坦桑尼亚鲁夸裂谷盆地氦气充注及成藏机理研究

doi:10.13745/j.esf.sf.2024.2.5

摘要/Abstract

摘要：

氦气成藏机理具有特殊性,比油气系统更复杂。自1967年在坦桑尼亚克发现富氦温泉以来,尚未发现规模氦气田,鲁夸裂谷盆地能否形成富氦气藏值得关注。本文利用地球化学、地震、钻井、测井等资料,综合分析了该盆地生氦资源量、氦气释放过程和充注机制,进而探讨了氦气勘探潜力。研究表明:中、新生代裂谷对盆地氦气的运移和聚集具有重要控制作用;地表氦气含量为1.0%~10.2%,载体气类型为氮气、二氧化碳和甲烷,³He/⁴He值在0.039~0.053 R_a之间,表现为壳幔混源特征,盆地基底和沉积岩生氦量为367亿m³;氦气从源岩到圈闭以及地面经历了生成、释放、运移、充注和溢出5个过程。氦气充注机制主要表现为氮气-氦气脱溶充注、煤层气-氦气萃取充注和二氧化碳-氦气萃取充注3种。其中氮气为深部成因的无机气,与氦气具有同源特征,为盆地的主要充注模式;煤层气来源于盆地沉积中心,与氦气为异源同储;二氧化碳为变质成因无机气,与氦气共生机制与煤层气相同。盆地的有利成藏区带为盆地边界断层(BMF)带。在此处的上覆土壤带,氦气含量比背景值高出35%,目前已发现12个盆地边界断层圈闭(BMFC),风险前氦气远景地质资源量为57.4 亿m³,占盆地待发现资源量的64.6%,成为裂谷盆地的有利勘探目标。

关键词: 气苗, 盆地边界断层圈闭, 脱溶, 萃取, 氦源, 聚集, 潜力

Abstract:

The mechanism of helium accumulation is unique and more complex than that of petroleum systems. Since the discovery of helium-rich hot springs in Tanzania in 1967, no large-scale helium fields have been identified. To establish the mechanism of helium charging and accumulation in the Rukwa Rift Basin, this study conducted research in five key areas using geochemical, seismic, drilling, and logging data: analyzing the helium and carrier gas content at the surface, calculating helium production in the craton basement, examining the helium release process, establishing the helium charging mechanism, and identifying favorable helium zones.The findings reveal that the Mesozoic-Cenozoic rifts play a critical role in controlling helium migration and accumulation within the basin. Surface helium content ranges from 1.0% to 10.2%, with carrier gases including nitrogen, carbon dioxide, and methane. The ³He/⁴He isotope ratio ranges from 0.039 to 0.053 R_a, indicating that helium originates from both crustal and mantle sources. Helium generation in the basement and sedimentary layers is estimated at 367 billion cubic meters. The release of helium from the peripheral rift of the Tanzanian Craton involves five key processes: generation, release, migration, charging, and overflow.Three helium accumulation models have been identified in the Rukwa Basin: nitrogen-helium desorption, coalbed methane-helium extraction, and carbon dioxide-helium extraction. Nitrogen, an inorganic gas of deep origin, is characterized by accumulation from homologous sources, with helium desorption from water being the primary helium charging mechanism in the basin. Coalbed methane, primarily sourced from the depositional center of the basin, accumulates independently of helium. Carbon dioxide, an inorganic gas of metamorphic origin, shares a symbiotic accumulation mechanism with helium similar to that of coalbed methane.The most favorable helium-rich zones in the basin are located in the Basin Margin Fault Closures (BMFCs). In the overlying soil of these traps, helium content is 35% higher than the background value. To date, 12 BMFCs have been identified, with unrisked prospective geological helium resources estimated at 5.74 billion cubic meters, accounting for 64.6% of the undiscovered resources in the basin. These zones represent favorable exploration targets in rift basins. The results of this study enhance the understanding of helium accumulation mechanisms in rift basins and provide valuable guidance for optimizing helium exploration in favorable areas.

Key words: seep, BMFC, desorption, extraction, helium source, accumulation, potential

中图分类号:

吴义平, 王建君, 陶士振, 王青, 雷占祥, 李谦, 张宁宁, 王晓波, 杨怡青. 坦桑尼亚鲁夸裂谷盆地氦气充注及成藏机理研究[J]. 地学前缘, 2025, 32(2): 261-276.

WU Yiping, WANG Jianjun, TAO Shizhen, WANG Qing, LEI Zhanxiang, LI Qian, ZHANG Ningning, WANG Xiaobo, YANG Yiqing. Research on helium charging and accumulation mechanism in Rukwa Rift Basin in Tanzania[J]. Earth Science Frontiers, 2025, 32(2): 261-276.

图/表 18

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储层	地层	沉积环境	储层岩性	储层孔隙度/%	渗透率/mD	特征	盖层
上湖层A和 B	更新统	滨岸带河流沉积	分选良好、细-中粒砂岩,交错层理发育	19.6	2 200	沿边界断层形成良好储层	碳酸盐岩、泥岩、现代薄层蒸发岩
上湖层 B	上中新统	滨岸带河流沉积	分选良好、细-中粒砂岩,交错层理发育	19.6	2 200	沿边界断层形成良好储层	碳酸盐岩、泥岩、现代薄层蒸发岩
红色砂岩C	渐新统	辫状冲积河道砂岩	浅黄到白色的石英砂岩, 净毛比40%	13~26	170~390	粒间孔为主,占0~16%;粒内孔占2%~15%	Nsungwe组块状碳酸盐火山灰烬/凝灰岩,伊利石-蒙脱石是主要的黏土矿物
红色砂岩D	上白垩统 Galula组	厚度600~3 000 m, 辫状冲积河道砂岩		26,变化大		粒间孔为主,占0~16%;粒内孔占2%~15%	Nsungwe组块状碳酸盐火山灰烬/凝灰岩,伊利石-蒙脱石是主要的黏土矿物
卡鲁超群E	二叠系- 下三叠统		砂岩	>12	最大1 320, 平均143	储集能力强	层间泥岩
基底F	前寒武系		变质岩	变化大			顶部泥岩

储层	地层	沉积环境	储层岩性	储层孔隙度/%	渗透率/mD	特征	盖层
上湖层A和 B	更新统	滨岸带河流沉积	分选良好、细-中粒砂岩,交错层理发育	19.6	2 200	沿边界断层形成良好储层	碳酸盐岩、泥岩、现代薄层蒸发岩
上湖层 B	上中新统	滨岸带河流沉积	分选良好、细-中粒砂岩,交错层理发育	19.6	2 200	沿边界断层形成良好储层	碳酸盐岩、泥岩、现代薄层蒸发岩
红色砂岩C	渐新统	辫状冲积河道砂岩	浅黄到白色的石英砂岩, 净毛比40%	13~26	170~390	粒间孔为主,占0~16%;粒内孔占2%~15%	Nsungwe组块状碳酸盐火山灰烬/凝灰岩,伊利石-蒙脱石是主要的黏土矿物
红色砂岩D	上白垩统 Galula组	厚度600~3 000 m, 辫状冲积河道砂岩		26,变化大		粒间孔为主,占0~16%;粒内孔占2%~15%	Nsungwe组块状碳酸盐火山灰烬/凝灰岩,伊利石-蒙脱石是主要的黏土矿物
卡鲁超群E	二叠系- 下三叠统		砂岩	>12	最大1 320, 平均143	储集能力强	层间泥岩
基底F	前寒武系		变质岩	变化大			顶部泥岩

序号	降低氦气系统风险的重要程度	有效的氦气聚集的时间序列
1	氦源(至关重要)	储层沉积的质量
2	储层(通常很多,但必须与有效盖层和圈闭相匹配)	合适的盖层沉积
3	盖层(同储层)	圈闭形成
4	圈闭(构造、地层):一个封闭的空间,阻止流体浮力到地表	充注:氦气从基底到圈闭的释放和运移

序号	降低氦气系统风险的重要程度	有效的氦气聚集的时间序列
1	氦源(至关重要)	储层沉积的质量
2	储层(通常很多,但必须与有效盖层和圈闭相匹配)	合适的盖层沉积
3	盖层(同储层)	圈闭形成
4	圈闭(构造、地层):一个封闭的空间,阻止流体浮力到地表	充注:氦气从基底到圈闭的释放和运移

编号	温泉名称	数据来源文献	He含量/%	CO₂含量/ %	N₂含量/ %	氩含量/ %	HCO₃^- 含量/%	CH₄ 含量/%	离最近的火山距离/km	水温/ ℃
1	Rukwa2#/Rukwa2#b	[7]	2.49		96.0
2	Ivuna	[16]	8~10.2
3	Rock of Hades	[39]	4.2	0.8	87.5		0	5.4	139	66
4	Songwe Rambo	[39]	0.01	97.2	2.1		79.9	0.1	40	65
5	Maji ya Weta	[39]	0.06	89.9	9.8		71.1		43	72
6	Mtagata	[39]	0.01	6.4	90.9	1.1	55	0.5	135	57
7	Utete	[39]	0.25	12.4	83.9		0	0.8	147	58
8	Songwe River	[39]	0.01	99.2	0.6			0.1	40	55
9	Rukwa1#/MMCT001	[40]	0.005
10	Rukwa1#/MMCT002		0.004