C8 Light Hydrocarbon Parameters to Indicate Source Facies and Thermal Maturity Characterized by Comprehensive Two-Dimensional Gas Chromatography

• Published in: Energy & fuels Vol. 31; no. 9; pp. 9223 - 9231
• Main Authors: Xiangchun, Chang, Lixin, Mao, Youde, Xu, Tiantian, Li
• Format: Journal Article
• Language: English
• Published: American Chemical Society 21.09.2017
• ISSN: 0887-0624; 1520-5029
• DOI: 10.1021/acs.energyfuels.7b01595

C8 light hydrocarbons (LHs) were characterized for 23 crude oils from two different deposits by comprehensive two-dimensional gas chromatography. Dimethylcyclohexanes (DMCyC6) and trimethylcyclopentanes (TMCyC5) are the predominant compounds in C8 LHs and geochemically significant. Used in tandem with deposition-diagnosed parameters such as pristane/phytane (Pr/Ph), dibenzothiophene/phenanthrene (DBT/P), C22/C21 tricyclic terpane (C22/C21TT), C29/C30 hopane (C29/C30H), and monoterpane ratios (MT1, MT2, and MTR), C8R ratio ((1trans,4-+1cis,3-+1,1-) DMCyC6/(1cis,2trans,4cis- + 1cis,2trans,3cis-) TMCyC5) can distinctly distinguish marine oils derived from source rocks deposited under anoxic conditions from the terrigenous oils originated from source rocks deposited in oxic/suboxic conditions, for their lower C8R (<5.0), Pr/Ph, and C22/C21TT values, and higher DBT/P, C29/C30H, and monoterpane ratio values. Followed after the classic isoheptane (P1) and heptane (P2) ratios, isooctane (O1) and octane (O2) ratios were proposed tentatively to define thermal maturity. The linear correlation between the O1 with the P1, and the O2 with the P2 values confirm their validity to assess and differentiate the thermal maturity according to the approximate same boundary values defined by that of P1 and P2 ratios.