Precursor and Mechanism of Hydrocarbon Generation for Shale Oil in Lucaogou Formation, Jimsar Sag

doi:10.7657/XJPG20240301

Abstract

Abstract:

In order to clarify the differences in hydrocarbon-generating precursor and mechanism of the shale oil between the upper and lower sweet spots of the Lucaogou formation, the source rocks of the Lucaogou formation in the Jimsar sag were characterized ultra-microbiologically using field emission scanning electron microscopy, electron probe, and Fourier transform infrared spectroscopy experiments. The results show that the main hydrocarbon-generating precursor of the shale oil in the upper sweet spot is lamalginite (Microcystis), with straight-chain aliphatic series in dominance, and the main hydrocarbon-generating precursor in the lower sweet spot is telalginite (Tasmanian algae), which is rich in branched-chain aliphatic, aromatic, and sulfoxide functional groups. Due to the significantly higher activation energy required for the cleavage of long straight-chain saturated hydrocarbons than that for branched-chain hydrocarbons, as well as the lower bond energies of carbon-sulfur and carbon-nitrogen bonds, the activation energy of the precursor of the shale oil in the lower sweet spot is lower than that in the upper sweet spot. Consequently, early-stage hydrocarbon generation occurs, leading to the formation of high-density crude oil rich in non-hydrocarbon bitumen at low maturity, which is the primary reason for the relatively heavy and viscous nature of the crude oil in the lower sweet spot.

Key words: Junggar basin, Jimsar sag, Lucaogou formation, shale oil, algae, biomarker, activation energy, hydrocarbon generation mechanism

CLC Number:

TE122.11

WANG Jian, LIU Jin, PAN Xiaohui, ZHANG Baozhen, LI Erting, ZHOU Xinyan. Precursor and Mechanism of Hydrocarbon Generation for Shale Oil in Lucaogou Formation, Jimsar Sag[J]. Xinjiang Petroleum Geology, 2024, 45(3): 253-261.

Figures/Tables 12

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井名	深度/m	显微组分	总有机碳含量/%	镜质体反射率/%	热解峰温/ ℃	游离烃含量/ （mg·g^-1）	热解烃含量/ （mg·g^-1）	生烃指数/ （mg·g^-1）
J10025井	3 506.8	结构藻	1.80	0.87	440	0.59	6.62	366
J10025井	3 530.8	层状藻	14.90	0.56	444	1.52	103.29	692
J10025井	3 569.2	层状藻	3.10	0.65	443	0.41	18.34	592
J10025井	3 576.6	层状藻	17.00	0.55	449	1.79	117.24	691
J10025井	3 624.3	层状藻	3.60	0.50	443	1.02	26.42	713
J10025井	3 679.5	结构藻	3.10	0.72	435	1.07	8.59	276
J10025井	3 696.9	结构藻	2.50	0.60	433	0.70	6.21	248
J10025井	3 708.3	结构藻	4.40	0.52	437	0.70	26.00	598

井名	深度/ m	生烃母质类型	生烃活化能/ （kJ·mol^-1）	主体活化能/ （kJ·mol^-1）	频率/ %
J10024井	3 510.3	层状藻	58~70	58	99.70
J10025井	3 530.8	层状藻	65	65	100
J10025井	3 576.6	层状藻	63~68	63	99.07
J10025井	3 624.3	层状藻	64~69	64	99.56
J10025井	3 547.8	结构藻	39~71	59	86.30
J10025井	3 679.5	结构藻	32~60	49	49.28
J10025井	3 696.9	结构藻	32~59	49	61.32
J10025井	3 708.3	结构藻	34~63	52	74.34