India, April 22 -- The Government of India has issued a release:
Engineers drill glycerol, a sweet alcohol used in cough syrups, into rocks to push out the viscous oil. Now, a new study has unearthed a novel method to control mechanical behaviour of displaced clay that can help better understand the oil recovery process and aid in clay transport.
Fig 1. Blue represents the Newtonian Fluid - water, flowing through the non-Newtonian Clay,
represented by yellow
Viscosity is a fluid's resistance to flow. For example, honey is more viscous than oil, which is more viscous than water. When a less viscous fluid, such as water, pushes out a clay suspension in a confined space, the water creates interesting designs. A clay suspension is a non-Newtonian fluid, like toothpaste and mayonnaise. Their surfaces can hold peaks when still. By contrast, Newtonian fluids, such as water, have flat, featureless surfaces when still.
Although scientists have earlier studied global patterns created when water displaces clay, the microstructures and how these patterns grow, come into the spotlight in the present study by scientists from the Raman Research Institute (RRI), an autonomous institution of the Department of Science and Technology (DST).
"We find the observation of new modes of finger (branch) propagation, namely zig-zag and skewering, particularly exciting. The appearance of these modes was unexpected and had never been reported in previous studies," says Ranjini Bandyopadhyay, Senior Professor at RRI and co-author on the paper.
Fig 2. The left represents the zig-zag projection of the fingers of water through clay, while the right highlights the skewering projection of the fingers - the new modes of finger propagation observed in this study
When water encounters clay while flowing, a 'fluid flow instability' gets created at their interface, where the fluid deviates from its regular flow. "While in some situations, it is essential to suppress instability, in others, instability formation can be exploited to facilitate fluid mixing," says Vaibhav Raj Singh Parmar, PhD student at RRI and the lead author of the paper. "You need to understand instabilities to control instabilities."
For their experiment, the scientists first removed moisture from the clay by baking it in an oven. They then created a suspension of clay by mixing it into water. They also created separate solutions by mixing additives such as dimethylformamide (DMF), tetrasodium pyrophosphate (TSPP), NaCl, i.e., common salt, and KCl into water. Then they created separate suspensions by adding clay to each of them.
The clay they used consists of coin-like nanoparticles, 1 nm thick, with a diameter of 30 nm. Substances like TSPP delay aging or cracking of clay, while NaCl and KCl lead to faster fracturing.
The experiments were performed within the narrow gap between two glass plates about the size of a large bicycle wheel, having a central hole through which the clay and the water were injected. The arrangement is called a Hele-Shaw cell. A beautiful radial pattern of pathways spread out from the centre as water displaced clay.
What patterns formed depended on the clay's elasticity. A more elastic solid tends to return more readily to its original shape when distorted. For the case of clay dissolved in pure water, when water flowed through it, the network grew by tip-splitting, where the tip of a finger split into two separate fingers.
Fig 3. Incorporating additives affects the clay's elasticity, leading to water creating different patterns when pushing out the clay
When they repeated the experiment with the clay solution prepared using DMF and TSPP, in which case the elasticity of the clay was low, the channels in the clay sample through which fluids can flow became unevenly distributed, giving rise to novel patterns like skewering and zigzagging.
When they used clay prepared with NaCl or KCl, the clay became highly elastic and turned into a brittle sheet. "Under these conditions, the sample is really, really solid-like. So when water tries to propagate through this disordered solid, there's a lot of stress at the tip. So, it's just like taking a sharp object and banging on a piece of glass," says Bandyopadhyay. "It'll just crack."
Thus, by incorporating additives, they could modify the clay's elasticity and control the patterns. Their study can have applications in domains such as oil recovery and material transport.
"Instabilities are not desired during oil recovery. When oil in a porous rock is displaced by glycerol, its advancing fingers reduce the efficiency," says Parmar.
"You can [also] change the way clays talk to each other just by putting additives, and you can completely change the way the transport of clay happens," says Bandyopadhyay.
Publication link: DOI 10.1088/1367-2630/ae27ec
Disclaimer: Curated by HT Syndication.
