4:30 PM - 4:45 PM
[SCG58-11] Experimental measurements of transport pore radius of thermally cracked granite and the relationship of pore structure to permeability
Keywords:permeability, transport pore radius, water expulsion method
Thermally-cracked Aji granites were prepared to cylindrical shape (20 mm long and 20 mm in diameter). Thermal cracking was introduced by heating up to 600 ℃ and porosity of a heat-treated sample was about 2.4 % . The transport pore radius was determined by a manner similar to those reported in Yokoyama and Takeuchi (2009), which is an experimental method measuring gas pressure ΔPbreak (Pa) at which gas breaks through a water-saturated sample. From ΔPbreak and interfacial tension γ (N m-1), transport pore radius r (m) can be estimated as follows: r = 2γ/ΔPbreak. Permeability was determined from the flow rate at a constant pore pressure (Pp = 0.5 - 3 MPa). The flow rate was measured by a flow method using water as a pore fluid and permeability was calculated following Darcy’s law. Porosity was estimated using the gas porosimeter, where the grain volume and pore volume of a sample were determined by using Boyle’s law. Experiments were performed under confining pressure ranging 5 to 30 MPa at room temperature.
Transport pore radius and permeability of thermally-cracked Aji granite were 0.74 μm and 5.5×10-17 m2 under confining pressure of 5 MPa. These values decreased with increase in confining pressure and were 0.14 μm and 2.0×10-18 m2 under confining pressure of 30 MPa. Permeability k (m2) of granite can be approximated by pore radius r and porosity φ according to the relation: k = 5.32×10-3φr2. This indicates that permeability is primarily dependent on transport pore radius. These results are consistent with the conventional permeability model (Simpson et al., 2003) and estimation of transport pore radius is important for understanding permeability of granite.