Analysis of the contact forces on a blunt PDC bit

Yaneng Zhou, Emmanuel Detournay

Research output: Chapter in Book/Report/Conference proceedingConference contribution

17 Scopus citations

Abstract

Drilling with drag bits (PDC bits) simultaneously involves fragmentation of rock by the cutters and frictional contact on the cutter wear flats. While there is reasonable understanding of the forces arising from the cutting process, knowledge of the factors affecting the contact forces on the wear flats is still fragmentary. This paper focuses on determining the parameters that influence the mean normal stress σ on the cutter wear flats, and on mapping the dependence of a on these parameters, by analyzing the idealized problem of a slightly inclined rigid slider moving on the surface of a Mohr-Coulomb elastoplastic half-plane. Reminiscent of the problem of a blunt indenter, a continuous range of solutions from elastic to rigid-plastic contact exists. The number η = E'tan β/q (where E' is the plane strain modulus, q is the unconfined compressive strength, and β denotes the inclination of the slider) essentially controls the nature of the solution: elastic contact if η is small, rigid-plastic if η is large, and elastoplastic between these two limiting behaviors. The dependence of the scaled contact stress II = σ/q on η is determined by numerical simulations using the code FLAC. The theoretical results are broadly consistent with experimental data obtained with blunt cutters; in particular the inverse dependence of II on the friction coefficient at the wear flat/rock interface.

Original languageEnglish (US)
Title of host publication48th US Rock Mechanics / Geomechanics Symposium 2014
EditorsRay Sterling, Emmanuel Detournay, Will Pettitt, Joseph F. Labuz, Lee Petersen
PublisherAmerican Rock Mechanics Association (ARMA)
Pages306-314
Number of pages9
ISBN (Electronic)9781634395236
StatePublished - Jan 1 2014
Event48th US Rock Mechanics / Geomechanics Symposium 2014: Rock Mechanics Across Length and Time Scales - Minneapolis, United States
Duration: Jun 1 2014Jun 4 2014

Publication series

Name48th US Rock Mechanics / Geomechanics Symposium 2014
Volume1

Other

Other48th US Rock Mechanics / Geomechanics Symposium 2014: Rock Mechanics Across Length and Time Scales
CountryUnited States
CityMinneapolis
Period6/1/146/4/14

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