SEDL / STP / STP717-EB / STP30075S

Chemical Logging of Geothermal Wells

McAtee, RE
Senior chemist, E G & G Idaho, Inc., Idaho Falls, Idaho

Allen, CA
Manager, Biological and Earth Sciences, E G & G Idaho, Inc., Idaho Falls, Idaho

Lewis, LC
Manager, Analytical Services, Exxon Nuclear Idaho Co., Inc., Idaho Falls, Idaho

Pages: 11    Published: Jan 1980

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Abstract

Chemical logging was developed to permit identification of zones bearing geothermal water during drilling of geothermal wells. This technique consists of collection of circulation fluid samples at specified periods determined by drill-bit depth. These samples are analyzed for bicarbonate (HCO³⁻), Cl⁻, F⁻, Ca⁺⁺, and silicon dioxide (SiO²). The results are plotted as a function of depth, and the resulting log indicates the presence of water-bearing structures. It was discovered that the ratio of Ca⁺⁺ and HCO³⁻ concentrations is a temperature indicator. It was also found that chemical composition changes precede structural changes. This report describes chemical logging of three wells at the Raft River geothermal site, Idaho.