Understanding the connectivity of fracture networks in a reservoir and obtaining an accurate chemical characterization of the geothermal fluid are vital for the successful operation of a geothermal power plant. Tracer experiments can be used to elucidate fracture connectivity and in most cases are conducted by injecting the tracer at the injection well, manually collecting liquid samples at the wellhead of the production well, and sending the samples off for laboratory analysis. This method does not identify which specific fractures are the ones producing the tracer; it is only a depth-averaged value over the entire wellbore. Sandia is developing a high-temperature wireline tool capable of measuring ionic tracer concentrations and pH downhole using electrochemical sensors. The goal of this effort is to collect real-time pH and ionic tracer concentration data at temperatures up to 225 °C and pressures up to 3000 psi. In addition, this technology can be applied to oil and natural gas hydraulic stimulation operations when monitoring accurate changes in fluid pH downhole, and in real-time, are advantageous.

Development of an electrochemical sensor for downhole tracer and pH measurements in real-time

253rd National Meeting (2017)

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