Investigation of the Relationship between Organic Porosity and Thermal Maturity in the Marcellus Shale

Thermal maturity is important in determining whether shales containing organic material have produced hydrocarbons and whether those hydrocarbons are oil or gas. One method used to determine the thermal maturity of shales is vitrinite reflectance. Recently nanoscale pores have been observed in the organic material of different gas shales by scanning electron microscopy (SEM). These pores vary in size, number, and density. One possible explanation to the origin and diversity of these pores is that they are formed during the generation of hydrocarbons and thus would be affected by the thermal maturity of the shale.

Using focused ion beam milling (FIB) and SEM imaging, the organic porosity of Marcellus shale samples with vitrinite reflectances of R_o=1.1+ and R_o >>3.1 have been compared. The pores within the organic material have been investigated in relation to thermal maturity. Understanding the relationship between the porosity of the organic material and thermal maturity has implications for many gas shale parameters including the density of the organic material, and therefore total organic carbon (TOC), free and adsorbed gas in place (GIP), the wettability of the shale, and transport properties.