Characterization of carbonate rocks by combination of scattering, porosimetry and permeability techniques

Abstract

A mineralogical and microstructural study was conducted on rocks from formations in Cavala Gulf basin (PRINOS), Greece. The samples were obtained from six different depths of the petroleum drill and were characterized by ultra small-angle neutron scattering (USANS), nitrogen porosimetry and mercury porosimetry. The microstructure of all the samples is fractal ( D s ∼ 2.5 ) within the experimental Q region. Mercury porosimetry measurements showed that all samples present rather similar pore structure with rather low porosity and exhibit polydisperse pore size distributions, in agreement with the USANS data. Furthermore, three powder segments with different grain size in the range between 90 and 200 μm, possessing narrow size distributions, were selected with the aim to elucidate the possible existence of large macropores. As a next step, the pore structure and liquid flow properties of standard core samples (Berea sandstone) were examined by combining nitrogen and mercury porosimetry as well as permeability measurements. A good correlation of the experimental findings with the predictions of capillary permeability models was established. These models were also involved to predict the permeability properties of the rocks under investigation with main inputs the experimentally determined porosity and mean pore diameter. The aforementioned procedure was followed because the rocks exhibit extremely low permeability factors and, thus, the accuracy of the measurements with the existing experimental core holder setup would be uncertain.