A rock is made up of several blocks, as shown in Fig. 1.31. The unit block is a rectangular prism of nonporous, noncon- ductor material of length L and square cross section with side length d. A cylindrical hole of diameter d is drilled through the block and filled with brine. a. Determine the formation resistivity factor of this rock block. b. What relationship exists between the formation factor, F, and the porosity, , for this rock? Fig. 1.31-Unit block of porous medium of Problem 1.2