Introduction
1. Helium resources and geological characteristics
Table 1. Similarities and differences in the elements of the "helium-natural gas" geological systems |
Similarities and differences | Systems/ elements | Conventional natural gas system | Helium system | Basis and rationale for geological assessment |
---|---|---|---|---|
Similarities (unity) | Petroleum system | Compliance with the common patterns of the "petroleum system", from source rock to trap, with the same/similar static geological elements and dynamic geological processes. | Addressing the common characteristics of helium and natural gas, establishing a comprehensive helium geological evaluation methodology and workflow, referring to evaluating petroleum systems and petroleum accumulation systems. | |
Accumulation system | Sharing the six essential geological elements: source, reservoir, caprock, trap, migration, and preservation. | |||
Migration and accumulation driving forces | Carrier natural gas and helium migrate in mixed phases; for conventional carrier gas, buoyancy plays the dominant role, and for unconventional carrier gas, hydrocarbon generation pressurization and diffusion lead; for water-soluble helium, hydrodynamic or diffusive migration occurs, and due to the Henry effect at the gas-water interface of a trap, the helium degasses into the natural gas phase and accumulates. | |||
Accumulation characteristics | The same isotopic fractionation of gases exists during gas migration and accumulation. | |||
Differences (specificity) | Source | Organic matter | 235U, 238U, 232Th α-decay in the crust | Given the unique characteristics of helium, develop targeted resource evaluation methods: helium-rich reservoir evaluation methods that specialize in helium migration and accumulation and helium resource evaluation methods. |
Maturation and evolution | Thermal evolution of source rock burial, gas generated by organic matter. | Accumulation of helium released by prolonged decay of U- and Th-rich source rocks. | ||
Molecule properties | Relatively larger molecules, higher permeability, higher concentration. | Smaller molecule, extremely permeable, very low concentration. | ||
Primary migration | Hydrocarbon generation pressurization (phase change from solid kerogen to fluid petroleum resulting in volume increase). | Minerals heated above closing temperature, fracturing of rocks and minerals, and mineral dissolution. | ||
Driving force for secondary migration | Buoyancy drive (conventional gas), gas-pressurized piston drive, or diffusion (unconventional tight gas, etc.). | Groundwater, buoyancy, differential pressure displacement, Henry effect. | ||
Differentiation and fractionation | Relatively complex molecular structure, chemically diverse, experiencing relatively complex component differentiation and isotopic fractionation effects. | Relatively simple molecular structure, chemically stable, experiencing relatively simple or weak isotopic fractionation effects. | ||
Accumulation (reservoir + trap) | Natural gas accumulates in the effective traps or sweet spots. | Append to carrier gas in traps, helium-saturated water degasses or desolubilizes into natural gas reservoirs in the presence of a gas phase. | ||
Preservation | Capillary pressure sealing in caprock and lateral tight layer. | Effective sealing by the upper caprock and lateral tight layer. | ||
Subsidiary adjustment | Seepage and diffusion, tectonic activity adjustment or destruction, re-migration, loss, or accumulation. | Helium accumulation is more sensitive to seepage and diffusion tectonic activity adjustment or destruction; re-migration, loss, or accumulation with carrier natural gas. |
2. Helium sources and accumulation
Table 2. Division scheme and types of helium sources |
Division scheme | Type | Subclasses/characteristics |
---|---|---|
According to geosphere | Mantle source | 3He/4He > 1.1×10-5 |
Crust-mantle source | 3He/4He of 2.0×10-8-1.1×10-5 | |
Crust source | 3He/4He < 2.0×10-8 | |
Atmosphere source | 3He/4He = 1.4×10-6 | |
According to rock type | Igneous rock | Granite, pegmatite, coal rock etc. |
Sedimentary rock | Black shale, bauxite, coal rock etc. | |
Metamorphic rock | Gneiss, granite gneiss, slate. | |
According to natural gas system | Natural gas system | Source, reservoir, and caprock rocks. |
Basement | Various rocks with rich U and Th in the ancient basement. | |
Mantle | Primordial 3He during Earth's formation. |
Table 3. Formation conditions and main controlling factors for the enrichment of typical helium-rich gas fields in key basins |
Basin | Tectonic unit/ region | Gas field/ region | Carrier gas types and features | Range and average of helium and non-hydrocarbon compositions | Formation conditions for helium-rich gas fields | Main controlling factors for helium enrichment | Ref. | |||||||||||||||||||||||||||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Main pay | Types and features | He/% | R/Ra | CO2/% | N2/% | Helium source conditions | Transport system conditions | Helium accumulation conditions | ||||||||||||||||||||||||||||||||||||||||||
Anadarko Basin | Amarillo Uplift | Panhandle oil/gas field | K, P, C | Hydrocarbon gas from carbonate rocks | 0.01-2.20 (0.55/882) | 0.21 | 0-11.7 (0.26/882) | 1-98.2 (12.7/882) | Cambrian- Precambrian igneous basement | He-rich pore water migrates along basement faults | Large-scale alkane gas and anhydrite-shale whole seal in uplift zone | Large-scale alkane gas occurs in secondary migration for long distances. The whole region has low porosity, low permeability, low fluid potential, shallow burial, and is near the helium source; Cenozoic tectonic activity caused depressurization expansion, degassing, and accumulation with formation water migration | [9, 10] | |||||||||||||||||||||||||||||||||||||
Hugoton Subsag | Hugoton gas field | P, C | 0.02-6.99 (0.52/687) | 0.18 | 0-11.60 (0.11/687) | 1.23-95.8 (16.60/687) | ||||||||||||||||||||||||||||||||||||||||||||
Paradox Basin | Doe Canyon | Doe Canyon gas field | C | He-rich carbon dioxide reservoir | 0.19-2.62 (0.78/8) | 0.15 | 73.49- 97.24 (91.74/8) | 2.27-19.9 (6.11/20) | Regionally widespread basement magma | Carrier gas is partially dissolved in He-rich formation water, and degases into reservoirs after secondary migration along deep and large faults | Cenozoic magmatism provides large-scale carrier gas; salts and anhydrite rocks wholly seal | Helium-rich formation water with large-scale CO2 co-migrates, degases, and accumulates | [9, 11] | |||||||||||||||||||||||||||||||||||||
Paradox-Unita- Piceance Basin | Uncom- pahgre Uplift | Harley Dome gas field | J | He-rich nitrogen reservoir | 0.11-7.31 (3.86/20) | 0.11 | 0-1.1 (0.47/20) | 10.7-91.7 (62.1/20) | Precambrian basement granite, metamorphic rocks | Migrate along basement faults vertically in a short distance | Favorable trap conditions; basin-grade intact shale seals regionally | Helium accumulates in tectonic highs, sandstone reservoirs are only 300 m above the Precambrian basement (shallow burial with an average well depth of 236 m), and low-pressure zones | [9, 12] | |||||||||||||||||||||||||||||||||||||
Persian Gulf Basin | Qatar Uplift | North Dome- South Par gas field | P, T | Hydrocarbon gas from carbonate rocks | 0.04% | 2.23 | 3.37 | Precambrian granite, metamorphic basement | Faults cut reservoirs and diagenesis modifies reservoirs. | Interbedded dolomite, limestone, and anhydrite provide good reservoir and cap rocks. | Low resource abundance and the world’s largest natural gas field, good conditions for trapping and preservation | [13, 14] | ||||||||||||||||||||||||||||||||||||||
East Siberian Basin | East Siberian Basin | Kovykta and Chayanda gas fields | Riphean, Vendian, —C | Hydrocarbon gas from carbonate rocks | 0.13%- 0.67% | 0.05- 1.29 | 0.1-0.3 | 1.5-25.26 | Archaean gneiss, crystalline schist, granite, rhyolite | Deep-large basement faults and unconformities | Carrier gas in high of the ancient uplift | Vertical and horizontal unobstructed transport system, carrier gas from ancient uplift, and lower Paleozoic regional thick salt layer as caprock | [15] | |||||||||||||||||||||||||||||||||||||
Ordos Basin | Yimeng Uplift | Dongsheng gas field | P | Tight sandstone gas | 0.045- 0.487 (0.111 8/ 166) | 0.022- 0.025 | 0.03-0.20 (0.115/6) | 0.81-1.34 (1.18/6) | Proterozoic-Archean metamorphic-granitic rocks in the basement; U and Th content of Hangjinqi area is (1.49-19.40)×10-3 mg/g, followed by Upper Paleozoic U- and Th-rich hydrocarbon source rocks | The secondary large faults of Borjianghaizi-Ulanjilinmiao and quaternary faults effectively connect the basement helium source rocks and reservoirs | Carrier gas accumulates on a large scale but in low resource abundance; favorable spatial-temporal match of reservoir, caprock, trap, and preservation conditions | Helium is generated from the ancient metamorphic- granitic basement and ancient U-/ Th-rich hydrocarbon source rocks of the Upper Paleozoic, where the helium source connecting faults of the secondary faults intersect with the transport system of the quaternary faults, and where the helium content decreases from bottom to top vertically | [16-21] | |||||||||||||||||||||||||||||||||||||
Yishaan Slope | Sulige gas field | P | Tight sandstone gas | 0.054- 0.091 (0.072/11) | 0.01- 0.03 | 0.65-2.64 (1.304/12) | 0.8-16.94 (3.168/12) | Lower Paleozoic basin basement with strongly magnetic deep metamorphic rocks and Upper Paleozoic U-/Th-rich hydrocarbon source rocks as helium sources | Basement faults, natural gas accumulation faults, and conduit layers | Carrier gas accumulates in large areas and scales but in low resource abundance; favorable spatial-temporal match of reservoir, seal, trap, and preservation conditions | Helium-rich basin basements and faults supply helium; low resource abundance, low pressure coefficients, and good sealing and preservation conditions in favorable areas | [20, 21] | ||||||||||||||||||||||||||||||||||||||
Qingyang gas field | P | Tight sandstone gas | 0.073- 0.237 (0.11/12) | 2.86-3.72 | 0.88-0.89 | U-/Th-rich ancient basement granite-metamorphic rocks and Upper Paleozoic U-/Th-rich hydrocarbon source rocks as helium source | Basement faults connect lower bedrock and upper natural gas accumulation system | Moderate scale, low charging degree, low fluid potential areas, local uplift areas | U-/Th-rich ancient basement helium sources and Upper Paleozoic hydrocarbon source rock as helium source, transport system, local uplift zone, and low-pressure carrier gas | [21, 22] | ||||||||||||||||||||||||||||||||||||||||
Middle of Jinxi Flexure Zone | Shixi block | P | Tight gas in the west, coalbed methane in the east | 0.02-0.23 (0.089/81) | 0.01- 0.08 (0.025) | 0-1.22 (0.33/81) | 0.04-19.46 (1.63/81) | The helium source of Jianjiagou-Zijinshan basement magmatic body and Upper Paleozoic hydrocarbon source rocks as helium source | Deep supracrustal/intracrustal faults in Lishi area; basin seal, favorable fault development zones | Moderate carrier gas abundance and size, multiple seals overlap | Two helium sources: basement and hydrocarbon source rock, favorable transport system, multiple reservoir- caprock combinations, and good preservation conditions | [23] | ||||||||||||||||||||||||||||||||||||||
Weihe Basin | Xianyang | Xianyang | N | Geothermal water- associated gas | 0.61-2.31 (1.666/7) | 0.037- 0.068 (0.055/7) | 0.05-11.05 (4.47/7) | 70.29- 98.00 (82.309/7) | Proterozoic-Archean granites and gneisses of the basin basement, and peripheral Yanshanian and Indosinian granites. U and Th content are (1.9-11.8)× 10-3 mg/g and (10.6- 27.5)×10-3 mg/g | Xingping-Xianyang section of the Weihe fault, Doumenzhen- Lintong fault, and Sangzhen-Qinduzhen fault | Geothermal water, hydrocarbon gases, and favorable occurrence and preservation conditions for carrier gas | Granite basement and high-quality source rocks of carboniferous-Permian coal strata, inherited anticline and dome-like trap on the basement uplift of the Weihe Basin, and dominant channels of the fault system that cut the granite basement | [24] | |||||||||||||||||||||||||||||||||||||
Xi’an | Xi’an | 0.42-3.23 (0.953/13) | 0.023- 0.060 (0.039 2/ 13) | 0.02-0.46 (0.153/13) | 79.62- 98.79 (88.525/ 13) | |||||||||||||||||||||||||||||||||||||||||||||
Weinan | Weinan | 0-0.86 (0.236/9) | 0.054- 0.157 | 0.04-2.75 (1.403/9) | 0.26-96.05 (26.811/9) | |||||||||||||||||||||||||||||||||||||||||||||
Tarim Basin | Southwestern Tarim Depression | Hotanhe | O, C | Condensate oil and gas | 0.300- 0.370 (0.316/10) | 0.06- 0.08 | 0.09- 1.36 | 10.39- 12.80 | Neoproterozoic granite helium source at the base of the platform-basin area, mainly crust-sourced helium and less mantle- sourced helium | Mazhatage deep-large fault and shallow structural seams | Favorable traps, crust, and mantle sourced helium and organic gases accumulate together | Basement helium sources; faults; Helium accumulates and enriches in the tectonic highs during the readjustment of Himalayan tectonic activities | [25, 26] | |||||||||||||||||||||||||||||||||||||
Akmomu (Ak 1) | K | Mixing of organic pyrolysis gas with less deep gas | 0.038- 0.093 | 0.549 | 13.33 | 8.97 | Crust-mantle sourced helium in the basin- mountain coupling area, dominated by Paleoproterozoic granite | A fault system formed by the interaction between the fault fold belt of the South Tianshan Mt. and the Kunlun Mt | Favorable trap conditions for carrier gas formed by source and fault connection | Crust-sourced helium in the basement matches the fault transport system, and part mantle-sourced components migrate to the crust through the fault-fold zone and accumulate | [26, 27] | |||||||||||||||||||||||||||||||||||||||
Northern Tarim Uplift | Hade, Yingmaili | C, E | Hade: Oil-type gas; Yingmaili: Coal-type gas | 0.000 2- 0.290 0 | 0.024- 0.062 | 0.12- 5.89 (1.99/7) | 2.58- 52.45 (15/7) | Helium source of basement granite and metamorphic rock in the platform-basin area | Basement faults and seal-fault systems of the basin | Crust-sourced helium from the Yingmaili gas field migrates to trap along with organic gases and accumulates | Favorable basement helium sources; fault systems; Himalayan tectonic activity; favorable traps and preservation conditions | |||||||||||||||||||||||||||||||||||||||
Sichuan Basin | Southern Sichuan Basin | Weiyuan | Z, —C, P | Cracking gas of crude oil | 0.003- 0.342 (0.192/21) | 0.013- 0.022 | 1.23-5.07 (4.064/10) | 0.4-26.7 (6.872/22) | Pre-Sinian basement granite, Cambrian Qiongzhusi Formation shale, and Silurian Longmaxi Formation shale | Faults, fractures, pores, and other groundwater migration channels | Ancient uplift; long- distance migration, accumulation and adjustment along slope; extraction of helium in formation fluids | The helium source of the pre-Sinian granite basement; the U-/Th-rich mud shale of the Jiulaodong Formation; the ancient uplift with favorable trap conditions for helium accumulation in paleo-uplift | [28-31] | |||||||||||||||||||||||||||||||||||||
Eastern Sichuan Basin | Fuling | O—S | Shale gas | 0.034- 0.062 (0.045/44) | 0.05-0.37 (0.22/18) | 0.80-2.19 (0.89/18) | The contents of radioactive U and Th in shale are generally higher. The U content is (5.97-38.12)× 10-3 mg/g, averaging 24× 10-3 mg/g; The U content is (6.61-22.81)×10-3 mg/g, averaging 20×10-3 mg/g. There is a contribution of the basement helium source | Basement faults and caprock serve gas accumulation | The self-generated and self-stored carrier gas coexists with the self-generated and self-stored helium; U-/Th-rich basement helium source; the top and bottom plates seal; and the preservation conditions are good | The Wufeng Formation- Longmaxi Formation shale and U-/Th-rich basement are helium sources; and the shale gas layer has thick top and bottom plates with tight lithology, high breakthrough pressure, good sealing and preservation performance | [32, 33] | |||||||||||||||||||||||||||||||||||||||
Middle Sichuan Basin | Ziyang | Z2d | Hydrocarbon gas | 0.01- 0.32 (0.115/6) | 0.01-6.59 (3.925/6) | 0.97- 11.88 (4.835/6) | Pre-Sinian granite | Basement faults and fault systems in the caprock of the basin | Favorable carrier gas reservoir and trap conditions; Weiyuan gas field was uplifted by 4 000 m during the Himalayan period | The basement granite helium source; fault system; favorable natural gas carrier conditions; and late adjustment led to low helium content | [34, 35] | |||||||||||||||||||||||||||||||||||||||
Qaidam Basin | Dongping Slope | Dongping gas field | Bedrock | Cracking gas of crude oil | 0.045- 1.069 (0.331/31) | 0.007- 0.090 (0.031/4) | 0.01-2.02 (0.293/31) | 2.359- 30.490 (12.624/40) | Proterozoic, Caledonian and Indosinian granite and granodiorite and metamorphic basements | SN-trending deep-large faults and regional unconformities in the slope zone | Dongping Slope is between multiple hydrocarbon generation sags and has good carrier gases | The granite and granitic gneiss basement are widely distributed, and have the conditions for forming high helium content in the weathered crust of the bedrock and its highs | [36-38] | |||||||||||||||||||||||||||||||||||||
Jiandingshan Structure | Jianbei gas field | Bedrock, E | Crude oil cracking gas | 0.160- 0.569 (0.277/4) | 0.01-0.504 (0.139/4) | 15.54- 22.34 (17.473/4) | Proterozoic and Paleozoic basement granite or granitic gneiss | Basement faults and regional unconformities | Tectonic highs, with favorable conditions for the accumulation and preservation of carrier gases | The basement helium source and transport system are matched with favorable migration, accumulation, and preservation conditions | ||||||||||||||||||||||||||||||||||||||||
Songliao Basin | Changling Rift | Changling Sag | K | High CO2 content | 0-0.03 (0.008/7) | 1.9-2.3 (2.071/7) | 0.02-97.18 (17.95/15) | 0-6.73 (2.368/15) | Mantle source, basement granite, acidic volcanic rocks, and some sedimentary rocks | Deep-large faults, basin caprock faults and transport layer | Favorable carrier gas trap and preservation conditions; tectonic highs | The crust-mantle-sourced helium and the transport system match well with favorable traps | [39] | |||||||||||||||||||||||||||||||||||||
Xujiaweizi Rift | Qingshen gas field | C, P, J, K | Mainly hydrocarbon gas | 0.001 6- 0.046 0 (0.018/20) | 0.771- 5.843 (1.601/20) | 0.000 3- 95.830 0 (10.528/20) | 0.33-10.24 (2.503/20) | Mantle source; basement granite; from Yingcheng Formation to Huoshiling Formation, the U content of volcanic rocks is (2.42- 2.90)×10-3 mg/g, and the Th content is (4.14- 7.80)×10-3 mg/g | Xushen fault, secondary faults, and transport layer | Tectonic highs, favorable carrier gas trap, and preservation conditions | Deep-large faults, basement and mantle-sourced helium, and tectonic highs match well with favorable traps | [40] | ||||||||||||||||||||||||||||||||||||||
Bohai Bay Basin | Jiyang Depression | Pingfangwang gas field, Pingnan, Hua 17, Gaoqing, Yangxin | E, N | CO2 reservoir | 0.008 4- 0.084 7 (0.030/10) | 2.00-3.73 (2.84/13) | 68.85- 98.59 (84.635/19) | 0.06-5.43 (1.155/17) | Basement acid intrusive rocks, volcanic rocks, and organic-rich mud shale in the basin | Tanlu fault and branch system, natural gas transport system | Deep-large faults connecting favorable trap and preservation conditions | Tanlu (or branch) faults, basement, and deep helium source match well with favorable traps | [41] | |||||||||||||||||||||||||||||||||||||
Huanghua Depression | Gangxi fault, Gangdong fault, Banqiao Sag | E, N | CO2 reservoir | 0.001- 0.048 (0.012/14) | 0.24-3.62 (1.66/20) | 0.26-93.61 (11.250/20) | 0.19-1.91 (1.001/17) | Basement basic- intermediate to acidic magmatic rocks | Gangxi/Gangdong faults and magmas are migration carriers of mantle- sourced helium | Favorable trapping and preservation conditions for carrier gas near faults | Areas with favorable trap and preservation conditions near deep faults and active magma zones | [42] |
Note: The data after “/” means the sampling counts. The formation conditions and main enrichment factors of helium-rich gas fields in this table are based on references [9⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓-42]. The preliminary conclusions are extracted from exploration and production performance analysis combined with regional geological conditions. |
2.1. Helium source conditions and genesis identification
2.2. Helium migration conditions and mechanisms
Fig. 4. Schematic diagram of the "generation-migration-accumulation" process of helium. |
2.3. Accumulation and preservation
Fig. 5. Helium dissipation in seal under different medium conditions. (a) Schematic diagram of reservoir-caprock assemblage and micro-fractures in a gas reservoir; (b) SEM photograph of a shale [55]; (c) Pore distribution of the shale in Silurian Longmaxi Formation [56]; (d) Distribution of full pore sizes of shale pore volume in Silurian Longmaxi Formation [57]; (e) Anhydrous and gas-containing state of micro-fractures; (f) Gas-water mixed state of micro-fractures; (g) High aqueous state of micro-fractures; (h) Anhydrous gas-containing state of wide fractures; (i) Gas-water mixed state of wide fractures; (j) High aqueous state of wide fractures. |
Table 4. Diffusion coefficients of common natural gas components in water (25 °C) [64] |
Natural gas components | Diffusion coefficients/(10−5 cm2·s−1) |
---|---|
Air | 2.00 |
Ar | 2.00 |
CO2 | 1.92 |
C2H6 | 1.20 |
He | 6.28 |
H2 | 4.50 |
H2S | 1.41 |
CH4 | 1.49 |
N2 | 1.88 |
O2 | 2.10 |
3. Helium enrichment and distribution patterns
Table 5. Comparison of formation conditions and geological characteristics of helium between China and North America [71] |
Location | Geological background | Helium source rock | Reservoir characteristics | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Tectonic background | Sedimentary background | Types of source rock and organic matter | U, Th contents | Basement helium source rock | Deep mantle helium source | Main lithology | Reservoir distribution | ||||||||
North America | Stable tectonic background. | Mainly marine sediments. | Marine source rock, simple type of organic matter. | Higher content and stable distribution. | Ancient large craton releases much helium from U and Th decay. | Mainly in large tectonic magmatic activity zones (island arc and earthquake zones, etc.) | Carbonate rocks, clastic rocks. | Larger, stable, and continuous reservoirs. | |||||||
China | Multiple cyclic tectonic evolutions, strong late tectonic activities. | Marine, paralic, and continental facies. | Source rocks in marine, lacustrine, and paralic facies, and complex types of organic matter. | Various contents and strong heterogeneity. | Medium-small cratons release various amounts of helium from U and Th decay. | Eastern extensional region. | Carbonate rocks, clastic rocks, lacustrine carbonate rocks. | Small reservoirs with strong heterogeneity and worse continuity. | |||||||
Location | Transport system | Helium-rich/bearing reservoir characteristics | Preservation conditions | ||||||||||||
Basin basement | Basin caprock | Carrier gas | Helium | Sealing and preservation | Late destruction and adjustment | ||||||||||
North America | A relatively simple transport system, and a shorter distance. | Relatively simple types and structures of the transport system of marine geology bodies. | Large gas reservoirs/fields, complex and diverse components. | Generally higher content, wide distribution of helium- rich resources (>0.30%). | Relatively stable distribution of caprocks, better-sealing performance, and preservation conditions. | Relatively stable tectonic background, weaker late destruction and adjustment. | |||||||||
China | Relatively complex transport system, larger distance differences between east and west regions. | Relatively complex types and structures of the transport system of continental geological bodies. | Small gas reservoirs/fields, mainly hydrocarbon components, and small CO2-rich and N2-rich gas reservoirs/fields. | Generally lower content, and most helium resources are lean with a volume fraction of ~0.10% or below. | Unstable distribution of caprocks, worse sealing performance and storage conditions. | Relatively strong tectonic activity, stronger late destruction and adjustment. |
3.1. Helium sources on an effective scale are the resource base for the formation of helium-rich fields
3.2. Advantageous transport systems and favorable carrier media are necessary conditions for helium migration from the source to the carrier gas trap
3.3. Favorable helium-accumulating carriers and preservation conditions are key to the formation of helium-rich/containing gas fields
Fig. 10. Geochemical distribution of helium tectonic geochemical zones in petroliferous basins in China (modified from Ref. [87]). |
Fig. 11. Schematic diagram of the framework model of helium "source-migration-accumulation". |