1.0 Scope
A bailer can be used to remove sand and other particular debris and materials from a wellbore. This material may have bridged over or built up alongside the tubing wall.
2.0 General Information
There are different types of bailers: the pump bailer, the drive down bailer, and the hydrostatic bailer.
• Pump Bailer - The pump bailer has a cylinder-shaped barrel, where a rod is used on a piston assembly. This piston assembly sucks material into the barrel.
This material is trapped inside by a check valve (which is either a ball or flap-per). This check valve is called a “bailer bottom.” (see cautions).
• Drive Down Bailer - This bailer also has a cylinder-shaped barrel, but it differs from the pump bailer. This bailer has tip sub made up on top going a 5/8 in.
sucker rod thread. On the bottom of the bailer you have a check valve, or bailer bottom, as it is known. This bailer uses the hammering action of the wireline tool string to drive it into the material that is being bailed (see cau-tions).
• Hydrostatic Bailer - This is cylinder-shaped, consisting of a seal chamber that contains air at atmospheric pressure. The seal at the lower end of the barrel is a brass shear disc. A skirt and ball-type check valve is made up on the lower end of the barrel, below the shear disc. The skirt on the bailer bottom is designed with a larger I.D., which allows it to move down and around with the fishing neck of the subsurface control device. When the skirt stops on the downhole control device, a few downward jarring strokes will shear the brass disc. When this occurs, the sudden influx of well fluid or gas into the chamber will carry the remaining debris past the check valve and into the chamber.
Note Special junk baskets are designed to catch larger parts that cannot get around check valve. Also, a hydrostatic bailer should only be used for cleaning off a minor amount of debris above a fish neck or other hard component. Do not run in to bail soft material, since the bailer will suck itself into the material and may become stuck.
Slickline Operations Manual SL 2.23: Bailing Operations
3.0 Procedure
1. A proper gauge run should be made.
2. Attach to a tool string and zero at the tubing hanger.
3. Run in hole at moderate speed (taking consideration of nipples, tight spots, gas lift mandrels, collars). Once you reach the obstruction, sit down, then pick up on the tool string, slowly lifting the rod on the piston assembly. As this is done debris material is sucked into barrel. This procedure is done over and over until the operator sees that he is no longer making hole, or feels the bailer is full.
4. Remove the bailer from well. (Repeat as above. Clean up debris, sand, etc. as necessary).
CAUTION If the bridge that is being bailed has a pressure differential below it, the tubing above the bridge should be completely filled with a fluid and/or be pressurized to a pressure that is at least equal to the pressure below the bridge. This is to pre-vent the wireline tool string from being blown up the hole when the bailer breaks through or weakens the bridge.
After each upward pump stroke, the bailer should be pulled up the hole a few feet above the original depth of the top of the bridge. This will help to avoid the possi-bility of the bailer becoming stuck in the bridge.
Note A muleshoe bailer bottom seems to work best when bailing sand.
A flat-bottom bailer with noted chisel marks helps to give the operator indications when fishing on tools, wire, etc.
Also, while bailing, the bailer will sometimes get stuck. When this happens, pull a couple of hundred pounds over pickup weight and stop. Have patience and wait.
This will normally be enough to pull free.
During bailing operations, it is recommended to pickup out of debris to ensure that debris is not falling back on top of tools, causing the tool string to become stuck and/or lose jarring action.
Care should be used when breaking the bailer down because it is possible for sand to bridge over inside the bailer, causing a pressure differential.
Slickline Operations Manual SL 2.23: Bailing Operations
CAUTION The hydrostatic bailer should not be used until the sand has been removed from the tubing down to the top of the subsurface control device. When jarring down on a long sand bridge to shear the disc in the hydrostatic bailer, the bailer may be driven into the bridge and become stuck even if the disc does not shear. If the disc shears, the bailer may bury itself in the bridge to the extent that it may become stuck.
After retrieving the hydrostatic bailer to the surface, care must be taken when opening the bailer due to the possibility of pressure being trapped in the chamber.
Even though the bailer is equipped with an automatic pressure relief valve and also a normal pressure relief valve, it is possible that the internal pressure port leading to both relief valves could become plugged. The upper allen head set screw should always be backed out at least two to three rounds to allow the ball relief valve to move off seat before opening the bailer.
Note Shear disc come in: (Hydrostatic pressure ratings) Thin 4025 psi, Medium 7450 psi, Thick 12, 175 psi. Also, snorkel bottoms for hydrostatic bailers made to get inside locks.
Slickline Operations Manual SL 2.24: General BHP/BHT Surveys