Organic geochemical characteristics and comparison of the source rocks and the severely biodegradable oil sands around Karamay, China

• Main Authors: Chong Feng, Wenjun He, Hua Cai, Jingyuan Zhang, Yinlan Nie
• Format: Article
• Language: English
• Published: SAGE Publishing 2021-01-01
• Series: Energy Exploration & Exploitation
• Online Access: https://doi.org/10.1177/0144598720964879

For the sake of explaining the organic geochemical characteristics of the hydrocarbon source rocks (SRs) around Karamay, such as thermal maturity (TM) (evidences from the temperature of maximum pyrolysis yield (Tmax), the Carbon Preference Index (CPI) and Odd to Even Preference (OEP) values, the C 30 M/H versus Tm/Ts, the C 29 ββ/(ββ + αα) versus C 29 20 S/(20 S + 20 R)), hydrocarbon potential (HP) (evidences from total organic carbon (TOC) and rock pyrolysis (RP)), organic matter (OM) source input (evidences from n -Alkane distribution, the relative quantity of C 27 -C 28 -C 29 steranes, the (C 19  + C 20 )/C 23 tricyclic terpane (TT), and the Terrigenous/aquatic ratio (TAR)) as well as paleoenvironment (evidences from the pristane/phytane (Pr/Ph) and the Gammacerane index), and in order to analyze the biodegradation degree and source of oil sand (OS) oil, 55 core samples of SRs in all were selected to measure TOC and RP. 14 core samples of SRs and 3 OS samples were selected for gas chromatography–mass spectrometry (GC-MS) analysis. 11 core samples of SRs and 3 OS samples were used for organic carbon isotope (OCI) analysis. The results indicate that except the SR from Fengcheng formation (P 1 f ) which is in the stage of high or over evolution, the other SRs are in mature stage. OM type of Carboniferous (C) SRs are type Ⅱ kerogen, with the largest abundance. OM type of the SRs in Wuerhe formation (P 2 w ) and Jiamuhe formation (P 1 j ) are type Ⅲ kerogen with good and medium OM abundances. Almost all SRs were formed in the reduction environment of high salinity, and the main OM source input is the lower aquatic plants. Karamay formation (T 2 k ) and Badaowan formation (J 1 b ) oil sands (OSs) around Karamay have undergone serious biodegradation. It is suggested that OS oil are mainly from P 1 f SRs (evidences from the tricyclic terpanes (TT), triarysteranes, pregnane, homopregnane and OCI).