A Wirelessly Powered System of Coherent Sensing Nodes for Fracture Mapping Applications at Temperatures up to 250 °C and Pressures to 24 MPa

Fracture mapping is essential in hydraulic fracturing and finds applications in the oil and gas industry. Mapping of fractures using traditional radioactive or microseismic methods involves contamination and is prone to being inaccurate, thereby reducing the yield in fracturing applications. Therefore, wireless sensor networks (WSNs) with each sensing node having a small form factor and low power consumption are currently being investigated for use in such applications. This article presents a fully battery-less system of coherent sensing nodes using wireless energy harvesting. These nodes are capable of mapping fractures reliably at temperatures up to 250 degrees C and pressures up to 24 MPa. Each node comprises a microchip having the dimensions of 1.1 mm x 0.56 mm, two coils of 8 mm diameter each, and resonating capacitors. The microchip was fabricated in the Taiwan Semiconductor Manufacturing Company (TSMC) 0.18 mu m process. The node receives a 40.68 MHz radio frequency (RF) signal in the industrial, scientific, and medical applications (ISM) band and transmits back a locked subharmonic 13.56 MHz ISM band RF signal. The subharmonic signal is generated on-chip using a digital divide-by-3 circuit, drastically reducing the microchip power consumption compared with injection-locked oscillators or phase-locked loops (PLLs). The sensor nodes used in the system have a form factor of 17 mm x 12 mm x 0.2 mm and a minimum average power consumption of 1.5 mu W.