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Kerogen Maturity Determinations: New Techniques and Technologies

Malleswar Yenugu
University of Houston

Abstract

Interlinking of cross disciplines play an important role for successful characterization of shale reservoirs. This course discusses how the artificial kerogen maturity of organic-rich Green River shale affects the petrophysical, micro-structural, geochemical and elastic properties. The shale sample with total organic carbon (TOC) of ~28% is used in the examination. It is then subjected to anhydrous pyrolysis for artificial maturation by cooking the sample at 3500C for three days. We will show you pictures of horizontal cracks on the sample which are induced by hydrocarbon generation and expulsion.

We discuss how we measured the ultrasonic velocities on the shale plug before and after maturation. A significant change in the P-wave anisotropy (ε) is observed after maturation. We will discuss about the TOC measurements and Rock-eval pyrolysis and how the geochemical properties are affected by kerogen maturation.

This course also gives you an idea about how we characterize the changes in the internal structure of the source rock through kerogen maturation by using micro-structural techniques such as SEM imaging and micro-CT scanning. SEM images clearly show that a significant amount of porosity is 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.

We will discuss methods of kerogen isolation from the rock sample. We also show you the measured elastic properties of an immatured isolated kerogen. The bulk modulus of kerogen is found to be between 4-5 GPa. This course also focuses on the effect of kerogen content and its maturity on seismic velocities and anisotropy for different organic rich shales. We will show you how the seismic anisotropy is affected by different levels of kerogen maturity.

Brief Outline:

  • Introduction and goals
  • Kerogen in shales
  • Controls on organic-richness in sedimentary rocks
  • Example: Green River shale samples, USA
  • Methodology for kerogen maturity characterization
  • TOC and Rock-eval pyrolysis measurements
  • Anhydrous pyrolysis for artificial kerogen maturation
  • Microstructural characterization from SEM and micro-CT scanning
  • Ultrasonic velocity measurements
  • Comparison of petrophysical, geochemical, micro-structural and elastic properties before and after maturation
  • Isolation of kerogen from source rock samples
  • Elastic properties of isolated kerogen
  • Examples from different shales on the relationship between seismic anisotropy and levels of kerogen maturity
  • Conclusions

AAPG Search and Discovery Article #90205 © AAPG Geoscience Technology Workshop, Permian and Midland Basin New Technologies, September 4-5, 2014, Houston, Texas