The Situation

With pit space and hole volumes tight on this semi-submersible, extra tank space could not be certified in time for use. Consequently, to achieve a successful downhole clean-up and displacement of WARP oil-based drilling fluid OBM to a filtered completion brine required a particularly efficient wellbore clean-up chemical suite to be pumped between the two fluids to achieve a clean and discrete interface.

The Solution

On the basis of data from our VIRTUAL COMPLETION FLUIDS* (VCF) modeling program, the M-I SWACO Wellbore Productivity Group suggested the operator employ its newly engineered DEEPCLEAN , double emulsion wellbore clean-up chemical in the spacer suite to be pumped between fluid types. Since its introduction in 2010, this one - pit spacer had proven extremely effective in this type of environment and with this mud type. The tight space posed no restrictions. M-I SWACO expressed confidence in the success of the overall process that would combine VCF, downhole tools, surface filtration with the DEEPCLEAN spacer.

The Results

Rather than have the rig shutdown for what would otherwise have been three days, the displacement proceeded, despite unforeseen difficulties, including being unable to backload all of the surface volume of OBM. Furthermore, when receiving the completion brine, a transfer hose burst, followed by a weather delay that prevented additional brine from being transferred to the rig.

Compared to offset wells, no thick gelled pills were seen on this job. Once sufficient pit space was available on surface and more brine was received, the well was displaced out to spec brine with trace solids and 46 NTU – all in one circulation. Indications of a good clean up was seen with a heavily contaminated push pill, while the wash pill appeared clean. Despite full surface lines and pits that caused the rig pumps to be shut down before all of the pills had exited the well, it was decided to continue the operations. The online filtering of completion fluid continued on one pit and when the weather improved, surface waste (“slop”) volume and OBM were back loaded. Filtering continued on one pit to a 0.05% v/v solids specification, while cleaning surface pits and waiting on weather for more brine. The drill pipe was pulled clean.

The Details

The lower completion screens were run without any problems and the packer set at 6,717 ft (2,047 m). A 5 in. mule shoe was run in on 5 in. drillpipe and 5 in. heavy weight drillpipe to the top of the packer. The well was displaced to 9.3 lb/gal (1.11 s.g.) NaCl brine as per the program. The hole and riser volume was 711 bbl (113 m3).

The pill sequence was as follows:

• 0 bbl (9.5 DEEPCLEAN ) base oil
• 75 bbl (11.9 DEEPCLEAN ) HI-VIS DEEPCLEAN Pill
• 135 bbl (21.5 DEEPCLEAN ) DEEPCLEAN Wash Pill
• Displaced with 9.3 lb/gal (1.11s.g.) Sodium Chloride Brine

Once back at surface, the returning base oil, DEEPCLEAN pills, and interface were diverted to the pits and sand traps. Because of adverse weather conditions, it was impossible to backload the remainder of the OB WARP as well as the returned pills and interfaces. Once the brine had returned to surface, the pumps were shut down and the header box shaker sumps and flow lines were cleaned to allow discharge overboard. At that point, it was decided to circulate the well on a closed system utilizing only one pit for brine. This meant the brine would be pumped and returned to the same pit where the fluid would be filtered on itself during the operation. Normally, brine is pumped from one pit returned to another pit and then filtered from the returns pit to the suction pit. Between the two DE filter presses on board, a total of 1,100 bbl (175 m3) of brine was filtered.

At an appropriate lull in the weather, 940 bbl (149.5 m3) of oily waste water and 942 bbl (150 m3) of OB WARP were back-loaded. Pits were cleaned to brine standard and 950 bbl (151 m3) of 9.3 lb/gal (1.11 s.g.) sodium chloride brine prepared. Filtering then commenced on the two pit system and a further 1,422 bbl (226 m3) of sodium chloride brine was received.

With fresh stocks of brine on board, 860 bbl (262 m3) of 9.3 lb/gal (1.11 s.g.) brine was built and the well displaced to clean brine. An additional 550 bbl (87.5 m3) of 9.3 lb/gal (1.11 s.g.) brine was built and the well again was circulated to clean brine.

Circulation continued and three consecutive readings of less than 0.05% v/v solids were achieved over one full circulation. Afterwards, another circulation was carried out while adding 0.25 liters/bbl (0.04 l/m3) SAFE-CIDE* biocide, 2.0 liters/bbl (0.32 l/m3) SAFE-COR* 220X corrosion inhibitor and 0.04 liters/bbl (6 x 10-3 l/m3) SAFE-SCAV* NA oxygen scavenger.

The wellhead area was jetted and the upper completion was run as per program. A jetting sub was made up and run in the hole to wash out the hanger profile. Two riser volumes of brine were pumped followed by a 50 bbl (8 m3) high viscosity pill and two riser volumes of brine. No solids or oil contamination were observed. The jetting sub was then pulled out of the hole.

Questions? We’ll be glad to answer them.

If you’d like to know more about the DEEPCLEAN product and how it’s performing for our other customers, please call the M-I SWACO office nearest you.