forward in similar well conditions.