Apparatus for measuring resistivity of porous rock

Apparatus for measuring resistivity at a plurality of positions along the surface of a core sample of a porous rock under confining pressure and varying water saturations, comprising:

• (a) a sleeve containing a core sample of a porous rock saturated with a first fluid,
• (b) a fluid inlet positioned in a first end of said sleeve through which a second fluid is injected under pressure into a first end of said core sample for displacing said first fluid from a second end of said core sample, said second fluid being immiscible with said first fluid and of opposite electrical conductance,
• (c) a porous member positioned adjacent a second end of said core sample within said sleeve, and which is permeable to said first fluid and impermeable to said second fluid,
• (d) a fluid outlet positioned in a second end of said sleeve through which said first fluid is discharged from said sleeve after having been displaced from the second end of said core sample through said porous member,
• (e) a plurality of electrodes extending through said sleeve and making contact with said core sample at a plurality of spaced apart positions along the length of the core sample,
• (f) means for passing a current through said core sample,
• (g) means for applying a confining pressure through said sleeve to said core sample, and
• (h) means connected to said electrodes for measuring resistivities between adjacent pairs of said electrodes in response to the flow of said current through said core sample at said confining pressure as said second fluid displaces said first fluid from said core sample.