The surface areas of organic rich shale samples of varying maturities, total organic carbon (TOC), and clay content from four different shale formations were measured in the “as-received” and solvent extracted states. In the as-received state we show there is a poor relationship between surface area, total clay, and organic content even though these two components (clay and organics) have high surface areas. This underestimation is due to pore access problems resulting from residual fluids despite heating up to 100°C before making measurements. Surface area measurements on samples post Soxhlet solvent extraction (toluene:methanol in 8:2) reveal the expected correlation of surface area with clay and TOC as a function of maturity.
We observe the largest increase in surface area after solvent extraction (170%) for samples from the early oil (immature) window. The smallest increase is observed in the gas window (5%).We found an empirical relationship between surface area, TOC and clay content post-extraction. Our results indicate that the surface area is strongly a function of maturity and that gas adsorption increases with organic pore generation as an outcome of maturation. Grain density measurements pre- and post-solvent extraction were used to determine the “extra-porosity” associated with soluble bitumen and residual hydrocarbon removal. Solvent extraction leads to the following increases in porosity of 88% in the immature window, 40% in the oil window, 24% in the condensate window and 5% in the gas window. In all samples, there was a net increase in porosity after solvent extraction.
Shales have received widespread attention in the recent years because of their emergence as commercial hydrocarbon reservoirs in North America (Curtis, 2002; Montgomery et al. 2005; Bowker 2007; Jarvie et al., 2007; Scheiber, 2010; Sondergeld et al., 2010; Slatt and O’Brien, 2011). Shales have a complex microstructure and understanding the pore system is crucial to evaluating the storage mechanism and transport properties in these unconventional shale resources (Guo et al., 2013; Tian et al., 2013). Unlike the conventional reservoirs, which are characterized by pores in the micrometer scale, shales have pores in nanometer range (Javadpour et al., 2007; Javadpour, 2009; Loucks et al., 2009; Sondergeld et al., 2010, Curtis et al., 2012).
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