Development and Testing of Stick/Slip-Resistant PDC Bits

Abstract

Abstract Stick/slip vibrations are known to cause damage to drill bits and other drilling system components. Recent investigations reported by the authors determined that the design of polycrystalline diamond compact (PDC) bits has a significant influence on stick/slip behaviour of the drilling systems. Among various bit design methodologies, a depth-of-cut (DOC) control technique has emerged as an effective way of mitigating bit-induced stick/slip. The research reported in this paper aims at enhancing this technique to accurately identify the optimal application of DOC control for maximum reliability and performance. A comprehensive testing program on a full-scale research rig was undertaken to characterize the optimal type, positioning, and extent of DOC control required for mitigating stick/slip. Several PDC bits incorporating strategically configured DOC control elements were designed and tested. The stick/slip tendencies of bits were determined based on diagnostics from downhole drilling dynamics monitoring devices while the surface operating parameters were varied in a controlled manner. Test results indicated that certain DOC control characteristics were the most effective in mitigating stick/slip. While under-application of DOC control did not mitigate stick/slip, over-application reduced performance without mitigating stick/slip. Formation type played a major role in instigating stick/slip, and was a significant factor in designing DOC control. The paper presents analysis details and proposes design guidelines based on testing in multiple formations within three research wells. These design guidelines are also supported by field evidence from the North Sea, where statistics on many bit runs indicate superior performance with properly tuned DOC control.