Probing the surface fractal dimension of shale with N2 molecules
Abstract
Adsorption isotherms and small-angle scatering techniques have been used to show that pore-grain interfaces in many natural porous materials exhibit fractal behavior. The adsorption technique typically use molecules with different sizes as "yardsticks" to measure the corresponding surfaces areas. This method is subject to the uncertainty in the size of the adsorbed molecules and in the "monolayer area" given by the BET method. It is also quite restricted in the range of length scales it can probe. We report an adsorption study of N2 in several shale samples. We used the Kelvin equation to relate the measured vapor pressure to the pore size in the capillary condensation region of the adsorption isotherm, and found that the number of adsorbed molecules exhibits a power-law dependence on the pore size throughout the entire region. The fractal dimension D, however, is consistently lower than the values obtained from the small-angle neutron scattering measurements on the same samples. This raises some interesting questions about the isotherm interpretation of the fractal behavior. * Supported by ACS-PRF Grant #32191-AC2-SF98
- Publication:
-
APS March Meeting Abstracts
- Pub Date:
- March 1998
- Bibcode:
- 1998APS..MAR..M701M