Circulating sub ensures effective cementing operations
Churchill Drilling Tools’ DAV MX circulating sub has helped cut process time and costs for two cementing operations in wells in the US Gulf of Mexico and offshore Norway.
The multi-function, multi-cycling circulating sub (CircSub) is activated using Churchill’s MX Smart Dart technology. Its valve assembly operates on a piston and spring mechanism, which is activated when a dart is pumped down the drillstring.
In one deepwater well in the GoM, several failed lost circulation material (LCM) pills had been deployed at a depth of 28,000 ft (8,534 m).
A 250-bbl cement slurry of 16.6 ppg was directed into the formation via the DAV MX ports to protect the lower bottomhole assembly (BHA), with the cement delivered directly to the loss zone.
According to Churchill, the system’s ‘latch and seal’ capability prevented ingress into the lower BHA while the ‘lock open’ feature allowed bypass at low flow rates to restrict dynamic losses.
In a high angle well in the Norwegian North Sea, acement slurry was delivered through a closed DAV MX and onto the bit to cure severe losses at 18,823 ft (5,737 m).
Two treatments of fracture-sealing cement were pressured into the formation and activator balls were chased through (without opening the DAV MX) to clean any residual material from the pipe.
At the TD of 20,748 ft (6,324 m), the CircSub was then activated in ‘split flow’ mode to allow rotation of the string for hole cleaning purposes.
Churchill CEO Mike Churchill said: “In these high-risk operations, it is important that the technology is as robust as possible because cement ingress can compromise valve functionality - causing non-productive time.
“The most likely type of damage would be an inability to re-seal after the closing cycle, however in these two cases, the operators were not exposed to valve NPT due to the robustness of the DAV MX.”