Abstract:
With the comparable sedimentary organic phase, the relative abundance of rearranged hopanes can be correlated to maturity degree. By the approach of artificial maturation experiments of low-maturity (
Ro=0.58%) and organic-rich (TOC=3.87%) mud shale collected from the Ordos Basin, 17
α(H)-diahopanes in expelled and retained oils were examined by gas chromatography-mass spectrometry (GC-MS). The thermal evolution characteristics of parameters related to 17
α(H)-diahopane were discussed, and the maturity range of these parameters as maturity indicators was proposed, combined with the random mean vitrinite reflectance (
Ro) of maturated rock samples of each step of pyrolysis. Results show that the parameters of C
29*/(C
29*+C
29H) and C
30*/(C
30*+C
30H) have similar three-stage variations. As experimental temperature increased, the values of the two parameters decreased firstly, then increased and finally decreased again, indicating that they may be good indicators for oil-source correlation. Before 325 ℃, i.e.
Ro < 1.01%, both parameters showed insignificant changes. However, they both showed an obvious upward trend with increasing temperature from 325 to 385 ℃, indicating that they were valid indicators for maturity from the moderate to the early stages of high maturity (i.e. 1.01% <
Ro < 1.48%).