The adequate cementation of an expandable tubular can be challenging but is essential for long-term casing integrity. Such cementing jobs are especially crucial under high-pressure/high-temperature (HP/HT) conditions for many reasons, including but not limited to rigorous HP/HT laboratory testing schedules, selection of proper cement volume and fluid density, etc. A failed cement job in expandable casing does not allow for a remedial cement job and thus can jeopardize the entire well.
An operator in Egypt required running and cementing a 9 5/8-in. expandable casing at 5625 m inside a 12.25-in. open hole (OH). The length of the expandable tubular was approximately 850 m, which corresponds to an expansion time of 8 1/2 to 9 1/2 hr. Accordingly, an adequate cement slurry would require a minimum of 13 to 14 hr of thickening time, with a very long zero gel time. As no centralizers were run, homogenous slurry distribution was also one of the main concerns for this job. Another potential issue for the slurry design was the presence of a possible gas zone in this section, which could cause flow and create a permanent channel in unset cement during casing expansion.
An 18.5-lbm/gal anti-gas-migration slurry was designed and tested under 16,300-psi bottomhole pressure (BHP) and at 315°F bottomhole static temperature (BHST) to meet the job requirements. Various numerical simulators were run to calculate hydraulics and displacement efficiency to achieve the zonal isolation objectives and optimum cement sheath around the casing. A specially designed casing shoe was also used to accommodate a foam ball, which acted as a bottom plug to help minimize cement slurry contamination while pumping.
This paper describes the challenges, solutions, and lessons learned during the design and execution phase while cementing the deepest expandable casing in Mediterranean offshore Egypt.