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Autonomous Sensing Microsystem with H2S Compatible Package and Enhanced Buoyancy for Downhole Monitoring


 We report an autonomous microsystem intended for deployment in harsh fluid environments. The microsystem incorporates pressure, temperature, and inertial sensors and Bluetooth Low Energy (BLE) communication electronics; power is supplied via secondary battery, recharged using Qi wireless power transfer. Sensors and electronics are incorporated within a circuit board measuring ø26.7 × 1.5 mm3 which is embedded in a package with volume <25 cm3 and density <1200 kg/m3. The small size and density permit enhanced buoyancy control and deployment through narrow apertures. The package is comprised of a fluorocarbon elastomer VitonTM shell, which provides the necessary mechanical and chemical protection, and is filled with low bulk density cenospheres, which reduce the overall density while still allowing pressure to be transferred to the board-mounted sensor. This integration approach allows reclamation and repackaging of the electronics for rapid evaluation in a variety of harsh environments. Microsystems were tested in laboratory conditions at pressures up to 41.5 MPa and temperatures up to the battery limit of 85°C while successfully recording data for >96 hours. The VitonTM packaging was tested in H2S, diesel fuel, and 15% brine. Microsystems were then successfully evaluated in field deployment conditions in an oilwell to a depth of 1290 m, recording pressure, temperature, and inertial data.