Stuck Depth

Stuck depth, abbreviated as SD, is the specific point or section along the drillstring where the pipe becomes immobilized and cannot move.  This is the depth at which the drillstring is held in place by an obstruction or formation that causes it to be stuck, preventing further drilling operations or movement of the drillstring.

Causes of Stuck Pipe

Differential Sticking  -  This occurs when the drillstring becomes stuck against the wellbore wall due to differential pressure between the drilling fluid and the formation.
Mechanical Sticking  -  This happens when physical obstructions, such as cuttings, cave-ins, or debris, trap the drillstring.
Key Seating  -  This occurs when the drillstring wears a narrow groove into the wellbore wall, usually in deviated or directional wells.
Bridging  -  This is when the formation collapses and traps the drillstring.

Importance of Identifying the Stuck Depth

Recovery Planning  -  Knowing the exact depth where the pipe is stuck helps in planning the recovery operations more effectively.
Minimizing Damage  -  Accurate identification of the stuck depth helps in avoiding unnecessary force on the drillstring, reducing the risk of breaking the pipe or causing further damage.
Operational Efficiency  -  Reduces non-productive time (NPT) by streamlining the troubleshooting and recovery process.

Determining the Stuck Depth

To determine the stuck depth, operators typically use a combination of tools and techniques:

Free Point Indicator (FPI) Tool  -  This wireline tool measures the stretch and torque applied to the drillstring at various depths.  By analyzing where the drillstring can still stretch and rotate, the FPI tool helps pinpoint the depth where the pipe becomes stuck.
Stretch Measurement  -  Apply tension to the drillstring and measure its stretch response.  The section that stretches is free, while the section that does not stretch indicates the stuck point.
Torque Measurement  -  Apply torque to the drillstring and monitor its rotation.  The section that rotates is free, while the section that does not indicates the stuck point.

Example Scenario

Initial Problem  -  The drill string gets stuck while drilling at a depth of 10,000 feet.
Deploying an FPI Tool  -  The FPI tool is run into the wellbore to measure responses at different depths.
Collecting Data  -  The tool indicates that the drillstring stretches and rotates freely down to 9,800 feet but shows no movement below this depth.
Identifying the Stuck Depth  -  The stuck depth is determined to start at 9,800 feet, meaning the drillstring is immobilized from this point downward.

The stuck depth is the point along the wellbore where the drillstring becomes immobilized due to various causes such as differential sticking, mechanical sticking, key seating, or bridging.  Accurate identification of the stuck depth is critical for efficient and effective recovery operations, minimizing downtime, and preventing further damage to the drillstring and wellbore.

  

Stuck Depth formula
\( SD \;=\;  735,294 \; E \; DP_w \;/\; P  \)   (Stuck Depth) \( E \;=\;  SD \; P  \;/\; 735,294 \; DP_w  \) \( DP_w \;=\;  SD \; P  \;/\; 735,294 \; E \) \( P \;=\;  735,294 \; E \; DP_w \;/\; SD \)
Symbol	English	Metric
\( SD \) = Stuck Depth	\(ft\)	-
\( E \) = Modulus of Elasticity (psi)	\(lbf\;/\;in^2\)	-
\( DP_w \) = Drill Pipe Weight (ppf)	\(lbf\;/\;ft\)	-
\( P \) = Overpull Difference Between Max. and Min. Pull of Pipe	\(lbf\)	-