Step Change in Performance: Upgraded Bit Technology Significantly Improves Drilling Economics in GOM Motor Applications
Authors: Grimes B. , Kirkpatrick B. 
Published: December 2007

With vast regions of the Gulf of Mexico (GOM) rapidly becoming mature provinces, operators are constantly looking for ways to systematically reduce the costs of drilling development wells, especially with improved technologies that deliver reliable performance and decreased risk. The application of a new steel tooth rollercone bit with a technically advanced metal seal bearing has achieved this goal and is having a significant impact on drilling economics in the GOM. Improvements in bearing life, seal reliability and cutting structure durability have resulted in more time on bottom, thereby giving the operator the confidence to apply the new rollercone bits in long directional hole sections. Most of the wells drilled are directional, and heavy water-based drilling fluids are often required in the intermediate hole sections; heavy synthetic muds are sometimes used deep in the wellbore. Relatively high bottomhole temperatures combine with extremely high bottomhole pressures and balling shales to present a challenging drilling environment. Operators strive to increase rate of penetration, maximize hours on bottom for each bit, reduce risk, and complete the section with fewer bits to reduce the number of trips.

The bit development phase consisted of a thorough analysis of field application data, along with rigorous forensic examinations of representative dulls from around the world to identify the downhole conditions and sealed bearing wear mechanisms that limited the current metal sealed bit life. A host of design and material improvements were conceived and developed to deliver an improved metal sealed bearing with significantly longer life and higher reliability. The improvements included metal seal surfaces up to 20% wider; a proprietary wear resistant surface on one seal face that greatly reduced both the seal wear rate and the coefficient of friction; improved back-up ring geometry and gland; and design features that enable more consistent manufacturing assembly processes to be utilized. The new rollercone bearing package proved to deliver unequaled life and reliability in high rotary speed drilling applications, superior to all current rollercone sealed bearing systems.

The new steel tooth bit's long life, resistance to balling in water-based muds, highly steerable characteristics, and ability to be combined with various hole-opening systems make it the bit of choice for many GOM applications. The authors show actual GOM performance data of the new bits achieving an 80% reliability of nearly 700,000 total bit revolutions (TBR), compared to existing technology bits at less than 400,000 TBR. Specific case studies show examples of one new style bit replacing two to three current technology steel tooth bits, effectively doubling the footage drilled and TBR in the process. Another example shows 1 of the new technology bits replacing two current technology steel tooth bits with associated substantial cost savings due to higher ROP's and less flat time due one less trip. Cost savings of up to $156,000 USD are documented in these examples. The authors will also document the bit's improved performance in diverse international drilling locations including Mexico.