Preliminary Casing Design

Preliminary Casing Design

Exploring Preliminary CSG Design: Key Insights and Procedures 

Key Parameters:

• Formation Strength “Fracture Pressure”
• Pore Pressure

Results:

• Casing Setting Depths
• Mud weight for each section

Calculation Procedures:

1. Obtain fracture pressure and pore pressure vs. depth.
2. Convert pressures to pressure gradient (ppg).
3. Subtract a safety factor (0.5 ppg) from formation strength.
4. Add a safety factor (0.5 ppg) to pore pressure.
5. From TVD, draw a vertical line from safe pore pressure to safe fracture pressure.
6. Draw a horizontal line from fracture pressure to the next pore pressure.
7. Continue this pattern until reaching the surface (0 ft).

Considerations:

• Formation lithology and drilling challenges from offset data.
• For example:
  • In shale formations, if mud weight and additives are insufficient, adjust casing setting depth accordingly.
  • For high-pressure zones following low-pressure zones, insert casing at the high-pressure zone before adjusting mud weight for the next section.

Summary:

• Obtain pore pressure and fracture pressure.
• Convert them to gradients.
• Adjust for safety factors.
• Draw vertical and horizontal lines from safe pore pressure to fracture pressure until reaching the surface.
• Adjust casing setting depths as per lithology and drilling issues.

We have attached an excel sheet example