In Archie's equation for formation conductivity, what values are commonly assumed for n (tortuosity exponent) and m (cementation exponent) when local parameters are unknown?

In Archie's equation for formation conductivity, what values are commonly assumed for n (tortuosity exponent) and m (cementation exponent) when local parameters are unknown?

• A. n = 1, m = 2
• B. n = 2, m = 1
• C. n = 0.5, m = 1.5
• D. n = 1.5, m = 2

Answer: (A)

Archie’s law uses m to capture how pore geometry and grain contacts (cementation) influence conductive paths, and n to describe how tortuosity and connectivity change as the fluid saturations vary. When you don’t have site-specific parameters, the common starting point is to take the cementation exponent m around 2, reflecting typical sandstone pore connectivity, and the tortuosity exponent n around 1, representing a simple, first-order effect of saturation on conductivity. This combination provides a simple, widely used baseline for formation conductivity in the absence of detailed measurements. Other exponent pairs imply different rock textures or stronger saturation effects and are less typical as defaults.

Archie’s law uses m to capture how pore geometry and grain contacts (cementation) influence conductive paths, and n to describe how tortuosity and connectivity change as the fluid saturations vary. When you don’t have site-specific parameters, the common starting point is to take the cementation exponent m around 2, reflecting typical sandstone pore connectivity, and the tortuosity exponent n around 1, representing a simple, first-order effect of saturation on conductivity. This combination provides a simple, widely used baseline for formation conductivity in the absence of detailed measurements. Other exponent pairs imply different rock textures or stronger saturation effects and are less typical as defaults.