Development of a HT Seismic Downhole Tool

Abstract

Enhanced Geothermal Systems (EGS) require the stimulation of the drilled well, likely through hydraulic fracturing. Whether fracturing of the rock occurs by shear destabilization of natural fractures or by extensional failure of weaker zones, control of the fracture process will be required to create the flow paths necessary for effective heat mining. As such, microseismic monitoring provides one method for real-time mapping of the fractures created during the hydraulic fracturing process. This monitoring is necessary to help assess stimulation effectiveness and provide the information necessary to properly create the reservoir. In addition, reservoir monitoring of the microseismic activity can provide information on reservoir performance and evolution over time. To our knowledge, no seismic tool exists that will operate above 125°C for the long monitoring durations that may be necessary. Replacing failed tools is costly and introduces potential errors such as depth variance, etc. Sandia has designed a high temperature seismic tool for long-term deployment in geothermal applications. It is capable of detecting microseismic events and operating continuously at temperatures up to 240°C.

This project includes the design and fabrication of two High Temperature (HT) seismic tools that will have the capability to operate in both temporary and long-term monitoring modes. To ensure the developed tool meets industry requirements for high sampling rates (>2ksps) and high resolution (24-bit Analog-to-Digital Converter) two electronic designs will be implemented. One electronic design will utilize newly developed 200°C electronic components. The other design will use qualified Silicon-on-Insulator (SOI) devices and will have a continuous operating temperature of 240°C.