Abstract

Shallow water flows pose a significant risk to wells drilled in offshore environments due to the risk of uncontrolled release of fluids and destabilization of seabed leading to potential subsidence, and potential loss of well or location in extreme cases. The flows are typically encountered just below the seabed in overpressured formations while drilling and cementing tophole sections and present additional complexity to the cement job design where the margin available between the pore and fracture gradients is narrow. Successful isolation and the ability to provide long-term integrity for subsequent structures is of paramount importance from a cementing perspective. For the slurry to be able to provide isolation, good transition time from liquid to solid phase and early compressive strength development with lightweight cement slurries are to be considered. Concerns about post placement cement sheath shrinkage providing a path for fluid migration to surface must also be addressed

The Caspian Sea is known to possess many geohazards, especially in the shallow formations close to the seabed, which can prove detrimental to the safety of the projects during the well construction phase and long-term well integrity during the life of the well. Furthermore, stringent well integrity and environmental standards require additional mitigations to be put in place to provide long-term solutions, thereby mitigating the potential for remediation work after primary cement job placement. Case studies illustrate the approach taken for surface casings cemented in the southern Caspian Sea with optimized slurry design used in conjunction with mechanical barriers to deliver success.

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