12.25 Inches

12.25 inch drill bits (311.2mm) are the standard choice for surface hole sections in oil and gas wells, typically drilled to set 9-5/8" surface casing. At this diameter, the bit needs to remove significant rock volume while maintaining hole stability—making hydraulic design and cutting structure equally important. You'll also see 12.25" bits in large-diameter water wells and geothermal well drilling where high flow rates are essential.

Core Advantages:

- Available in 5-8 blade PDC, tricone TCI, and milled tooth configurations

- API 6-5/8 REG pin connection for large-diameter drill strings

- High-flow nozzle configurations to handle 800-1,500 GPM circulation rates

- Aggressive cutting profiles for fast ROP in soft surface formations

- Extended gauge rows for hole diameter stability in unconsolidated formations

- Shock-absorbing cutter placement to handle boulders and cobble layers

Q: Why is 12.25 inches the standard surface hole size?

A: It provides sufficient annular space to cement 9-5/8" casing properly, which is the most common surface casing size in the industry. This combination ensures wellbore integrity and supports deeper drilling operations.

Need 12.25-inch bits for your surface hole sections? Share your casing design and we'll recommend the optimal bit type for your surface geology.