1 pessier and fear introduced a bit specific

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Unformatted text preview: um drilled. 1 Pessier and Fear introduced a bit specific coefficient of sliding friction to express torque as a function of WOB on the MSE correlation, as follows: 3 T DB * WOB (2) 1 μ * DB *WOB 36 (3) μ = 36 Or T= Substituting T in Eq. 1 by Eq. 3 yields: MSE = WOB 13.33 * μ * RPM * WOB + AB DB * ROP (4) For field applications, μ is usually assumed to be equal to 0.25 for tricone bits, and 0.5 for PDC bits. 2 SPE 116667 The correlation between MSE and the rock strength has been used to evaluate the drilling efficieny.1, 3,4,5, 6 EFFD = MSEmin UCS *100 = * 100 MSEactual MSE (5) Based on field observations, Dupriest and Koederitz assumed a uniform drilling efficiency equal to 35% regardless of bit type or WOB.5 Including this assumption on Teale’s original equation yields: ⎛ WOB 120 * π * RPM * T ⎞ ⎟ MSE = 0.35 * ⎜ ⎟ ⎜A + AB * ROP ⎠ ⎝B (6) Rabia presented a simplified version of the specific energy correlation for bit selection, as follows: 7 SE = 20 * WOB * RPM DB * ROP (7) Correlating MSE with rock strength is not an easy task because MSE is usually higher than rock unconfined compressive streng...
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