Full
AIKERANMU·Wusimanjiang,born in 2000,is a postgraduate student. He majors in geological resources and geological engineering. E-mail: 1943564374@qq.com.
Outline
While gravity flow deposits have been identified in the Chang 7 member of the Yanchang Formation in the Wuqi area,northern Shaanxi Province,Ordos Basin,no such deposits have been reported in the Chang 8 and Chang 9 members. This study aims to comprehensively reveal the presence,types,and controlling effects of gravity flow deposits in the Chang 7-Chang 9 members on reservoir properties and oil-bearing potential.Through centimeter-scale core observations,grain-size analysis,and well-log interpretation of the Chang 7-Chang 9 members in the Wuqi area,an integrated analysis was conducted to determine the genetic types and characteristics of gravity flow sandstones. Gravity flow deposits are widely distributed in the Chang 7-Chang 9 members of the Wuqi area,dominated by turbidity current deposits,followed by sandy debris flow deposits,with additional gravity-driven slide-slip deposits. Multi-parameter identification criteria for gravity flow deposits in the Chang 7-Chang 9 members have been established: (1)Core structures: slide-slump deposits exhibit deformed and convolute bedding;sandy debris flows show thick massive bedding and mudstone clasts;turbidites display stacked,incomplete Bouma sequences. (2)Grain-size characteristics: sandy debris flows typically show “short-tailed” bimodal distributions(>95% saltation sub-population,steep slope;<5% suspension sub-population,gentle slope). Turbidites generally exhibit unimodal distributions. (3)C-M diagrams: C-M values parallel the C=M baseline,consistent with gravity flow deposition. Comparative analysis of reservoir properties,oil saturation,and well testing results demonstrates that sandy debris flow deposits significantly outper form turbidites. The widespread distribution of gravity flow deposits in the Chang 7-Chang 9 members holds substantial exploration significance. Sandy debris flows should be prioritized as prospective targets for tight oil exploration in the lower petroleum assemblage of the Yanchang Formation,followed by turbidite deposits.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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