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Fluid surprise: Century old law on flow overturned

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For over a century, scientists have used a formula known as Darcy’s Extended Law to model how fluids move through rocks. The premise of the law is that gases move through rocks via their own, separate, stable, complex, microscopic pathways.

Darcy’s Extended Law has long underpinned engineers’ approaches to modelling fluid flow, but engineers from Imperial College London have now dispelled it.

The scientists used the UK’s Diamond Light Source facility’s synchrotron particle accelerator to make 3D videos to show in greater detail than ever before how fluids flow through rock. Remarkably, the scientists from Imperial have shown that rather than moving in a relatively stable pattern, the fluid flows are in fact very unstable. The pathways the fluids flow through last only a short period of time, tens of seconds at most, before re-arranging and forming into different ones. The team have dubbed the process dynamic connectivity.

Dr Catriona Reynolds, lead author on the study recently published in the Proceedings of the National Academy of Sciences, said: "Trying to model how fluids flow through rock at large scales has proven to be a major scientific and engineering challenge. Our ability to predict how these fluids flow in the subsurface is not much better than it was 50 years ago despite major advances in computer modelling technology. Engineers have long suspected that there were some major gaps in our understanding of the underlying physics of fluid flow. Our new observations in this study will force engineers to re-evaluate their modelling techniques, increasing their accuracy."


Industry applications

According to the team, the new observations on fluid flow could have a significant impact across a range of fluid handling industries. For instance, they could lead to advances in Carbon Capture and Storage (CCS), the process where industrial emissions are captured before reaching the atmosphere and then stored in rock under the ground.

The new insights will allow scientists and engineers to measure fluid flow on a large scale. This could be hugely significant to the production, transportation and storage of oil and gas, and other fluids, as well as revealing new information on the migration of fluids deep in the earth's crust.