Geochemical characterization and quantitative evaluation of shale oil reservoir by two-dimensional nuclear magnetic resonance and quantitative grain fluorescence on extract: A case study from the Qingshankou Formation in Southern Songliao Basin, northeast China

Abstract

Abstract Understanding the content and geochemical characteristics of shale oil are two significant aspects of shale oil exploration and evaluation. This paper details the analysis of 32 shale samples extracted by sealed coring from the first member of the Upper Cretaceous Qingshankou Formation (K2qn1) in the Southern Songliao Basin, northeast China. Geochemical techniques including Rock-Eval pyrolysis, contents of total organic carbon (TOC) and clay mineral identification by X-ray diffraction (XRD) were performed on the samples. A total of 13 samples were further analyzed using two-dimensional nuclear magnetic resonance (2D NMR) and the quantitative grain fluorescence on extract (QGF-E) technique to determine the content and properties of different types of organic matter (OM) in the shale reservoir. The OM content and spectral intensity obtained from the NMR and QGF results were positively correlated with TOC content and pyrolysis S1 of the samples, respectively. In addition, the characteristic fluorescence parameters (R1, R2) of the shale extract and crude oil obtained by total scanning fluorescence (TSF) indicated that the crude oil in the studied shale reservoir was a thick-medium oil in the medium mature stage. The comprehensive experiment with the combined use of high-frequency 2D NMR and QGF technologies realized the quantitative characterization of shale oil composition and maturity, and demonstrated advantages of nondestructive, rapid and quantitative detection of OM, especially oil content in shale. New shale oil evaluation parameters obtained from these experiments, therefore, are more significant than traditional measurements such as Soxhlet extraction and pyrolysis.