Cement dress-off tool eliminates drillstring trip during P&A
Developed by SLB, the cement dress-off tool (DOT) saved a complete pulling out of the hole (POOH) and running in hole (RIH) verification trip, enabling SLB to pump, tag, and dress off cement all in the same run.
For years, safety and service quality risks have been linked to pumping cement plugs through a bottomhole assembly (BHA) or drill bit. This is because the cement slurry often gets swabbed and disturbed during the process of POOH. Computer simulations don't currently consider the swabbing effects, which means the determination of the theoretical top of cement (TTOC) isn't as dependable as when cement plugs are placed using a drillpipe or “stinger.” Faced with this challenge on the Norwegian Continental Shelf (NCS), the objective was to improve plug TTOC reliability during plugging and abandonment (P&A) while saving rig time.
The solution was the cement dress-off tool. Developed by SLB, this innovative tool provides both effective cement plug placement and cost-saving operational efficiency. The DOT is equipped with gauge protection features to prevent or minimize casing wear. It also has a polycrystalline-diamond compact (PDC) cutting structure with a high back rake angle for efficient tagging and dressing-off. It eliminates the need for an entire drillstring trip, both POOH and RIH, thus saving valuable time during P&A operations.
The DOT features a bullet-shaped bit body with aerodynamic blades for minimum slurry disturbance during POOH. An antiballing coating is applied to the bit to ensure minimum disturbance of slurry. The tool is dressed with a PDC cutting structure for effective tagging and dressing off ability and gauge protection to prevent or minimize casing wear. On the NCS, the DOT has been used on numerous offshore runs on multiple wells and depths. In all cases, it has consistently proven effective in tagging and dressing the cement top. After POOH, the tool was dull graded and maintained its gauge with the cutting structure remaining sharp on all corners. There was no wear observed on the body of the DOT, and both the threads and cutter face were in excellent condition.
The DOT has been successfully used for HPHT P&A operations on the NCS where three cement plugs were successfully placed. A total of three cement plugs were pumped wet-on-wet through the tool with volumes of 8.8 m3, 8.8 m3, and 10.7 m3 of heavy 2.10-sg cement slurry. This technology was also used on a campaign of lost circulation plugs where a total of three cement plugs were pumped through the DOT with volumes of 50.2 m3, 61.0 m3, and 35.3 m3 of 1.92-sg cement slurry. Two sponge balls were pumped through the DOT for each plug to perform mechanical separation with no issues. The first two plugs were tagged with 5 metric tons and 10 metric tons of applied weight, while the third plug was tagged with the drilling BHA as the rig was able to run in earlier after eliminating two trips.
Using the cement dress-off tool eliminated the need for a full pulling out of the hole process as well as a running in hole verification trip. This allowed SLB to pump, tag, and dress off the cement in a single run.
