Dual porosity system (pore and fracture) permeability in volcanic tuffs by computed tomography
This project investigates the active Campi Flegrei Caldera (Napoli, Italy) from the petrophysical standpoint. Surface samples of the dominant rock type, the Campi Flegrei tuff, were deformed in a triaxial rock deformation apparatus at a range of confining pressures, fluid pressures, and strain rates. The samples display a range of Mode I (pure dilational) and Mode II (shear) fractures. Formation of such fractures should, respectively, generate isotropic and double-couple seismic events so we should be able to determine which sort of fractures are likely to be seen at depth beneath Campi Flegrei – and where – from active seismicity catalogues. We expect substantial microscopic fractures – invisible in hand specimen – were also generated. Additionally, the samples will have primary (pre-deformation) porosity. The porosity induced is a function of fluid-rock interaction, which is particularly likely at grain/microscopic scale because the volumetric changes and thus induced stresses that would accompany reaction of these poorly-crystalline (thus highly reactive) glasses may be significant.
Neapolitan yellow tuff blocks were collected in an open quarry on the edges of the Quarto Plain area NW of Naples, Italy. Cylindrical samples were drilled out and petrophysical parameters were measured to describe the facies of these rocks. Thereafter, samples were deformed at different conditions and pressure settings until failure. To investigate structures developed during loading, 3D images of the deformed samples were acquired using X-ray computed tomography (CT) and examined. Porosity and permeability measurements were obtained through image analysis and results were compared with the equivalent petrophysical parameters recorded in laboratory tests. Also, the impact on fracture trajectory generated by flaws inside particles (pumices, lithics, and crystals) and the particle-matrix grey value contrast, related to the attenuation coefficient of the mineral phases present, was inspected.
|Effective start/end date||1/04/19 → …|
- University of Portsmouth
- Johannes Gutenberg University Mainz (lead)