Five weeks at Stanford University and the Lawrence Berkeley National Laboratories in California

My name is Ronny Pini and I am a Lecturer in the Department of Chemical Engineering at Imperial College London. I was awarded the UKCCSRC International Collaboration Fund (Call 3) to spend five weeks in California as part of a joint research collaboration involving Stanford University (with Sally Benson) and the Lawrence Berkeley National Lab (with Jim O’Neil and Nick Vandehey). The goal of the visit was to carry out a series of experiments to study solute mixing and spreading in reservoir rocks by applying a novel – and very promising – experimental approach that combines two non-invasive imaging methods, namely X-ray Computed Tomography (X-ray CT) and Positron Emission Tomography (PET).

A great challenge in working with rocks is to understand the link between a fundamental process (solute transport in our case) and the inherent heterogeneity of natural systems. Because it makes flow paths and velocity distributions uncertain, this heterogeneity also limits our current ability to use laboratory experiments to predict transport at larger scales. Here is where imaging techniques come to the rescue. While X-ray CT can be used to create 3D images of the internal structure of a rock sample, PET enables tracking the movement in real-time of a minuscule amount of substance injected into the same specimen. By analogy with clinical disciplines, we are thus able portrait both the anatomy and the physiology of the rock environment. Thanks to this the new level of observation detail, we hope to improve our understanding of flows in complex and opaque porous media and to use this knowledge to make better predictions of solute transport in the subsurface. In fact, transport through dispersion and diffusion represents a key component of the fluid-rock interaction, as it provides the driving force for any interaction between the rock and the CO₂-rich brine that inevitably contribute to the fate of the injected CO₂.

Besides bringing together a group of scientists with backgrounds in the fields of chemical engineering, hydrology and imaging technology, this research collaboration granted me access to facilities and expertise not readily available elsewhere. In fact, the key component of PET is the use of a radiotracer; in our experiments, we decided to use 11C as the active component to be injected, which, with its short decay time (half-life of only about 20 min), requires a well-thought experimental plan (in addition to physical proximity between the source (i.e. a cyclotron) and the imaging lab!). This is also one of the reasons why we aimed for a visit split in two separate slots of a few weeks each. Throughout the study, the laboratory of Sally Benson at Stanford University served as the “base camp” to prepare the rock sample and test the core-flooding system prior to the experiments, which were conducted at LBNL, where both the cyclotron (at the Biomedical Isotope Facility) and the PET/CT scanner (Department of Radiotracer Development and Imaging Technology) are located. We were able to conduct a total of ten radiotracer injections by varying total flow rates and fluid saturations (gas/water), while continuously acquiring PET and X-ray CT scans. I am coming home to London with a large and very promising set of data that I will analyse in the next months together with my students. As well as for the experimental work, during one of the visits I exploited the opportunity to be in the Bay Area to give an oral presentation at the AGU Fall meeting in San Francisco, where I showed some of the results we obtained during the first visit.

I would like to thank UKCCSRC for giving me this opportunity and for providing the funding to make this visit possible. Special thanks go to Sally Benson at Stanford University for hosting me and for the time spent discussing about the experiments, as well as to colleagues at LBNL (in particular Nick Vandehey and Jim O’Neil) who have been instrumental in making the experiments work so smoothly. I am confident that we have set the basis for an exciting and fruitful collaboration that will last for years to come.