The Need for High-Frequency Vibration Measurement Along with Dynamics Modeling to Understand the Genesis of PDC Bit Damage

Abstract

Drilling vibration can be harmful to the bit and the bottomhole assembly (BHA), resulting in damage and tool failure and subsequent non-productive time (NPT). Bit damage while drilling offshore is costly, and any improvement in bit life can save multiple unplanned trips and lead to savings for operators. Consequently, dynamic dysfunctions have been the focus of industry research to understand and mitigate their effects. In this paper, the authors present a field case study from an offshore application. A high-frequency, in-bit sensing device (1400-Hz sampling frequency) was installed into the bit shank in conjunction with a well-established measurement while drilling (MWD) tool in the BHA. The intent was to capture the dynamics behavior of the BHA and the dynamics directly at the bit. Multiple measurements along the BHA gave a better understanding of the behavior of the entire drilling system. The measurements were then used, along with dynamics modeling and simulation, to correlate bit and cutter damages with instances of backward whirl and stick/slip. The developed kinematic model of whirl corroborated well with measurements and showed how polycrystalline diamond compact (PDC) cutters can exhibit relative backward motion that potentially leads to severe cutter damage. The extended frequency range of the measurement module also enabled the capture of new dynamics phenomena at much higher frequencies than are usually reported in literature. The insights gained in bit dynamics and cutter damage helped to improve bit design by building dynamically stable PDC bits with increased rate of penetration (ROP) and reduced NPT. The need for high-frequency measurements is also discussed and the benefits are presented, i.e., avoiding bit design iterations around misunderstood vibration issues. In today's challenging drilling applications, the measurements are important in characterizing the harsh drilling environment and understanding high-frequency dynamics phenomena that are rarely measured or discussed.

Continuous High-Frequency Measurements of the Drilling Process Provide New Insights Into Drilling-System Response and Transitions Between Vibration Modes

“…No borehole-caliper measurement was available, but using the method in Lesso et al (2011) to examine the stabilizer positions and rate of penetration (ROP) suggested the transition was the result of two different BHA contact points entering an interval of overgauge hole. In this overgauge hole, the clearance was thought to be large enough to allow the BHA to bow out because of centripetal forces and enter into a steady state of whirl (Shyu 1989;Vandiver et al 1990). Transition out of the whirl was caused by the stabilizers moving back into an in-gauge hole.…”

“…Bending moment MðxÞ corresponding to vðxÞ is given by the moment-curvature relationship (Shyu 1989):…”

“…Different BHA whirl types have been identified with transverse bending-moment sensors and transverse magnetometers (Close et al 1988;Shyu 1989;Vandiver et al 1990;Macpherson et al 2001). Other researchers have used two sets of accelerometers in an RSS to detect and quantify collar/stabilizer whirl (Minett-Smith et al 2010).…”

A New Model of High-Frequency Torsional Oscillations (HFTO) of Drillstring in 3-D Wells

“…According to paper [7], the normal force at the wear flat (14) where l ϭ overall wear flat length: l ϭ nl n ; l n ϭ wear flat length per blade; ϭ rate of change of the contact length with depth d at small depths of cut; S ϭ normal stress acting at the cutter wear surface. The stress S may be considered permanent and approximately equal to the intrinsic specific energy e [15].…”

“…In recent years downhole measurements revealed high-frequency torsional oscillations of the order of hundreds of hertz with sufficiently great amplitude [10,14]. It is considered that these oscillations propagate within the BHA for comparatively short distance.…”