Microsystem Design and Package Integration Concepts for Pipeline and Downhole Monitoring

Abstract

Autonomous microsystems capable of sensing temperature, pressure, and inertial parameters are needed for many applications, including pipeline integrity monitoring and data collection in downhole environments for oil and gas exploration. A representative microsystem is comprised of sensing elements, micro-controller and interface electronics, communication module, a power source, power management and charging elements, and package. Small diameter pipelines limit microsystem size to centimeter scale and consequently limit available volume for power sources, necessitating low power consumption and compact system design with fully integrated sensing functionality. High temperature and pressure downhole environments cause numerous challenges in microsystem design, requiring that all system components be designed in tandem to operate seamlessly together. Two of the most critical microsystem aspects are the power source and system package, as these are shared resources for other components such as communication, control, and sensing.

This dissertation focuses on investigating critical elements of system design and package integration for environmental sensing autonomous microsystems, specifically for pipeline monitoring and downhole monitoring applications. The research goals are to investigate 1) system level design compromises, relationships between the building blocks, and overall performance limits under deployment conditions – including those at elevated temperatures and pressures, 2) an integration approach within a package that permits deployment, retrieval, and reusability of downhole sensing systems, and 3) a scalable fabrication method for incorporating microbatteries within autonomous microsystems.

System level design compromises and overall performance limits were investigated for environmental logging microsystems (ELM6 and ELM7) for pipeline and downhole monitoring, respectively. The systems used resonant inductive charging and Bluetooth low energy (BLE) protocol for communication. They were designed to accommodate up to 70 MPa pressure. The ELM6 had a standby current of 8 µA at room temperature (RT) which permitted a lifetime of 10 days using a 9 mAh lithium ion microbattery.

The ELM7 microsystem was intended for downhole monitoring at temperatures and pressures up to 85°C and 35 MPa, while maintaining an overall volume of <25 cm3 and density <1.2 g/cc. The package integration approach must protect the electronics from the harsh environment while permitting transfer of external pressure and temperature to the sensors during deployments; between deployments it must allow wireless charging and wireless communication, and in certain situations it must also allow the removal of the package and reusability of the system hardware. The ELM7 was successfully tested up to 85°C at pressures up to 41.5 MPa and up to 160°C for all elements excluding the battery in laboratory conditions. Field trials of these packaged systems were successfully completed by repeated deployment in an operational oil well to a depth of 1,290 m, during which data was successfully logged.

A scalable fabrication method for rechargeable nickel-zinc micro batteries was demonstrated. The fabricated batteries had a footprint of ≈0.048 cm2, nominal voltage of 1.7 V, and energy density of 2.28 mWh/cm2.

Systems capable of sensing temperature, pressure, and inertial data, permitting resonant inductive charging and BLE communication, and consuming low power within a small form factor for pipeline and downhole monitoring applications were successfully investigated, designed, and demonstrated in both laboratory and field conditions.