Abstract
Drilling the intermediate (12¼-in) section in Ecuador's Oriente (East) Basin involves passing through interbedded sequences of claystone and conglomerates with chert cobbles and pebbles, which generate high impact forces that damage PDC bit cutting structures. Roller-cone bits with tungsten carbide inserts (TCIs) have been the most reliable option to drill within challenging levels that are known to chip and break cutting mechanisms; however, dedicated runs through conglomerates caused additional trips to replace bits before reaching total depth of the section. To drill the entire section, PDC bits were requested with improved cutter technology and enhanced procedures to reduce damage on cutting structures. There were events, however, of destroyed bits within conglomerates without finishing all conglomerate levels, requiring another bit to drill the entire chert level, and low ROP to mitigate cutter breakage and chipping. The operator sought a new type PDC bit that could ensure drilling the entire conglomerate intervals with enhanced ROP and longer footage for the section after the chert-composed beds.
To develop a bit solution, engineers used finite element analysis–based modeling to implement a new-type hybrid bit by strategically positioning multiple conical diamond elements (CDEs) across the cutting structure from bit center to gauge. The CDE's unique geometry applies a concentrated point load to fracture high-compressive-strength formations more efficiently than flat cutters. The combination cutting structure (CDE/flat PDC) creates a high-efficiency plowing and shearing action that improves durability yet keeps the bit aggressive enough to obtain the required ROP in lithologies found after conglomerates.
The 12¼-in hybrid CDE bit was tested in three separate wells in the Shushufindi and Aguarico fields, increasing ROP in the difficult lower chert conglomerate section compared with six direct offsets drilled with 519/616-(5 bladed PDC bits with 19-mm cutters and 6 bladed bits with 16-mm cutters) standard type PDC bits and where only one bit was used to drill entire interval considering different well profiles and used drives. In one well, the CDE bit drilled the lower conglomerate at 60.2 ft/h, 34% faster than the best offset ROP of 44.7 ft/h set with a conventional 616 PDC. The hybrid CDE bit was pulled in good dull condition (1-1) with minimum damage considering the high rpm used in the lower conglomerate.
