Schlumberger

Case Study: DEEPCLEAN Double-Emulsion Clean-Up Pill Proves its Worth in Difficult Displacement

Challenge: A Gulf of Mexico operator planned to re-enter a well that had been shut in for at least 10 years with 10.5 lb/gal (1.2 sg) synthetic based mud. The operation would require drilling a sidetrack before attempting to complete the well. Owing to the unknown condition of both the mud and casing, the operator required an additive that offered the best possible efficiency for cleaning and water wetting the casing.

Solution: The operator selected a wash spacer formulation incorporating the new dual purpose DEEPCLEAN product, which also was specified as an additive in the transition spacer. The DEEPCLEAN product is engineered for thorough and efficient cleaning of technically demanding well cleanups. DEEPCLEAN product was especially designed and tested to outperform other cleaning products even in laminar flow. In addition, the displacement was designed using M I SWACO best practice design techniques.

Result: After circulating only 200 bbl of seawater, the NTU reading was less than 100, indicating a successful casing cleanup and displacement. Further evidence of a successful cleanup was observed when the well was displaced with the clear brine and the final NTU reading was reduced to 25 with only a trace of solids.

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:

  • 60 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.


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“Having DEEPCLEAN on this operation was a big step change in the right direction from previous jobs, considering pit space was tight and efficient clean-up of downhole tubular was imperative.”
Ken Adam
Senior Completions Engineer
Maersk UK