Understanding Stuck Pipe Phenomena and Prevention

During well drilling, complications related to the sticking of drilling tools constitute a significant proportion of all drilling accidents. Resolving such situations requires substantial time and resources, leading to increased operational expenses and delays.

Primary Causes of Stuck Pipe:

1. Adhesion to Wellbore Walls: Occurs when the drill string remains stationary for extended periods, allowing it to stick to the borehole walls.
2. Bridging Due to Borehole Narrowing and Mud Cake Buildup: Thick layers of mud cake can cause the wellbore to narrow, leading to pipe sticking.
3. Wedging of Tools: Happens during tripping, drilling, or reaming operations with a full-size bit.
4. Collapse of Unstable Formations: Loose or fractured rock formations can cave in, trapping the drill string.
5. Sticking and Wedging in Keyseats: The drill string becomes lodged in grooves or channels eroded into the wellbore walls.
6. Wedging Due to Foreign Objects: Debris or dropped objects inside the well can cause the drill string to become stuck.
7. Sticking from Fluid Influxes and Losses: Inflows or losses of water, oil, or gas can destabilize the wellbore, leading to sticking.
8. Settling of Drilled Cuttings: Accumulation of cuttings around the drill string can cause it to become immobilized.

More than 50% of all stuck pipe incidents result from the drill string adhering to the wellbore walls when left stationary. Extensive field and laboratory experiments have identified two primary factors influencing this phenomenon:

• Hydrostatic Pressure at the Sticking Point: Elevated pressures can cause the drill string to press against the wellbore walls more firmly.
• Stickiness of the Clay Mud Cake: High adhesive properties of the mud cake increase the likelihood of sticking.

Preventive Measures:

To prevent stuck pipe incidents, the following actions are recommended:

1. Maintain Drill String Movement: Avoid leaving the drill string stationary for prolonged periods. Regular movement prevents adhesion to the wellbore walls.
2. Use High-Quality Drilling Fluids: Employ drilling muds with excellent lubricating properties and low solids and colloidal content to reduce friction and mud cake buildup.

Dealing with Stuck Pipe:

Resolving a stuck pipe situation typically involves creating a separation layer between the clay mud cake and the drill string or breaking down the mud cake itself.

Methods for Freeing Stuck Pipe:

• Working the Drill String with an Oil Bath: The primary method involves applying an oil-based solution to reduce adhesion. However, this is not always effective, especially if the oil cannot penetrate the space between the mud cake and the drill string.
• Limitations of Oil Baths:
  • Restricted Penetration: Oil may not reach the sticking point due to the tight contact.
  • Density Constraints: In formations with high-pressure zones, there may be limitations on the maximum allowable density of the oil bath to prevent well control issues.

Alternative Solutions:

To address these challenges, water-based solutions containing deflocculating agents have been developed. These agents are designed to break down clay particles without adversely affecting the metal components of the drill string.

Mechanism of Deflocculating Agents:

• Disruption of Clay Lattice Structures: The agents weaken the structural bonds within the clay particles.
• Disintegration and Removal: The weakened particles are then unable to compact and are removed from beneath the stuck drill string.

Additional Preventive Measures:

1. Utilize Drilling Fluids That Minimize Mud Cake Thickness:
   • Formulate muds that prevent excessive buildup on the wellbore walls.
2. Ensure Thorough Cleaning of Drilling Fluid:
   • Regularly remove drilled cuttings and solids to maintain optimal mud properties.

Reducing Mud Cake Stickiness:

• Add Oil to the Drilling Fluid:
  • Incorporate 5–8% oil by volume to reduce adhesion. Note that adding oil may slightly increase the mud viscosity.
• Counteract Increased Viscosity:
  • Introduce 0.8–1.5% silvery graphite to the mud to combat viscosity-related issues that can lead to differential sticking.

Fishing Operations and Tools Used

During drilling, other unforeseen events may occur, such as the dropping of foreign objects into the well or the parting of the casing string. Normal operations can resume only after all obstructions are removed.

Common Fishing Tools:

1. Spears
2. Overshots
3. Fishing Jars
4. Impression Blocks
5. Milling Tools

Detailed Overview of Fishing Tools:

• Spear:

  • Purpose: Used to retrieve parted drill pipe or tubulars from the wellbore.
  • Design: A tapered, truncated cone with a fishing thread at the lower end and a connection thread at the upper end.

• Overshot:

  • Usage: Employed when the spear cannot engage the top of the fish (the object to be retrieved).
  • Types:
    • Full-Bore Overshot: Used when the broken pipe has an irregular end.
    • Releasing Overshot: Allows for disengagement if retrieval is unsuccessful.
  • Mechanism: A heavy-walled tube with internal grapple or spiral grooves that latch onto the exterior of the fish.

• Fishing Jar:

  • Function: Provides upward or downward impact forces to free stuck equipment.
  • Application: Often used in conjunction with other fishing tools to enhance effectiveness.

• Impression Block:

  • Purpose: Determines the shape and condition of the top of the fish.
  • Method: Lowered onto the fish to create an impression, aiding in selecting the appropriate fishing tool.

• Milling Tools:

  • Use Case: When protruding metal parts need to be removed or dressed.
  • Operation: Grinds away metal obstructions, turning them into small cuttings for removal.

• Fishing Magnet:

  • Application: Retrieves small ferrous metal objects, such as bits of broken tools or milling debris.

• Wireline Grab (Fishing Tool):

  • Purpose: Used to recover logging cables and steel wireline from the well.
  • Design: A rod with welded hooks or barbs that latch onto the wireline.

About Our Course

The Technical Education Academy offers the course "WELL007. Stuck Pipe Prevention and Fishing Operations". Participants will gain in-depth knowledge and understanding of: 

• Mechanisms of Stuck Pipe Occurrences:
  • Learn about the causes and contributing factors of stuck pipe incidents.
• Reduction and Elimination Techniques:
  • Explore effective strategies to minimize the risk of stuck pipe, thereby reducing non-productive time and operational costs.
• Fishing Tools and Methods:
  • Get acquainted with various fishing tools and their appropriate applications during recovery operations.

Course Highlights:

• World-Class Presentations:
  • Engage with high-quality instructional materials that cover the latest industry practices.
• Practical Discussions:
  • Participate in interactive sessions to discuss real-world scenarios and solutions.
• Comprehensive Learning Materials:
  • Access top-tier educational and reference resources to enhance your understanding of drilling technology and downtime prevention methods.