A fixed PDC element creates an inherent limitation because only a small portion of the cutter contacts formation and as the cutter wears/chips drilling efficiency declines. It is well documented that wear flats generate a high degree of frictional heat which breaks the diamond bond. To solve the issue an R&D initiative was launched to investigate different methods to enable a PDC shearing element to rotate while drilling to increase overall cutting efficiency and bit life. Engineers investigated different retention methods to create the optimal driving force and allow full cutter rotation.
The assemblies were modeled using an FEA based engineering system and then tested in the laboratory to evaluate function and strength. Experiments confirmed the new rolling cutter (RC) was able to shear an extended section of rock with a consistent force level (lbs). A traditional fixed-cutter assembly required steadily increased force to drive the cutter the same distance. Examination of the rolling cutter's dull condition clearly indicated significantly improved durability and cutting efficiency.
The recent introduction of a new rolling cutter PDC bit that utilizes the entire 360° of diamond edge has delivered positive results in field trials. Initial testing was targeted at the highly abrasive Granite Wash formation in Western Oklahoma/Texas Panhandle where cutter wear is the predominant failure mechanism. A six-bladed prototype PDC bit, with three rolling cutters positioned in the shoulder area was run on PDM and increased total footage capabilities compared to conventional PDC.
The next prototypes were equipped with a smaller, yet more robust generation-3 retaining device. Starting in Q4 2012, the total RC count/bit was progressively increased on five/six bladed designs from 3, 5, 7, 10 and then 12. The 13mm designs are consistently exceeding footage totals compared to offsets in central USA, North Dakota and Canada. In central USA, which contains the largest data set (13 RC runs) the rolling cutter has increased average footage totals by 34.4% compared to offsets drilled with standard PDC from various manufacturers. Case studies will document performance improvement in these challenging drilling environments. The authors will discuss plans to develop a rolling cutter bit to extend lateral run length in an abrasive Middle East formation.