Published: 12/11/2013
Published: 12/11/2013
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.
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.
The BHA drilled 1,140.2 m in one run at an average ROP of 38.4 m/h. The bent-motor BHA maintained verticality throughout the section without any corrections and had a 0.08° difference in inclination from the beginning to the end of the run. The section was drilled without any significant shock or vibration, retaining the bit's good cutter condition.
The optimized BHA and operating parameters enabled Starc Limited to drill an additional 220 m while still completing the 12 1/4-in hole section 3.5 days ahead of schedule, resulting in cost savings of USD 3.5 million. Starc Limited used Smith drill bits to drill the entire well, which was completed 6.5 days ahead of AFE plan, saving the operator more than USD 6 million.
Challenge: Avoid NPT while drilling a 12 1/4-in vertical borehole through interbedded claystone and sandstone formations with large differences in unconfined compressive strengths (UCS), causing impact damage and wear to the PDC cutters.
Solution: Use IDEAS integrated drillbit design platform to develop a BHA solution comprising SHARC MDSi716 high-abrasion-resistance PDC drill bit and PowerPak steerable motor with 0.78° bend, and establish recommendations for optimal operating parameters.
Results:
