"Cleaning and gauging the 4½ inch production casing is another...

"Cleaning and gauging the 4½ inch production casing is another risk mitigation measure arising from Cambay-76H lessons learned. Cleaning operations are imperative prior to any perforations to ensure a high quality operational result is achieved. Finally, Schlumberger worldwide centres of excellence have reviewed the planned coil tubing operations and fracture stimulation programme to ensure these maximize the chance of a trouble free result. "

Got to be happy with that kind of quality checking and cleaning.
I guess this is what you get when you hire a world class fracking company like Schlumberger....