Thermal and Paleoenvironment Evolution of the Fengcheng Formation of Permian in Mahu Depression, Junggar Basin

doi:10.19657/j.geoscience.1000-8527.2021.182

Abstract

Abstract:

Several exploration wells were recently drilled into the thick hydrocarbon source rock of Fengcheng Formation in the southern slope of Mahu Depression in the Junggar Basin, which brings an opportunity to reveal the source rocks there. This study collected data from five key exploration wells in the southern and northern Mahu Depression, and obtained the following findings: (1) the Fengcheng Formation source rocks are widely distributed in Mahu Depression, and the northern and southern Mahu Depression geochemical parameters show that the source rocks are of II-type and high-quality; (2) based on current geothermal, pyrolysis, biomarkers and group compositions, the Fengcheng Formation source rocks around the Mahu Depression entered mature and highly-mature stage at below 4,350 m and 4,800 m, respectively, and have entered the oil generation peak widely; (3) integrating multiple biomarker parameters, the Fengcheng Formation source rocks in northern Mahu Depression were deposited in a saline and reducing environment, and the source rocks of the Fengcheng Formation (2^nd member) in southern Mahu Depression were deposited in a saline and semi-reducing environment, whilst the 3^rd member (also in southern Mahu Depression) were deposited in a brackish and semi-reducing environment, and adsorbed more terrigenous organic matter. Paleoenvironment of the local Fengcheng Formation is featured by salinization (early) and desalinization (end), and the degree of salinity and reduction in the north is higher than that in the south. This study provides a theoretical basis for the subsequent exploration and deployment of tight oil and shale oil for the Fengcheng Formation in Mahu Depression.

Key words: Mahu Depression, Fengcheng Formation, thermal maturity, paleoenvironment

CLC Number:

TE122

JIANG Zhongfa, JIANG Mengya, CHEN Hailong, LIU Longsong, WANG Xueyong, BIAN Baoli, LI Na. Thermal and Paleoenvironment Evolution of the Fengcheng Formation of Permian in Mahu Depression, Junggar Basin[J]. Geoscience, 2022, 36(04): 1118-1130.

Figures/Tables 11

Fig.1 Structural map of the study area

Fig.2 Well-connecting profile across wells FC1, FN1, MH39 and MH28 of the Fengcheng Formation in Mahu Depression

Fig.3 Total organic carbon-hydrocarbon potential crossplot of Fengcheng Formation in Mahu Depression

Fig.4 Evaluation chart of organic matter type for the Permian Fengcheng Formation source rocks in Mahu Depression ((a) crossplot of hydrogen index and maximum pyrolysis peak temperature; (b) crossplot of kerogen oxygen/carbon-hydrogen/carbon ratio)

Fig.5 Organic matter maturity profile for the Permian Fengcheng source rocks in Mahu Depression

Fig.6 Typical source rock biomarker profile for the Permian Fengcheng Formation in Mahu Depression

Fig.7 Distribution map of the thermal evolution stage for the Permian Fengcheng Formation source rocks in Mahu Depression

Fig.8 Biomarker parameter profiles of sedimentary environmental characteristics for the Permian Fengcheng source rocks in Mahu Depression

Fig.9 Phytane/nC18-pristine/nC17 crossplot for the Permian Fengcheng Formation source rocks in Mahu Depression

Fig.10 Phytane/pristine-gammacerane/C30-hopane crossplot of Permian Fengcheng Formation source rocks in Mahu Depression

Fig.11 Crossplot of organic input parameters of the Permian Fengcheng Formation source rocks in Mahu Depression

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