- Stuck packers or other downhold assemblies.
- Multiple strings (wrap around) - normally tubing.
- Crooked pipe - usually caused by dropping of pipe - either by pulling into or malfunction of elevators, etc.
- Foreign object in hole - any foreign object dropped in hole that cannot by-pass collars, tool joints or bottom hole assembly.
Key Seat Sticking - Key seat sticking occurs when different angles are present in a well. The pipe working around a corner or dog leg will cause the pipe to wear a groove in the side of the well bore. Often this condition will allow pipe to travel a short distance or to the next upset in the pipe. The upset is generally larger than the groove that is worn into the well bore and does not allow tool joint to pass. Common fishing procedures involve either backing off the pipe below the key seat to shorten the string length or free point and backing off the pipe above the key seat and running wash pipe through the keys seated area.
Sloughing Hole Sticking - Sloughing hole sticking is a problem encountered in drilling through heaving shale or other formations that have a tendency to break off and fall in the bore hole. The formation lodges around tool joints, stabilizers or drill collars. At this point wash pipe may be run in the hole to properly wash and circulate sand out of the hole and freeing up pipe.
Under-Gauge Hole Sticking - Under-gauge hole sticking occurs when a shale formation deforms, a salt that has tendency to flow, or a bit that is worn on the outside diameter by abrasive sand. This often occurs when drilling in hard rock formations. Continued drilling with an undersized bit will result in pipe being wedged into a hole that is too small and thus cause the pipe to be stuck. Common fishing procedure with this is finding free point then backing off above it and running in hole with jars to knock pipe free with upward jars.
Differential Pressure Sticking - Pipe can get stuck in an open hole when the pipe string comes in contact with a permeable formation of lesser pressure than the hydrostatic pressure of the drilling fluid. In this situation, the differential pressure causes the pipe to be held against the wall in the lower pressure zone. Common fishing procedures involve either adjusting mud weight to equalize hydrostatic and formation pressure, or free point and backing off pipe and using wash pipe through the lower pressure zone.
Underground Blow-Out Sticking - When underground pressure exceeds the existing hydrostatic pressure of the well fluid, it can cause sand, shale, other formations and even pipe protector rubbers to be blown up the hole, bridge over and string of pipe. Underground blow out is caused by pressure from one zone being too great for another zone. The blowout occurs when the higher pressure zone fluid breaks through into the lower pressure zone causing the fluids to flow into the lesser zones. This can cause several problems down hole that include differential sticking, sand sticking, gas kicks. Common procedures for this situation is running noise/temp logs to determine where fluid is being lost, and which zones are communicating so that next procedures can be determines. Often the next procedures will involve running bond logs, setting plugs, pumping cement.
Cement Sticking - Cementing may cause stuck pipe when there is a mechanical malfunction, human error, a lost circulation problem or during cementing to contain a blowout. Pipe can become stuck during cementing due to human or mechanical error. Running the pipe into green cement is the most common issue that is encountered. The common fishing procedure is running a free point to determine top of cement and then backing off above the cement. The next step includes running wash pipe and washing over and circulating the cement out of the hole.
Lost Circulation Sticking - This is an occurrence that normally react to hole sloughing or well blowouts. Lost Circulation Sticking is caused when drilling into a depleted or lesser zone that breaks down when exposed to higher hydrostatic pressures. The loss of circulation does not allow the cuttings and sands to be circulated out of the hole. This causes the cuttings to pile up around the downhold assembly sticking pipe. Commonly when circulation is lost, pipe will be pulled up to establish circulation and then lost circulation materials will be used as they begin down hole again. When pipe becomes stuck because of this, it is common to treat it as if it is a differentially stuck situation.