Optimized PDC Bit Designs for Percussion Performance Drilling System Deliver Higher Penetration Rates
Authors: Markandeya S , Merchant D , Sha D , Zhoucheng S , Yonxian D 
Published: March 2016

The 9-1/2 in. vertical section in the endorheic Tarim basin of China, is drilled through the Triassic – Devonian stratas, which are composed of mudstone, sandstone, conglomerates, dolomites, and in some instances volcanics. Bits drilling these formations lacked durability in the volcanics and had issues with slow rates of penetration (ROP) and bit balling in claystones. The previous bit designs also failed to maximize the potential performance benefits provided by the percussion performance drilling system (PPDS). The PPDS combines the torsional power of a conventional positive displacement motor with a mechanically created high-frequency axial motion.

The objective was to improve the drilling performance through a system matched approach of optimizing the polycrystalline diamond compact (PDC) bit design for use on the PPDS.

A highly focused research and development team conducted a more in-depth study of the unique mechanism of the PPDS, PDC bit design characteristics, and factors affecting their performance when used in conjunction. The team came up with a new approach that involved designing a cutting structure for PPDS applications that maximized aggressiveness while maintaining optimal durability. This was accomplished by strategically setting the back rake of each cutter to suit its respective trajectory based on the application requirements. The optimized back rake applied to each cutter allowed the required depth of cut (DOC) to be achieved at a minimum weight on bit (WOB) while maximizing the volume of leached diamond presented to the rock for improved durability. An in-depth knowledge of the cutter geometry, composition, leaching, and positioning was required to conduct this process. Specific depth-of-cut control (DOCC) features that engage at a pre-defined depth of cut were also incorporated. The depth of cut at which the DOCC features engaged was optimized by matching the calculated bit torque to the PPDS based on the lithology of the section drilled.

Two different PDC bits were designed based on the new system matched approach. Detailed laboratory tests using these designs were then conducted to validate and justify the optimization methodology and incorporated bit features. Immediate field trials of the newly designed bits along with the PPDS were then conducted. The runs delivered record breaking drilling performances in terms of increased penetration rates, proving the system matched approach of optimizing bit designs for use on PPDS.

When optimizing drilling performance, completing a specific interval in the fastest time possible is a key requirement. One of the main contributing factors for improved performance is the drill bit, which needs to have an optimized cutting structure that is matched to the drive type to meet the application's needs.

The paper introduces a novel approach of system matching the high performance percussion performance drilling system (PPDS) with an optimized drill bit design for improved drilling performance.