Fighting Scale—Removal and Prevention

Few production problems strike fear into the hearts of engineers the way scale can. Scale is an assemblage of deposits that cake perforations, casing, production tubing, valves, pumps and downhole completion equipment, thereby clogging the wellbore and preventing fluid flow. Scale, just like the scale found in home plumbing or tea kettles, can be deposited all along water paths from injectors through the reservoir to surface equipment. Most scale found in oil fields forms either by direct precipitation from the water that occurs naturally in reservoir rocks, or as a result of produced water becoming oversaturated with scale components when two incompatible waters meet downhole. Whenever an oil or gas well produces water, or water injection is used to enhance recovery, there is the possibility that scale will form. In some areas, such as the North Sea and Canada, where entire regions are prone to scale, it is recognized as one of the top production problems. Scale can develop in the formation pores near the wellbore—reducing formation porosity and permeability. It can block flow by clogging perforations or forming a thick lining in production tubing (above). It can also coat and damage downhole completion equipment, such as safety