What is Stuck Pipe Calculation ?

Stuck pipe calculation is a process used in the oil and gas drilling industry to estimate the forces and pressures acting on a drilling string when it becomes stuck in the wellbore. When drilling a well, the drilling string (consisting of drill pipe, drill collars, and other components) is used to advance the wellbore by rotating the drill bit and applying downward force. However, sometimes the drilling string can become stuck in the wellbore due to various factors, such as differential pressure, wellbore geometry, or formation conditions.

1. Differential Pressure: The pressure difference between the wellbore and the formation outside the drilling string plays a significant role in causing pipe sticking. Differential pressure can result from formation fluids (e.g., oil, gas, or water) flowing into the wellbore or from drilling mud filtrate invading the formation.
2. Frictional Forces: The frictional forces between the drilling string and the wellbore wall can hinder its movement. The calculation considers the contact area, coefficient of friction, and applied force to overcome these frictional forces.
3. Buoyancy: The buoyant force acting on the drilling string due to the density of drilling fluid inside the wellbore is also considered.
4. Wellbore Geometry: The size and shape of the wellbore, as well as any ledges, key seats, or narrow sections, can contribute to pipe sticking.
5. Drill String Weight: The weight of the drilling string and its components is also a crucial parameter in the calculation.

By taking these factors into account, engineers and drilling personnel can estimate the forces acting on the stuck drilling string and decide on the appropriate actions to free it. Remedial actions may involve applying more weight on the drill string, circulating specialized chemicals to reduce differential pressure, or employing mechanical fishing tools to retrieve the stuck section.

It is important to note that stuck pipe situations are costly and can cause significant delays in drilling operations. Therefore, drilling teams rely on careful planning, real-time data monitoring, and the application of best practices to mitigate the risk of stuck pipe incidents.

The steps of calculation are as follows:

1 ) Determine the free point constant (FPC) by this following formula:

FPC = As x 2500

where: As = pipe wall cross sectional area, sq in.

As = (OD²-ID²) x 0.7854

OD and ID are inch unit

2) Determine depth of stuck pipe by this following formula:

Depth of stuck pipe = (Pipe stretch in inch x free point constant (FPC)) ÷ Pull force in thousands of pounds

Please see the example below to demonstrate you how to apply those 2 formulas above into real drilling operation.

Example#2: Determine the free point constant (FPC) and the depth the pipe is stuck using the following information:

3-1/2” tubing # 9.5 lb/ft

3-1/2” tubing ID = 2.992 inch

20 inch of stretch with 25 Klb of pulling force

a) Determine free point constant (FPC):

FPC = (3.5² – 2.992²) x 0.7854 x 2500

FPC = 6475.5

b) Determine the depth of stuck pipe:

Feet of free pipe (ft) = (20 inch x 6475.5) ÷ 25

** 25 is the kilo-force to pull to 20 inch **

Feet of free pipe (ft) = 5,180 ft