The streaming potentials generated by the flow of both liquid and gas through either a Pyrex capillary tube or else an unconsolidated Pyrex porous medium were investigated. This mixture of distilled water plus nitrogen gas simulated wet steam but allowed experiments to be run at room temperature. Single-phase flow of distilled water alone resulted in a constant voltage-to-pressure drop ratio, WAp, of +0.15 v/psi for the capillary tube and -0.52 v/psi for the porous medium. For both single- and two-phase flow through the capillary tube, the upstream potential was always positive relative to the downstream electrode while the opposite was true for the porous medium. The maximum two-phase potentials generated in the porous medium were about four times as great as those generated in the capillary tube for similar gas fractions, r. For the capillary tube experiments the potentials generated when r c = 0.5 were equal to or slightly less than those for single-phase flow, while for the porous medium the potentials were always greater than those for singlephase flow. When r > = 0.5 for both kinds of flow systems r had a profound effect on streaming potential and reached a pronounced maximum when 0.94 c r c 0.99. The implications of these streaming potentials for geothermal exploration and delineation of geothermal reservoirs is also discussed in the paper.

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