Abstract
The shale oil of the Lucaogou Formation in the Jimusaer Sag of the Junggar Basin was divided into two sweet spots for exploration and development. Crude oil in the upper and lower sweet spots comes from the upper and lower source rocks. After years of exploration, it has been found that the crude oil in the lower sweet spot has worse physical properties than that of the upper sweet spot. In this study, through the physical and geochemical analysis of crude oil in the upper and lower sweet spots, combined with the organic petrological observation of the upper and lower source rocks, the cause of the poor physical properties of the crude oil in the lower sweet spot has been identified. n-Alkanes in the saturated hydrocarbons of crude oil in the upper and lower sweet were complete while odd-to-even predominance was evident, indicating that the poor physical properties of the crude oil are unrelated to biodegradation. In addition, the correlation between the biogenic parameters and the physical properties of crude oil was analyzed, finding that the difference in crude oil is mainly related to the composition of biogenic precursors of upper and lower source rocks. Combined with organic petrological observation, the lower source rock was found to be rich in telalginite (green algae), which is therefore the primary reason for the difference in physical properties. In comparing results from the characteristics of crude oil biomarkers from both the upper and lower sweet spots, crude oils in the upper sweet spot are similar to each other, indicating that the enrichment of crude oil has experienced a certain migration. In contrast, the differences in biomarkers between the crude oils of the lower sweet spot were relatively large and changed regularly with depth, suggesting the self-generated and self-stored characteristics of crude oil enrichment. At the same time, it was found that the crude oil in the lower sweet spot is also affected by the maturity of adjacent source rocks under the condition of a consistent parent material source. Overall, it was determined that the lower the maturity of source rocks, the poorer the physical property of the crude oil produced.
Highlights
The Lucaogou Formation in the Jimusaer Sag of the Junggar Basin is of great significance for shale oil exploration and development in China ([1]; Zhu et al, 2019; [2])
Based on the analysis of physical properties, family composition, and biomarkers of crude oils from the upper and lower sweet spots of the Lucaogou Formation in the Jimusaer Sag of the Junggar Basin, it was found that the physical properties of crude oil from the lower sweet spots were poorer than those from the upper sweet spots
By comparing the physical properties of crude oil with biogenic parameters of saturated hydrocarbon biomarkers, it was found that the physical properties of crude oils in the upper and lower sweet spots were affected by the parent material
Summary
The Lucaogou Formation in the Jimusaer Sag of the Junggar Basin is of great significance for shale oil exploration and development in China ([1]; Zhu et al, 2019; [2]). In the course of exploration, the Lucaogou Formation was divided into upper and lower sweet spots (i.e., reservoirs), which are the primary targets for the exploration and exploitation of shale oil resources. Crude oil in the upper and lower sweet spots comes from the upper and lower source rocks [3, 12]. The physical properties of crude oil in the same sweet spot layer are internally different, which has caused problems in the shale oil extraction scheme. Through the physical and geochemical analysis of crude oil Geofluids
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