Relationship Between Pore Structure and Fluid Transport in Argillaceous Rocks

Abstract

Mudrocks represent the major constituents of sedimentary basins. They form aquitards, chemical barriers and seals for hydrocarbon accumulations. Their low permeabilities and high capillary entry pressures [1, 2] are controlled by rock microstructure and chemical interactions between minerals and the pore fluid. For a pore system containing two immiscible fluids the sealing efficiency is characterised by the capillary displacement pressure [2–7]. This is usually quantified based on Mercury Porosimetry data because other, more direct measurements are difficult and time-consuming. However, for mudstones the conversion of Mercury-air Injection data to other fluids has been questioned in recent papers [8, 9]. The following two sections summarize the findings from two studies which were performed (a) in order to get a better understanding of the processes that occur during invasion of mercury in very fine-grained sediments [10] and (b) to compare the pore volume distribution determined by Mercury Injection and gas breakthrough experiments which were performed under subsurface conditions.