Organic petrology of Fukang Permian Lucaogou Formation oil shales at the northern foot of Bogda Mountain, Junggar Basin, China

The Fukang oil shale zone, located in the northern Bogda Mountain, on the southern margin of the Junggar Basin, was deposited in a deep lacustrine environment. Permian Lucaogou Formation shale samples collected from six measured outcrop profiles were characterized using organic petrographic and geochemical techniques. The macerals can be divided into four groups: bituminite, liptinite, vitrinite, and fusinite. Oil shales are different from coal by their lower content of vitrinite and fusinite but generally high content of bituminite and liptinite. All samples containing sufficient hydrogen-rich organic matter (Types I and II) are considered to have a high potential for oil generation. The organic matter was deposited in a clastic, algal-dominated, deep-water environment, and it mainly consists of unstructured bituminite and mineral-bituminous groundmass. The oil shales with a sapropelitic constituent content lower than 5%, 5% to 15%, 15% to 25%, and over 25% correspond to non-oil shale, low-quality, medium-quality, and high-quality oil shales in industrial grade, respectively. Approximately 65% of the samples belong to sapropel-containing shales, with an oil yield between 3.5% and 10%, which are low-quality and medium-quality oil shales. The total maceral content can be used as an auxiliary index to classify the industrial grade of oil shales. Oil yields of 3.5%, 5%, and 10% correspond to total organic matter contents of 7.8%, 9.8%, and 17.5%, respectively.

► Four maceral groups can be observed: bituminite, liptinite, vitrinite, fusinite. ► A petrological classification was proposed to compare oil yields. ► The kerogen types comprise types I and II, with the dominance of Type II1. ► Maceral content is an auxiliary index to classify the quality of oil shales.