TECHNICAL INFORMATION

Conclusion

Annulus cleanliness is the key to a reliable gaslift installation, Debris can adversely affect or completely block gaslift valves. This can result in high cost production downtime and extra well-service entries.

The annuli of all wells, in particular gaslift wells, must be clean. Fluids must be fine filtered, sound practices adopted during completion and walkover operation and, most importantly, all tubular goods should be thoroughly cleaned before installation. This means the removal of millscale from the inside surfaces of production casing and the outside surfaces of tubing.

Most recent research has shown that the internal surface of ex-mill 10,000 ft of 9 5/8" casing can contain over 800lbs. of millscale, while the externals of the same length of 5 1/2" can also yield over 800lbs. This amounts to in excess of 1600lbs. installed in the annulus of a well if untreated tubulars are used. Not all of it will be deposited in the annulus, but even if 50% were, this would amount to approximately 40 ft of fill in the annulus.

Have another look at the illustrations below. The most effective way of treating well tubular goods is by expert abrasive blast cleaning...

Millscale Debris