Petrographical and geochemical investigation on maturation and primary migration in intact source rock micro-plugs: Insight from hydrous pyrolysis on Woodford Shale

Abstract

This study proposes a new approach to investigate primary migration in petroleum source rocks under laboratory conditions. It was conducted on organic carbon-rich, type II kerogen-bearing Upper Devonian-Lower Mississippian Woodford Shale. Hydrous pyrolysis was performed on polished source rock micro-plugs at different temperatures. Maceral characteristics are observed before and after the different pyrolysis experiments. Applying this new approach, in situ maceral changes at different maturities are directly visualized at the exact same place after artificial maturation at 300 °C, 320 °C, 330 °C, and 340 °C for 24 h. After each heating step, the surface was cleaned with dichloromethane. The bitumen adsorbed to some of the Tasmanites surfaces leads to the brighter fluorescence color after chemical extraction. Leiosphaeridia alginites are less stable than Tasmanites; they first expand and then shrink during thermal evolution partly leaving empty holes in the matrix. Tasmanites keep a strong yellow fluorescence and start to bituminize at the edge of the particles. Liptodetrinite shows significantly decreasing fluorescence intensities already at low pyrolysis temperature (320 °C) and disappears to a great extent at 330 and 340 °C.