Mechanical Pipe Sticking
1 Introduction To Mechanical Pipe Sticking:
Mechanical Pipe sticking is when any part from the Drill String such as Drill Pipe, Heavy Weight Drill Pipe HWDP, Drill Collars, Drilling Bit or Bottom Hole Assembly BHA is stuck in a borehole due to mechanical reasons as cutting accumulation, junk, large cement cutting and changing Drill String geometry and cannot be recovered from the bore without damage to the drill pipe. It can occur because of a variety of reasons as will be discussed below.
2 What Is The Real Mechanical Stuck Pipe Causes
Key Seating As a Mechanical Stuck Pipe Cause
Undergauge Hole Mechanical Stuck Pipe
|Undergauge Hole Stuck Pipe|
Under gauge Holes can easily cause a Mechanical Pipe Stuck as it happens after the Drilling Bits and the Stabilizers gauges got worn while drilling abrasive rock, so the following section using the same Drilling Bit will produce Undergauge hole. And if it was decided to run new in gauge Drilling Bit after that, it will have difficulty to run in the last Undergauge section and reaming will be required to pass this Under gauge section.
If it was decided to run quickly without reaming, the Drilling Bit can jam in the Under gauge hole and become stuck.
Ledges and Doglegs
|ledges at formation changes|
Ledges and Doglegs are one of the causes of mechanical stuck pipe. We can define ledges as following: The well bore passes through rock of varying types and ledges develop at the interfaces between layers of differing hardness.
Closely spaced ledges decreases the effective diameter of the hole and produce a “shouldered” hole surface. The stiff casing string requires a smooth, more in-gauge hole diameter for free passage and not to stuck.Also Doglegs can be defined as following: While drilling a well bore, the characteristics of the rock cause the Drilling Bit to be deflected and can result in a change in Azimuth. Likewise when drilling with a directional Bottom Hole Assembly BHA, sudden changes in angle can cause a kink in the well bore direction. Sharp deviations in wellbore direction are called doglegs.
Metal Junks Dropped Or Parted Cause Mechanical Stuck Pipe
We mean by junk any material, any tool or any piece of equipment may fall down from surface of from downhole Bottom Hole Assembly BHA and equipment. Th junk may jams the Drill String and produce easily a good junk stuck. This type of mechanical stuck pipe usually occurs:
- Due to poor housekeeping on the rig floor.
- The hole cover not being installed.
- Downhole equipment failure.
Collapsed Casing Mechanical Stuck
Casing collapses either if pressure conditions exceed its original rated collapse pressure or the original collapse pressure rating of the casing is no longer valid due to casing wear and/or corrosion. Casing wear due to friction or corrosion decreases the effective collapse pressure rating of the casing,
Mechanical Stuck Pipe In Cement Blocks
|Cement Blocks Stuck|
The Drill String becomes jammed in the hole by cement blocks falling around the drill string. This mechanism normally occurs when : Hard cement becomes unstable around the casing shoe, open hole squeeze plugs and kick-off plugs.