Abstract
Helium, a rare gas widely applied in high-tech fields, is a significant strategic resource in China. The foreign-trade dependence ratio of helium in China is 95%. The work reviewed the applications and market analysis of helium and reservoir modeling and distribution of helium in Changqing Gas Field as well as the helium extraction techniques from natural gases. According to the analysis of the component test and the dynamic monitoring of exploited gas wells and gas-gathering stations, the average helium content in Changqing Gas Field was 0.028%. Helium was rich in the northwest of Changqing Gas Field, but poor in the central and eastern regions. The helium volume contents in Qingyang Gas Field, Huanglong Gas Field, and the central, western, and southern regions of Sulige Gas Field have reached the industrial development standard. PetroChina performed the economic-feasibility evaluation and production-factor matching research on helium development and selected Changqing Gas Field as the demonstration for development. A large helium plant was established in Changqing Gas Field using the cryogenic method with/without membrane separation for helium extraction. Then, a helium development scheme was formulated and implemented to build the industry chain of helium in China. Changqing Gas Field is rich in helium resources. Developing helium has entered a strategic period with the technological advancement in extracting helium from natural gases and the increased prosperity of the international helium market. There are broad prospects and great benefits to exploiting helium resources in Changqing.
1. Introduction
Energy security has become a major strategic support for national economic development. China has put forward the ambitious goal of peaking carbon dioxide emissions before 2030 and will strive for carbon neutrality before 2060. The energy field will also be changed. Traditional oil and gas companies face severe challenges concerning economic benefits in achieving carbon neutrality and low-carbon transformation. The “14th Five-Year Plan” is crucial for reforming China’s energy sectors. The oil consumption is expected to reach its peak during the period. As natural gases are important chemical raw materials that are low-carbon and energy-saving, the demand for them increases rapidly. About 40% of the global natural-gas output is used for the chemical industry, 20% for civil use, 25% for commerce and electricity, and 15% for other uses. The demand for natural-gas chemical products such as synthetic ammonia, methanol, and acetylene is still growing steadily, but the natural-gas product structure is gradually adjusted for high technology contents and high added values. Developed countries have taken helium extraction from natural gases as a key business [1].
Helium is one of the most favored industrial gases for global manufacturing due to its amazing properties. The supply and demand relationship in the global helium market is tense, with rising prices. China’s demand for helium increases rapidly, but it heavily relies on imports. With the mature helium extraction technology, Changqing Oilfield plans to build a large helium extraction plant to develop rich helium resources in the Ordos Basin. Therefore, the deep processing and comprehensive utilization of downstream natural gases should be expanded based on strengthening the main business of upstream natural-gas exploration and development. It is a rational choice for oil and gas companies to realize the integrated development of oil and gas and new energy as well as a business chain with upstream and downstream multienergy complementarity.
2. Applications of Helium
Helium is widely used for its unique properties, such as low boiling point, low density, low solubility, high thermal conductivity, and inertia [2]. It is used for magnetic resonance imaging, lifting gases, analytical and laboratory applications, welding, engineering and scientific applications, leak detections, and semiconductor manufacturing [3] (see Figure 1). The electronic market, dominated by the United States, represents one of the key terminal applications of helium. The Asia-Pacific region is one of the major semiconductor powerhouses, with Japan, South Korea, and China and Taiwan Province providing semiconductors and electronic components for the globe. Technological progress, increasing demand, and increased research centers support the expanded helium market.
The largest use of helium (about 32% of the total output) is to create a low-temperature environment. Liquid helium is a popular low-temperature material used to manufacture superconducting magnets and study superconducting phenomena [3]. It is also used as a cooling medium for various magnets in the special processes for medical NMR spectrometers and MRI scanners [4]. Helium is irreplaceable due to its minimum specific heat of the lowest boiling point or melting point of any gases and elements. The atomic mass of helium is the second smallest among all elements, only smaller than the relative atomic mass of hydrogen. As a gas lighter than air, helium has been employed as the lifting gas for airships and balloons, such as airships, Led Zeppelin, antiaircraft balloons, and weather balloons. That is the most important application of helium until the end of World War II because it is inflammable and much safer than hydrogen.
Helium has the lowest melting and boiling points of all gases, melting and boiling at temperatures close to absolute zero. Being a gas at very low temperatures, it can be used as a purge gas for fuel tanks and fuel delivery systems [5]. These systems are filled with cold liquids such as liquid hydrogen and liquid oxygen. Helium can replace these fuels without freezing because it is inert with a low freezing temperature. NASA uses large amounts of helium to purge rocket propulsion systems [2]. This low reactivity makes helium a valuable gas used in manufacturing and repair processes when an inert atmosphere is required.
Helium also has the second-lowest density of all gases, while its thermal conductivity is very high. These properties make helium used as a shielding gas in the growth of silicon and germanium crystals, titanium and zirconium production, and gas chromatography. Also, it is useful in supersonic wind tunnels and pulse equipment.
Helium has a very low viscosity and a high diffusion coefficient, making it the smallest atom of any element. Helium escapes if the container leaks; therefore, it is used to test leaks in high vacuum systems, fuel systems, and other containers. Helium and other inert gases are used to prepare breathing mixtures for deep-water diving and medical treatment because it is inert with very low viscosity and breathes more easily than any other gas under pressure. Helium is also used in welding as a protective atmosphere. An inert gas atmosphere protects the hot metal from oxidation and other reactions that occur rapidly at high temperatures.
3. Market Analysis of Helium
According to section 16 of the U.S. Public Law 113-40, the United States Geological Survey (USGS) was required to complete a national helium assessment. It has been finished coordinately by the Bureau of Land Management (BLM) and the USGS in fall 2021. The mean volume of recoverable helium within the known geologic natural gas reservoirs in the United States was estimated to be 8,490 million cubic meters (306 billion cubic feet). The BLM has analyzed about 22,720 natural gas samples from 26 countries and the United States in a plan to examine the worldwide helium resources as of December 31, 2021. According to a report on mineral products released by the USGS in 2021, the global total helium resource was estimated to be about m3, in which m3 of the main mineral deposits and resources was distributed in the United States, m3 in Qatar, m3 in Algeria, m3 in Russia, m3 in Canada, and m3 in China (see Figure 2). Besides, Poland and Australia also had some helium resources.
The U.S. government established the national helium reserve in Amarillo, Texas, in 1925 to supply military airships in wartime. Meanwhile, as a monopolist of helium, the U.S. promulgated the Helium Act to prohibit its export. After World War II, the helium market was sluggish, but the reserve was expanded in the 1950s to ensure the supply of liquid helium as a coolant. Therefore, rocket fuels of oxygen or hydrogen were manufactured during the space race and the Cold War [8]. The U.S. Congress passed the Helium Privatization Act in 1996 to reduce helium reserves and began to sell helium in 2005 due to the excessive liabilities of helium reserves [9]. All-natural gas used to process helium in the United States comes from Colorado [10], Kansas, Oklahoma [11], Texas, Utah, and Wyoming. The natural gas produced by these gas fields contains 0.3% to more than 7% helium.
Helium is extracted from natural gases for commercial sales [1]. The United States has produced more than 90% of the world’s commercial helium since the early 1990s. A new factory in Arzew, Algeria, began to operate with an output of m3 until the mid-1990s. Factories such as Ras Laffan in Qatar and Skikda in Algeria were put into operation one after another from 2004 to 2006. New helium plants went into production in Qatar, Russia, and Wyoming in 2021 [7]. Russia will build m3 helium plants in 2024, but the helium shortage cannot be relieved as expected (see Figure 3).
The price of crude helium in the US market is calculated by BLM according to the lowest price formula of helium stipulated by the Helium Act, and it is linked to the CPI index. Figure 4 shows the open market price trend of crude helium in the United States. Especially after the BLM added enrichment index and protection index to the minimum price formula of helium in 2011, the price of crude helium continued to rise. Then, the auction system of helium sales and supply quota was opened [9], leading to further market tension (see Figure 4).
When the whole world is haunted by COVID-19 in 2019, the sales of the global helium market were estimated to be US$ 2.2 billion in 2020 and expected to reach the revised US$ 2.8 billion by 2026, with a compound annual growth rate (CAGR) of 4.3%. The helium market in the United States would be worth 607.4 million dollars in 2021. At present, China has a market share of 27.01% in the global helium market, consuming about 4,300 tons of helium every year. The CAGR of Japan and Canada is expected to increase by 3 and 4.1%, respectively. In Europe, the CAGR of Germany is expected to be about 3.3%, while other European markets will reach 411.5 million US dollars. However, the helium production capacity in China is weak, and 95% of helium is heavily dependent on imports. It is projected that the helium market scale of China will reach 387.6 million US dollars by 2026, with a CAGR of 5.8% in the whole analysis period.
Changqing Gas Field is the largest natural gas field in China. In 2021, 46.523 billion cubic meters of natural gases were produced. Local areas are rich in helium, with the huge geological reserves of helium. The industrial development plan for helium resources will make Changqing Gas Field the first and largest commercial helium source in China. Good economic benefits can be achieved, with a safe and reliable Chinese helium industry chain established.
4. Accumulation and Enrichment of Helium
Most of the helium on the earth comes from radioactive decay. Helium is also abundant in minerals containing uranium and thorium [12], including uraninite and its varieties such as cleveite, pitchblende, vanadate, and monazite [13]. The helium concentration in the crust is 8 parts per billion, while it is only 4 parts per trillion in seawater. Besides, a small amount of helium exists in mineral springs, volcanic gases, and siderite [14, 15]. The maximum natural helium concentration on the earth is in natural gases, from which the most commercial helium is extracted [11].
There are three main geological conditions for helium enrichment [16]: (1) granite bedrock is rich in uranium and thorium. (2) Cracks and faults in basement rocks provide escape channels for helium. (3) The porous sedimentary rocks above the basement fault have impervious rock salts or anhydrite-rich caprock (see Figure 5). The decay of uranium and thorium in granite bedrock produces helium, and the released buoyant helium moves to the surface in the pores related to the basement fault. Helium then migrates upward through the porous sediment layer until it is trapped under an anhydrite or salt layer with natural gases [17, 18].
Helium has the maximum atomic radius of about 0.2 nm among all elements. Therefore, it can pass through the very small pores inside sedimentary rocks after forming [19]. Rock salts and anhydrite are the only caprocks that can prevent helium atoms from moving upward. Shales filled with organic matter (kerogen) in pore space sometimes act as barriers with low efficiency (see Figure 5).
The discovered helium resources in the world are mainly distributed in sedimentary basins under the background of the late Proterozoic-Paleozoic platform [20]. Besides, the basement area with strong tectonic-magmatic activities [21] and ancient granites in the Meso-Cenozoic era develops helium-rich reservoirs [22].
Helium resources in China are discovered to be mainly concentrated in the central-western Sichuan Basin [23], Tarim Basin [24], Ordos Basin [25], southern Weihe fault depression [26], Qaidam Basin, and oil-bearing basins such as the Subei Basin on both sides of the eastern Tanlu fault zone, Bohai Bay Basin [27], Hailar Basin, Songliao Basin [28], and Sanshui Basin. Furthermore, helium is also found in geothermal wells and hot springs in some areas. Helium mainly comes from the crust [29] by analyzing the geological conditions of forming helium in Changqing Gas Field, including the helium-source basement rocks [30], helium migration, and reservoir caprock [25, 31].
The basement rocks of the Proterozoic Erathem and Archaean rich in radioactive elements uranium and thorium in the Changqing Gas Field generate helium during the decay of uranium and thorium. Then, tectonic movements cause the basement to fracture. Helium migrates diffusely through rock pores and pore water along basement faults. High water/gas volumetric ratio and low pressure favoured higher helium concentrations in gas [11]. It is collected and preserved under the barrier of multiple sets of huge thick salt rocks in the Majiagou formation of the Lower Ordovician system, the upper Shihezi formation of the Middle Permian system, and the huge thick mudstone caprocks of the Shiqianfeng formation of the Upper Permian system. Helium is finally filled in the carbonate gas reservoirs of the Majiagou formation and the sandstone gas reservoirs of the Lower Shihezi formation and Shanxi formation (as shown in Figure 5). Brown proposed that Paleozoic strata sedimentary rocks and crystalline basement were two generalized helium sources. Refer to the analytical models to evaluate helium generation and migration in Panhandle–Hugoton field [11], a sedimentary source should be considered main (50% or more) for helium in gas accumulations in the Changqing gas field, the basement-sourced helium contributes approximately 20%-30% of the total helium, and hydrodynamics contributes the rest.
5. Distribution of Helium in Changqing Gas Field
Most raw natural gases contain trace amounts of helium, but few contain enough helium for exploitation [6]. A natural gas reservoir containing at least 0.3% helium can be considered a potential source of helium. Although the decay of radioactive minerals in the crust continuously produces helium, it accumulates helium at a very slow rate. Therefore, helium must be listed as a nonrenewable resource. The international standards for evaluating whether helium-containing natural gas fields reach the industrial level are as follows: fields extremely rich in helium (helium volume ), helium-rich fields (helium volume -0.5%), helium-bearing fields (helium volume -0.15%), helium-lean fields (helium volume -0.05%), and fields extremely lean in helium (helium volume ) (see Table 1).
The east and north of the Ordos Basin have low helium contents, and the west and south have high helium contents [32]. In the west of Ordos Basin, helium-bearing gas fields include the southern, central, and western areas and Gaoqiao region of Sulige Gas Field, Qingyang Gas Field, and Jingbian Gas Field. In the eastern Ordos Basin, helium-lean gas fields include the eastern area of Sulige and the south area of Sudong, Yichuan Gas Field, Zizhou Mizhi Gas Field, Yulin Gas Field, and Shenmu Gas Field. Huanglong Gas Field is rich in helium (see Figure 6).
According to the statistics of 30,711 gas component tests of 6,655 wells in Changqing Gas Field, helium was measured by gas chromatography (see Figure 7); the average volume content of helium in natural gases is 0.028%. 18.9% of gas wells do not contain helium, the median helium volume content is 0.026%, and the average is 0.040%. However, the analysis of the natural gas composition of 925 gas wells with more than 10 tests in gas fields over years shows that the average helium content and the maximum helium content of a single well are different, indicating that the helium content in natural gases produced by a single gas well is unstable.
According to the data from the composition test of natural gases, the helium content in natural gases in Changqing Gas Field is relatively lean, and the helium content in a single well is unstable. However, the total amount of helium resources is considerable. According to the natural gases output of Changqing Gas Field in 2021, there are about 2,000 tons of helium in the natural gases produced. Therefore, studying the helium extraction process from natural gases and the separation and recycling of helium can increase the added value of natural-gases products and has important strategic significance for the helium supply in China.
6. Helium Extraction Process from Natural Gases
The process of extracting helium from natural gases mainly includes the low/nonlow temperature method. Table 2 shows that the low-temperature method is used to extract crude helium with a volume content of 40 to 70%. Then, crude helium is refined to get grade-A helium. The low-temperature method, pressure adsorption method, and low-temperature adsorption method are adopted in this step.
The technological method of using low temperatures for deep cooling is relatively mature and has been widely used in the helium extraction process and most helium extraction projects in the U.S. Since helium has a lower boiling point than any other elements, low temperatures and high pressures are used to liquefy almost all other gases (mainly nitrogen and methane). Crude helium is purified by exposure to low temperatures, and all remaining nitrogen and other gases are separated from the gas mixture.
According to the engineering experience from overseas, the helium recovery rate using the deep cooling method is usually larger than 95%, with the good stability of the whole system. However, the investment and energy consumption in this process are slightly high. The adsorption method and membrane osmosis method play a role in gas separation with the advanced synthetic materials and automation technology [33]. They can also be combined with the low-temperature method for industrial helium extraction.
The techniques for extracting helium from natural gases are often used in combination. Taking the Ras Laffan Helium Plant built by the Qatar Natural Gas company in 2005 as an example, its production output of liquid helium is 8.65 tons/day [35]. A combined process of low-temperature distillation of crude helium, dehydrogenation through catalytic oxidation, and pressure swing adsorption to purify crude helium is adopted (see Figure 8). Raw helium-containing gases are from the crude helium (without CO2, heavy hydrocarbon, water, and mercury) produced by the seven LNG plants located upstream. Those plants have set up helium recovery units, which use a low-temperature distillation process and increase the helium content to 45%. Then, helium is purified by low-temperature distillation, dehydrogenation through catalytic oxidation, cooling dehydration, and pressure swing absorption.
Based on the practical situation [37], deep cooling and membrane separation are more suitable for the helium extraction projects in Changqing Gas Field by comparing several techniques of extracting helium from natural gases. In Figure 9, the deep cooling process involves the pretreatment of natural gases, crude helium extraction, and helium purification. (1) Pretreatment: the devices to decarbonize and dehydrate naturally. (2) Crude helium extraction: low-temperature distillation device, low-pressure methane compressor, medium-pressure methane compressor, high-pressure methane compressor, and nitrogen refrigerant compressor. (3) Helium purification: catalytic-oxidation dehydrogenation device, crude helium molecule dehydration device, pressure-swing-adsorption purifying device, and low-temperature adsorption device. If deep cooling is directly used to extract helium, more energy will be consumed. When the helium price is lower than 200 yuan/Nm3, the deep cooling process is not appropriate and needs to be further optimized to reduce energy consumption.
The membrane gas separation technique has great potential in processing and purifying helium [38]. Using polymeric and inorganic membrane as the supplementing aids for helium recovery and purification is technically feasible [39]. The helium extraction process of membrane separation and deep cooling includes helium content extraction, crude helium extraction, and helium purification. (1) Helium extraction: filter separator, centrifugal compressor with permeator, and membrane separation device. (2) Crude helium extraction: alcohol-amine-solution decarbonization device, molecule dehydration device, mixed refrigerant compressor, natural-gas compressor, and low-temperature distillation device. (3) Helium purification: catalytic-oxidation dehydrogenation device, crude-helium molecule dehydration device, pressure-swing-adsorption purifying device, and low-temperature adsorption device (see Figure 10).
A comprehensive economic evaluation of the helium extraction project from natural gases in Changqing was carried out according to the plane distribution of helium contents, the local government’s energy-saving and environmental protection requirements, the technical costs of different helium extraction processes, and the market price of helium [40]. When the market price of the helium gas is lower than 125 yuan/Nm3, the feasibility of building the helium extraction plant in Changqing Gas Field decreases. The project is feasible when the market price of helium is higher than 130-140 yuan/Nm3 by analyzing the financial indices of helium at different prices (see Table 3). Changqing Helium Extraction Plant is planned to be built with an annual helium production scale of 700,104 Nm3, an area of 13.3 hectares, and an investment of 4.5 billion USD. The construction period is 2 years, with an operation period of 20 years, and the project approved for 3 billion yuan. Based on the unit price of 125 yuan/Nm3, the internal return rate (IRR) of the project is 7.04%, with a return on investment (ROI) period of 10.88 years, and its total investment return rate of 5.57% [41].
7. Conclusions
Helium is a unique, special, and rare element, facing severe supply shortages. Natural gases as clean low-carbon energy are in great demand in China. With the development of high technology, high-value-added helium is extracted from natural gases, which has broad prospects. Its market price continues to rise. Changqing Gas Field has a huge amount of helium resources with its northwestern area rich in helium, while helium is in shortage in its central and eastern areas.
Helium reservoirs in Qingyang, Huanglong, and the central, western, and southern of Sulige have a high value for industrial development and are of great strategic significance to ensure the security of helium supply in China. China should push forward the leapfrog development of the helium supply chain in its extraction, condensation, storage, shipping, selling, and pricing system. Great efforts should be taken to promote the basic geological survey and research, make technological breakthroughs in its extraction from natural gases, and formulate encouraging and supporting policies. The development plan for the helium extraction from the natural gas project in Changqing Gas Field is proposed as follows: (1)Strengthen the dynamic monitoring of the helium contents in Changqing Gas Field to lay a solid foundation for its future extraction(2)Study the geological conditions of the formation and enrichment of helium in Changqing Gas Field to evaluate the potential of helium resources, especially the basement and faults of helium source rocks rich in uranium and thorium, the migration and accumulation mode of helium, and caprock(3)Given the large natural gas production and low helium contents in Changqing Gas Field, transformed and optimized techniques should be developed for the low-cost helium extraction process. Besides, natural-gas comprehensive utilization plants are required to be established
Data Availability
The data used to support the findings of the work are available from the corresponding author upon request.
Conflicts of Interest
The authors declare that there is no conflict of interest.
Acknowledgments
The authors gratefully acknowledge the professor level senior engineer Wei Xinshan, who provided help during the research and preparation of the manuscript. The work was supported by the National Science and Technology Major Project (Grant No. 2016ZX05050) and the National Natural Science Foundation of China (Grant No. 41872166).