西湖凹陷迎翠轩地区钻遇古新统证据探讨及意义

doi:10.13809/j.cnki.cn32-1825/te.2025.05.005

摘要/Abstract

摘要：

东海陆架盆地西湖凹陷新生界发育巨厚沉积，目前对于西湖凹陷始新统、渐新统及中新统地质条件及成藏研究较多，但缺乏古新统地层研究。近期研究表明，西湖凹陷古新统生烃量潜力巨大，也是一套重要的烃源岩层系，直接关系到西湖凹陷的油气生成富集。为了搞清古新统地层发育特征及对油气的影响作用，研究基于西湖凹陷斜坡北段迎翠轩地区J-1井资料，从4个方面开展区域对比分析认为西湖凹陷J-1井已钻遇古新统地层：①区域地震相对比认为J-1井深层表现为中—高频、中弱振幅、中—低连续反射，地层出现明显褶皱，T₄⁰地震反射界面之下削截，为古新统地层顶部典型地震相特征。②岩性组合特征对比认为J-1井下部岩性见标志层红褐色泥岩，指示了古新统辫状河三角洲—湖泊沉积环境。③古生物对比认为研究区古新统孢粉特征与长江凹陷古新统孢粉具有相似性，且均未见海相有孔虫。④古新世时期形成大型断陷构造，受基底断裂控制，断裂下降盘具备发育巨厚古新统的地质条件。通过分析J-1井古新统烃源岩地化特征，同时对比东海陆架盆地其他凹陷古新统烃源岩地化指标，认为西湖凹陷古新统发育中等—较好的烃源岩，具备较大生烃潜力。迎翠轩近洼区发育巨厚古新统烃源岩（暗色泥岩），是下步寻找规模油气的有利区。研究对于西湖凹陷油气勘探部署具有重要指导意义。

关键词: 西湖凹陷, 迎翠轩地区, 古新统, 地震相, 孢粉组合, 生烃潜力

Abstract:

The Xihu Sag of the East China Sea Shelf Basin is characterized by thick Cenozoic sediments. Extensive research has been conducted on the geological conditions and hydrocarbon accumulation of the Eocene, Oligocene, and Miocene strata, with limited studies on the Paleocene strata. Recent studies indicate that the Paleocene strata in the Xihu Sag have significant hydrocarbon generation potential and constitute an important source rock system, which plays a key role in oil and gas generation and accumulation in the Xihu Sag. To clarify the development characteristics of the Paleocene strata and their implications for oil and gas accumulation, this study analyzed data from well J-1 in the Yingcuixuan area, located in the northern slope segment of the Xihu Sag. Four lines of evidence supported that well J-1 has penetrated the Paleocene strata: ⑴ regional seismic correlation suggested that the deep layers of well J-1 exhibited medium-to-high frequency, medium-to-weak amplitude, and medium-to-low continuity reflections, with distinct stratigraphic folding. The strata below the T40 seismic reflection interface showed truncation features, which are typical seismic facies characteristics of the top of the Paleocene strata. ⑵ Lithological assemblage comparison revealed that the lower section of well J-1 contained marker layers of reddish-brown mudstone, indicating a Paleocene lake-delta depositional environment. ⑶ Palynological comparison showed that the Paleocene sporopollen characteristics in the study area were similar to those in the Changjiang Sag, both lacking marine foraminifera. ⑷ During the Paleocene, a large fault-depression structure formed, controlled by basement faults. The downthrow side of a fault provided favorable geological conditions for the formation of thick Paleocene strata. By analyzing the geochemical characteristics of the Paleocene source rocks in well J-1 and comparing them with geochemical indicators from other sags in the East China Sea Shelf Basin, it was concluded that the Paleocene strata in the Xihu Sag host medium-to-good source rocks with significant hydrocarbon generation potential. This study provides valuable guidance for oil and gas exploration deployment in the Xihu Sag. The findings suggest that the area near the depression in the Yingcuixuan area is favorable for large-scale oil and gas exploration due to the development of thick Paleocene source rocks (dark mudstone).

Key words: Xihu Sag, Yingcuixuan area, Paleocene, seismic facies, sporopollen assemblage, hydrocarbon generation potential

中图分类号:

TE122

江东辉,庄建建,杏绿芽, 等. 西湖凹陷迎翠轩地区钻遇古新统证据探讨及意义[J]. 油气藏评价与开发, 2025, 15(5): 750-759.

JIANG Donghui,ZHUANG Jianjian,XING Lyuya, et al. Discussion and significance of evidence for Paleocene strata by drilling in Yingcuixuan area of Xihu Sag[J]. Petroleum Reservoir Evaluation and Development, 2025, 15(5): 750-759.

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区域位置层位	岩性	井号	有机质丰度	有机质类型	有机质成熟度	生烃潜力评价
长江凹陷（美人峰组）	灰黑色泥岩	M1井	ω（TOC）介于0.08%~2.13%，均值为0.72%；S₁+S₂介于0.02~1.34 mg/g	Ⅱ-Ⅲ型，含少量Ⅱ型	成熟阶段	中等
长江凹陷（美人峰组）	灰色、深灰色、灰白色、黑色泥岩	CJ-1井、 CJ-2井	ω（TOC）介于0.2%~3.4%，均值为1.3%；S₁+S₂介于0.02~5.40 mg/g，均值为0.80 mg/g	Ⅱ-Ⅲ型，含少量Ⅱ型	成熟阶段	中等—好
瓯江凹陷（月桂峰组）		LS36-1-1井、 WZ26-1-1井	ω（TOC）均值为2.11%；S₁+S₂均值为4.15 mg/g	Ⅲ型	低熟—成熟阶段	中等—好
	褐黑色，灰黑色泥岩	W4井	ω（TOC）介于1.86%~3.75%，均值为2.57%；S₁+S₂介于3.20~15.29 mg/g，均值为8.61 mg/g	Ⅱ₁-Ⅱ₂型		好—很好
	暗色泥岩	JJ4-1井、 JJ6-1井	ω（TOC）介于1.86%~2.65%，均值为2.31%；S₁+S₂介于3.20~9.46 mg/g，均值为7.46 mg/g	Ⅱ₁-Ⅱ₂型	未低熟—低成熟阶段	好—很好
西湖凹陷（古新统）	暗色泥岩	J-1井	ω（TOC）介于0.62%~1.05%，均值为0.80%；S₁+S₂介于0.90~2.01 mg/g，均值为1.31 mg/g	Ⅱ₁型	成熟阶段	中等—好

层位	岩性	深度/m	Pr/Ph值	主峰碳	ω（TOC）/%	S₁+S₂/（mg/g）	T_max/℃
古新统	泥岩	4 460~4 480	2.86	nC₂₅	0.87	1.31	450
古新统	泥岩	4 620~4 640	1.71	nC₂₄	1.05	2.01	451
古新统	泥岩	4 700~4 720	0.82	nC₁₇	0.65	1.00	456
古新统	泥岩	4 820~4 840	1.62	nC₁₇	0.62	0.90	456