Free Point vs Stuck Depth

In the oil and gas industry, the terms "free point" and "stuck depth" refer to specific aspects of the drill string's condition within the wellbore when part of the string becomes immobilized.

Free Point  -  The depth along the drill string where the pipe can still move freely.  This is the uppermost point in the wellbore where the drill string is not stuck, meaning that above this depth, the pipe can be stretched and rotated without significant restriction.

Stuck Depth  -  The location along the drill string where the pipe becomes immobilized and cannot move.  This is the point at which the drill string is firmly held in place by whatever obstruction or formation is causing it to be stuck, such as differential sticking, mechanical sticking, or key seating.

Relationship and Differences

Definition and Location

• Free Point  -  The highest point in the wellbore where the drill string can still move freely.
• Stuck Depth  -  The lowest point in the wellbore where the drill string cannot move.

Purpose and Usage

• Free Point  -  Identifying the free point is crucial for determining how much of the drill string remains mobile and to guide the deployment of recovery tools and techniques.
• Stuck Depth  -  Identifying the stuck depth is necessary for understanding where the problem begins and planning the recovery or freeing operation.

Determination

• Free Point  -  Measured using tools like the free point indicator (FPI) or by analyzing stretch and torque responses along the drill string.
• Stuck Depth  -  Directly inferred once the free point is established, as it is the point immediately below the free point where the string can no longer move.

Practical Example

Assume a drilling operation where the drill string gets stuck at a certain depth.  The steps to identify the free point and stuck depth might include:

Deploying a Free Point Indicator (FPI)  -  A FPI tool is run into the wellbore on a wireline.  The tool measures the response to applied tension and torque at various depths.
Data Collection and Analysis  -  The FPI tool detects that the drill string stretches and rotates freely down to a depth of 8,500 feet.  Below this depth, the tool indicates that there is no significant movement.
Identifying the Free Point  -  Based on the FPI data, the free point is determined to be at 8,500 feet.  This is the highest depth at which the drill string can still move.
Determining the Stuck Depth  -  The stuck depth is immediately below the free point, starting at 8,500 feet.  This is where the drill string becomes immobilized.

Summary

Free Point  -  The depth where the drill string can still move freely, identified through tools and measurement techniques.
Stuck Depth  -  The depth where the drill string is immobilized, determined once the free point is known.

By accurately determining the free point and stuck depth, drilling operators can effectively plan and execute recovery operations to free the stuck section of the drill string, minimizing downtime and potential damage.