  Sedimentary rocks have complicated permeability fluctuations arising from the
geological processes that formed them. These permeability fluctuations
significantly affect the flow of fluids through the rocks. We analyze data on
two sandstone samples from different geological environments, and find that the
permeability fluctuations display long-range power-law correlations
characterized by an exponent $H$. For both samples, we find $H \approx
0.82-0.90$.
