Probing complex geophysical geometries with chattering dust

Laura J Pyrak-Nolte,William Braverman,Nicholas J Nolte,David D Nolte,Alan J Wright

doi:10.1038/s41467-020-19087-z

Laura J Pyrak-Nolte, William Braverman + Show 3 more

Open Access

https://doi.org/10.1038/s41467-020-19087-z

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Abstract

The modern energy economy and environmental infrastructure rely on the flow of fluids through fractures in rock. Yet this flow cannot be imaged directly because rocks are opaque to most probes. Here we apply chattering dust, or chemically reactive grains of sucrose containing pockets of pressurized carbon dioxide, to study rock fractures. As a dust grain dissolves, the pockets burst and emit acoustic signals that are detected by distributed sets of external ultrasonic sensors that track the dust movement through fracture systems. The dust particles travel through locally varying fracture apertures with varying speeds and provide information about internal fracture geometry, flow paths and bottlenecks. Chattering dust particles have an advantage over chemical sensors because they do not need to be collected, and over passive tracers because the chattering dust delineates the transport path. The current laboratory work has potential to scale up to near-borehole applications in the field.

Highlights

The modern energy economy and environmental infrastructure rely on the flow of fluids through fractures in rock
X-ray microscopy shows that the dust grains contain spherical bubbles of pressurized gas that range in size from 4.5 to 270 μm (Figs. 1 and 2)
Single dust grains with a larger initial area exhibited a longer duration of acoustic emissions (Supplementary Fig. 6a)

Summary

Introduction

The modern energy economy and environmental infrastructure rely on the flow of fluids through fractures in rock. There was a push to develop nano- or micro-sensors that could be transported and distributed into a subsurface formation to report back information on rock structure, lithology, fractures, and pore connectivity among other properties This effort was partially driven by the development of biophotonic sensors, such as functionalized photonic crystals, made from porous silicon, known as “smart dust”[12], as well as photonic devices made of polymers or silica matrix materials known as “PEBBLES”13,14 that had a wide range of potential applications outside of geophysics. The current laboratory work has potential to scale-up to near-borehole and civil infrastructure applications in the field

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