rathole

Understanding "Rathole" in Drilling & Well Completion: A Hole with Two Faces

The term "rathole" in the oil and gas industry refers to a specific type of hole used during drilling and well completion operations. Its function varies depending on the context, so understanding the two primary meanings is crucial:

1. The Rathole as a Protective Housing:

This "rathole" is a deep, cylindrical hole, typically 30 to 40 feet (9 to 12 meters) in depth, drilled into the rig floor. The hole is lined with casing, a strong steel pipe, which projects above the floor. This casing serves as a protective housing for the kelly and swivel, essential components used during hoisting operations.

• Kelly: A heavy steel pipe that connects the rotating drill string to the rotary table.
• Swivel: A rotating joint connecting the kelly to the drilling line, allowing the drill string to rotate freely while the drilling line remains stationary.

How it works:

When hoisting operations are underway, the kelly and swivel are lowered into the rathole. This protects them from damage and ensures their safe and efficient operation. The rathole also provides a stable base for the kelly and swivel, reducing the risk of slippage or instability during the hoisting process.

2. The Rathole as a Sidetrack:

This "rathole" is drilled within the main wellbore, but its diameter is smaller. It is typically drilled at the bottom of the main hole, sometimes referred to as a "sidetrack."

Purpose:

The purpose of this type of rathole can vary, but common applications include:

• Sidetracking: This involves drilling a new, smaller hole to bypass an obstacle in the main wellbore, such as a stuck drill bit or a collapsed formation.
• Directional Drilling: It can be used to drill a deviated wellbore, allowing for access to reservoirs that are difficult to reach from a straight, vertical path.
• Secondary Production: A rathole can be drilled to access a secondary reservoir or formation that lies adjacent to the main wellbore.

Conclusion:

The term "rathole" in drilling and well completion signifies two distinct yet important components. While one type provides protective housing for critical equipment during hoisting operations, the other serves as a sidetrack for accessing different formations or bypassing obstructions. Understanding these concepts is essential for anyone involved in oil and gas exploration and production.