东海陆架盆地丽水西凹陷油气地球化学特征及其成因和来源

doi:10.19657/j.geoscience.1000-8527.2022.052

摘要/Abstract

摘要：

东海陆架盆地西部丽水西凹陷油气成因和来源争议较大。根据钻井地球化学分析测试结果、地震勘探资料,运用天然气地球化学、油气成藏过程研究思路,重新认识丽水西凹陷L36气田油气成因和来源,提出下一步油气勘探方向。L36气田天然气组分、干燥系数分析表明,天然气为“凝析油-湿气带”演化阶段产物,天然气成熟度R_o不小于1.1%。通过天然气碳同位素组成与中国近海典型油型气碳同位素特征的对比分析,认为L36气田天然气为油型气,估算天然气成熟度R_o在1.12%~1.14%之间,天然气来源于丽水西凹陷下古新统月桂峰组湖相烃源岩。L36气田产出的凝析油C₇轻烃具有甲基环己烷含量占优特征,与湖相烃源岩来源的凝析油C₇轻烃组成特征存在显著差异;中古新统灵峰组浅海相烃源岩具有甾烷C₂₇20R/C₂₉20R小于1、不含C₃₀4-甲基甾烷、伽马蜡烷含量低的特征,指示L36气田凝析油来源于下古新统灵峰组浅海相烃源岩,证实了丽水西凹陷除发育下古新统月桂峰组湖相烃源岩外,还发育有中古新统灵峰组浅海相烃源岩。基于以上对烃源岩的分析,提出了丽水西凹陷下一步的油气勘探目标,即凹中断背斜构造背景上的岩性圈闭、凹中断鼻及其构造背景上的岩性圈闭和仙桥构造带,为寻找丽水西凹陷新的油气储量阵地提供新的认识。

关键词: 油气成因, 月桂峰组, 湖相烃源岩, 灵峰组, 浅海相烃源岩, 丽水西凹陷, 东海陆架盆地

Abstract:

The genesis and source of gas and condensate oil of Lishuixi sag in the western East China Sea Shelf Basin remain disputed for many years. Based on geochemical and drill well analyses and seismic exploration, the oil and gas genesis, source and exploration direction of L36 gas-field in the Lishuixi sag are reviewed with comprehensive research ideas and methods of natural gas geochemistry and oil and gas accumulation. The study shows that the natural gas in L36 gas-field is the product of “condensate-wet gas zone” evolution stage, and that the natural gas maturity R_o is no less than 1.1%. The carbon isotope composition of natural gas and the carbon isotope comparison with typical oil-type gas in China offshore revealed that the natural gas in L36 gas field is oil-type, with the estimated natural gas maturity R_o=1.12%-1.14%, which was originated from lower Paleocene lacustrine Yueguifeng Formation source rocks in the sag, which enriched the genetic types and sources of natural gas in the East China Sea basin. The C₇ light hydrocarbons of condensate oil produced in L36 gas-field are dominated by methylcyclohexane, significantly different from the C₇ light hydrocarbon composition of condensate oil from the lacustrine source rock. The lower Paleocene shallow marine Lingfeng Formation source rocks are characterized by < 1 sterane C₂₇20R/C₂₉20R, no C₃₀4-methylsterane and low Gamma wax content. This indicates that the condensate oil of L36 gas-field is from the Lingfeng Formation source rocks. It is confirmed that in addition to the Yueguifeng Formation source rocks, the Lingfeng Formation source rocks were also developed in the Lishuixi sag. The next natural gas exploration direction in the Lishuixi sag may include: (1) lithologic traps in the structural background of fault anticline and fault nose across the sag center; (2) Xianqiao structural belt. This provides theoretical guidance for the exploration of new hydrocarbon resource in the sag.

Key words: genesis, Yueguifeng Formation, lacustrine source rock, Lingfeng Formation, shallow marine source rock, Lishuixi sag, East China Sea Shelf Basin

中图分类号:

张迎朝, 胡森清, 刘金水, 蒋一鸣, 陈忠云, 覃军, 刁慧, 王超. 东海陆架盆地丽水西凹陷油气地球化学特征及其成因和来源[J]. 现代地质, 2022, 36(05): 1382-1390.

ZHANG Yingzhao, HU Senqing, LIU Jinshui, JIANG Yiming, CHEN Zhongyun, QIN Jun, DIAO Hui, WANG Chao. Geochemical Characteristics and Genesis of Oil and Gas in the Lishuixi Sag, East China Sea Shelf Basin[J]. Geoscience, 2022, 36(05): 1382-1390.

图/表 9

图1 东海陆架盆地西部丽水凹陷构造区划示意图

Fig.1 Structural division sketch map of Lishui sag in the western East China Sea Shelf Basin

表1 东海陆架盆地丽水西凹陷和琼东南盆地松东与宝岛凹陷天然气组分、干燥系数与碳同位素特征 (琼东南盆地数据据文献[14])

Table 1 Natural gas composition and drying coefficient and carbon isotope characteristics of the Lishuixi sag (in the East China Sea Shelf Basin), Songdong and Baodao sag (in the Qiongdongnan Basin) (cited from ref. [14])

区带	井号	井段/m	测试层号	地层	天然气组分/%				干燥系数	碳同位素δ¹³C/‰
区带	井号	井段/m	测试层号	地层	C₁	C_2-5	N₂	CO₂	C₁/C₁-C₅	C₁	C₂	C₃	C₄	CO₂
丽水西凹陷	L36-1	2 250~ 2 283	DST1- S1.2	上古新统明月峰组	54.75	6.96	3.79	34.50	0.89	-46.13	-29.31	-27.07	-26.93	-4.67
丽水西凹陷	L36-1	2 250~ 2 283	DST1- S1.3	上古新统明月峰组	55.45	6.85	3.55	34.15	0.89	-46.30	-29.55	-26.96	-26.86	-5.03
松东凹陷北坡	SF24-1-1	2 122.5	MDT	下古新统三亚组	74.30	9.80	6.77	7.81	0.88	-47.06	-30.92	-29.96	-28.64	-7.61
宝岛凹陷	BF13-1-1	1 573~ 1 580	DST	中中新统梅山组	86.14	10.24	2.46	0.72	0.89	-48.65	-30.53	-31.15	-27.82	-25.54
宝岛凹陷	BF13-3-1	1 740	MDT	中中新统梅山组	84.70	11.40	2.80	0.61	0.88	-48.91	-27.45	-27.93	-27.84

表2 丽水西凹陷天然气轻烃气相色谱C7系列数据

Table 2 Light hydrocarbon C7 series in the natural gas of the Lishuixi sag

井名	井深/m	样品	C₇系列/%
井名	井深/m	样品	直链烷烃	支链烷烃	环烷烃
L36-1	2 580~ 2 283	DST1-S1.7	15.26	23.85	60.53
L36-1	2 580~ 2 283	DST1-S1.8	14.17	24.28	61.55

表3 东海丽水西凹陷和南海北部天然气C7轻烃组分(南海北部数据据文献[14])

Table 3 Composition of C7 light hydrocarbon components of natural gas in the Lishuixi sag of East China Sea and northern South China Sea (cited from ref. [14])

盆地	井名	深度/m	地层	天然气C₇轻烃组分
盆地	井名	深度/m	地层	甲基环己烷 (MCH)/%	正庚烷 (nC₇)/%	二甲基环戊烷 (∑DMCP)/%	甲基环己烷指数/%
东海陆架盆地丽水西凹陷	L36-1	2 250~2 283	上古新统明月峰组	61.60	21.20	17.20	61.60
东海陆架盆地丽水西凹陷	L36-1	2 250~2 283	上古新统明月峰组	63.50	19.40	17.10	63.50
北部湾盆地涠西南凹陷	W-1	2 137.5~2 265.8	流一段	33.30	25.90	40.70	33.30
北部湾盆地涠西南凹陷	W-2	2 459.0~2 473.5	涠三段	35.71	32.14	32.14	35.71
琼东南盆地松东凹陷	SF24-1-1	2 122.5	下中新统三亚组	42.60	24.00	33.30	42.60
琼东南盆地宝岛凹陷	BF13-1-1	1 573~1 580	中中新统梅山组	40.00	20.00	40.00	40.00
	BF13-1-1	1 577.3		40.00	17.10	42.90	40.00
	BF13-1-1	1 740	中中新统梅山组	30.40	26.00	43.60	30.40

图2 东海陆架盆地丽水西凹陷、莺—琼盆地及珠江口盆地天然气中δ13C2和δ13C3相互关系

Fig.2 δ13C2 vs. δ13C3 plot of natural gas in Lishuixi sag in the East China Sea Shelf Basin, Ying-Qiong Basin, and Pearl River Estuary Basin

图3 丽水凹陷凝析油、烃源岩生物标志物特征

Fig.3 Biomarker characteristics of condensate oil and source rocks in the Lishui sag

图4 L36-1井天然气与烃源岩碳同位素值对比图

Fig.4 Natural gas and source rock carbon isotope comparison of L36-1 well

图5 丽水西凹陷L36-2井区埋藏史

Fig.5 Burial history of Lishuixi sag across L36-2 well

图6 丽水凹陷区成藏模式(剖面位置见图1)

Fig.6 Accumulation model in the Lishui sag (the section position shown in Fig.1)

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