Publications Details

Development of a High Temperature, High Pressure Logging Tool for Downhole pH Measurements

Henfling, Joe; Von Hirtz, Paul; Broaddus, Mark; Kunzman, Russ; Galisanao, Edward; Wright, Andrew A.; Hess, Ryan F.; Cashion, Avery T.

Sandia National Laboratories has developed technology enabling novel downhole electrochemical assessment in extreme downhole environments. High-temperature high-pressure (HTHP) electrodes selectively sensitive to hydrogen (H+), chloride (Cl-), iodide (I-) and overall ionic strength (Reference Electrode+-) have been demonstrated in representative geothermal environments (225°C and 103 bar in surrogate geothermal brine). This 2-year program is a collaboration effort between Sandia and Thermochem, Inc. with the goal of taking the prototype sensors and developing them into a commercial product that is operable up to 300°C and 345 bar. The Sandia-developed prototype HTHP chemical sensor package creates a capability that has never been possible to date. This technology is desired by the geothermal industry to fill a gap in available downhole real-time measurements. Only limited sensors are available that operate at the extreme temperatures and pressures found in geothermal wells. For the purpose of this paper, high temperature is defined as temperatures exceeding 200°C and high pressure is defined as pressures exceeding 35 bar. Chemical sensors exceeding these parameters and sized appropriately for downhole applications do not exist. The current Thermochem two-phase downhole sampling tool (rated to 350 °C) will be re-configured to accept the sensors. A downhole tool with an integrated pH real-time sensor capable of operation at 300°C and 345 bar does not exist and as such, the developed technology will provide the geothermal industry with data that would otherwise not be possible such as vertical in-situ pH-profiling of geothermal wells. The pH measurement was chosen as the first chemical sensor focus since it is one of the fundamental measurements required to understand downhole chemistry, scaling and corrosion processes.