Starc Limited Saves USD 3.5 Million Using BHA with High-Abrasion-Resistance PDC Drill Bit

Complex formations in deep water complicate run

Starc Limited was planning to drill a 12 1/4-in vertical borehole through highly interbedded claystone and sandstone formations in deep water off the coast of Equatorial Guinea in West Africa. The high UCS and the sandstone's quartz content resulted in impact damage and wear on PDC bits in nearby offset wells. Therefore, the operator needed a bit that can complete the section in one run while minimizing shock and vibration to the cutting structure and critical BHA components.

Aggressive PDC drill bit and steerable motor achieves higher ROP

Using the IDEAS drillbit design platform, Smith Bits recommended a BHA composed of a SHARC MDSi716 bit with seven blades and a PowerPak steerable motor with 0.78° bend. Operating parameters for optimal bit and motor speed were determined by producing a formation description based on log data from offset wells, most of which used SHARC MDSi816 bits with eight blades. However, based on simulations of various surface rotary and WOB combinations and its influence on vibration and torque levels, the MDSi716 bit design proved more dynamically stable in varying lithology. It also had a higher side rake angle and lower back rake angles, which increased bit aggressiveness to achieve higher ROP while reducing shock and vibration. The steerable motor enabled the bit to spin at a higher rpm to increase ROP and allowed corrections to be made if the well deviated from the vertical direction.