Diffusivity of rocks: Gas diffusion measurements and correlation to porosity and pore size distribution

Diffusivity was measured for 12 rock and construction material samples using a diffusion chamber method with oxygen as the tracer gas. Several steps were implemented to minimize leakage between the sample and the core holder, and rigorous tests were performed to evaluate and correct the overall leakage of the diffusion apparatus. This method was proven capable of rapidly measuring the diffusion coefficient for consolidated samples having dimensionless diffusivity values greater than 4.7 x 10(-4) in a relative short duration (hours to 1 day). Gas diffusion measurements were also conducted for 11 repacked sediments and sands. Our results are consistent with literature data from liquid tracer through-diffusion methods; the diffusivity versus porosity relationship for our data can be described by Archie's law. The m value in Archie's law was found to be correlated to pore size: the finer the pore size is, the larger the m value is. A linear regression equation can describe the change of m with ln d(50) (the volumetric mean pore diameter) for most rocks with d(50) < 1.3 mu m, while the outliers can be correlated to narrower pore size distribution.