The three main causes of stuck pipe are:

1.Cuttings and cavings: build up in the annulus when mud and hydraulics fail to keep the hole clean. Poor design, deteriorating mud systems, pump failure, holes in the pipe, or many other conditions may give the same result. The drill string may not move up or down, and circulation may be restricted or absent.
2.Keyseat sticking generally occurs while the pipe is moving upward. The top of the drill collars, the uppermost stabilizer, and the bit are the most likely parts of the drill string to hang up in the keyseat, or slot, cut into the dogleg by the downhole assembly. Complete circulation is nearly always present during keyseat sticking, and the pipe is more likely to have freer movement downward than upward. Wall stuck pipe generally displays full circulation, but both up and down pipe movement are restricted equally. This type of sticking nearly always occurs in the bottom hole assembly. It comes about when the drill string has been stationary for a time. It is common when drilling highly deviated holes and when keyseated.
3. Differential pressure across the drill collars forces strong contact between the drill collars and the side of the borehole. The mud properties conducive to wall sticking are overbalance and high water loss.

First Action:

When the drill string sticks, work it in the direction opposite to which it was moving when it became stuck, Work it for an extended time.

jarring if drilling jars are in the bottom hole assembly and above the free point; do not immediately call for the fishing equipment. Decide what type of sticking is involved, and use stretch table to determine where the free point. If the drill pipe is worn to less than nominal weight, stretch tables may not be accurate. It should be possible to determine if the free point is moving up the hole. If this is the case, it is time to do something else.