In drilling and well completion, an annulus refers to the space between two concentric objects. Here's a breakdown of how it applies in the context of oil and gas operations:

1. Drilling Annulus:

• Definition: The space between the drill pipe and the borehole wall.
• Function: It acts as a pathway for drilling mud to circulate. The mud travels down the drill pipe, carrying cuttings from the bottom of the well, and then flows back up the annulus to the surface. This circulation serves several purposes:
  • Cleaning: Removes drill cuttings from the wellbore.
  • Cooling: Cools the drill bit and the drilling equipment.
  • Pressure Control: Maintains pressure on the formation to prevent blowouts.

2. Completion Annulus:

• Definition: The space between the production tubing and the casing.
• Function: The completion annulus is used for a variety of purposes:
  • Cementing: The space can be filled with cement to provide structural support and isolate different zones in the well.
  • Injection: Used for injecting chemicals or fluids into the well for stimulation or workover operations.
  • Pressure monitoring: Sensors can be placed in the annulus to monitor pressure changes within the well.
  • Tubing movement: Allows for movement of the production tubing during well maintenance or workovers.

3. Other Annulus Uses:

• Tubing Annulus: The space between the production tubing and the packer. Used for various well operations, including injecting fluids, monitoring pressure, and isolating zones.
• Casing Annulus: The space between the casing and the wellbore wall. Can be used for cementing, injecting fluids, and isolating zones.

In summary, the annulus is a critical component in drilling and well completion. It provides essential pathways for fluid circulation, allows for various operations, and helps maintain the integrity of the wellbore.