Porosity, pore-size distribution and pore surface area of the Apache Leap tuff near Superior, Arizona using mercury porosimetry

Abstract

Characterization and quantification of fluid flow is dependent upon the distribution, size and interconnectedness of pores in an unsaturated rock matrix. This study examines the use of mercury porosimetry in determining porosity, pore-size distribution and pore surface area of an unsaturated, slightly welded to densely welded tuff near Superior, Arizona. 121 samples of tuff were subjected to mercury intrusion pressures to 200 MPa. A bimodal pore-size distribution exists for all samples of slightly welded tuff with the larger pore size class mode diameter averaging 2.91 μm and the lower pore size class mode diameter averaging .07 μm. Interconnected porosity, pore surface area and bulk density averaged 14.62%, 3.46 m²/gm and 2.13 gm/cm³, respectively. On average, 52.73% of the porosity was accounted for by the large pore size class while 96.28% of the pore surface area was accounted for by the small pore size class. Samples of densely welded tuff exhibited a unimodal pore-size distribution with an average mode diameter of .035 μm.