The "GLoC" concept for studying key processes of multiphase reactive transport applied to CO2 geological storage – CGSµLab

The scientific and technical consortium built around the CGSµLab project has skills, equipments, and the necessary infrastructure to the GLoCs microfabrication, their implementation coupled with the use of advanced characterization techniques (microscopic observations, Raman spectroscopy, average in situ IR fluorescent optic fiber, Brillouin, X, X tomography), and development codes and numerical simulations methods suitable for the description of an essentially multi-scale problem. This innovative approach is designed to acquire data for the theoretical approaches of the thermo-hydro-physico-bio-geo-chemical mechanisms. It will also usefully complement multiphase interfacial behavior studied by the consortium with the silica capillary tubes technique (open or sealed), coupled with the Confocal Raman microspectroscopy. This ambition to reach a clear understanding of the couplings between the mechanisms observed in of real experimental geological simulators must lead to integration, in numerical models, of a validated theoretical description on a small scale. This integrated approach is a unique parameterization of predictive tools. Their application, at different scales of space and time, may, from the stage of injection of CO2 and from the behavior observed in the close-well field, be facing trials and results by exploiting the existing or future pilot sites. They are then used to predict with certainty the evolutions of this greenhouse gas across the most complex reservoir systems.

The first GLoCs have already been made. They have been successfully implemented to measure, by Raman microscopy, the CO2 solubility in different brines, and to validate the measurement feasibility of the carbonate precipitation by X-ray diffraction. The concept of geological laboratory on chip is now applied to the study of confined flow of CO2 to identify and measure the respective CO2 and water clogging of representative porous media from geological reservoirs for deep storage of this gas. Furthermore, the interests and disadvantages of microfluidic Silicon/Pyrex systems for in-situ chemical reactions analyses within the microchannels using X-ray scattering could be evaluated at ESRF.
Measurements of the CO2 diffusion coefficient in water-sodium chloride mixtures in sealed capillary tubes have highlighted the influence of salinity of the aqueous solution on the diffusion of CO2. Raman spectroscopy has helped quantifying dissolved inorganic species (CO2(aq), HCO3- and CO3-2) in both salted and very alkaline aqueous systems. The first detection tests of supercritical CO2 using a new in situ optical sensor based on chalcogenide Dy+ 3 doped fiber, inserted in a GloC, and fully developed within the project, are underway.
Similarly, the first innovative studies of the biology part of the project have shown that, unlike a classical culture in bottles, the use of a micromodel and the addition of a (high concentration of CO2) stress on the sulfate-reducing thermophilic bacteria Desulfotomaculum thermocisternum seems to cause quickly (8 days) the formation of a bacterial cluster, likely to evolve into a biofilm. The early work on optical testing and coloring of biofilm have also been made using a percolation device.

The project aims to create a broad interactive network for the use of different geological laboratories on a chip coupled with advanced analysis methods. Such a network will address the multiple aspects specific to the geological storage of CO2 in making full use of the complementarity of skills of the different partners. Thanks to close cooperation between academic, industrial and commercial teams of the CGSµLab consortium, analytical development and validation of the numerical simulations will also reach the complementary objective to provide scientific and technical specifications necessary for the deployment of deep storage technologies that meet societal and environmental demands. Finally, beyond strengthening our basic knowledge, one of the new approaches made possible by the project is interested in the potential impact on deep biotopes and opens access to a field of knowledge still completely blank.

A thesis has been sustained on November 22, 2013 at the University of Bordeaux on the validation of the concept of Geological Laboratory on a Chip for the temperature and pressure operating conditions found in geological formations. The first publications in scientific journals (3 published, 2 accepted, 1 submitted) and the first oral communications to international congresses (7 Congresses including 1 where a project partner is chairman) illustrate the significant advances made in areas covering the microfabrication of GLoCs, their use coupled with analytical in situ methods (Raman, IR spectroscopy via in-situ optical fiber, and X), and the implementation of the silica capillary techniques coupled with the Confocal Raman microspectroscopy.

The main aim of the CGSµLab project is to devise, implement and exploit the most recent scientific advances in supercritical microfluidics to address some of the major issues in the field of the CO2 geological storage (CGS). This project is a pioneering approach in the world, based on several key technological steps in miniaturization of instrumentation under high pressure and high temperature based on the upgraded development of the new concept of geological laboratories on chips (GLoC). The project address fundamental small scale knowledge of the geochemical processes by tuning and simulating on GLoC the experimental behaviors of most of injected real gases in complex lithospheric aqueous fluids, flowing and interacting then with geological minerals at the temperature and pressure conditions of the geological formations. These original and innovative on-chip studies applied to CGS can be then a winning scheme that benefits from the many advantages of the size reduction of the microfluidic systems widely evidenced in a rich literature, to provide larger, faster and cheaper screening of the important key parameters such as permeability, porosity, temperature, pressure, concentrations, flow velocities, dissolved CO2 amount, chemical nature of the injected fluids, formations fluids, formation materials. In addition, there are specially designed in order to implement and develop original instrumentation and in situ microcharacterization technics provided by the partnership, such as micro Raman and RX analyses, microcalorimetry, etc.
GLoCs are then adapted to treat the following relevant CGS scientific locks: i) the description of fluids (brines and gases/supercritical fluids) repartition in the porosity of the rock reservoir, including interfacial and capillary phenomena, fluids trapping mechanisms; ii) the description of fluids flows and their evolution during time, hysteretic behaviors, impacts of flow regimes on the transport of CO2, preferential flows; iii) the description of geochemical processes, their location and kinetics in terms of dissolution precipitation reactions but also in terms of differential solubility of gas mixtures, their impacts on the local hydrodynamic properties of the reservoir rock ; iv) the description of biological activity (evolution of the microbial communities and of their metabolisms); v) the progressive integration of GLoC experimental results and relevant parameters in numerical tools for allowing extrapolation to near well bore and reservoir simulation models.
The originality, the novelty and the expected scientific and technologic breakthrough of the project are due to the unique character of the participant scientific workforce, resulting from the highly relevance of their complementary skills for advanced instrumental, measurement, modelling and simulation tools, as well as their international high level expertise in solid state chemistry, materials science, geochemistry and geophysics, biology and sub- and super-critical hydrodynamics, and mainly managed with a common focus on CGS field. Indeed, the project gathers one US partner involved in a commercial-scale CGS project in Alabama, French academic and applied research institutions, and one industrial Group, all having focused their respective high-level expertise to interact and cover the issues addressed in the project.
The results of applications and extrapolations according to scenarios of exploitation based on the experiences of the pilot and current industrial operations return should allow evaluating and identifying the real progress and developments made by the project with perspectives and recommendations.