Once validated by simulation, the FlexSTONE flexible cement technology
was pumped downhole, followed by formation integrity testing to evaluate the
The UGS well is drilled in four stages, which include the surface
casing, first intermediate casing, second intermediate casing, and production
In the third stage, FlexSTONE technology is used as tail slurry in the
second intermediate casing to cement and seal the caprock of the depleted
reservoir and ensure a complete entrapment, while the normal slurry system is
used as lead.
During the last stage, FlexSTONE technology is used in the production
liner cementing. The liner is perforated and natural gas will be injected and
withdrawn through the liner into the depleted gas reservoir.
Establishing long-term well integrity and preventing remedial jobs
A total of 32 wells were successfully drilled and cemented according to
their individual stress requirements, giving PetroChina its first underground
gas storage field in western China, which is capable of holding 4.51 ×
109 m3. Formation integrity tests for the newly constructed wells showed no
losses, excellent bonds, and good formation arrivals, proving the strong
coupling between the cement and the formation.
The high quality and flexible nature of the FlexSTONE advanced cement
technology gave wells integrity to last 30 years or more under high-intensity
injection—preventing costly remedial jobs entirely. Furthermore, the
careful and intentional design strategy employed by the Schlumberger team
ensured safe operations close to the populated areas of Hutubi.