Microgeometry II: Testing for homogeneity in Berea sandstone

Geological sample characterizations rely on statistical assumptions of homogeneity and isotropy. There is also a tacit assumption of homogeneity at some size scale in theoretical geophysics predicated on power spectra or ensemble averaging, for example, acoustics (Devaney and Levine, 1980)or electromagnetics (Lee, 1979).Discussion is presented of a homogeneity test performed on Berea sandstone to develop methods for assessing homogeneity and for delimiting the scale at which homogeneity can be assumed. The Wilcoxon sum-of-ranks and signed-ranks tests are applied to scanning electron microscope image data. Anisotropy is found at some scales, and not at other scales. The homogeneity assumption for Berea sandstone is supported by agreement between estimates which depend for accuracy on homogeneity and values obtained by other independent methods such as bulk measurements or calculations from run-lengths.