Category Archives: Stuck Pipe

Shale Instability Causes Stuck Pipe

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Shale instability happens when shale formation becomes unstable and finally, formations break apart and fall into an annuls.

Water in the mud absorbed by shale formations causes a swelling effect on formations. When there is a lot of water, shale will not be able to hold their particles together and finally will fall apart into the well. Finally, shale particles will jam a drill string.

The shale instability is a chemical reaction which is time dependent. It means that it may not be seen on the first day but it will be able to see after drilling has been carried out for several days.

The three illustrations below will help you get more understanding about shale instability and stuck pipe.

Day#1: Water is absorbed by shale

Day#1: Water is absorbed by shale

Day#2: Shale swelling due to water and shale starts falling apart.

Day#2: Shale swelling due to water and shale starts falling apart.

(Day#4: A lot of shale falls down and causes stuck pipe)

Day#4: A lot of shale falls down and causes stuck pipe

Warning signs of shale instability

• Torque and drag increase. An over pull may be observed.

• Mud properties became worse. You will see an increase in plastic viscosity, yield point (drilling mud becomes thicker).

• Pump pressure increases.

• Observe soft shale over shale shakers.

Indications when you stuck due to shale instability

• When it happens, you may observe very high pump pressure at a small rate and sometimes circulation may be impossible.

• Most of the time it will happen when pulling out of a hole. However, it can be possibly occurred while drilling as well.

What should you do for this situation?

1. Attempt to circulate with low pressure (300-400 psi). Do not use high pump pressure because the annulus will be packed harder and you will not be able to free the pipe anymore.

2. If you are drilling or POOH, apply maximum allowable torque and jar down with maximum trip load.

3. If you are tripping in hole, jar up with maximum trip load without applying any torque.

4. Attempt until pipe is free and circulate to clean wellbore.

Preventive actions

1. For water based mud – you may need to add some salts that are compatible with a mud formula in order to reduce chemical reaction between water and shale. Moreover, you should consider adding some coating polymers to prevent water contact with formation.

2. Use oil based mud instead of water based mud because oil will not react with shale.

3. Keep good flow rate to ensure good hole cleaning.

4. Perform back reaming and/or wiper trip.

5. Keep good mud properties.

References

John Mitchell Drilbert Engineering, 2002. Trouble-Free Drilling Volume 1: Stuck Pipe Prevention. Edition. Drilbert Engineering Inc.

Fanarco.net. 1999. Stuck Pipe Prevention Self-Learning Course. [ONLINE] Available at: http://www.fanarco.net/books/drilling/stuck-pipe.pdf. [Accessed 21 June 2016

 

Cutting Settling in Deviated Wells Cause Stuck Pipe

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For deviated wells, cuttings tend to accumulate at the low side of the wellbore and form a cutting bed. When there is a lot of cutting bed, it will fall down and pack the string when circulation is ceased. Moreover, while pulling out of a hole, BHA will move some cutting beds and finally, the cutting bed will pack BHA and drill string (stuck pipe).

Note: A well which has an inclination of more than 35 degrees is classified as a deviated well.

Cutting movement while drilling in a deviated well

Cutting movement while drilling in a deviated well

Cutting settling while stop drilling in a deviated well

Cutting settling while stop drilling in a deviated well causes stuck pipe

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Cutting Settling in a Vertical or Near vertical Wellbore Causes Stuck Pipe

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Cuttings in the wellbore are not efficiently removed from the annulus because the drilling fluid does not sufficient carrying capacity and/or there is not enough flow rate to create good annular velocity. When pumps are off, cuttings fall down due to gravitational force and pack and annulus. Finally, it results in stuck pipe. Typically, the wells classified as vertical or near vertical wells have an inclination of less than 35 degrees.

Note: In order to clean annulus effectively, the annular velocity must be more than the cutting slip velocity in a dynamic condition. Moreover, mud properties must be able to carry cutting when pumps are on and suspend cutting when pumps are off.

cutting-while-pump-on

Cutting While Pump On

Cutting Falling Down While Pump Off

Cutting Falling Down While Pump Off

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Differential Sticking Causes Stuck Pipe

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Differential Sticking is one of the most common causes of pipe stuck. It can happen when there is differential pressure (overbalance pressure) pushing a drill string & BHA into permeable formations.

Four Factors Causing the Differential Sticking

Permeable formation 

Permeable formations for example are sand stone, lime, carbonate, etc.

Overbalance 

Typically mud weight in the well is more than formation pressure. The more overbalance in the wellbore, more chance of getting differential sticking.

Filter cake 

Poor and thick filter cake increases the chances of sticking the drill string.

Pipe movement

If the drill string is stationary for a period of time, the filter cake will tend to develop around permeable zones and the drill string. Therefore, the potential of getting differentially stuck is increased.

Differential Sticking Diagram (Top View)

Differential Sticking Diagram (Top View)

Differential Sticking (Side View)

Differential Sticking (Side View)

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Stuck Pipe Introduction

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This topic will give you an overview of stuck pipe and how people classify stuck pipe.

stuck-pipe-introduction-cover

Definition of Stuck Pipe

 

Stuck pipe is a situation when the drill string cannot be moved from the well. The drill string may be partially moved and circulation & rotation may or may not be possible. Personnel on the rig must be able to identify the cause of stuck pipe in order to figure out the right way to free the pipe.

Stuck pipe categories

There are 3 categories of stuck pipes as follows:

Pack off and Bridging

Pack off and bridging are occurred when there is something in the wellbore, such as formation cutting, junk, etc. accumulating around the drilling string/BHA and that stuff blocks the annulus between the drill string and the wellbore. You should remember that either big or small debris can stick in the pipe.

According to statistics around the world, pack off and bridging is the most frequent cause of stuck pipe situations in the world. It normally occurs when the mud pumps are off for an extended period of time, such as when pulling out of a hole. It is quite a tough job to free the pipe in case of packoff or bridging and the chance of success is lower than differential or wellbore geometry sticking mechanism.

Differential Sticking

Differential sticking happens when drill string is pushed against permeable formations by differential pressure between hydrostatic and formation pressure. The frictional force between drill string and formation is so high that you will not be able to move the pipe. The differential sticking tends to easily happen when drilling through a depleted reservoir is conducted. Moreover, this stuck mechanism almost always happens when the drill string has  stopped moving for a long time.

Wellbore Geometry

Wellbore geometry stuck pipe mechanism occurs when the shape of the well and the bottom hole assembly (BHA) don’t match each other. Therefore, the drill string is not able to pass through that section.

Note: All of the details about stuck pipe mechanism will be described in later chapters.

References

John Mitchell Drilbert Engineering, 2002. Trouble-Free Drilling Volume 1: Stuck Pipe Prevention. Edition. Drilbert Engineering Inc.

Fanarco.net. 1999. Stuck Pipe Prevention Self-Learning Course. [ONLINE] Available at: http://www.fanarco.net/books/drilling/stuck-pipe.pdf. [Accessed 21 June 2016].