Petrographic Features of Kerogen in Unconventional Shales and Their Effect on Hydrocarbon Petrophysics

摘要

Despite the extensive use of new technologies for the exploration of unconventional organic rich shale resources and vast work on the prediction of the quantities of light hydrocarbons (Gas in Place, GIP), many questions remaining concerning the storage, migration and production of natural gas in unconventional gas shales. There is a need for a deeper understanding of the physics and chemistry of light hydrocarbon molecules within the micro- and nanopores in the kerogen. A number of research results have been published that emphasize the importance of nanopores in kerogen for the unconventional shale resource plays, and our previously published laboratory results have shown that it is possible for gas to condense into liquid in the nanopores of kerogen once the Kelvin equation is satisfied. Petrographic features of several Woodford shale core samples were studied using Scanning Electron Microscopy (SEM) on splintered and Focused Ion Beam (FIB) milled surfaces. The morphologic features and the connectivity of the pores in kerogen were recorded. We performed gas condensation experiments on these samples using hexane and found that there is a close relationship between the amount of condensed gas and the porosity within the kerogen. Based on the nanopore physics the flow of gas within the organic matter will be significantly impacted by capillary condensation. Nuclear Magnetic Resonance (NMR) measurement on the samples with condensed gas components show that the relaxation is also significantly affected by the properties of the nanopores within the kerogen of the unconventional shale samples and must be properly accounted for in the formation evaluation.