(U)SANS and imaging analysis of changes n multiscale porosity in the St. Peter sandstone with burial diagenesis

The multiscale pore structure of the rocks and the mineralogy assocd. with those pores are crit. factors for estg. a no. of reservoir properties including fluid mass in place, permeability, and capillary pressures as well as geochem. interactions between the rock and the fluid. Combination of small and ultrasmall angle neutron scattering (U)​SANS with backscattered electron and​/or X-​ray computed tomog. imaging provides a means by which the pore structures can be quantified at scales ranging from aproximately 1 nm to 1 cm - 7 orders of magnitude. To examine the effects of burial diagenesis on sandstone, and compare those to the effects of overgrowth formation [1] we obtained samples of St. Peter Sandstone from drill cores obtained in Sangamon, Clinton, Marion and Montgomery counties in Illinois and Arenac in Michigan at depths of ∼ 2700, 3200, 4100, 5200 and 10800 ft, resp. Larger-​scale (< 10 μ) porosity shows the expected decrease in porosity with depth, although there is significant variation in in each sample group. However, (U)​SANS data show that small-​scale porosity increases with depth, and more careful anal. of the results suggest that pore structures exist and change at several distinct scales within these rocks. Pore vol. distributions show that there are scatterers at four scales, approximatey < 30 Å, 4 to 50 nm, 50 nm to 10 μ, and 3 μ to 0.2 mm. the finest of these scales is primarily present only in the shallowest samples. In addn., as suggested in our previous work on sandstones cemented by quartz overgrowths these data again show that porosity in sandstones cannot be described by a single, wide-​scale fractal dimension.[1] Anovitz et al., (2013) GCA 102, 280-​305.