D Exponent
The "d" exponent is derived from the general drilling equation: R — N = a (Wd  D)
where R = penetration rate d = exponent in general drilling equation, dimensionless
N = rotary speed, rpm a = a constant, dimensionless
"d" exponent equation: "d" = log (R  60N)  log (12W  1000D)
where d = d exponent, dimensionless R = penetration rate, ft/hr N = rotary speed, rpm W = weight on bit, 1,000 lb
Example: R = 30 ft/hr N = 120 rpm W = 35,000 lb D = 8.5 in.
Solution: d = log [30  (60 x 120)]  log [(12 x 35) (1000 x 8.5)] d = log (30  7200)  log (420  8500) d = log 0.0042  log 0.0494 d = — 2.377  — 1.306 d = 1.82
Corrected "d" exponent:
The "d" exponent is influenced by mud weight variations, so modifications have to be made to correct for changes in mud weight:
where dc = corrected "d" exponent MWi = normal mud weight — 9.0 ppg MW2 = actual mud weight, ppg
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Bonacata6 years ago
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mike1 year ago
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