[
m]) can be calculated using Ohm's law after correction for the length (L [m]) and contact area (S = m2) of each sample as follows:
Electrical resistivity was measured on the cube-shaped samples by the simple apparatus shown in Figure F2. Two cells contain a conductive medium of agar-agar with KCl. Samples were placed tightly in the central support member between these cells, and measurements were taken along three orthogonal directions (Fig. F1). The electric current was measured at constant voltage. Resistivity ( [m]) can be calculated using Ohm's law after correction for the length (L [m]) and contact area (S = m2) of each sample as follows:
where R is electric resistance (in ). Measurements are accurate to within 10%. Samples were first oven dried at 105°C for 24 hr and allowed to cool in a desiccator. Resistivity measurements were then obtained (dry resistivity). Resistivity was again determined after samples were soaked in distilled water for 24 hr (wet resistivity). All the data are shown in Tables T1 and T2. Ten of the cube samples had resistivities too high to measure using our equipment (i.e., >9999.9 m). Wet resistivities of whole-round cores were also measured along the vertical (z) direction (Table T3).
Wet resistivity data are compared to downhole measurements of resistivity obtained with the Dual Laterolog (Fig. F3). Hydrothermal deposits and interpillow material show the highest resistivity anisotropy, and the resistivities of discrete samples are generally higher than those of downhole logging, although they show similar trends. This difference is primarily because of downhole logging sensitivity to larger-scale porosity.
