Photo caption: Electron microscopy image of the coated sample for the team’s 3D printed reservoir rock models
Researchers at Khalifa University have developed a new way to 3D print reservoir rock replicas that have complex porous structures and mimic a carbonate rock’s natural mineralogy. The 3D printed rocks are transparent, and allow researchers to image precisely how fluid flows through the ultra-tiny pores of rock – information which could help develop effective strategies for hydrocarbon and geothermal energy extraction, carbon sequestration, and even ice mining and water extraction from the ground during planetary exploration.
“While recent improvements in 3D printing enable scientists to fabricate 3D structures that have complicated porous structures by using polymeric materials, these structures ultimately lack in surface functionality. We overcame this problem by integrating high-resolution 3D printing with an internal coating to create structures that functionally replicate the natural rock,” explained Dr. TieJun Zhang, Associate Professor of Mechanical Engineering, and the principal investigator of a reservoir characterization and modeling project.
His team, which includes, Hongxia Li, Aikifa Raza, Qiaoyu Ge, and Jin-You Lu, recently published a paper in the journal Soft Matter describing the new micro-3D printing and mineral coating technique. This approach has been filed as both International PCT and GCC Patents.
Highly porous materials exist in all sorts of applications, from concrete and filtration to biology and oil and gas extraction. Engineers have been studying how fluids flow through porous materials for some time – a branch of study known as microfluidics. Because pore sizes can be as small as a single micrometer, and the porous material being studied can be in hard to reach places, like underground or within the human body, creating devices that can be used to simulate the way fluids flow through porous materials has been the primary way that scientists have advanced understanding of microfluidics.
Even better microfluidic devices, like the 3D printed porous structure developed by Dr. Zhang’s team, could open the door to a vast array of opportunities in quickly modelling and predicting microfluidic flow behaviors in applications such as geology and hydrocarbon extraction.
Traditional microfluidic chips show how fluids move through the pores of the rock and are typically made from glass or silicon. For some applications, this is enough, but carbonate rock is a material susceptible to fluids underground, and the microfluidic model needs to take into account the strong interactions between the fluid and the rock.
3D printing has emerged as one solution to this but many of the issues in fabricating complicated porous networks arise from the limitations in printing materials.
“Conventionally, we can enhance the thermal, electrical, and mechanical properties of 3D-printed devices by adding nanomaterials into polymer ink,” explained Dr. Li, the leading author of this work. “However, these added particles often cause severe light scattering, which impacts printing precision.
It’s then much harder to create the microstructures of natural porous materials like rock. Another issue is that this composite material has poor light transparency, meaning seeing the fluid flow through the device is much more difficult.”
To overcome these issues, the KU researchers used an alternative to polymer ink: in-situ mineral growth in 3D-printed device.
“On complex surfaces, putting a thin layer of a mineral coating on the inner surface of the micromodel mimics the natural surface mineralogy, but can mean that the crystal growth isn’t uniform,” explained Dr. Li. “To overcome this, we coated a seed layer of calcite nanoparticles on the inner surface. This facilitated calcite crystals to grow uniformly, resulting in a device that functioned precisely like carbonate rock. We made a ‘real’, yet transparent, rock.”
This device can then be used as a sort of ‘rock-on-a-chip’ to analyze how various fluids move through the pores and can be readily tailored to test, observe and analyze fluidics in biological, soft robotics, aerospace, and other emerging applications. This ‘rock-on-a-chip’ use has also been demonstrated by the team in another publication.
The transparent, 3D printed rock created at Khalifa University makes microfluidic technology more accessible to researchers in various fields and accelerates innovation. It could also be used to gain key insights into how to extract more hydrocarbons from the UAE’s oil fields in a more sustainable and cost-effective way.
25 August 2020