We can define Key seating term in drilling as it s a groove in the hole side made by the Drill Pipe rotating against the bore hole wall at the same point and wearing a groove or key seat in the wall. During trip out of hole , the Bottom Hole Assembly BHA, Drill Collar , Stabilizer, Mud Motor or any big diameter component may wedge into one of these large grooves, which may be too small for it to pass though. This Key Seat sticking is likely to happen in a soft formation in directional wells while dropping the inclination. It can also occur at the casing shoe if a groove is worn in the casing.
Below is a nice video to show you the meaning of the term key seat in drilling.
Where the drilling problem Key seat happen:
- At abrupt changes in angle or direction in medium-soft to medium-hard formation. This abrupt change will make the drill pipes always make a channel in the same postion as drilling continues
- Where high side wall forces and Drill String rotation exist.
- While pulling out of the hole.
- After long drilling hours with no wiper trips through the dogleg section. As wiper trips will help in smoothing such key seat and will help to RIH and POOH through it with lower probability of Stuck Pipe problem.
How to avoid Pipe Stuck Caused By Key Seating?The Preventive measures depend on keeping any turns or ant angle changes in the well bore gradual and smooth and enlarging the grooves created by Drill Pipe so that the larger diameter tools as Drill Collar, Heavy Weight Drill Pipe HWDP, Bottom Hole Assembly BHA and the casing strings will pass through it.
- First thing to think about is the Wiper Trips.
- Directional Driller had to build angles and turn smoothlysto decrease dogleg severity.
- In the well planning phase if you suspect a key seat problem, you have to plan for using String Reamers and Key seat wipers in Bottom Hole Assembly BHA.
What is the Key Seat Wipers
The Key Seat Wiper is installed just above the top Drill Collar. It contains a sliding Reamer sleeve with an O.D. slightly larger than the Drill Collar. When POOH, its sliding Reamer sleeve meets the key seat first - instead of the Drill Collar - by becoming wedged in restricted space.
By releasing the Drill Pipe, the sleeve may be jarred out of the key seat. A clutch-drive on the bottom of the sleeve and the lower body is engaged by right-hand rotation.
Slowly raising the Drill String and continuing rotation allows the sleeve to function as a Reamer and wipe out the key seat. The operation may be repeated to further enlarge the area, thus permitting free passage of the Drill Collar.
How you could recognize the drilling problem "Key Seat"It is so simple to detect such key seat. from its definition we already known that you can expect it while POOH with the Drill String, in soft formations, abrupt change in Inclinations and azimuth. Below the main indications that you would like to know.
- Occurs only while POOH.
- Sudden overpull as Bottom Hole Assembly BHA reaches dogleg depth.
- Free Drill String movement below key seat depth possible if not already Stuck in key seat.
- Cyclic erratic overpull at Tool Joint intervals on trips as the each Tool Joint keep meeting the key seat.
- Large dogleg.
- Highly deviated wells.
- Circulation possible.