The permeability of stylolite-bearing limestone

Abstract

Stylolites are planar features that form due to intergranular pressure solution. Due to their planar geometry and relative abundance in limestone reservoirs, their impact on regional fluid flow has attracted considerable interest. We present laboratory permeability data that show that stylolites can be considered as conduits for flow in the stylolite-bearing limestones measured. A combination of analysis techniques shows that this is due to a zone that surrounds these stylolites that is more porous and contains larger pores than the host rock. Our data also show that the water permeability of a sample containing a stylolite parallel to fluid flow is typically lower than its permeability to gas, explained here as a result of the expansion of minor amounts of clay found in the stylolite, and that, due to their microstructural similarities, tectonic and sedimentary stylolites affect sample permeability similarly. Finally, we show that the permeability anisotropy that develops in the rock mass due to the presence of sedimentary stylolites makes it appear as though the stylolites are acting as barriers to fluid flow, and may explain the discrepancy between laboratory measurements and field-scale observations. This approach can provide estimates for the equivalent permeability, and permeability anisotropy, for stylolite-bearing limestone reservoirs worldwide.

Mixed Brittle and Viscous Strain Localization in Pelagic Sediments Seaward of the Hikurangi Margin, New Zealand

“…Larger porosity losses in more porous sediments (19R1W in Figure 4) show stylolites develop better in finer grained, higher porosity sediments. Similar to previous workers, we find zones of increased porosity immediately adjacent to stylolites (Figure 4, Heap et al, 2018). This is consistent with smaller grain contact areas supporting higher stresses, therefore localizing dissolution.…”

The Permeability Evolution of Tuffisites and Implications for Outgassing Through Dense Rhyolitic Magma

“…Assuming a cylindrical pore shape, the average pore radius a used by the gas molecules can then be estimated using the following relationship (Civan, ; Firouzi et al, ): where T is the temperature (293 K for room temperature laboratory conditions), M w is the molar mass of the argon pore fluid (0.03995 kg/mol), and R g is the ideal gas constant (8.31 J mol −1 K −1 ). This method has been used to estimate the average pore radius of the flow path in shales (e.g., Firouzi et al, ; Heller et al, ; Letham & Bustin, ), volcanic rocks (Heap, Reuschlé, Farquharson, et al, ), and limestones (Heap, Reuschlé, Baud, & et al, ). We find an average pore radius of 0.75 μm for the BTB sample at a confining pressure of 1 MPa (Figure a).…”

Quantitative analysis of stylolite networks in different platform carbonate facies

“…Some studies suggest that stylolites can act as baffles to fluid flow (e.g., Burgess and Peter, 1985;Finkel and Wilkinson, 1990;Dawson, 1998;Alsharhan and Sadd, 2000;Gomez-Rivas et al, 2015;Martín-Martín et al, 2017) based on field and petrographic observations. Alternatively, stylolites have been found to act as conduits that improve permeability along their orientation as observed in some carbonate reservoirs and outcrops (e.g., Carozzi and Bergen 1987;Bergen and Carozzi, 1990;Lind et al, 1994;Harris, 2006;Chandra et al, 2014;Barnett et al, 2015;Paganoni et al, 2016;Martín-Martín et al, 2017;Morad et al, 2018) in addition to laboratory permeability tests (e.g., Heap et al, 2014Heap et al, , 2018Rustichelli et al, 2015). The development of localised porosity around stylolites has been associated with preferential dissolution along existing stylolite planes (Bergen and Carozzi, 1990) and an increase in the average size of pore throats (Baud et al, 2016).…”

“…Along with sub-seismic-scale fractures, understanding the controls on stylolite network distribution is hampered by the high reactivity and complex mechanical behaviour of carbonates (Fabricius, 2014). Stylolites can control petrophysical properties and fluid flow in different ways (e.g., Paganoni et al, 2016;Martín-Martín et al, 2017;Heap et al, 2018;Toussaint et al, 2018;Bruna et al, 2019). However, despite their abundance in carbonate rocks, less attention has been paid to their study compared to fracture networks.…”