Study of Kerogen Maturity using Transmission Fourier Transform Infrared Spectroscopy (FTIR)

Abstract

Abstract Maturity of kerogen in shale governs the productivity and generation hydrocarbon type. In the industry, there are generally two methods used to measure kerogen maturity; one is the measurement of vitrinite reflectance, and another is the measurement of Tmax through pyrolysis. However, each of these techniques has its own limits; Vitrinite reflectance measurement cannot be applied to marine shale and pre-Silurian shales lacking plant materials. Tmax measurement is questionable for mature and post-mature samples. Fourier Transmission Infrared Spectroscopy can be applied for both qualitative and quantitative assessment on organics maturity in shale. The technique does not require separating organic matter or identifying macerals. CH2/CH3 index calculated from FTIR spectra is more objective than other measurements. The index increases with maturity (both natural maturation and artificial maturation by hydrous and dry pyrolysis). The new maturity index CH2/CH3 calibrates to Vitrinite Reflectance is: greater than 1.6±0.2 for immature window; from 1.6±0.2 to 1.3±0.3 for oil window; from 1.3±0.3 to 1.13±0.05 for wet gas window; and less than 1.13±0.05 for dry gas window.