Chemistry of interfaces between inorganic minerals and porous carbons: Implications for the mechanical properties of gas shale
Gyorgy Hantal (MIT), Laurent Brochard (MIT/ENPC), Roland Pellenq (CNRS/MIT), Franz-Joseph Ulm (MIT), Benoit Coasne (CNRS-MIT)
Engineering Mechanics and Materials in the Oilfield
Tue 9:00 - 10:30
Sayles 105
Gas and oil shale are unconventional deposits of hydrocarbons that represent important reserves worldwide. Their importance in gas and oil production has been significantly increasing due mostly to substantial recent technological developments. Organic-rich shales are natural composites as they consist of different inorganic minerals and a porous carbonaceous organic material, called kerogen. As kerogen, representing only a small fraction of the rock, is encapsulated in a quasi nonpermeable inorganic matrix, the usual exploitation technique is based on hydraulic fracturing. Understanding how the different gas shale components influence the fracture properties of the composite system is thus crucial to increase the hydrocarbon recovery from organic-rich shales. In this work we study the chemistry and mechanical properties of the interface of kerogen and two of the most typical inorganic constituents of shales: silica and clay (illite). In the first part, functional groups, on both the organic and the inorganic surfaces, are characterized by means of quantum chemistry in terms of their ability to form stable bonds with the other surface. Based on this information, different plausible organic/inorganic interfaces are established as a function of the type and maturity of the shale. In the second part of the work, fracture properties of the pure phases as well as of the organic/inorganic interfaces are characterized. To simulate bond breaking and formation a reactive potential, ReaxFF is applied. While kerogen and silica can be unequivocally characterized, respectively, with high ductility and brittleness, illite is found to show either very brittle or very ductile behavior depending on the loading mode. Furthermore, illite and the kerogen/illite interface turn out to be very soft: they have one order of magnitude lower toughness values than silica, kerogen and their interface.