Resistivity studies of the Imperial Valley geothermal area, California

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Journal Article: Resistivity studies of the Imperial Valley geothermal area, California

Abstract

Electrical resistivity has been employed for mapping thehnperial Valley of California as part of a multi-disciplinaryapproach to assess its geothermal potential. Vertical and lateralresistivity changes were determined from Schlumherger deptilsoundings with effective probing depths up to 8000 ft.Chie/ conclusions were: (1) Known geothermal anomaliesappear as residual resistivity lows superimposed on the regionalgradient which decreases northwest.ward from the southeastcorner of the Imperial Valley, near the Colorado River, tovalues about two orders of magnitude lower at the Salton Sea.(2) A regional salinity gradient in the hnperial Valley trendsnorthwest from a very low salinity at the Colorado River nearYuma, Arizona, to a very high salinity at the Saiton Sea geothermalfield. (3; Abrupt changes in salinity exist across thehnperial fault, with salinities being much higher west of tilefault. (4)Maximum salinities can be estimated by combiningthe ground resistivity survey and formation factor-depth relationshipscompiled from well logs.From a technical point of view, the apparent-resistivityand longitudinal-resistivity maps are nearly identical at a probingdepth of 3000 ft. Hence continuous profiling at a SchlumbergerAB/2 spacing of 3000 ft should permit an effective, lowcostreconnaissance method for still-unsurveyed areas of theImperial Valley.