Pore connectivity and structure-transport relationships in rocks from the Aphrodite gas field

Pore structure-transport relationships greatly impact potential gas storage within, and producibility from, rocks of the Aphrodite Mediterranean gas field, but the former are difficult to discern with current typical methods. However, rarely-used gas overcondensation data have been shown here to be essential for representative and accurate invasion percolation-based determination of the pore connectivity for pore sizes over the whole range from ∼100s μm down to nanometres in these rocks. Combined gas overcondensation and scanning curves have revealed the presence of two sub-networks of large macropores, each shielded by very differently-sized necks, and enabled the separate pore body size distribution and pore connectivity to be obtained for the sub-network shielded by pore-blocking necks. A ‘pore-sifting’ strategy, implemented with either serial nitrogen and iodononane adsorption, or integrated gas sorption and mercury porosimetry, has assessed the different accessibility and/or mass transport contributions of each sub-network. Independent findings from nitrogen kinetic gas uptake suggested, perhaps counter-intuitively, that mass transport rates are faster in the sub-network ultimately shielded for desorption by smaller orifices, though explanations for this have been provided. Computerised X-ray tomography, SEM and PFG NMR have suggested that the pore bodies are associated with the cavities of planktonic foraminifera, while the shielding necks with the semi-permeable fossil shells or embedding clay matrix.