A Note on the Intrinsic Porosity of Organic Material in Shale Gas Reservoir Rocks

摘要

In working with organic shales the information about rock composition is generally supplied in a mix of volume percentages and weight percentages. Total organic carbon (TOC) is typically supplied as a weight percentage of the total sample weight, Fourier transform infrared spectroscopy-derived (FTIR) mineralogy as a weight percentage of the samples inorganic weight, and porosity is defined as a volume percentage. In building regressions and combining datasets it is generally necessary to convert to a consistent composition reference system. In this note Φ_k, the porosity due to the organic material is expressed in terms of the intrinsic porosity of the organic material Φ_(ki), the mass fraction of the organic material F_o, the matrix density of the organic material, ρ_k, and the bulk density of the inorganic material ρ_(ib). This expression is used with experimental data of the methane porosity, TOC, and realistic estimates for ρ_k and ρ_(ib) to estimate the intrinsic organic porosity. Five Barnett Shale samples from a single well all had intrinsic organic porosity of approximately 30%. A high porosity is consistent with ion-milled SEM images of Barnett Shale samples (Passey et al, 2010, Sondergeld et al, 2010).