Petrophysics, Core Analysis & Tight-Gas Reservoir Engineering
Klinkenberg Gas-Slippage Core Permeability Formula
Calculate True Liquid-Equivalent Klinkenberg Permeability k_inf (mD), Low-Pressure Lab Overestimation (%), In-Situ High-Pressure Reservoir Gas Permeability (mD), and Slippage Multiplier.
Correct low-pressure core-plug gas permeability for Klinkenberg wall slippage—or overstate tight gas by 80%!
Unlike liquids (which obey a zero-velocity no-slip boundary at pore walls), gas molecules in sub-micron tight-sandstone or carbonate pore throats have a mean free path comparable to pore radius at low laboratory core-holder pressures (1.5–3.0 atm)—creating non-zero wall slip velocity! Under Klinkenberg’s (1941) Equation, Apparent Gas Permeability is k_g = k_inf * (1 + b / P_mean), so True Liquid-Equivalent (Infinite-Pressure) Permeability is k_inf = k_g_lab / (1 + b / P_mean_lab)! Entering raw low-pressure helium/nitrogen lab k_g into a high-pressure reservoir model overstates deliverable flow capacity severely.
Verify on a Tight-Gas Sandstone Core Plug—Measured_Lab_Gas_Perm k_g = 1.4400 mD (B2), Klinkenberg_Slip_Factor b = 1.60 atm (B3), Lab_Mean_Pore_Pressure P_m = 2.00 atm (B4 -> Slippage Multiplier = 1 + 1.60 / 2.00 = 1.80x in E5), and InSitu_Reservoir_Pressure = 160.0 atm (B5): True Klinkenberg Permeability k_inf equals 1.44 / 1.80 = 0.8000 mD (E2), proving raw lab k_g overestimated matrix permeability by +80.00% (E3), while In-Situ Reservoir Effective Gas Permeability at 160 atm is 0.8000 * (1 + 1.60 / 160) = 0.8080 mD (E4)!
| Klinkenberg Core Analysis KPI (k_g = 1.44 mD @ 2.0 atm, b = 1.60 atm, P_res = 160 atm) | Formula | Verified Output |
|---|---|---|
| True Klinkenberg Perm k_inf (mD) | Lab_kg_mD / (1 + b_atm / Lab_Pmean_atm) | 0.8000 mD |
| Lab Slippage Overestimation (%) | ((Lab_kg - k_inf) / k_inf) * 100 | 80.00% (20.00% @ 8 atm Back-Press) |
| In-Situ Reservoir Gas Perm (mD) | k_inf * (1 + b_atm / Reservoir_P_atm) | 0.8080 mD |
| Lab Slippage Factor (1 + b/Pm) | 1 + b_atm / Lab_Pmean_atm | 1.80x (1.20x @ 8 atm) |
Klinkenberg Infinite-Pressure Core Permeability Formula
Validate Lab_kg > 0, Slippage_b >= 0, Lab_Mean_Pressure > 0, and Reservoir_Pressure >= Lab_Mean_Pressure!
=LET(kg_l, B2, b_sl, B3, pm_l, B4, pr_r, B5, IF(OR(kg_l <= 0, b_sl < 0, pm_l <= 0, pr_r < pm_l), "Invalid Core Perm Input", ROUND(kg_l / (1 + b_sl / pm_l), 4)))Back-Pressured Core-Holder Verification Check (0.96 mD @ 8.0 atm Mean Pressure)
Re-test the same core plug under back-pressure at B4 = 8.00 atm where measured k_g B2 drops to 0.96 mD: True Klinkenberg Permeability E2 remains invariant at 0.8000 mD, while Lab Slippage Overestimation E3 shrinks from 80.00% down to 20.00%!
=IF(ISTEXT(E2), E2, ROUND(E2 * (1 + B3 / B5), 4))Try the example
Use the original values or change them to test your understanding.