## Differential Stuck Pipes

### Definition Of Differential Stuck

This kind of stuck is happened when the hydrosatic pressure,*p*

_{h}, which acts on the outside wall of the

**Drill Pipe**, is more than the pore pressure,

*p*

_{ff}, which leads to force the

**Drill Pipe**into the mud cake , then the pipe is said to be differentially stuck. This can happen on

**Drill Pipe,**

**Heavy Weight Drill Pipe HWDP or**

**Drill Collar**but the differential stuck is more likely to take place in the

**Drill Collar**as it has larger diameter than

**Drill Pipe**and

**Heavy Weight Drill Pipe HWDP.**

The differential pressure acting on the part of the

**Drill Pipe**which is differential stuck in the drilling mud cake can be calculated from the below equation:
The pull force, F

_{p}, which are able to free the differential stuck pipe is calculated by below equation:**Where:**

- The differential pressure, Δ
*p.* - The coefficient of friction,
*f*. - The contact area,
*A*_{c}, between the drilling mud cake and the differential stuck pipe surfaces.

*A*

_{c }can be calculated from this equation:

**Where**:

*L*_{ep}is the length of the permeable interval.*D*_{op}is the differential stuck pipe outside diameter.*D*_{h}is the drilled hole diameter.*h*_{mc}is the thickness of the filter cake.- The dimensionless coefficient of friction,
*f*, its range from +/- 0.04 for OBM to +/- 0.35 for WBM with no lubricants.

### Factors Affecting Differential Stuck Force

**Above Equations**shows the main factors that will cause the increase in the differential stuck force and the decrease of the probability of

**Freeing The Differential Stuck Pipe**.

These factors are:

- Unnecessarily high differential pressure between hydrostatic pressure and pore pressure.
- Thick filter cake (high fluid loss to the formation)
- Low lubricity filter cake (higher friction coefficient)
- Excessive differential stuck pipe length in the filter cake (time delay in freeing differential stuck)
- Hole and pipe diameters
- Inclination play a role in the differential stuck force. they are uncontrolled variables once they got chosen for the well design objectives. However,
**Drill Collar**shape, such as spiral grooves , external-upset tool joints or square can minimize the differential stuck force.

### Differential Stuck Pipe Indicators & Signs

There will be signs or indicators while drilling permeable or depleted zones. if these indicators happen, you should think that you may get a differential stuck :

**Torque And Drag**increase.

- Unable to reciprocate or in some times rotate the
**Drill String.**

- Uninterrupted Drilling mud circulation.

### Differential Stuck Pipe Prevention And Mitigation

Simple precautions tips to decrease the possibility of Differential pipe stuck if drilling through high permeable intervals are taken:

- Decrease drilling mud fluid loss.
- Decrease amount of drilled solids in the drilling fluid system, or, if it is OK, remove all drilled solids.
- Use the lowest possible mud weight to decrease hydrostatic pressure so that decrease the differential stuck force
- Decrease
**Friction Coefficient**by - Decrease connection time and keep rotating
**Drill String**all the time.