Klinkenberg correction

In petroleum engineering, a Klinkenberg correction is a procedure for calibration of permeability data obtained from a minipermeameter device. When using nitrogen gas for core plug measurements, the Klinkenberg correction is usually necessary due to the so called Klinkenberg gas slippage effect.

Permeability is measured in the laboratory by encasing a core plug of known length and diameter in an air-tight sleeve (the Hasseler Sleeve). A fluid of known viscosity is injected into the core plug while mounted in a steel chamber. The samples are either full diameter core samples that are intervals of whole core cut, typically 6 inches long, or 1-in plugs drilled from the cores. The pressure drop across the sample and the flow rate are measured and permeability is calculated using Darcy's law.

Normally, either nitrogen or brine can be used as a fluid. When high rates of flow can be maintained, the results are comparable. At low rates, air permeability will be higher than brine permeability. This is because gas does not adhere to the pore walls as liquid does, and the slippage of gases along the pore walls gives rise to an apparent dependence of permeability on pressure. This is called the Klinkenberg effect, and it is especially important in low-permeable rocks.

In probe permeametry (mini-permeameter) measurement nitrogen gas is injected from the probe into core through a probe sealed to a core slab by a gasket. The gas flows from the end of a small-diameter tube that is sealed against the core surface. The pressure in the probe and the corresponding volumetric gas flow rate is measured together. The gas permeability is determined by the equation:

:$K\_g\; =\; C\; q\_1\; mu\_g\; frac\{P\_1\}\{a\}\; G\; (P\_1^2\; -\; P\_2^2)^2$ Where,

:$K\_g$: Gas permeability:$q\_1$: Flow rate:$P\_1$: Injection pressure:$P\_2$: Atmospheric pressure:$mu\_g$: Gas viscosity:$a$: Internal radius of tip seal:$G$: Geometric factor (halfspace solution):$C$: Constant (unit convertion)

Obviously what can be obtained from minipermeameter measurement is gas permeability. Gas slippage will occur during the measurement because nitrogen is injected quickly from probe to core and it is very difficult to get to equilibrium in very short time span. Therefore, to get the permeability equivalent to the brine permeability at formation condition Klinkenberg calibration is necessary.

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