Lab on a Chip Blog

Figure 1. Natural gas extraction from shale rock.

Shale is a type of fine-grained rock that contains silt, clay, mineral particles, and pores ranging from meter to nanometer scales. The high organic material content in shale rock is used in natural gas extraction, for which shale reservoirs are mechanically stimulated to create permeability in the pores. A preferred stimulation method is called hydraulic fracturing, where a pressurized fluid fractures shale stone and keeps the fractures open for gas extraction (Figure 1). Natural gas extraction from shale rock is a relatively new process compared to existing energy sources. It has attracted growing interest in America and Asia especially after the 2000s because of being an environmentally friendly alternative to other consumable energy sources. On the other hand, the gas industry currently struggles with optimizing the use of pore space and fractions for efficient extraction of the gas. In a newly opened shale rock reservoir, volatile components vaporize from meter to micrometer-scale pores first, leaving heavier components in hard-to-access nanometer-scale pores. Extraction of the remaining components is necessary for full utilization of the reservoirs but poses a hard-to-solve problem for the industry.

In a recent study published in Lab on Chip, David Sinton and co-authors review the current state of the technology and demonstrate a nano-scale physical model of shale with pores. The authors also study the dynamics of gas production in nanopores via imaging the system optically and developing an analytical model for gas vaporization. They first created a microchip model matching shale nanoporous matrix properties (e.g., dominant pore sizes and permeability) (Figure 2). The microchip model contained approximately 5800 pores connected via 23000 throats, where a hydrocarbon mixture was injected. In the model, the number of the small pores (≤10 nm) is designed to be greater than the number of the larger pores (∼100 nm) to store most of the accessible hydrocarbons. This pore size distribution captures the influence of nanoscale throats connecting the larger pores and is relevant to shale production. High, medium, and low superheat was applied to the filled microchip to investigate the spatiotemporal dynamics of vaporization via optical imaging. An analytical model and experimental results showed that phase change (liquid to vapor) in a pore is largely independent of phase change in neighboring pores.

This work supports the hypothesis that the rapid decline in production rates is due to a shift from the large connected features to the nanoporous matrix, as over time the smallest pores become enriched with heavier fractions. The authors reveal that vaporization rate slows down 3000 times thanks to the nanoscale throat bottlenecks at high temperatures, while the rates reduce further with vaporization of light components in large pores at low temperatures. Even the pores with 10 nm and fewer diameters can significantly influence the production from larger pores by severely gating transport. The authors found that this problem can be solved by applying very low pressures, although currently not available in the field, during the later stages of hydraulic fracturing. This finding seems to open a new avenue in the field of shale rock processing for energy.

Figure 2. Close up view of shale rock, the description of how the evaporation works, and the description of the microchip operation.

To download the full article for free* click the link below:

Natural gas vaporization in a nanoscale throat connected model of shale: multi-scale, multicomponent and multi-phase

Arnav Jatukaran, Junjie Zhong, Ali Abedini, Atena Sherbatian, Yinuo Zhao, Zhehui Jin, Farshid Mostowfi and David Sinton

Lab Chip, 2018, Lab on a Chip Articles

DOI: 10.1039/c8lc01053f

*Article free to read until 7th May 2019

About the Webwriter

Burcu Gumuscu is a researcher in Mesoscale Chemical Systems Group at University of Twente in the Netherlands. Her research interests include the development of microfluidic devices for quantitative analysis of proteins from single-cells, next generation sequencing, compartmentalized organ-on-chip studies, and desalination of water on the microscale.

The plasma membrane is a key component of living organisms and is essential to all life. It separates the inside of the cell from the outside, compartmentalizes reactions, and selectively allows transport across it. While a lot of research has gone into how different proteins and surface molecules control the functions of the plasma membrane, less is known about how lipid composition gives rise to specific properties. For instance, transmembrane proteins, which are also a large class of drug targets, may have different requirements for the lipid environment or may have their function modified depending on local lipid composition. Recently, researchers from the David Weitz Lab at Harvard, have developed a microfluidic chip which they used to screen the largest lipid library to date, in order to identify which lipid compositions have specificity for certain protein transmembrane domains. This allows researchers to investigate the effect of local lipid concentration on transmembrane proteins.

The plasma membrane is often described as a ‘simple barrier’. But if that’s the case, then “why does nature go through the trouble of making so many different types of lipids?” explained Roy Ziblat, the lead author on the paper. Ziblat believes that the lipid membrane role is far bigger than a mere barrier and it serves as a substrate for accelerating bio-reactions. The role of the lipids composing the membrane is to control which biomolecules participate in these reactions, by their selectivity to membrane proteins. Having limited success with existing techniques, Ziblat turned to microfluidics to try to answer this question.

The microfluidic chip comprises an array of 108 wells in PDMS where lipid films can be deposited and dried before sealing the chip with another layer of PDMS. Liposomes are generated within the wells by swelling in aqueous buffer. These liposomes are then tested to see whether or not transmembrane domain peptides will insert into them. However, because the transmembrane domain peptides are insoluble, they can’t simply be added into the chip. To get around this, Ziblat et al. turned to cell-free protein synthesis. By loading the chip with DNA for the transmembrane domain peptide and PURExpress (a commercial cocktail of ribosomes, enzymes, and nucleotides for transcription and translation), the peptides can be synthesized in close proximity to the liposomes, thus minimizing precipitation and increasing the chance of insertion. The paper by Ziblat et al., which was featured on the cover of the 7^th December issue of Lab on a Chip, also includes a helpful video description of these methods. Ziblat said he first made the video to better communicate his methods with his supervisor and colleagues, but it really helps the reader understand a very technical methodology.

Going forward, Ziblat hopes to use the device to study other membrane interactions, such as virus-cell binding. There’s also hope that this new device and method can be used to identify what the authors call “druggable lipids”—peptides that interact with specific lipids and thus better direct drugs toward specific cells or even organelles.

To download the full article, click the link below:

Determining the lipid specificity of insoluble protein transmembrane domains

R. Ziblat, J. C. Weaver, L. R. Arriaga, S. Chong and D. A. Weitz

Lab Chip, 2018, 18, 3561

DOI: 10.1039/c8lc00311d

About the webwriter

Darius Rackus (right) is a postdoctoral researcher in the Dittrich Bionalytics Group at ETH Zürich. His research interests are in developing integrated microfluidic tools for healthcare and bioanalysis