Investigation of the morphology of pore space in mudstones—first results

A suite of selected Tertiary mudstones was studied to improve the knowledge about microstructure and related transport processes in mudstones. Samples were investigated by mercury- and Wood’s metal injection, SEM, XRD, and grain size analysis. Wood’s metal injection has the advantage of visualising the ‘frozen’ injection process. The smallest pore casts observed were down to 40 nm in diameter, while the largest, bottle-shaped pores were up to 5 mm in diameter. Bottle-shaped pores occurred in all the samples, usually around silt or sand grains. One sample, which had a porosity of 28.5% according to mercury injection data, had not been impregnated by the molten alloy. We suggest this to reflect a strong deformation of the clay fabric by the high pressure without intrusion into the matrix. This raises questions about the reliability of mercury injection data for very fine-grained, highly porous sediments. After excluding these very fine-grained samples and one very calcareous sample regressions were found which relate porosity ðfÞ; clay content (C), and sand content (S) to capillary displacement pressure ðPdðHgÞÞ : PdðHgÞ ¼ 225:05 þ 0:63 C þ 0:29S ðR 2 ¼ 0:92Þ; and PdðHgÞ ¼ 210:24 þ 0:47 C 2 0:15f ðR 2 ¼ 0:88Þ: