What is the term for the gas slippage effect at low pressure that leads to overestimation of absolute permeability in a gas-saturated core?

• A. Klinkenberg effect
• B. Fick's law
• C. Bernoulli effect
• D. Laminar effect

Answer: (C)

Gas slippage occurs when pore throats are tiny compared with the gas molecules’ mean free path. In that regime, molecules slip along the walls instead of sticking to them, so gas can flow more easily than Darcy’s law with no-slip would predict. That makes a permeability measured with gas at low pressure appear higher than the rock’s true, intrinsic permeability. This is known as the Klinkenberg effect. It’s why gas permeability measurements change with pressure and why a correction is used to recover the intrinsic permeability. A common way to express the correction is that the apparent permeability k_app relates to the intrinsic permeability k_intrinsic by k_app ≈ k_intrinsic(1 + b/p), with p being the gas pressure and b a parameter dependent on gas properties and pore structure. The other terms listed don’t describe this slip-guided increase in apparent permeability: Fick’s law governs diffusion, Bernoulli relates to energy changes in flow without addressing slip at walls, and laminar effect isn’t the standard descriptor for this phenomenon.