Keyseating is one of the primary reasons for fishing during drilling. A key seat is a small hole cut into the well bore wall due to the movement of the downhole drilling assembly. This cut usually happens when the hole changes direction, the hump of doglegs, in undetected ledges near washouts. A part of the drilling assembly can get stuck in the key seat. In other words, Keyseats are the primary cause of mechanical sticking not differential stuck. This is why we need the key seat wiper.
The sticking typically happens when tripping a pipe out of a hole. As the drill pipe passes through the slot, larger diameter components, such as drill collars or stabilizers, become wedged into the keyseat. Fortunately, we can detect key seats in advance, and take preventive measures before having a stuck pipe problem. To prevent this, it is essential to identify its signs and immediately take steps to eliminate it.
What is The Key Seat Wiper?
The Key seat Wiper is a tool that we use to eliminate keyseats from the wellbore. Its cutting structure is made of crushed tungsten carbide, which is usually dressed to a size larger than the maximum outer diameter of the drill collars used in the BHA. The tool is highly effective due to its aggressive cutting structure.
Benefits
- It allows for tripping in and out with lower drag (also check torque and drag).
- Efficient removal of keyseats.
- It abrupts doglegs in soft formations.
- Minimizes damage to the borehole wall.
- Decrease the probability of the mechanical stuck problem.
Key Seat Wiper Mechanism
When it comes to drilling operations, a key tool to know about is the Key seat Wiper or Reamer. This tool comprises a mandrel and sleeve with spiraling Tungsten Carbide strips, and it sits above the drill collars in the string. The Sleeve is just a bit larger than the drill collars, and it works to cut clearance for the collars using the Tungsten Carbide strips. During drilling, the sleeve stays engaged with the Positive Clutch and rotates along with the drilling bit. But what if the sleeve gets stuck and won’t rotate? No need to worry – the Overriding Clutch located at the upper end of the tool can produce a downward blow to help dislodge the sleeve. With the Key Seat Wiper or Reamer in play, drilling operations can be a bit more manageable than they may seem at first glance.
References:
- NOV Fishing Tools Manual
- Bowen Fishing Manual