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Beyond the Tool String: All about Slurry Bailers

This Month, We Get into Bailers Used in Cable Tool

As we drill hole and add water, the drill tools form a slurry. After a few feet — or, perhaps, quite a few feet — we have to remove that slurry from the hole. For this, we need a bailer, a piece of pipe or tubing smaller than the inside diameter of the casing we use. Bailers vary from 2½-inches OD for 3-inch ID casing all the way up to 14-inches OD for 16-inch ID casing. Bailers range from 10- to 30-feet-long, and weigh from 40 to 1,000 pounds depending on the length and diameter. Drillers can also use bailers, in a limited capacity, to test pump a completed well.

Flat-Bottom Bailers in Drilling

Next, I want to talk about the shorter flat-bottom bailer. While not as popular as the dart-valve bailer, it also comes in many different diameters. It features a flat bottom, or flapper, in place of the dart valve. The flapper functions much more effectively than the dart valve in sands and gravels. The flapper also cleans out closer to the bottom of the hole than the dart valve can. This feature helps when baling inside a well screen to remove sand pulled in through development. The flat-bottom bailer has the big disadvantage of having to be tipped or upset to dump, hence the shorter length.

For best results when running either a dart-valve or flat-bottom bailer, when you reach the bottom of the hole raise it a foot or two and let it drop several times before raising to the surface.

Sand Pump Bailers in Drilling

A third type of bailer called a sand pump or vacuum bailer shares the tubular construction of the dart-valve or flat-bottom types, but has a plunger inside attached to a rod that comes out the top. This bailer excels in sand and gravel. It lowers to the bottom of the hole and the plunger goes to the bottom of the bailer. When raised, the plunger creates suction, pulling sand and gravel into the bailer proper. Operators can do this once or several times on each trip to the bottom.

These bailers have a removable bottom, usually a flat type, that allows contents to drop out when removed. Depending on the formation, water levels in the casing and other factors, these bailers can vary from very effective to extremely ineffective. If we drill in sand and gravel, I’d call having one of these vacuum bailers or sand pumps essential to the operation. They are usually no more than 10-feet long.

Remember, regardless of type, every bailer varies in effectiveness with the geology and the characteristics of the hole.