Source Rock Maturation: Its Effect on Porosity and Anisotropy in Unconventional Resource Plays
The interlinking of cross disciplines plays an important role in the successful characterization of shale reservoirs. This talk discusses how the artificial kerogen maturity of organic-rich Green River Shale affects the petrophysical, micro-structural, geochemical and elastic properties. A shale sample with total organic carbon (TOC) of ~28% is used in the examination. It was subjected to anhydrous pyrolysis for artificial maturation by cooking the sample at 1111 degrees C for three days. Horizontal cracks were obvious on the cooked sample, which were induced by hydrocarbon generation and expulsion.
Ultrasonic velocities were measured both before and after the pyrolysis. A significant change in the P-wave anisotropy (ε) was observed after maturation. The TOC and hydrogen index (HI) decreased after maturation. Microstructural imaging, through a computed tomography (CT) scan, showed that the kerogen maturation altered the internal structure of the sample. A significant amount of porosity was developed in the organic matter during maturation. This porosity is due to conversion of solid kerogen to liquid or gaseous hydrocarbons. Grain density also increased due to the decomposition of lighter kerogen during pyrolysis. The ultrasonic velocities of isolated kerogen were also measured. The measurements were carried out on the immature kerogen sample. The bulk modulus of kerogen was found to be between 4–5 GPa. The study focused on the effect of kerogen content and its maturity on seismic velocities, as well as the anisotropy for different organic-rich shales. It was observed that seismic anisotropy had different trends based on the kerogen maturity.
AAPG Datapages/Search and Discovery Article #90219 © 2015 GCAGS, Houston, Texas, September 20-22, 2015