PDC cutters could not drill through the formation, very high levels of vibration were encountered, and ROP was limited. TLJOC planned an 8½-in., 3217-m, 3D horizontal granite section with three distinct objectives: build inclination from 20° to 85.6° at a dogleg severity of 3.65°/30 m, hold the lateral, and turn from 62° to 14.3° azimuth. These targets had to be accomplished while drilling to TD at 6280-m MD.
The traditional method of drilling the granite section in Vietnam is using a downhole bent motor, 8½-in. roller cone bit, and a reliable, simple MWD tool to take surveys and measure vibrations. Issues with using this BHA configuration include increases in torque and drag, poor toolface control and weight transfer to the bit, low ROP, premature bit failure, and risk of a lost cone incident. High vibration levels can also result in high rates of failure for electronic tools.
Based on the previous record holder for an ERD basement well, NOV and TLJOC built a model that helped determine friction factors, torque and drag, and string buckling in the basement section with and without use of the Agitator system. After implementing the Agitator system as part of the optimized BHA configuration in difficult sections, TLJOC ultimately achieved the project objectives while drilling the longest and most directionally challenging basement section ever in Vietnam. The company drilled the section to TD and connected all the targets despite the extreme difficulty of drilling such a complex and challenging well due to the robust BHA optimization methodology and use of the Agitator systems for axial oscillation and friction reduction. The overall actual drilling operation time was 21% shorter (9.6 days saved) compared with the planned time, representing cost savings of 35.42% below AFE.