Published: 01/18/2013
Published: 01/18/2013
The relatively low rotational velocity at the center of conventional PDC bits limits the amount of rock they can remove, especially in hard formations. And when drilling lithologies with high unconfined compressive strength (UCS), a PDC drill bit's center cutters can incur damage that reduces ROP and bit durability.
To increase ROP and reduce the number of bits required to drill vertical sections in the hard, abrasive, and interbedded formations associated with applications in North Dakota's Bakken basin, Smith Bits conducted a program to develop more effective cutting elements for PDC bits. For this program, bit design engineers set a primary goal: Fit a PDC bit with a more durable cutting element or elements that would fail hard and abrasive, interbedded, and transitional formation rock more efficiently to increase ROP.
To increase drilling efficiency and stability across a wide range of PDC bit applications, the innovative Stinger conical diamond element was developed. The element has twice the diamond thickness of conventional PDC cutters and is manufactured from synthetic diamond material engineered to provide superior resistance to abrasive wear and impact loading. Combining this capability with the Stinger element's unique conical geometry resulted in a cutting element that can significantly enhance a PDC bit's durability.
To ensure that placement of the Stinger element at the PDC bit's center would maximize drilling efficiency, engineers used IDEAS integrated drillbit design platform to further optimize the cutting structure. This effort included selectively abbreviating the blades that held the PDC bit's low-velocity center cutters and placing the Stinger element at the center of the PDC bit's cutting structure.
By opening up the center of the cutting structure, a stress-relieved rock column is allowed to develop at the bit's center during drilling. As the Stinger element engages it, the rock column is continuously crushed and fractured, thereby improving drilling efficiency. With fewer cutters, there is less division of the weight on bit (WOB), which increases cutter loading and maximizes drilling efficiency. This effect has also proven to increase stability and reduce vibration.
The MDSiZ616 SHARC high-abrasion-resistance PDC drill bit fitted with 16-mm cutters and a Stinger element run on a directional BHA drilled 8 3/4-in vertical sections of between 6,209 and 6,477 ft in single trips. Bits attained an average ROP of 168 ft/h and a maximum ROP of 203 ft/h. When compared with the next best average ROP reported by other bits in offset wells, the SHARC bits with a Stinger element increased ROP 46%.
Challenge: Increase ROP and reduce the number of bits required to drill 8 3/4-in vertical sections of at least 6,000 ft in the hard and abrasive interbedded formations that compose North Dakota’s Bakken basin.
Solution: Run an 8 3/4-in MDSiZ616 SHARC high-abrasion-resistance PDC drill bit fitted with 16-mm cutters and a Stinger conical diamond element on a directional BHA to increase vertical control.
Results: Drilled 8 3/4-in vertical sections of between 6,209 and 6,477 ft with an average ROP of 168 ft/h, and when compared with the next best average ROP reported by other bits in offset wells, the SHARC bits with a Stinger element increased ROP 46%.
