美国典型富氦无机成因气田中氦气地质特征与聚集机制

doi:10.13745/j.esf.sf.2024.1.70

摘要/Abstract

摘要：

美国广泛发育具有经济效益的富氦无机成因天然气田,如其中富氦氮气田甚至可以含有高达10%的氦。原地和周边地区的基底提供充足的氦源而氮气可来自不同圈层,且通常N₂/He (He>0.1%)在5~50之间。但是富氦氮气田在美国独特地质环境之外是否也有发现还需要进一步的研究。富氦二氧化碳气田中的氦主要也来自壳源且产量可观。科罗拉多高原上的富氦二氧化碳气田均被认为是来源于新生代晚期的岩浆活动,且该地区岩浆岩具有较高的U、Th含量。地下水溶气脱气-再溶解(Groundwater Gas Stripping and Re-dissolution, GGS-R)模型被普遍认为可以合理解释CO₂气藏中氮气、氦等惰性气体的聚集成藏机制。具体来说,幔源CO₂载体气充注时将溶解在地下水中的大气源惰性气体与壳源惰性气体脱出成藏,并与地下水达到水/气溶解平衡。虽然不同气田的平衡值各有不同,但是科罗拉多高原上的各气田均显示出相似的范围值,即在相应的储层压力和温度下为0~100 cm³水/cm³气。本文系统分析美国无机成因富氦气藏的氦气生成、运移和聚集机制,讨论氦气在经历氦源岩内游离相扩散初次运移后通过水溶相、气容相集流或是多相渗流方式进行的二次运移及由无机成因载体气N₂和CO₂共同参与的富集成藏机制,既可为我国氦气勘查提供理论认识依据,也可为二氧化碳地质评价和开发利用及安全封存提供参考。

关键词: 氦气, 富氦气田, CO₂气田, N₂气田, 非烃气, 无机成因, 地质特征, 聚集机制

Abstract:

Economically viable abiotic helium-rich gas fields are widely developed in the United States. He-rich N₂ gas fields, for example, contain as much as 10% He, as the basement rocks in situ and in the surrounding area provides sufficient crustal He and N₂ to yield an N₂/He (He > 0.1%) ratio typically between 5-50. However, He-rich N₂ gas fields so far are only found in the United States, and further research is needed to determine whether they are due to unique geological conditions, or yet to be discovered elsewhere. He-rich CO₂ gas fields also contain significant quantity of crustal helium. He-rich CO₂ gas fields in the Colorado Plateau are all thought to have originated from late Cenozoic magmatism, and the magmatic rocks in the region have high U/Th contents. The groundwater gas stripping and re-dissolution (GGS-R) model is commonly used to explain the trapping mechanism of noble gases in CO₂ gas reservoirs. According to this model, mantle-sourced CO₂ carrier gas stripes air-sourced noble gases dissolved in the groundwater to charge reservoirs along with crustal-derived noble gases, and dissolution equilibrium subsequently reestablishes between the noble gases and groundwater. While the water/gas ratios at equilibrium differ between different gas fields, they are similar in all gas fields in the Colorado Plateau ranging between 0-100 (at reservoir pressure and temperature). By systematic analysis and summarization of the source, migration, and accumulation mechanisms of helium in helium-rich abiotic gas reservoirs in the United States, and discuss the enrichment of helium of primary migration by diffusion in helium source rocks, and of secondary migration by water phase mass flow or multiphase porous flow/seepage with inorganic carrier gases N₂ and CO₂, this paper provides a theoretical basis for helium exploration in China, and can be used as a reference for geological evaluation of CO₂ reservoirs and development of CO₂ safe storage.

Key words: helium, helium-rich gas field, CO₂ gas field, N₂ gas field, abiotic natural gas, inorganic genesis, geological characteristics, enrichment mechanism

中图分类号:

杨怡青, 陶士振, 陈悦. 美国典型富氦无机成因气田中氦气地质特征与聚集机制[J]. 地学前缘, 2024, 31(1): 327-339.

YANG Yiqing, TAO Shizhen, CHEN Yue. Geological characteristics and mechanism of helium accumulation in typical abiotic helium-rich gas fields in the United States[J]. Earth Science Frontiers, 2024, 31(1): 327-339.

图/表 17

表1 美国典型无机成因富氦天然气田表(数据来源于文献[4,12-13])

Table 1 Typical helium-rich abiotic natural gas fields in the United States (sourced from [4,12-13])

气田类型	气田名称	所属盆地	天然气储量/(10⁸m³)	层位	平均氦含量/%	R/R_a
CO₂气田	Big Piney-La Barge	Green River盆地	48 988.1	密西西比系	0.50	0.050~0.070
	McElmo Dome	Paradox盆地	8 495.1	密西西比系	0.20	0.057~0.215
	St. Johns	Holbrook盆地	2 520.2	二叠系	0.63	0.394~0.455
	Doe Canyon	Paradox盆地	1 444.2	密西西比系	0.78	0.150
	Sheep Mountain	Raton盆地	877.8	白垩系、侏罗系	0.10	0.963
	McCallum	North Park盆地	792.9	下白垩统	0.28	0.402
	Kevin Dome	Williston盆地	3 964.4	泥盆系	0.29
N₂气田	Pinta Dome	Holbrook盆地	1.85 (总产量)	二叠系	7.20	0.20~0.22
N₂气田	Harley Dome	Unita-Piceance盆地	未完全开发	侏罗系	3.90	0.11

图1 美国主要富/含CO2天然气田分布(a)及北美克拉通与地质构造单元(b)(据文献[6,10]修改)

Fig.1 (a) Distribution of major CO2 rich natural gas fields in the United States; (b) North American Craton and geotectonic units. Modified after [6,10].

图2 美国科罗拉多高原/四角地区富CO2天然气田分布(据文献[4]修改)

Fig.2 Distribution of CO2-rich natural gas fields in the Four Corners area, Colorado Plateau, U.S.A. Modified after [4].

表2 美国主要富氦CO2天然气田参数表(数据来源于文献[6,12])

Table 2 Basic information on major helium-rich CO2 natural gas fields in the United States. Compiled from [6,12].

气田参数	各气田参数情况
气田参数	McElmo Dome	Doe Canyon	St. Johns	Big Piney-La Barge
产区面积/km²	824.4	331.8	890.3	2 630.5
天然气储量/(10⁸ m³)	8 495.1	1 444.2	2 520.2	48 988.1
氦气储量/(10⁸ m³)	17.0	11.3	15.9	244.9
储层	密西西比纪Leadville 组白云岩, 三叠纪Shinarump组砾岩	密西西比纪Leadville 组石灰岩	二叠纪Supai组 Arkosic砂岩、断裂的前寒武纪基底	密西西比纪Madison 组石灰岩、白云岩、砂岩
平均深度/m	2 000~2 545	2 730	462	4 750~5 500
产层厚度/m	21~45	18	23	85
孔隙度/%	3.5~25(平均11)	10	10~15	6~12(平均9)
渗透率/(10^-3 μm²)	23		10	10~50
圈闭类型	构造-岩性地层圈闭	构造圈闭	构造圈闭	构造圈闭
盖层	Paradox组盐岩/ 硬石膏	Paradox组盐岩/ 硬石膏	盐岩/硬石膏	Sabkha砂砾岩、喀斯特碎屑岩
气藏压力/psi	2 580(497 m以深)	3 960	508	6 585~7 625
所属盆地	Paradox盆地	Paradox盆地	Holbrook盆地	Green River盆地
采气方式	压力、较少水驱		气顶驱动	气顶驱动
He含量	0.20%	0.78%	0.63%	0.50%
R/R_a	0.057~0.215	0.150	0.394~0.455	0.050~0.070
CO₂含量	98.2%	91.7%	92.6%	79.6%
N₂含量	1.6%	6.1%	6.5%	4.8%
CH₄含量	>0.2%	1.2%	0.05%	12.7%

图3 美国科罗拉多高原北部富氦气田及氦含量(a)与McElmo Dome气田Leadville石灰岩顶面构造图(b)(据文献[4,12]修改)

Fig.3 (a) Helium-rich gas fields and helium content in the northern Colorado Plateau, United States, and (b) top surface map of the Leadville limestone at McElmo Dome gas field. Modified after [4,12].

图4 四角地区CO2气田CO2成因来源(据文献[4]修改)

Fig.4 Genesis discrimination diagram of CO2 in CO2 gas fields in the Four Corners region. Modified after [4].

图5 St. Johns气田二叠纪Supai组顶面构造图(a)与22-1X井富氦Supai组测井结果(b)(据文献[4,17]修改)

Fig.5 He-rich Permian Supai formation in the St. Johns Dome gas field. (a) Top surface map. (b) Logging results from well 22-1X. Modified after [4,17].

图6 Big Piney-La Barge气田地质特征(据文献[12,20]修改) a—BP-LB气田位置;b—气田Madison组顶面构造图与CO2含量分布等值线图;c—盆地地层岩性柱状图。

Fig.6 Big Piney-La Barge gas field. (a) Tectonic location. (b) Top surface map of the Madison Formation overlaying with CO2 contour map. (c) Lithologic of the Green River basin strata. Modified after [12,20].

表3 美国主要富氦N2天然气田参数表(数据来源于文献[5,12-13,23])

Table 3 Basic information on major helium-rich NG natural gas fields in the United States. Complied from [5,12-13,23].

气田参数	气田参数情况
气田参数	Pinta Dome	Harley Dome
产区面积/km²	19.9	1.3
储层	二叠纪Coconino砂岩	侏罗纪Entrada砂岩
深度/m	311~334	236
产层厚度/m	21	27
孔隙度/%	14
渗透率/(10^-3 μm²)	110	低
圈闭类型	地层-构造圈闭	构造圈闭
盖层	Moenkopi组页岩	Mancos组页岩
气藏压力/psi	124	154
所属盆地	Holbrook盆地	Unita-Piceance盆地
采气方式	气顶驱动
He含量/%	地区平均7.2 生产井平均8.5	地区平均3.9 生产井平均7
R/R_a	0.20~0.22	0.11
CO₂含量/%	0.46	0.50
N₂含量/%	90.0	62.1
CH₄含量/%	0.22	31.50

图7 富氦氮气田Harley Dome及其附近富氦烷烃气田氦气运移成藏模型(据文献[23]修改)

Fig.7 Helium migration model of the Harley Dome helium-rich N2 field and nearby He-rich natural gas fields. Modified after [23].

图8 Pinta Dome气田氦气分布特征(据文献[22,26]修改) a—Coconino组顶面构造与氦含量分布平面图;b—测井与岩性地层图。

Fig.8 Pinta Dome gas field. (a) Helium contour map. (b) Well logging data and simplified lithostratigraphic column. Modified after [22,26].

图9 U-P盆地氦气含量与N2(a)和CO2(b)含量关系图(据文献[23]修改)

Fig.9 Plot of He content vs. (a) N2 and (b) CO2 in the U-P Basin. Modified after [23].

表4 不同δ15N对应天然气中可能的N2来源(据文献[27]整理)

Table 4 Classification of probable N2 sources in natural gas fields based on δ15N values. Compiled from [27].

δ¹⁵N/‰	天然气中可能的N₂来源
-19~19	成熟和低成熟的沉积有机质
-2~10	成熟的沉积有机质
+1~+2	深部壳源或幔源
0(N₂/Ar为38~84)	大气来源
+1~+4	变质产生的含铵盐黏土矿物
+4~+18	高成熟的沉积有机质

图10 富氦氮气藏形成模式图

Fig.10 Model of formation of He-rich N2 reservoirs

图11 天然含碳物质δ13C范围(据文献[35]修改)

Fig.11 Range of δ13C values in natural carbonaceous materials. Modified after [35].

图12 幔源CO2与壳源氦的GGS-R充注模型由载体气和大气源惰性气体指征(据文献[4]修改)

Fig.12 GGS-R model for mantle-sourced CO2 and crustal-sourced helium. Modified after [4].

图13 四角地区碳氢化合物、 CO2与惰性气体关系图(据文献[29]修改)

Fig.13 Hydrocarbon-CO2-noble gas ternary diagram for the Four Corners area. Modified after [29].

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