The objective of a cementing operation is to achieve a long-term well integrity by providing good zonal isolation. In cementing operations in the northern part of the United Arab Emirates (UAE), thick salt formations, potential high-pressure zones, lost circulation zones and planned high pressure casing test added to the complexity of the cement job.
The presence of 3,000-ft or thicker salt formation posed a key challenge. The chemically reactive salts in the salt sections affects slurry placement and hydration. Salt from formation can be incorporated into cement slurry while placement and adversely affects the fluid loss, rheology, and setting characteristics. Thus, first, the cement system needed to be designed to be tolerant of such effects. Also, high pore pressure was expected while drilling so the planned mud density varied from 15.5 ppg to 18 ppg. The highest cement slurry density of 19.2 ppg was required to cover this wide range while maintaining the density hierarchy requirement for optimum placement. Additionally, a high-pressure test planned after the casing was set resulted in additional stresses, which also posed substantial risks to the integrity of the cement sheath.
A methodical approach was applied by first following the standard cementing practices and then categorizing the key factors in overcoming field specific challenges. Stress analysis using advanced software helped to identify the needed mechanical properties for the flexible and expanding cement system to remain intact under extreme pressure changes. After the in-depth lab testing, a fit for purpose compatible for placement against salt formation cement system was introduced. The use of engineered lost circulation fibers in the cement system would help to mitigate the losses during the cement job.
The engineered high-density salt compatible flexible expandable cement system was designed to provide the desirable outcome to the complex challenges. Comprehensive lab testing along advanced zonal isolation software helped in successful first-time execution.
The first-time application of this salt compatible flexible and expanding cement system has proven to be a robust solution for the cementation and could be the basis of design for all future wells industry-wide.
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