Low Power Autonomous Microsystem for Oil Well Logging Applications

Abstract

Downhole environmental monitoring can provide significant benefits to the petroleum industry. The rapid development of semiconductor technology enables autonomous sensing microsystems to operate at extreme environments. By injecting these microsystems into the boreholes and retrieving them after deployment, the geophysical conditions in the area of interest can be obtained. Challenges include high temperature, high pressure, miniaturized system size and packaging. This dissertation describes three generations of the environmental logging microsystem (ELM) for downhole geophysical logging applications. The first generation of the microsystem, ELM1.0, is designed for temperature logging in downhole environments. Each system consists of a power management circuit, a microcontroller with an integrated temperature sensor, and optical indicators. The system electronics are integrated on a flexible printed circuit board and packaged in a steel shell. The ELM1.0 has a packaged size of 8.9×8.9×6.85 mm3. It was tested at up to 125°C, 50 MPa in high salinity condition. The second generation (ELM2.0 & ELM2.1) is upgraded from ELM1.0 by adding a micromachined capacitive pressure sensor for pressure sensing up to 50 MPa. The ELM2.0 & ELM2.1 systems are packaged in steel shells filled with transparent polymer for pressure transfer. The packaged systems have a dimension of 9.5×9.5×6.5 mm3. The third generation (ELM3.0) is upgraded from ELM2.0 with a power switch and a low-cost polyimide pressure sensor for coarse pressure measurement up to 50 MPa. Both ELM2.0 and ELM3.0 systems were successfully tested at up to 125°C, 50 MPa in corrosive environments using laboratory instruments, and in a brine well at a depth up to 1235 m. A progressive polynomial calibration method was used for interpretation of the pressure sensor data from these tests. In addition, a high power micromachined RF switch for radio transceiver applications was designed, fabricated and tested. The RF switch can potentially be used to establish antenna networks for RF communication in the ELM. The switch consists of a bridge structure for electrostatic actuation and capacitive contact. The switch was fabricated with a 7-mask process. The fabricated device showed limited RF performance because of challenges related to the control of residual stress in suspended elements.