Up close and pore-scale personal

Elaine Maslin

January 1, 2016

Voxels, submicrons and synchrotronic optics are coming to an oil and gas laboratory near you. Well, almost. Elaine Maslin reports on the University of Aberdeen’s new high-spec scanner.

High-resolution core scan images from the university’s X-ray microscope. Images from the University of Aberdeen.

Voxels, submicrons and synchrotronic optics are the language of microscopic X-rays, which might seem alien to the oil and gas industry, but in fact they are being used to help under- stand reservoir properties and more at a micrometer scale.

Earlier this year, the University of Aberdeen’s School of Engineering took delivery of a Zeiss, Xradia Versa 410 XRM (X-ray microscope), which its Californian maker says bridges the gap between high-performing X-ray microscopes and less powerful computed tomography (CT) systems.

The instrument was bought thanks to a £1.1 million grant to a consortium of universities, of which the University of Aberdeen is one, from the Scottish Funding Council, via the Oil and Gas Innovation Centre, for use in teach
ing and research related to the oil and gas industry. It is the only scanner of its type in Scotland and a resolution down to 1 micrometer (or 1000th of a millimeter).

So what can it do? 3D X-ray microscopes are enabling micrometer scale resolution scanning of rock samples, the computed models of which can then be used for simulating reservoir properties to aid understanding around areas such as enhanced oil recovery and geological storage of CO2.

All or part of rock samples weighing up to 15kg can be scanned on the ma- chine, with a 300mm maximum sample size. A single 3D volume takes 2- 24hrs depending on the resolution. The instrument can achieve 0.9 μm true spatial resolution with minimum achievable voxel size of 100 nanometers.

While use of this sort of technol
ogy has been around for about 5-10 years, companies are gradually getting interested in using it, says Professor Dubravka Pokrajac, from the University of Aberdeen’s School of Engineering. “It is still primarily a research tool, but it is moving towards industrial use, such as understanding the processes occur- ring in the reservoir during production or enhanced recovery of hydrocarbons,” she says.

“Using the 3D models created from the scans we can run computer simulations without running a physical experiment or we can compare with experiment and check if the 3D model is representative of real rock. Once this is confirmed, the 3D model becomes a virtual experimental sample that you can feed in to the computer and run virtual permeability or core flooding experiments and understand the absolute and relative permeabilities, which are crucial for enhanced oil recovery.”

A lot of money can be saved by enabling the modelling of core flooding without actual core samples. Furthermore, the scanner provides a detailed information on how exactly the injected fluid moves through the core through time. This kind of information is not available from conventional core flooding tests.

MSc and PhD projects at the university will be looking at pore structure configuration and its statistics for various types of rocks, permeability studies, single phase flow, multiphase flow – all of which are relevant for reservoir engineering.

The Versa XRM 410 will also be used for other areas of research, such as ma- terials science. In this area, tension or compression tests on various materials, such as aluminum or polymer can be carried out while they are still inside the scanner, so that the resulting crack propagation within the material can
be determined from successive scans. With the results, the scientists can calculate mechanical properties important for fatigue and durability of various materials.

The University’s Department of Geology and School of Engineering are also interested in using the scanner for research into geological storage of CO2. “One of the things we would like to
do, depending on securing additional equipment, is to understand how CO2 moves at reservoir conditions such as high-pressure and high-temperature,” Pokrajac says. “It would also help towards understanding how CO2 is trapped within a reservoir and how much of it can be stored. To do this, i.e. simulate CO2 injection into depleted oil fields or brine aquifers as potential storage places, the university would need to build a flow loop and perform core floods inside the scanner.”

The university is also getting a second scanner, which is due to arrive in January 2016. This is a complementary unit – it is able to scan bigger samples but with a coarser resolution. By using both together, the university will be able to combine fast but relatively coarse scoping investigations with very detailed microscopic studies of selected regions of interest. This will enable studying samples such as rock cores at different spatial scales, and open a possibility for a new level of understanding of upscaling, which
is the key issue in many practical applications, for example in reservoir engineering.