Enter value and click on calculate. Result will be displayed.
`d=([log R/[60×N]]/[log [12×W]/[1000×D]])×(ρ_n/ρ_m)^c `
R = Penetration Rate N = Rotary Speed
W = Weight on Bit D = Drill Bit Diameter
ρn = Mud Weight Equivalent ρm = Mud Weight Used
C = Shale Compactibility Coefficient
This concept was first developed by Jordan and Shirley as a factor in evaluating drilling rates and predicting abnormal pore pressure zones.
All things being equal, the d-index should increase with depth when drilling in the normal pressure range. A reversal of this trend is when drilling indicates potential overpressure.
Example of use
Input data: Permeability: 10Ft/Hr; Rotation speed: 20Rev/Minute; Weight on bit: 20 1000 Lb; Bit diameter: 10Inches; Mud equivalent: 60Lb/Gal; Mud weight: 40Lb/Gal; Mudstone compaction coefficient: 6
Click "Calculate", d index: 14.6211