Simultaneous Detection of Vanadyl, Nickel, Iron, and Gallium Porphyrins in Marine Shales from the Eagle Ford Formation, South Texas

Fang Zheng, Chang Samuel Hsu, Yahe Zhang, Yongge Sun, Yangyang Wu, Hong Lu, Xun Sun, and Quan Shi^*

State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249, P. R. China 

Institute of Environmental and Biogeochemistry (ebig), School of Earth Sciences, Zhejiang University, Hangzhou, Zhejiang 310027, P. R. China

Petro Bio Oil Consulting, Tallahassee, Florida 32312, United States 

Department of Chemical and Biomedical Engineering, Florida A&M University/Florida State University, Tallahassee, Florida 32310, United States

State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Wushan, Guangzhou 510640, P. R. China 

Bureau of Economic Geology, University of Texas at Austin, 10100 Burnet Road, Austin, Texas 78758-4445, United States

^*Corresponding Author: E-mail: ygsun@zju.edu.cn; sq@cup.edu.cn

DOI: 10.1021/acs.energyfuels.8b01728

Keywords: Aromatic Compounds; Hydrocarbons; Ionization; Iron; Pyrroles

Abstract: Metalloporphyrins in immature shales of the Late Cretaceous Eagle Ford Formation from South Texas were analyzed by positive-ion electrospray ionization (ESI) Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Vanadyl, nickel, iron, and gallium porphyrins were detected in a single mass spectrum. The iron porphyrins were most abundant, followed by vanadyl, nickel, and gallium porphyrins, consistent with the metal contents determined by elemental analysis. The distribution of porphyrins shows that deoxophylloerythroetio (DPEP) porphyrins, dicyclic-deoxophylloerythroetio (di-DPEP) porphyrins, and porphyrins containing oxygen functional groups are the main components. The detection of oxygen-containing porphyrins, such as iron porphyrins with formulas of C_nH_mN₄FeO, C_nH_mN₄FeO₂, and C_nH_mN₅FeO₂, would offer new clues of petroporphyrins formation mechanism from biological sources, such as chlorophylls and hemes. To our knowledge, this reports for the first time the presence of oxygen-containing iron porphyrins and gallium porphyrins in geological samples other than coals and lignites. The discovery of these petroporphyrins could provide additional insights into the diagenetic pathway of petroporphyrins and novel applications in petroleum geochemistry/exploration and oil refining. The composition of metalloporphyrins may potentially provide clues to decipher the redox conditions during deposition in the Eagle Ford Formation and provide better understanding of the Oceanic Anoxic Event 2 (OAE-2).