Expanding Application of PDC into Harder, More Abrasive Formations: Performance Step Change in Saudi Arabia
Authors: Thomas Shaji , Aljezany Mahdy , Klink Zeinoun , Scott Dan 
Published: December 2007

The operator has attempted to efficiently drill the 16" and 8-3/8" hole sections using roller cone TCI and PDC technology. For the 16" section, TCI had unacceptably low ROP with short life that required multiple runs to reach section TD. In the 8-3/8" section, abrasive wear due to hard sharp sandstone limited PDC bit life. While the PDC delivered acceptable ROP, impact damage from vibration induced by lithology changes and abrasive formations resulted in inconsistent run lengths. The operator evaluated several designs but even the toughest PDC could not withstand the vibrations or the abrasivity of the formations resulting in poor performance due to severe PDC cutter damage/wear.

The operator required new PDC bit and cutter technology. A team was assembled that analyzed PDC technology using numerical models in addition to laboratory and field tests. Engineers focused on the interface between the diamond table and the substrate that determines the cutter's response to residual and service stresses. Diamond table properties were evaluated in an effort to raise their durability and wear resistance. This resulted in a tougher, more abrasion resistant cutter capable of maintaining an efficient edge in the hard dolomite and abrasive sands. Patented depth-of-cut control technology provided smoother, more stable drilling through interbedded formations. The result was a new, aggressive PDC bit design/cutter technology package that consistently drills hard/abrasive formations at the highest possible ROP.

Drilling the 16" hole section in Hawiyah field, consisting of interbedded carbonates, abrasive sandstone and dense dolomite, the new PDC cut average cost/t from $163 to $94, a reduction of 43% over a five well offset average. It also increased average ROP from 14.8 ft/hr to 22.3 ft/hr an increase of 51% and set a Hawiyah field single run footage record of 4432 ft. The shoe to shoe run saved on average four trips for new bits saving the operator $1550/hr in rig cost and motor rental.

For the 8-3/8" hole section, directional drilling through hard and abrasive sandstone with 105 pcf overbalanced mud has proven to be a drilling challenge. For TCI, poor penetration rate while sliding and severe bit wear resulted in short runs, lost cones causing extensive fishing and milling operations. Fixed cutter bits were previously tried in similar formations with minimal success due to severe PDC cutter wear.

This new technology was put to the test in the sliding portion of the hole. Using TCI bits with diamond enhancements, a total of 3 bits were used to drill 75 ft in 36.5 hrs, for an average ROP of 2 ft/hr with a resulting cost/ft of $2240. Using the new cutter technology, four bits were used to drill 543 ft in 116 hrs at an average ROP of 4.68 ft/hr and a cost/ft of $778. One bit drilled a record 279 ft at 4.73 ft/hr, while two other bits were pulled for hole condition with minimal wear.

This new technology has significantly impacted PDC performance in the toughest most abrasive application achieving 65% reduction in drilling cost saving over $750,000 in one well by reducing drilling time as well as eliminating expensive fishing operations.