Precise maturity assessment over a broad dynamic range using polycyclic and heterocyclic aromatic compounds. (October 2020)

• Record Type: Journal Article
• Authors: Noah, Mareike; Horsfield, Brian; Han, Shuangbiao; Wang, Chengshan
• Is Part Of: Organic geochemistry. Volume 148(2020)
• Publication Date: 2020-10
• Subjects: Songliao basin -- FT-ICR-MS -- Maturity -- ICDP -- Metagenesis; Organic geochemistry -- Periodicals; Biogeochemistry -- Periodicals; Géochimie organique -- Périodiques; 553.205
• DOI: 10.1016/j.orggeochem.2020.104099
• Languages: English
• ISSNs: 0146-6380

Abstract

Highlights: New thermal maturity parameters in the zones of late catagenesis and metagenesis investigated. APPI(+) FT-ICR-MS analysis reveals systematic maturity-induced molecular changes. A broad maturity range is covered, from 0.9% to 2.2% vitrinite reflectance (Ro ). Allows tracing of heat-induced cyclization, aromatization and cracking on a molecular level. Important new maturity indices in deep Earth exploration for energy resources. Abstract: The construction and reliable application of maturation indices is extremely important in deep Earth exploration, yet predicting levels of maturation on a molecular level, especially at overmature stages, is still a major challenge. Here, we report robust, broad ranging and precise maturity parameters that were developed using a continuous core of thermally overmature lacustrine deposits (Shahezi Fm.) from the deep Songke-2 Well (SK-2), Songliao Basin, China, augmented by shallow cores of lower maturity marine deposits (Posidonia Shale) from the Hils Syncline, Germany. The novel indices presented here are based on the general process of thermally-induced cyclization, aromatization and aliphatic chain cracking of hundreds to thousands of compounds during maturation. The newly developed parameters, with an extremely broad dynamic range extending from catagenesis and into metagenesis (vitrinite reflectances (Ro ) range from 0.9% to 2.2%), are based on polycyclic and heterocyclic aromatic compounds measured using Fourier transform-ion cyclotron resonance-mass spectrometry (FT-ICR-MS). The high coefficient of correlations between the new maturity parameters with Ro and Tmax demonstrate their utility for assessing precisely the thermal maturity of overmature shales.