Published: 06/15/2016
Published: 06/15/2016
An operator was drilling the Cygnus field in the North Sea. Traditionally, complying with North Sea environmental restrictions requires the use of lower-performance chemicals, resulting in increased costs, waste volumes, and rig time for well cleanup. Because pit space was limited on the operator’s rig, the operator sought to optimize displacement efficiency by deploying a casing cleanup chemical that would fulfill performance requirements while meeting the strict environmental standards of the region.
M-I SWACO proposed using the SAFE-SURF EU casing cleaning agent, which features a gold rating in the Centre for Environment, Fisheries, and Aquaculture Science (CEFAS) list of Chemical Hazard and Risk Management (CHARM) chemicals. The agent provides effective cleanup performance for efficient displacement while enabling operators to meet North Sea environmental standards. Designed primarily for downhole cleanup in oil and gas wells, the SAFE-SURF EU agent performs the tasks of thinning, dissolving, and dispersing oil-base mud residues as well as leaving all downhole tubulars and metal surfaces in a water-wet state.
On the basis of previous displacement operations in the Cygnus field, M-I SWACO prepared a detailed pit management program. Spacers were prepared in advance, and the wellbore cleanout string was run in the hole. A concentration of 10.8-lbm/galUS [1,296-kg/m3] VERSAPRO invert-emulsion reservoir drill-in fluid system was circulated and conditioned.
The pill train consisted of
The chemicals were placed directly in the pits and blended by agitators in the pits. No foaming was observed after adding the chemicals.
The pill train was pumped at 3 bbl/min [0.48 m3/min] down the 5-in drillpipe and 2 3/8-in washpipe to the no-go landing nipple located at 12,374-ft [3,772-m] MD. Once all of the pills were 500-ft [152-m] MD above the MFCT multifunction circulating tool technology, the tool was opened, and the flow was increased to 14 bbl/min [2.2 m3/min].
Challenge: Optimize displacement efficiency on a rig with limited pit space and reduce costs through improved cleanup times.
Solution: Use the SAFE-SURF EU casing cleaning agent to enhance cleanup performance.
Results: Achieved operator objective of decreasing solid-in-brine level to less than 0.05% and demonstrated water-wet pipe with no residual oil after the pipe string returned to surface.
