The majority of the fields in southeast Mexico require 1,000m to 3,400m of 17-1/2 hole to set 13-3/8 casing at the top of Encanto/Deposito formation. Lithology is typically weak sandstone with shale stringers (UCS 2,000-6,000 psi). Operators have attempted to use PDC to drill the hole section in one run with limited success. Operators required an updated steel-tooth rollercone to cut costs by reducing trips/bits to complete the section. Examination of steel-tooth dulls indicated erosive and abrasive wear due to the high sand content was the major factor limiting performance improvement.
To cut drilling time/costs, the service company implemented a new steel-tooth bit with a new generation metal bearing seal and improved cutting structure that has significantly increased total cumulative footage and ROP drilling the 17-1/2" hole section. The metal bearing seal has significantly increased bit life relative to offsetting performance. To further capitalize on increased bearing reliability, the cutting structure has been strengthened by high-performance hardfacing further enhancing tooth/spearpoint durability. New design has added gauge holding ability and reduced cuttings inflow to the seal area further improving bearing life. By comparison, standard steel-tooth bits were often pulled with half to none of the tooth height remaining. This added durability dramatically reduces dulling of the cutting structure allowing the operator to maintain maximum ROP throughout the run while almost doubling total meterage.
The authors will present case studies that document the new bit design has increased meterage by at least 46%, ROP by 12%. Total bit runs have decreased from six to four and the total cone revolutions have increased by 60% compared to average values of best offset runs in several fields. This has saved the operator an average of $140,000USD per 17-1/2" hole section per well.