Drilling the 16" hole section in Saudi Arabia's Deep Gas fields is particularly challenging due to a complex stratigraphic section that consists of carbonates interbedded with tough bands of hard stringers in addition to an abrasive sandstone followed by dense dolomite. The operator has attempted to efficiently drill the section using both roller cone tungsten carbide insert (TCI) and polycrystalline diamond compact (PDC) technology. The roller cone TCI bits had unacceptably low rates of penetration (ROP) with short bit life that required multiple runs to finish the required section. PDC technology delivered acceptable penetration rates but inconsistent run lengths due to impact damage from vibration induced by either the bit, bottom hole assembly (BHA) or formation change. The operator evaluated several PDC designs from different manufacturers but all suffered similar problems including short bit life due to impact damage.

The operator determined to efficiently drill the section in one run and meet performance requirements would require new PDC/BHA technology. They organized a cross functional team to aggressively seek new PDC/BHA technology and state of the art motors and drilling practices to drill the interbedded rock section in one run. The team analyzed drilling operations from virtually every perspective using numerical models in addition to laboratory and field tests. The team identified PDC damage from BHA/bit whirl and vibration problems as the primary obstacle to achieving performance goals and focused their work on vibration management. The team performed BHA modeling analysis in order to develop a PDC solution that would minimize lateral and torsional vibrations. The modeling also helped determine the optimal range of operating parameters in order to meet performance requirements and eliminate BHA/bit whirl. The system solution combined high-power positive displacement motor to drive the bit harder and advances in PDC technology including improved bit stability and new cutter technology.

Due to the collaborative effort, the operator completed the demanding 16" hole section for the first time in one run using the new BHA/PDC bit combination. The application of this new technology has reduced cost/foot from $195.84 to $121.59 for a total saving of $365,681 over 4,925 ft and 226 drilling hours. The average section ROP went up from 14 ft/hr to 21.8 ft/hr, a 55% increase in ROP resulting in 38% reduction in drilling cost.

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