Adaptive PDC Drill Bit Reduces Stick-Slip and Improves ROP in the Midland Basin
Authors: Phillips Anthony , Gavia David , Noel Afton , Savage Michael , Stefanik Thomas 
Published: February 2018

In-bit vibration sensors reveal that stick-slip and lateral dysfunction are the primary cause of poor polycrystalline diamond compact (PDC) bit performance in the 12 ¼ -in section of the Midland basin. Premature dulling as a result of vibrations leads to low penetration rates and failure to reach the targeted depth. New drill bit technologies have been designed to mitigate stick slip and lateral vibrations. This paper shows the method utilized to reduce drilling vibrations and increase penetration rate and footage to meet the operator's objectives.

Performance benchmarks were established by conducting a post-run analysis of drilling parameters incorporating in-bit sensing vibration data and through PDC bit dull evaluation from offset runs. This analysis led to new designs incorporating shaped diamond elements (SDE) to mitigate lateral vibrations and ovoid's with adaptive exposure that mitigate stick-slip without hindering rate of penetration (ROP). After the field runs showed a poor dull on the 6-blade frame and low performance from the 7-blade frame, they were tested in multiple states in a high-pressure downhole simulator to determine which elements have the highest effect on performance. The learnings from these where applied to a more durable, higher performing design.

The 6-bladed bit drilled 6636 feet, which is average footage, compared to offsets. However, the vibrations recorded during the 6-bladed bit run were significantly lower than the typical offsets, 82% of the drilling hours registering with low levels compared to the 52% smooth drilling typically seen in this interval. The bit was tripped short of target depth, due to low ROP with a ring-out in the shoulder. To improve durability the team recommended a 7-blade PDC bit, which resulted in low performance through ROP. With this result, the bit was laboratory tested replicating the ROP observed at the end of the field run by selecting an equivalent carbonate rock and adjusting the simulator to the overburden pressure. This provided a baseline that could evaluate the true impact of design changes, on field performance. Comparison of the all the features indicate that edge geometry, blade count, cutter size and backrake angle can increase ROP by making the bit drill more efficient while decreasing overall bit aggressiveness at lower ROP's. The findings show the primary benefit is improved ROP at high power levels, and reduced bit reactive torque at low power levels, at the time when lateral vibrations typically occur. The adaptive and SDE features will further add to this performance by reducing vibrations. This holistic approach allowed the team to identify the primary performance limiters through field, laboratory and downhole vibration analysis. The suite of full bit simulator tests established several key learnings, to improve performance. These learning when applied to the new design, proved to have good durability, reduced vibration and high performance, meeting the customer's objectives.

Design improvements were achieved based on the results of field tests and a series of full bit high-pressure simulator tests. The combination of adaptive PDC drill bit technology and shaped diamond elements was used to reduce downhole vibrations, thereby enabling the operator to improve overall bit performance and durability.