Andrew Dykes speaks with the team attempting to create “smart rocks” – 3-D printed, sensor-packed models which will offer unprecedented insight into oil and gas-bearing microporous structures
For centuries, geologists have sought to understand what goes on inside the minute porous structures of oil-bearing rocks. Now, sensors embedded within the rocks themselves may be able to tell them.
The European Research Council (ERC) has recently awarded a 3 million euro (US$3.35 million) grant to a team of engineers and scientists at Scotland’s Heriot-Watt University to achieve just that. Led by Professor Mercedes Maroto-Valer – who holds the current Robert M Buchan Chair in Sustainable Energy Engineering – the research team is seeking to create exact replicas of porous rocks using 3-D printing. By embedding micro sensors in these “smart rocks” as they are laid down, the team can then run experiments to collect information on porosity, flow temperature and more, at a scale which has never been achieved before.
Professor Maroto-Valer heads a nearly 30-strong interdisciplinary team at the university, tasked with developing novel chemical and engineering solutions which can aid the pursuit of energy, and with a particular focus on clean and sustainable technologies. Although trained as an applied chemist, she has spent most of her career in chemical engineering departments, and now works with a range of expertise “all the way from mechanical and reservoir engineers to chemists and geologists.”
In an interview with InnovOil, she explained that Heriot-Watt had been examining the area of research for some time, within her own research group and others. “We have been working for quite a number of years looking at flow in porous media for different applications, either oil and gas or industrial processes. But as with any project looking at the subsurface, it can be very difficult to see what’s actually happening, particularly at the pore level.”
“We realised we needed to approach this from a different angle,” Maroto-Valer said. “Rather than getting cores and trying to instrument them, we wondered if we could actually print the rock – or something that would be very similar in terms of its physical and chemical properties.”
The solution, it transpired, lay just across campus in another of the university’s departments.
“We started talking to colleagues at Heriot-Watt from Manufacturing and from Sensing about research, in terms of the challenges that we were facing which had stopped us pushing this into the frontier,” she explained. It was through these discussions that Professor Maroto-Valer learned how advanced sensing technology had become – especially that it could withstand the temperature and pressure of downhole conditions, and could be placed with minute accuracy.
“We came up with the idea to 3-D print porous rocks, get the sensors in and then run our flow-through and standard experiments,” she continued.
First, core samples are 3-D scanned to create a highly detailed digital model. This model then allows the team to print an exact replica of the core, while sensors can be placed in areas of particular interest – for example, where there are specific fractures or particularly challenging microporous structures which warrant investigation.
These sensors can measure and report on a number of variables, she added, including temperature, pressure, pH and fluid/gas composition. “They can do really incredible things in terms of being able to collect information within a very small micro-environment. They can not only sense a particular parameter, but communicate that information to the outside,” she continued. “We know from work that has been done here at Heriot-Watt before what type of sensors we can use, what type of optical fibres, how small we can do them, how precise we can position them, and what type of information they can collect at the pore level.”
These printed cores, formed from polymers, glass and steel, can then be subjected to the same conditions as the reservoir, enabling a far more in-depth understanding of oil, gas and water transport behaviours. This should allow chemical engineers, for example, to test how surfactants will interact within the pore structure in EOR applications, or which structures are best for holding CO2 in a carbon-sequestration scenario. “We will be able to tell you what happens in that core in detail you would not have been able to get before,” she said.
The group’s intention is that these printed models should – as much as possible – mimic the core samples the industry is used to. “Right now we are aiming for typical core size – around 1 inch (25 mm) in diameter is quite standard nowadays. Its length is just a matter of how many layers we want to print. Our intention is that they will look basically the same as if you were to drill a core – but you won’t have to actually drill it,” she explained.
The potential implications of that capability are substantial. As 3-D scanning and seismic data become even more sophisticated, geologists of the future may never have to remove cores from a reservoir to understand it accurately. With sufficiently detailed scanning and digital models, it may be possible to print samples from any part of a formation; producers could understand how the pores are structured and how fluid or gas will behave inside them before any drilling has even begun.
Retrieving the information should also be straightforward. Sensors’ data are sent out of the core using tiny optical fibres, also incorporated within the layers of the model as it is made. These high-bandwidth fibres will deliver that information in real time, meaning researchers should not only have access to more detailed results, but they should also have them faster than has been possible before.
Professor Maroto-Valer believes that the knowledge gained from these sensors will also help to improve current structural models, making them much more robust. “Rather than not knowing what happens [in a particular formation] or having to model or predict it, you can visualise the whole process,” she added.
The level of detail and complexity that these printers can achieve is staggering. “We’ll be looking at micron features,” she noted. “That’s how far you can go. It’s a compromise between how far you want to print, how big you want to make them and how many sensors you want to insert…it’s all a balance between how small and how complex the structure looks. But the technology itself can go well into the micron range.”
In addition to understanding fluid flow in oil-bearing rock, the group is bullish on the potential of its research for numerous other fields: “The applications are mind-blowing,” Maroto-Valer enthused. As well as the aforementioned opportunities in hydrocarbons, water and gas recovery – hydraulic fracturing is a notable candidate – it holds intriguing prospects for geothermal exploration and industrial processes, all of which are controlled by pore-level mechanics.
In particular she highlighted gas drying in a refinery, a process whereby wet gas is passed through porous media and liquid and water vapour is removed via adsorption. Incorporating sensors into 3-D printed versions of these systems would enable a much greater understanding of how gas interacts and moves through this media. “If you can understand all those processes at a fundamental level you can optimise them,” she added.
Going beyond that, there are porous media everywhere which could benefit from this kind of analysis, even in the architecture of organs in the human body. The team is optimistic that there could be medical benefits to its work too.
In the long term, discussions are already taking place as to how far the technique can be pushed. It is possible that with refinement and more specific sensors, even more variables can be measured in the pores. Professor Maroto-Valer is even exploring the feasibility of printing these pore structures at nanometre-scale.
The five years of research funded by the ERC is sure to throw up its fair share of challenges too – “It all sounds easy but then we actually go in the lab…” she laughs – but the team is confident that it has an established technique and the right skills in place. Although still in its early stages, management and logistics are beginning to come together, and the team is eager to get started. There has also been interest in commercial applications, and the team is currently in discussions with several parties.
What is perhaps most pleasing about the project is its multi-disciplinary involvement, something the commercial oil and gas industry is only just beginning to embrace. Professor Maroto-Valer, however, is a firm believer in the process as an essential method of pushing scientific understanding. “When you are addressing a complex challenge it is very difficult to do it just within your own lab, or your own discipline… [Sometimes] the only way to move beyond the state of the art is to bring in other elements from other areas, techniques which might have been developed for another purpose maybe, and that allows you to move forward,” she said. “Otherwise you get stuck in your own ways of thinking.”