Development of a Downhole Tool Measuring Real-Time Concentration of Ionic Tracers and pH in Geothermal Reservoirs

Abstract
For enhanced or Engineered Geothermal Systems (EGS) geothermal brine is pumped to the surface via the production wells, the heat extracted to turn a turbine to generate electricity, and the spent brine re-injected via injection wells back underground. If designed properly, the subsurface rock formations will lead this water back to the extraction well as heated brine. Proper monitoring of these geothermal reservoirs is essential for developing and maintaining the necessary level of productivity of the field. Chemical tracers are commonly used to characterize the fracture network and determine the connectivity between the injection and production wells. Currently, most tracer experiments involve 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. While this method provides accurate tracer concentration data at very low levels of detection, it does not provide information regarding the location of the fractures which were conducting the tracer between wellbores. Sandia is developing a high-temperature electrochemical sensor capable of measuring tracer concentrations and pH downhole on a wireline tool. The goal of this effort is to collect real-time pH and ionic tracer concentration data at temperatures up to 225 degrees C and pressures up to 3000 psi.

In this paper, a prototype electrochemical sensor and the initial data obtained will be presented detailing the measurement of iodide tracer concentrations at high temperature and pressure in a newly developed laboratory scale autoclave.
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Additional Info

DOE Project Name: High Temperature Chemical Sensing Tool for Distributed Mapping of Fracture Flow in EGS
DOE Project Number: FY14 AOP 1.1.5.1
DOE Project Lead: Greg Stillman
Last Updated: over a year ago
Mar
2014
Data from March, 2014
Submitted May 1, 2014

Sandia National Laboratories

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505.284.2532

Authors

Ryan F. Hess
Sandia National Laboratories
Timothy J. Boyle
Sandia National Laboratories
Steven Limmer
Sandia National Laboratories
William G. Yelton
Sandia National Laboratories
Samuel Bingham
Sandia National Laboratories
Greg Stillman
United States Department of Energy
Scott Lindblom
Sandia National Laboratories
Grzegorz Cieslewski
Sandia National Laboratories

Keywords

geothermal, EGS, downhole tool, reservoir monitoring, chemical tracers, high temperature electrochemical sensor, high temp, high temperature, electrochemical sensor, ionic tracers, Engineered Geothermal Systems EGS, Sandia National Labs, SNL, doi: 10.1117/12.2051151, tracer, downhole, high pressure

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