Study of Kerogen Maturity using Fourier Transform Infrared Spectroscopy (FTIR) and Thermogravimetric Analysis (TGA)

Maturity of kerogen in shale governs the productivity of a shale formation. Produced fluids are strongly dependent upon organic type (governed by depositional fossils and environment) and thermal history. Different maturity measurement methods (vitrinite reflectance, Rock Evaluation, biomarkers) have been studied, but failed to precisely determine maturity levacross all levels of maturity. Vitrinite reflectance (%Ro) measurement cannot be applied for marine shales and pre-Silurian shales, which do not include plant materials. Tmax (main maturity indicator from Rock Evaluation pyrolysis) measurement is questionable for mature and post-mature samples. Most of biomarkers become useless when maturity level reaches condensate window. In this study, we introduce using Fourier Transmission Infrared Spectroscopy (FTIR) and Thermogravimetric (TGA) for both qualitative and quantitative assessment on organic maturity in shale. Separation of organic matter or identification macerals is not required by either technique; they are quick and objective tests providing two IR-based maturity indices. The first index, CH2/CH3, (from FTIR alone) shows good sensitivity up to the end of the condensate window. CH2/CH3 index decreases with more mature samples. The following CH2/CH3 values are used to define the immature (>1.63 ± 0.22), oil window (1.63 ± 0.22 to 1.3 ± 0.25), wet gas window (1.3 ± 0.25 to 1.13±0.05), and dry gas window (