Classification of Sweet Spots in Shale Oil Reservoir of Lucaogou Formation in Jimsar Sag，Jurggar Basin

doi:10.7657/XJPG20250201

Abstract

Abstract:

The shale oil reservoir of Permian Lucaogou formation in the Jimsar sag of the Junggar Basin can be divided into two sweet spots from top to bottom. These sweet spots vary significantly in productivity and remain unclear for controlling factors, making sweet spot prediction challenging. By using geological, petrophysical experiment, logging, and formation testing data, the enrichment mechanisms of shale oil were identified, the main factors controlling sweet spots in the shale oil reservoir were investigated, sweet spot index was constructed, and a classification standard for sweet spots was established. The research results show that the dominant reservoir rocks in the sweet spots in the study area are silty-fine sandstone and psammitic dolomite, with good pore structure, relatively abundant free oil, and moderate brittleness. The development, distribution, and effectiveness of micro-fractures in the shale oil reservoir are influenced by formation overpressure. The sweet spots in the shale oil reservoir are mainly controlled by free oil saturation, formation overpressure, and brittleness index. The sweet spot index is greater than 45 for Class Ⅰ sweet spots, 25-45 for Class Ⅱ sweet spots, and less than 25 for Class Ⅲ sweet spots. Class Ⅰ and Class Ⅱ sweet spots are considered as prime targets for horizontal wells, while Class Ⅲ sweet spots are reserved for future development.

Key words: Junggar Basin, Jimsar sag, Lucaogou formation, shale oil reservoir, free oil saturation, formation pressure coefficient, rock brittleness, sweet spot classification

CLC Number:

TE122.2

QI Hongyan, WANG Zhenlin, ZHANG Yanning, LIN Jingqi, HU Xuan, SU Jing, XU Rui, CAO Zhifeng. Classification of Sweet Spots in Shale Oil Reservoir of Lucaogou Formation in Jimsar Sag，Jurggar Basin[J]. Xinjiang Petroleum Geology, 2025, 46(2): 127-135.

Figures/Tables 12

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岩性	排驱压力/ MPa	最大孔喉直径/ μm	平均毛细管直径/ μm	直径大于0.148 μm 孔喉占比/%	最大进汞饱和度/%
砂屑白云岩	4.4	1.02	0.32	63.8	80.6
粉细砂岩	3.7	2.48	0.72	61.7	86.6
泥晶白云岩	4.3	0.96	0.28	22.0	83.6
白云质粉砂岩	4.1	0.54	0.18	38.0	80.0