D.C. Resistivity

Current flow (electricity) in rocks is either conducted:

• electronically - graphite and native metals
• electrolytically - movement of ions in interstitial fluids

Resistivity is controlled by:

1. fractional volume of rock occupied by water
2. salinity or free-ion content of the connate water
3. interconnection of pore spaces (permeability)
4. temperature

Archie’s Law

holds for porous sandstones and limestones, the bulk resistivity, , depends upon the porosity, ,and on the resistivity of the connate water, _w. a is a number of the order of 1 and b is a number the order of 2.