Striking a balance between aggressiveness and steerability has always been a challenge in engineering new bit designs. The purpose of this paper is to highlight the engineering steps and challenges faced with designing a more aggressive bit that will drill faster while improving directional control and limiting vibrations to suit the application.
North Kuwait's 8.5″ build up section's geology comprises of layered carbonates, shale and sandstone. The section is known to induce vibrations in conventional RSS BHAs and can be challenging for directional work.
As a rule, less blades in a PDC bit makes a more aggressive bit that is therefore harder to steer with. Historically Kuwait's 8.5″ sections are drilled with a 6 bladed bit design. While proving stable, such a medium-set bit design limits performance in these formations.
The engineering process involved:
In depth analysis of current bit designs involved studying wear patterns, comparing designs that drilled faster sections and those that minimized downhole vibrations
Analyzing different drive system specific requirements and the designs found most stable.
Selecting the most appropriate PDC depth of cut management technology that would allow the bit to sustain higher parameters without generating extensive torque
Drilling and hydraulics simulation software to optimize flow and simulate depth of cut management
Extensive field trials
The result was the first 5 bladed PDC bit run in Kuwait; which improved drilling rate of penetrations by 24% while minimizing vibrations and maintaining precise steerability on RSS and AKO mud motor BHAs.
By managing the bits aggressiveness, a more aggressive PDC bit design was proposed and trialed on several wells proving consistent performance improvement on field average rate of penetrations while maintaining accurate steerability to successfully land the wells.