Yo Wng, Chi-hui Guo, Shu-rong Zhung, Xi-ji Chn, Li-qiong Ji, Z-yu Chn, Zi-long Xi,Zhn Wu

a Development and Research Center of China Geological Survey, Beijing 100037, China

b China University of Geosciences (Beijing), Beijing 100083, China

c East China Normal University, Shanghai 200241, China

d China Institute of Water Resources and Hydropower Research, Beijing 100038, China

e Nanjing University, Nanjing 210000,China

Keywords:Carbon neutrality Carbon peaking Carbon emissions Carbon sequestration Key minerals Renewable energy Climate change Geosciences Geological technology China

ABSTRACT In the context of global climate change, geosciences provide an important geological solution to achieve the goal of carbon neutrality, China’s geosciences and geological technologies can play an important role in solving the problem of carbon neutrality. This paper discusses the main problems, opportunities, and challenges that can be solved by the participation of geosciences in carbon neutrality, as well as China’s response to them. The main scientific problems involved and the geological work carried out mainly fall into three categories: (1) Carbon emission reduction technology (natural gas hydrate, geothermal, hot dry rock, nuclear energy, hydropower, wind energy, solar energy, hydrogen energy); (2) carbon sequestration technology (carbon capture and storage, underground space utilization); (3) key minerals needed to support carbon neutralization (raw materials for energy transformation, carbon reduction technology).Therefore, geosciences and geological technologies are needed: First, actively participate in the development of green energy such as natural gas, geothermal energy, hydropower, hot dry rock, and key energy minerals, and develop exploration and exploitation technologies such as geothermal energy and natural gas; the second is to do a good job in geological support for new energy site selection, carry out an in-depth study on geotechnical feasibility and mitigation measures, and form the basis of relevant economic decisions to reduce costs and prevent geological disasters; the third is to develop and coordinate relevant departments of geosciences, organize and carry out strategic research on natural resources, carry out theoretical system research on global climate change and other issues under the guidance of earth system science theory, and coordinate frontier scientific information and advanced technological tools of various disciplines. The goal of carbon neutrality provides new opportunities and challenges for geosciences research. In the future, it is necessary to provide theoretical and technical support from various aspects, enhance the ability of climate adaptation, and support the realization of the goal of carbon peaking and carbon neutrality.

1. Introduction

Climate change has brought about frequent extreme events in recent years. The ocean ecosystem was degraded severely,including ocean acidification, sea-level rise, and glaciers retreat. The extreme weather and climate events not only resulted in major economic loss, but also caused many human death and injuries, and also increased the incidence of infectious diseases which has big impacts on human society(Hashim JH and Hashim Z, 2016). Climate change is mainly caused by increasing CO2, CH4,and other greenhouse gases,which are produced from the combustion of fossil fuels. The Paris Agreement adopted by 195 nations at the 21st Conference of the Parties to the UNFCCC in December 2015 included the aim of strengthening the global response to the threat of climate change by “holding the increase in the global average temperature to well below 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5°C above pre-industrial levels”. However, the World Meteorological Organization (WMO) report on the Global Climate in 2015–2019 shows that the global average temperature has increased by 1.1°C since the pre-industrial period, current plan and progress can hardly reach the requirement of the Paris Agreement (Yeh TK et al., 2019).

To address the negative impacts of climate change, carbon neutrality targets were proposed by the global society.“Carbon neutrality” or “Net zero carbon” is a term used to describe the state of an entity (such as a company, service,product, or event), where the carbon emissions caused by them have been balanced directly, or indirectly, out by carbon saving measures such as replacing fossil fuels with renewable energy, planting trees, energy-saving and carbon reduction. In September of 2020, Chinese goverment has declared that China would scale up its nationally determined contributions and adopt more vigorous policies and measures to peak carbon dioxide emissions before 2030 and achieve carbon neutrality before 2060 at the General Debate of the 75th Session of the United Nations General Assembly.

Geosciences and geological technologies have played a critical role in achieving the carbon neutrality target. In 2020,World Bank released a report on “Minerals for Climate Action: The Mineral Intensity of the Clean Energy Transition”, which states that the low carbon future is mineral intensive, so geological work must play an important role.The origin and formation of geological minerals should be understood which are indispensable parts of electric cars’battery and wind turbine, then enhance the exploration and extraction intensity. Stephenson M and colleagues have argued that geosciences are very important for decarbonization, its role in the process of carbon neutrality is unique and incomparable (Stephenson M, 2018). Here the authors proposed several scientific questions which need to be addressed in carbon neutrality by the geoscience community of China, and examined the role and contribution of geosciences and geological technologies in this process, and defined opportunities for geosciences and geological technologies to contribute to carbon neutrality.

2. Research background

2.1. The role of geosciences in carbon neutrality

For a long time, geoscience has been an important part of the research of carbon neutrality. The importance of geoscience to carbon neutrality research can be summarized into three aspects: Research on carbon reduction and carbon sequestration technology, exploration of new energy and raw materials required for new energy, and help for the development of new energy.

From the perspective of geoscience, the increase of global average temperature is mainly caused by changes in the intensity of solar activity, changes in atmospheric aerosol concentration, changes in land use, and ocean interactions(Wang SW et al., 2010). Many scholars in the field of geoscience research have pointed out that the rapid industrialization and urbanization of human society in the past 100 years is one of the most important factors leading to global climate change (Tong XH et al., 2020). Due to the large-scale use of fossil fuels in the industrial revolution,global CO2emissions have increased rapidly, triggering the greenhouse effect. Focusing on this issue in the field of geosciences, many scholars have done a lot of research on the carbon cycle, carbon capture, and carbon sequestration, and put forward a lot of feasible measures.

Currently, China’s energy consumption is still dominated by coal power (Fig. 1). To achieve the goal of carbon neutrality, it is essential to accelerate the development of clean energy, and geoscience can provide support in this regard. To meet the requirements of sustainable development,China has taken a lot of measures to improve the energy consumption pattern and consumption structure, which reduce the dependence on fossil energy. The development of environmentally friendly, clean, widely sourced, and highly efficient new energy has become an urgent need for China’s energy market (Yan Q et al., 2010). As one of the key points of geoscience, mineral exploration engineering has played a huge role in the exploration of new energy and raw materials required for new energy (Lü YB, 2009). As an important way to obtain crustal information, continental scientific deep exploration can directly probe the lithosphere in the deep continent, revealed the material composition and sphere structure of the crust, which helps grasp the distribution of geothermal energy and materials required for the development of new energy sources, and provide decision-making assistance for the mining. For example, Jin BF and Cheng LJ(1992) used the resistivity sounding method as the main method of thermal field exploration to carry out the geothermal field exploration work in Tibet of China (Jin BF and Cheng LJ, 1992). In addition to traditional detection methods, remote sensing data (such as NOAA satellite thermal infrared remote sensing data) can also help energy survey work, like Hao YM et al. (2001) used Landsat5/TM data to explore geothermal resources in the Xiazhuang area of Handan City, Hebei Province, China (Hao YM et al., 2001).For some clean energy, such as wind power and solar power,geoscience has contributed to the determination of the new energy facilities’ location, by analyzing natural factors like wind speed and light.

Fig. 1. Power source structure in China (Liu MP, 2021).

2.2. Relevant geological work and policies in China

China is actively cooperating with the international community to achieve carbon neutrality targets and put forward specific strategic goals from the national level (Fig. 2).Among them, the geological work in China is mainly reflected in the following aspects.

At a press conference held on January 19, 2021, the National Development and Reform Commission (NDRC) said that China will step up research and introduce relevant policies and measures to actively promote green, low-carbon economic transformation and sustainable development (China Geological Survey, 2021). There are some actions including reducing emissions from carbon sources, accelerating the construction of new power systems that can adapt to the development of a high proportion of renewable energy,improving the long-term mechanism for absorbing clean energy, adjusting the energy structure, and replacing lowcarbon energy with high-carbon energy and renewable energy with fossil energy. Natural gas, hydrogen, geothermal, nuclear energy, hydropower, metal energy (such as electric vehicles,wind energy, and solar energy, their production process requires a large amount of metallic material), marine energy(such as tidal energy, saltwater power, ocean thermal energy),bioenergy (such as bioenergy (BECCS) negative emission technology equipped with carbon capture and storage) are all belong to low-carbon or carbon-free energy. China’s geoscience plays an essential role in the development of lowcarbon and carbon-free energy. For example, it steadily advancing the development of hydropower, safely developing nuclear power, and accelerating the development of photovoltaic and wind power. In addition, the application of geographic information system technology to promote the development of energy digitization and intelligence, and to accelerate the improvement of the intelligence level of the energy industry chain can also help carbon source emission reduction.

At the Fourth Session of the 13th National People’s Congress, the Chinese government made a report on the work of the government, pointing out that it should make good efforts to achieve carbon peaking and carbon neutrality.Mainly include: Develop an action plan for carbon emissions to peak by 2030, improve China’s industrial structure and energy mix, promote the clean and efficient use of coal,develop new energy sources, use nuclear energy while ensuring safety, expand the catalog of corporate income tax credits for environmental protection and the conservation of water and energy, and promote the development and application of new types of energy-efficient and eco-friendly technologies, equipment and products, and the cultivation of energy-saving and environmental protection industries to ensure the conservation and efficient use of resources;accelerate the development of national markets for trading energy use rights and carbon emissions rights, and improve the system to control both the total amount and intensity of energy consumption, introduce special policies on providing financial support for green and low-carbon development,devise instruments for supporting the reduction of carbon emissions, and enhance the carbon absorption capacity of ecosystems.

At the same time, China Geological Survey (CGS) also proposed to carry out strategic research on natural resources under the constraints of carbon peak and carbon neutral. It focuses on the study of comprehensive investigation,monitoring, and evaluation of natural resources such as forests, grasslands, wetlands, and water, and research of research on the development path of hot dry rock clean energy industrialization, research on ecosystem restoration models for the forest, grass, wetland, and others, and research on evaluation of the suitability of CO2geological storage sites.These studies are helpful to solve the geologic problems in the process of China’s carbon neutrality.

Fig. 2. China’s major climate policies in recent years (Liu MP, 2021).

3. The key scientific issues and status of geological work

To strengthen the global response to the threat and risk of climate change, the Chinese government signed the Paris Agreement, which aims to hold the increase in the global average temperature to well below 2°C above pre-industrial levels and pursue efforts to limit the temperature increase to 1.5°C above pre-industrial levels. And declared that China will “aim to have CO2emission peak before 2030 and achieve carbon neutrality before 2060”. With this challenging goal of climate change, an array of scientific solutions should be designed and implemented based on Chinese geoscience researches and discoveries. There are 3 sections of geological work including 12 key scientific issues in the future, which is:(1) Carbon reduction technology section, which includes eight issues: Natural gas hydrate, geothermal energy, hot dry rock,nuclear energy, hydropower, wind energy, solar energy,hydrogen energy. (2) carbon storage technology section,which includes two issues: Carbon capture and storage, and utilization of underground space; (3) key minerals section,which includes two issues and could support other carbon neutrality processes: Raw minerals of energy transition, and carbon reduction minerals. Except for the above key issues,other issues such as science policy, social science insights of the energy transition, decarburization with geological technology, and geoscience, should also be considered and explored.

3.1. Carbon reduction technology

3.1.1. Natural gas hydrates

Natural gas hydrates (NGH) are ice-like solids composed of water and gas, most commonly methane. NGH is a kind of new energy that is clean and efficient and treated by the strategic commanding heights of future global energy development. Some studies have found that there are lots of NGH in both land and ocean area in China (Sha ZB et al.,2019). With the development of geophysics, geology,geochemistry, and biology, China Geological Survey (CGS)investigated, summarized, and evaluated the distribution of NGH in mainland and ocean of China, and found that the formation environment and exploration potential is quite suitable and abundant in Qinghai-Tibet Plateau. Up to now,one NGH accumulation, two inferred NGH accumulations,and a series of NGH-related anomalous indicators have been discovered in the Plateau, with NGH resources predicted to be up to 8.88×1012m3(Zhu YH et al., 2021). Natural gas hydrate, oil, and gas have been discovered in the Qilian Mountain permafrost area. They are closely related to each other in temporal, spatial, and genetic terms, and they mutually form a natural gas hydrate-oil-gas system (Lu ZQ et al., 2020). In the ocean field, CGS found that the NGH resources were up to 800×109t oil equivalent in the South China Sea, and delineate six perspective mineralization areas,25 favorable mineralization areas, and 24 drilling target areas in the northern slope of the South China Sea. With three voyage explorations since 2007, CGS has found two combustible ice mines, which resources were up to 1012m3scale natural gas reserves (CGS, 2019).

NGH resources survey in China has three stages, which include the pre-investigation stage (during 1985–2001),intermediate investigation stage (during 2002–2010), and trail mining stage (during 2011–2020) (Fig. 3). The Chinese government launched a major national special project: “NGH resources investigation and production test project” in 2011(which include some “973” and “863” special projects), and based on the process of exploration, CGS has launched different NGH surveys in different levels and different areas,especially in Qinghai-Tibet Plateau and South China Sea (Li JF et al., 2018; Zhu YH et al., 2021; Lu ZQ et al., 2020;Zhang GX et al., 2018; Ye JL et al., 2018). For example,some researchers found many kinds of NGH resources with high thickness and high purity in the western waters of the Pearl River Mouth Basin in 2015 and 2018 (Sha ZB et al.,2019) and mapped the NGH resources distribution in sedimentary basin in Northern South China Sea, as shown in Fig. 4. In 2017, CGS started the first offshore NGH production test in the Shenhu Test Area, South China Sea(Fig. 5). To improve the imaging precision of natural gas hydrate in this area, especially for fault and fracture structures, the present work proposes a velocity stitching technique that accelerates effectively the convergence of the shallow seafloor, indicating seafloor horizon interpretation and the initial interval velocity for model building. In the depth domain, pre-stack depth migration and residual curvature are built into the model based on high-precision grid-tomography velocity inversion, after several rounds of tomographic iterations, as the residual velocity field converges gradually. Test results of the Shenhu area show that the imaging precision of the fault zone is significantly improved, the fracture structures appear more clearly, the wave group characteristics significantly change for the better and the signal-to-noise ratio and resolution are improved.These improvements provide the necessary basis for the new reservoir model and field drilling risk tips, help optimize the favorable drilling target, and are crucial for the natural gas resource potential evaluation (Xue H et al., 2020). The test lasted for 60 days from May 10th when starting to pump, drop the pressure and ignite to well killing on July 9th, with gas production of 0.31×106m3in total, which is a world record with the longest continuous duration of gas production and maximal gas yield (Li JF et al., 2018). The results from environmental monitoring indicated that the test did not cause ground subsiding, methane leaking, or any other geohazards,thus no adverse effects were made on the environment and this successful test brings a significant breakthrough on safety control of NGH production.

With the success of the first offshore NGH production test, CGS started the second offshore NGH production test from October 2019 to April 2020 (Fig. 6). This test result showed that the accumulated NGH production and daily NGH production were significantly increasing, the production process was continuing in 30 days and the daily NGH production is 28.7×103m3, which is 5.57 times of first test results, and the accumulated NGH production is 861.4×103m3.Meanwhile, the results from environmental monitoring in the second test also indicated that the test did not cause ground subsiding, methane leaking, or any other geohazards. This successful test also indicated that it is possible to produce NGH safely and efficiently in viscous silt reservoirs and provided strong support in the NGH production industry (Qin XW et al., 2020).

In the land field, many studies focus on the exploration and research in NGH resources in the southern edge of the Qilian Mountains and Qinghai-Tibet Plateau, since the NGH example was founded in Muli, Qilian Mountains in 2008 (Lu ZQ et al., 2020; Zhu YH et al., 2021). For example, He MX et al. (2020) carried out a comprehensive study of geophysical and geochemical exploration in the depression, to find out the geological structure characteristics and gas hydrate accumulation conditions of the Hala Lake Depression (He MX et al., 2020).

Fig. 3. The exploration history of Natural Gas Hydrate resource in China (CGS, 2019).

Fig. 4. Depositional basins and gas hydrate surveying in the northern South China Sea (Wu SG and Wang JL, 2018).

Fig. 5. Blue Whale Ⅰ-conducting the first NGH production test in the South China Sea. The production test platform ’BLUEWHALE #1’ (a)and the flame from the venting gas (b) (Li JF et al., 2018).

Fig. 6. Blue Whale II-conducting the second NGH production test in the South China Sea.

3.1.2. Geothermal energy

Geothermal energy means that under the current technical,economic, and geological environment conditions, The thermal energy in the rock and in the geothermal fluid with the associated useful components that can be developed in the earth’s crust scientifically and reasonably (Mock JE et al.,1997). The utilization of geothermal energy mainly includes power generation and direct utilization (Fig. 7). According to the World Geothermal Congress 2010, there are 78 countries around the world are developing and using geothermal energy technology, 27 countries use geothermal power to generate electricity, the total installed capacity is 10715 MW, annual power generation is 67246 GW·h (Xu TF et al., 2016).

According to the estimation of Wang GL et al. (2018), the shallow geothermal energy of key cities in China are about 0.28×1021J, the annual available geothermal energy is about 2.89×1012kW·h, it is equivalent to 0.36×109t standard coal.In 287 cities above the prefecture-level, the geothermal energy of 200 m in the shallow layer is 77.1×1012kW·h/a.The geothermal energy of 12 major sedimentary basins in China is about 25.0×1021J, and the allowable amount of exploitation close to 7.5×1021J. The total heat discharged from the hot spring area is about 0.13×1018J/a, and the exploitable resources are about 0.67×1018J/a, which is equivalent to 22.60×106t standard coal (Wang GL et al.,2018, 2020a).

Geothermal energy in China is widely distributed. The global Mediterranean-Himalayan geothermal belt and the Circum Pacific geothermal belt run through the southwest and southeast coastal areas of China. The medium-low temperature geothermal energy is almost all over the country,mainly distributed in Songliao Plain, Huang-Huai-Hai Plain,Jianghan Plain, Shandong Peninsula, and southeast coastal areas. Its main thermal reservoir is the Tertiary sandstone and conglomerate with a thickness of hundreds to thousands of meters (Wang GL et al., 2013). High-temperature geothermal energy is mainly distributed in Tibet, Yunnan, western of Sichuan, Taiwan, Fujian, Guangdong. In terms of the geological structure, geothermal energy in China are mainly distributed in the active tectonic zones and large sedimentary basins, and their types are mainly uplifting mountain and sedimentary basin (Fig. 8; Wang GL et al., 2018; Pang ZH et al., 2020; Huang YH et al., 2020).

Ji-Yang Wang and his group is developing geothermal resources in Jimo district of Shandong Province, and created an energy supply model based on geothermal (Zhang SK et al., 2020). The group has completed the investigation and survey of the distribution of shallow and medium-deep layer geothermal resources, the results show the annually available shallow and medium-deep layer geothermal resources are 95.1×109MJ and 3.24×1012MJ. According to the regional planning, traditional energy resources are not allowed to enter this region, and renewable energy-based heating systems will be the only choice. According to an estimation from the Chinese development network (2020), this project can provide heating energy for the buildings within 46.38×106m3, which accounts for 52% of the total area in this region. Integrated and cascading development and utilization of the geothermal plus other energy sources model can effectively promote energy security in China, and contribute to carbon peaking and carbon neutrality.

Fig. 7. Application of geothermal energy in China. Yangbajing geothermal power station (a); geothermal heating in Baicheng City, Jilin Province (b); geothermal energy vegetable greenhouse in Yangling, China (c); and geothermal energy fish culture in Xiong’an, China (d).(source: (a) http://blog.hbddrn.com; (b) xinhuanet.com; (c) https://www.sohu.com; (d) Chinanews.com).

Fig. 8. Distribution of geothermal energy in China (Wang GL et al., 2018).

To support the planning and construction of the Xiong’an New Area, CGS has carried out a series of investigations, and achieved a series of results in a comprehensive geological survey of the area (Wang Q, 2019). It has been found that Xiong’an New Area is rich in geothermal energy, which is characterized by large reserves, high temperature, good water quality, and easy recharge. It is suitable for large-scale development and utilization under feasible conditions of technology, economy, and environment, and can provide stable and safe clean energy supply for building a green,ecological and livable new urban area (Lin LJ and Hu QY,2017; Pang ZH et al., 2017; Table 1). Gonghe Basin is a Cenozoic downward-bending basin, located in the northeastern of the Qinghai-Tibet Plateau and distributed on the important nodes of the transfer of several blocks in the northwest to a central orogenic belt. The basin has a high heat flow value and obvious thermal anomaly. Geothermal energy is mainly hot dry rocks and underground hot-water. Feng YF et al. (2018) put forward the geothermal formation mechanism of “heat source-heat transfer-heat storage-cap-heat system” in Gonghe Basin. It is further speculated that the favorable structural location and special geological evolution history provide a unique environment for the formation of the geothermal system, and the eastern of the basin may be heat storage, which is expected to be a favorable exploration area for hot dry rocks.

Several promising areas of HDR geothermal resources in China have been identified based on China’s regional structure, volcanic geology, and lithology, as well as data from geochemistry, geophysics, and shallow borehole temperature measurement, including Tengchong in Yunnan,Changbai Mountain in Jilin Province, Wudalianchi in Heilongjiang Province and Yangbajing in southern Tibet. The three-dimensional static heat conduction model was established to study the characteristics of underground temperature gradients in the Tengchong Rehai geothermal field and Tibet’s Yangbajing geothermal field, indicating that China has abundant HDR geothermal resources, and proposed that if the power of 100×106kW is developed, the coastal The Leihai and Yangbajing geothermal fields will be able to generate electricity for 1560 years (Wan Z et al., 2005). CGS has carried out geothermal geological surveys in the Dongli Lake area since 2017 (Liu J et al., 2012; Wang GL et al.,2017). It conducted a geothermal resource survey and deep geothermal exploration in key areas and built a large-depth,high-precision comprehensive geophysical exploration method for deep thermal storage. It developed high-efficiency geothermal drilling and coring technologies in deep complexcarbonate formations and carried out reservoir modification stimulation tests, and achieved a 54% increase in single well productivity. It carried out monitoring technology research and development to form shallow, medium, deep geothermal monitoring technology methods and equipment. At the same time, the “Tianjin Dongli Lake Geothermal Development and Utilization Demonstration Base Construction Plan” was prepared to support Tianjin’s construction of a demonstration base integrating technology research and development,engineering demonstration, product promotion, scientific research cooperation, cultural publicity, and popular science education (Wang GL et al., 2020b; Ru HJ et al., 2018).

Table 1.Estimation of geothermal energy and reserves in Xiong’an New Area.

3.1.3. Hot dry rock

Hot dry rock refers to an abnormally high-temperature rock mass buried deep in the earth with no or only a small amount of fluid, and the temperature is higher than 180°C,mainly dense metamorphic rock or granite. An enhanced geothermal system (EGS) is an effective means to develop hot dry rock geothermal resources. Deep underground bottom pores and low permeability rock masses are transformed into artificial geothermal reservoirs with higher permeability through reservoir stimulation methods such as hydraulic fracturing. And from the medium and long-term economically extract a considerable amount of heat energy to use (Xu TF et al., 2016).

China’s hot dry rock thermal reservoirs have superior accumulation conditions and huge resource potential, the geothermal resources in the hot dry rock area with a depth of 3–10 km in mainland China are about 25.2×1024J. If only 2%of EGS resources can be recovered, geothermal energy is equivalent to 5300 times of China’s current total annual energy consumption (2010: 95.2×1018J) (Wang GL et al.,2020a). The possible resources of hot dry rocks in China have been calculated and evaluated based on the reference methods such as geothermal heat flow value, geothermal gradient,inner burial depth, burial depth of low-velocity and highconductivity layers in the crust, volcanic magmatic activity,radioactive heat generation rate, et al, which are closely related to hot dry rocks, it is considered that the total amount of hot dry rocks (greater than 150°C) at a depth of 3–10 km in Mainland of China is 20.9×106EJ, which can be converted into standard coal 714.9×1012t (Wang JY et al., 2013; Pang ZH et al., 2020).

The exploitation and utilization of hot dry rock mainly realize the extraction of heat through the circulation of the heat exchange medium. The developed countries in Europe and America have carried out more than 40 years of research and development and industrial cultivation, which has realized the innovation and application of mining technology and provided useful experience for the exploitation of hot dry rock resources. In general, China has the conditions for the industrialization of hot dry rock resources and has made great progress in research and development, including the following major events.

(i) In 2017, CGS delivered an academic report on the theme of “Evaluation of Hot Dry Rock Resources in the Gonghe Basin” at the 6th International Conference on the Efficient Development and Utilization of Middle-Deep Geothermal Resources. It introduced the survey and evaluation of geothermal resources in the Gonghe Basin by the Water Environment Center of China Geological Survey in recent years (Fig. 9), and proposed the stage division plan for the investigation and resource evaluation of hot dry rock resources in China. The process and results of the delineation of hot dry rock evaluation area and resource evaluation in Gonghe Basin were described in detail (Table 2; Li Q et al.,2020).

(ii) CGS participated in the implementation of a hot dry rock exploration project in Gonghe Basin, Qinghai Province.In 2017, 236°C high temperature hot dry rock masses were drilled in the depth of 3705 m in Gonghe Basin (Feng YF et al., 2018; Zhang SQ et al., 2018; Zhang SS et al., 2019).Using thermal infrared remote sensing, high-precision aeromagnetic measurement, natural seismic background noise tomography technology, magnetotelluric (MT) sounding,radioactiveγenergy spectrum measurement, and other comprehensive technical means, it has successfully overcome high-temperature drilling and deep-hole high-temperature and high-pressure temperature measurement and other key technologies successfully achieved a series of breakthroughs in China’s hot dry rock exploration.

3.1.4. Nuclear and uranium deposits

Fig. 9. Construction drawing of hot dry rock site in Gonghe County, Qinghai Province (Source from Internet).

The proportion of fossil fuels in energy consumption is still at an absolute advantage. Compared with thermal power plants, nuclear power plants are very clean energy. They do not emit these harmful substances and do not cause the“greenhouse effect”, so they can greatly improve the environmental quality and protect the ecological environment on which human beings depend. Nuclear power in the world for many years statistical data show that although the plant investment higher than that of coal-fired power plants,however, due to the fuel cost is far below the cost of coal, on the contrary, the energy released by the nuclear reaction was far stronger than the energy released by the burning of fossil fuels, and nuclear fuel is inexhaustible, this makes the plant’s total generating cost is lower than coal-fired power plants.

China is stepping up efforts to adjust its energy structure and actively developing clean and high-quality energy such as nuclear power, wind power, and hydropower. China’s energy structure is still dominated by coal, while the proportion of clean and high-quality energy is low, and nuclear power is mainly located in coastal areas (Fig. 10).

It is estimated that the installed nuclear power capacity will be about 40×106kW by 2020 (Zhou D, 2018). According to estimates by different departments, China’s installed nuclear power capacity by 2050 can be divided into three scenarios: The high, medium, and low scenario are 360×106kW, 240×106kW, and 120×106kW, accounts for about 30%,20% and 10% of China’s total installed power capacity(Zhang QX, 2011). In addition, according to the National Development and Reform Commission of China’s Civil Industry Plan for Nuclear Power Development, China’s total installed power capacity is expected to be 900×106kW by 2020, with nuclear power accounting for 4% of the total power capacity. That is to say, around 2020, China will build 40 nuclear power plants equivalent to the Daya Bay nuclear power plant (Fig. 11) with a megawatt level.

From the general trend of nuclear power development,China’s technical and strategic routes for nuclear power development have long been clear and are being implemented.Pressurized water reactors will be developed at present, fast neutron reactors in the medium term, and fusion reactors in the long term. Specifically, uranium resources adopt the technical route of the uranium-plutonium cycle and develop fast breeder reactor nuclear power plants in the medium term.The long-term development of fusion reactor nuclear power plants can solve the contradiction of energy demand “forever”(Zou SL et al., 2005).

Table 2. Estimation of hot dry rock resources in Gonghe Basin (Zhang SS et al., 2019)

Fig. 10. Main distributing map of the nuclear energy in China (Xu BC et al., 2010).

Fig. 11. Daya Bay Nuclear Power Plant in China (Source: Daya Bay Nuclear Power Operation Management Co., Ltd).

Tianjin Center of China Geological Survey has carried out a lot of work at the Dongsheng Uranium Mine in the Ordos Basin. From the previous data collected in the drill hole of coal and uranium, they analyzed the orefield geological distribution from north to south, determined the sandstone/mudstone rock mineral composition, analyzed the green sandstone/mudstone formation in the ore field of Jurassic Zhiluo formation. The results show that the greenstone/mudstone has undergone a sedimentary rock diagenesis process similar to diagenesis and has not been transformed by large-scale regional fluid. Further enrichment of enriched uranium in the diagenesis process leads to the final formation of uranium deposits (Jin RS et al., 2020).Based on summarizing the characteristics and regularity of uranium mineralization in the famous Lujing uranium deposit field in Zhuguang Mountains, Hunan Province, China, Xiao ZH et al. (2020) discusses the controlling factors of different types of uranium deposits in this area and predicts that the uranium deposits in the six ore-forming target areas are closely related to granite in terms of genesis and space. They are formed in different structural parts subjected to the same metallization. The above studies are beneficial to enrich the metallogenic mechanism of sandstone-type uranium deposits and can provide some references for the exploration and deployment of uranium resources in China.

3.1.5. Hydropower storage

Pumped Storage Power Station is the most mature energy storage device in the power system. It plays an important part in the development of new energy. China’s pumped storage stations began in the 1960s. Although they were launched later than abroad, they have developed rapidly. Beginning in 1956, China’s geological and mining departments conducted large-scale surveys and comparisons on the site selection of the Three Gorges Dam. The engineering geological conditions of Sandouping are relatively simple. The weathering crust is not thick and the Zhongbao Island in the river valley is convenient for diversion. Engineering geological conditions such as the stability of the crust, the strength of the dam foundation rock, and the permeability are also the best (Liu GR, 1992). After many years of comparison, Sandouping was finally determined to be the site of the Three Gorges Dam in 1979 due to the superior hydroelectric energy storage potential of Sandouping (Fig. 12).

China has successively built many large-scale pumped storage power stations such as Panjiakou, Guangzhou, Ming Tombs, Tianhuangping, Shandong Taishan, Jiangsu Yixing,Henan Baoquan, etc. (Table 3).

Fig. 12. China’s Three Gorges Dam (Source: www.vcg.com).

Pumped storage power stations use the electricity generated by high-efficiency and low-coal-consumption units to replace the electricity generated by low-efficiency and high-coal-consumption units, thereby realizing effective energy conservation and emission reduction in the power system, which has obvious coal-saving effects. Pumped storage power stations can store water and generate electricity, which can also be jointly dispatched and operated with wind and photovoltaics to effectively compensate for the volatility of wind power and photovoltaics. Pumped storage power stations have advantages of rapid start and stop, safety,and environmental protection, which promotes the highquality and sustainable development of new energy.According to the “13th Five-Year Plan for Hydropower”issued by the National Energy Administration, China’s cumulative installed capacity of pumped energy storage will reach 38 GW by the end of 2020. As of the end of 2020, the scale of hydropower installed capacity has steadily expanded,and China’s newly added hydropower grid-connected capacity has reached 13.23×106kW.

Hydropower generation continues to grow, with the utilization hours of hydropower equipment exceeding 3800 hours for the first time. Sichuan Province is a major hydroelectric power generation province in China. In 2020,Sichuan Province’s annual hydropower utilization rate was 95.4%. The additional issuance of hydropower in Sichuan Province is equivalent to reducing 12.67×106t of standard coal combustion, achieving remarkable results by reducing carbon dioxide by 31.68×106t and sulfur dioxide by 800000 t.China’s “2020–2021 National Electricity Supply and Demand Situation Analysis and Forecast Report” pointed out that the construction of pumped storage power stations should be accelerated. The “14th Five-Year Plan” predicts that China’s total installed capacity of pumped storage power stations will reach 65×106kW and 120×106kW by 2025 and 2035.

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Table 3. China’s completed pumped storage power stations (not all).

3.1.6. Wind energy

Wind energy is a kind of available energy provided to human beings due to the work of airflow, which belongs to renewable energy. The higher the air velocity, the greater the kinetic energy. By 2008, there are about 94.1×106kW of power generated by wind power in the world, and the power supply has exceeded 1% of the world’s consumption (Shen DC, 2009). Wind energy is nearly endless, widely distributed,clean, and can mitigate the greenhouse effect.

The global wind energy is about 130×109kW, which is 10 times larger than the total amount of water energy that can be developed and utilized on the earth. China is vast in territory,with a border length of over 20000 km, a coastline of 18000 km,with more than 5000 islands in the marginal sea, has rich wind energy resources. The annual average wind speed of existing wind farms is over 6 m/s. Many regions of China,such as Shandong and the Liaodong Peninsula, seashore of the Yellow Sea, South China Sea coast to the west of Nan’ao Island, Hainan Island, and South China Sea Islands, Inner Mongolia from the north of Yinshan Mountains to the north of Daxinganling Mountains, Daban City, Xinjiang, Alashan Pass, Hexi Corridor, lower reaches of Songhua River,Northern Zhangjiakou, and mountain pass and top of some regions in China have abundant wind energy in China. The total theoretical exploitable capacity of wind energy in China is 3.226×109kW, and the actual exploitable amount is 253×106kW (Chen JW and Chen XS, 2011).

The wind power in China was a cloth awning windmill with various wood structures in the late 1950s. By the mid-1960s and 1970s, wind energy development and utilization has been developed rapidly and was listed in the national key projects of the sixth five-year plan in China. Since the mid-1980s, China has successively imported many medium and large-scale wind turbines from Denmark, Belgium, Sweden,the United States, and Germany, and established many demonstration wind farms in Xinjiang, Inner Mongolia, and other places, with an installed capacity of 8 MW in 1992 (Gu WD, 2006). However, compared with developed countries,the development and utilization of wind energy in China are still quite backward, not only the development speed is slow,but also the technology is backward, far from forming a scale.In the 21st century, China will increase investment in the development and utilization of wind energy, so that efficient and clean wind energy will occupy its due place in China’s energy pattern (Table 4; Chen JW and Chen XS, 2011).

With the rapid development of wind energy resources, a large number of lands are needed to build wind farms.Inevitably, complex engineering geological problems will be encountered, which will bring some difficulties to the foundation treatment of wind turbines. Taking the foundation investigation of wind power units, for instance, Yang PQ(2007) deals with the basic physical mechanic property of special soil (salty soil, soft soil, loess, and soft), analyzes engineering geological problems of the special soil layer, and advances corresponding treatment measures for the project.High altitude mountain wind farm is an important area ofwind power development in the future. Wind energy resource analysis and microsite selection play a very important role in the construction of high-altitude mountain wind farms (Fig. 13).Microsite selection is to realize the feasibility layout of wind turbines on the topographic map, and then according to the wind turbine type determined by bidding, combined with the terrain conditions of wind farm site, installation platform setting, construction road comparison, environmental impact,turbulence and wake impact and other factors, on the premise of ensuring the stable and safe operation of wind turbines, The wind turbine layout and power generation calculation software are used to analyze the overall power generation of the wind farm under different layout schemes, and the economy is considered at the same time (Gao YH et al.,2008). A computer program is developed and used to automatically perform the task process of micro-location, to achieve the overall goal of the automatic layout of the wind farms, improve efficiency and reduce the error caused by human factors (Li JK et al., 2020).

Table 4. Chinese Renewable Energy Industries Association’s prediction of China’s medium- and long-term wind power development.

3.1.7. Solar energy

Among the various renewable energy sources, solar technology shows great potential for future energy development due to its decreased cost and low environmental impact. Many countries around the world, such as Italy and Japan, have begun to develop ground-mounted photovoltaics to achieve renewable energy goals and climate goals(Agostini A et al., 2021). According to statistics, about 100 GW of solar photovoltaics were installed globally in 2019,accounting for 55% of the newly installed renewable energy capacity. China has vast territories and abundant solar energy resources (Fig. 14). The annual solar radiation in China is more than 5000 MJ/m2, and more than two-thirds of the area has more than 2200 hours of sunshine per year, which has great development potential and is especially suitable for the development of solar energy technology (Shen F and Liang XC, 2006).

In the early 2000s, China’s solar policy was mainly export-oriented. Between 2004 and 2008, almost all photovoltaic modules in China were exported (Zhang S et al.,2014). As the global financial crisis has reduced the demand in the international market, the Chinese government has begun to develop the domestic photovoltaic market and introduced various subsidy policies (Hayashi D, 2020).

Fig. 13. Wind power generation in Tibet (Source: www.vcg.com).

So far, China’s photovoltaic module production ranks among the highest in the world. In 2019, China’s photovoltaic module production was 88.6 GW, accounting for 87% of the world’s total output. Due to abundant solar energy resources and national policy support, China’s installed photovoltaic capacity has increased rapidly. As of 2017, China’s cumulative installed photovoltaic capacity has reached 130 GW, accounting for one-third of the world’s power generation. Fig. 15 shows the changes in installed PV capacity in China in recent years. According to estimates from related institutions, China’s installed solar PV is expected to surpass wind energy and account for 22% of China’s total electricity generation by 2040 (Li JL and Huang J, 2020).

Fig. 14. China’s solar energy resources. Grid parity in Hong Kong, Macao, and Taiwan is not analyzed. (Zhang MH and Zhang Q, 2020).

Fig. 15. Cumulative installed PV capacity by the province in China(Data source: http://enesup.com/).

Fig. 16. “Super Mirror” Power Station in Dunhuang, China(Source: AFP/GETTY IMAGES).

Currently, Chinese solar energy is in the process of switching from centralized to distribute. In the early days, due to policy reasons and regional geographic factors, solar power generation in China was mainly concentrated in PV plants in the northwest of the country (Fig. 16). However, there is a limit to the amount of light that can be consumed for power generation, due to the low level of overall economic development in the Northwest, which results in significant light wastage and a significant waste of resources (Zhou Q and Yang SY, 2018). In recent years, the government has restricted the development of concentrated solar energy by formulating plans and adjusting feed-in tariffs, which have promoted the development of distributed solar energy in China, especially in the eastern coastal areas (Li JL and Huang J, 2020). In the future, China’s solar energy industry will become one of the important measures to achieve the goal of carbon neutrality. The development of the solar energy industry will help alleviate energy problems, reduce carbon emissions and pollution problems caused by fossil fuels, and greatly reduce environmental pressures. As one of the strategic resources of the solar energy industry (Li JW et al., 2016), high-purity quartz sand is currently facing increasing demand and insufficient self-sufficiency (Shen BL et al., 2012). This requires efforts to promote the development of high-purity quartz sand purification technology and related industries, which is important for the development of the solar energy industry. High-purity quartz sand has important applications in the photovoltaic industry: high-purity quartz sand can produce high-purity solar-grade polysilicon through carbothermal reduction; quartz crucibles can be used as reaction vessels for polysilicon ingots; photovoltaic glass is used as an important component for solar power generation.The above applications all have strict requirements on the purity of quartz sand. For example, the chemical index of quartz sand for solar photovoltaic glass is (%): SiO299.5,Al2O30.05, Fe2O30.006, TiO20.02; particle size index:+0.6 mm0.5%, −0.6–+0.125 mm95%, −0.125 mm4.5% (Li JW et al., 2016). How to effectively reduce the content of impurity elements in quartz sand is a hot topic of research at present.

3.1.8. Hydrogen economic

The world’s energy supply today comes mainly from the combustion of fuels such as coal, oil, and natural gas. The combustion of these hydrocarbon fuels emits carbon dioxide and other pollutants. To achieve low carbon emissions and energy transition, the concept of “hydrogen economy” was first introduced by physicist John Bockris in 1970. The“hydrogen economy” is a vision of a future economic structure that uses hydrogen as an energy source for storage,transportation, and transformation. Hydrogen energy is a secondary energy source that is widely available, efficient,safe, and clean, and has a high energy density (Sherif SA et al., 2005; Mah AXY et al., 2019).

China’s hydrogen energy industry is at a turning point in the transition from industrial raw materials to large-scale applications. The overall product chain is full of development potential. In 2018, China’s annual hydrogen production reached 21×106t, becoming the world’s largest producer of hydrogen (Bai W and Zhang L, 2020). At the same time, the production and sales of metal hydrogen storage materials in China have surpassed that of Japan, becoming the world’s largest producer and seller of hydrogen storage materials. In 2020, China’s hydrogen production reaches 25×106t.Hydrogen production mostly comes from petrochemical enterprises, including 10×106t/a from coal gasification, 3×106t/a from natural gas, and 3×106t/a from oil.

By 2020, China has built 128 hydrogen refueling stations(Fig. 17), including the hydrogen station with the world’s largest daily fueling capacity in Beijing’s Daxing District.Integrated energy stations providing multiple energy supplies are gradually becoming a mainstream trend in the way hydrogen refueling stations are built. In addition, the number of integrated hydrogen production plants and refueling stations is gradually increasing. In 2020, the Ningxia Baofeng Energy Group started construction of the world’s largest solar hydrogen project (Runyon J, 2020). It is the integration of solar energy hydrogen production, hydrogen storage, and hydrogen energy utilization and is truly “green hydrogen”. As one of the important applications of hydrogen energy (Table 5),the development of hydrogen energy vehicles in China has just started. In 2019, China’s hydrogen energy vehicle production and sales completed 2833 and 2737 units respectively, an increase of 85.5% and 79.2% over last year.China attaches great importance to the development of hydrogen energy. In 2016, the Chinese government released the “Innovation Action Plan of Energy Technology Revolution (2016–2030)”, which put forward renewable energy hydrogen production, hydrogen energy, and fuel cell technology innovation as the key development content. In March 2019, hydrogen energy was included in China’s Government Work Report for the first time, proposing that the construction of charging and hydrogen refueling facilities will be promoted. This marks the inclusion of the hydrogen energy industry into the national energy strategy.

Fig. 17. The number of hydrogen refueling stations built in China each year (Data source: China Hydrogen Energy Alliance).

Table 5. China’s hydrogen energy vehicle production and sales.

At present, hydrogen production is still dominated by industrial hydrogen production. Extracting hydrogen from the geological environment can avoid the carbon emissions caused by industrial hydrogen production and realize the sustainable production of hydrogen (Meng QQ et al., 2021).The hydrogen content varies greatly in different geological environments on the earth’s surface. Therefore, it is necessary to strengthen the understanding of hydrogen formation conditions and geographical distribution of high-content hydrogen in future research (Fig. 18).

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3.2. Carbon storage technologies

3.2.1. Carbon capture and storage

Global warming caused by the greenhouse gases produced by the burning of fossil fuels is a major environmental problem faced by mankind. The most effective way to reduce the CO2content in the atmosphere is to use CO2geological storage technology. CO2geological storage technology refers to the carbon capture and storage technology of the IPCC fifth assessment report (carbon capture and storage, CCS). CCS refers to the capture of carbon dioxide produced by the burning of fossil fuels and then transports it to the ground through pipelines or ships to the seabed for storage. To assess the conditions and prospects of CO2geological storage in China, Wen GD et al. (2014) conducted CO2geological storage potential and suitability evaluations on 417 sedimentary basins across the country, providing references to governments and enterprises with the use of CO2geological storage technology to reduce CO2emissions. Shepherd JG(2012) proposed that carbon capture and storage (CCS) of bioenergy can reduce the global atmospheric carbon dioxide concentration by 0.005% to 0.015%. CCS can not only promote large-scale greenhouse gas emissions, but also promote low-carbon use of fossil energy, which becomes an important choice for the global response to climate change.

Fig. 18. Drilling hydrogen energy in Shaanxi Province, China(Source from Internet).

Coal consumption has increased by 44% as China’s economy has continued to grow since 2006. It had reached 2.4×109t of standard coal by 2013, which is equivalent to half of the world’s coal consumption. CO2emissions increased by about 34% during the same period, reaching 830×106t in 2010 (World Bank, 2014). Coal has the advantages of low price, abundant reserves, and widespread distribution. It has always occupied a dominant position in China’s energy structure. Fossil fuel combustion accounts for more than 80%of China’s CO2emissions, of which coal accounts for 75%.ADB Reports (2015) used the C-GEM model to evaluate the effect of CCS in China’s climate change mitigation strategy.The results proved that CCS technology will play a vital role in reducing emissions and produced a scenario figure of China’s emission reduction based on the C-GEM model(ADB, 2015) (Fig. 19).

The Chinese government has invested more than 3×109RMB in CCS technology research and development since 2008. In the “Roadmap for Carbon Capture and Storage Demonstration and Deployment” (2015) (ADB, 2015), the development history and the current development priorities of China’s CCS technology are introduced. CCS demonstration projects are essential for verifying technology, strengthening capacity building to reduce costs, and answering questions from governments, industries, and the public. The Chinese government has been committed to CCS technology research and development. Since the 10th Five-Year Plan(2001–2005), mainly focusing on the assessment of emission reduction potential, CO2capture technology, CO2enhanced oil displacement and geological storage, and CO2conversion and utilization technology (Fig. 20; Zhang EY, 2012; Gao HL and Fan JJ, 2021). To develop technology with independent intellectual property rights, Shenhua Group has cooperated with some universities, research institutions, and technology and equipment suppliers on oxy-fuel combustion technology.China Huaneng Group has established a cooperative research and development network for pre-combustion capture.PetroChina with other oil companies is working together to promote the development of enhanced oil displacement technology. China Huaneng Group and PetroChina jointly established the Carbon Capture and Storage Technology Industry Alliance in August 2014. The development of these research cooperation has greatly promoted the development of China’s CCS technology.

Fig. 19. China’s emission reduction scenarios based on the C-GEM model (ADB, 2015). CCS–Carbon capture and storage, CO2–carbon dioxide, GtCO2–109 t of carbon dioxide

3.2.2. Utilization of underground space

By 2020, China’s installed capacity of wind and solar power will reach 281×106kW and 253×106kW respectively.To achieve the carbon neutrality target, China’s total installed capacity of wind and solar power is expected to reach more than 1.2×109kW by 2030. Large-scale integration of wind power into the grid poses challenges to the stable operation of the power grid, which has caused a curtailment of wind and solar power generation. Large-scale energy storage technology can reduce power fluctuations in renewable energy generation, help improve the compatibility of renewable energy and the grid and provide support for energy structure transformation (Solomon AA et al., 2014).

Compressed air energy storage (CAES) provides a valuable and eco-friendly choice for large-scale energy storage (Fig. 21). CAES is an approach to storing electrical energy produced at times of excess supply and making it available again at times of high demand. In a CAES system,electrical energy is used to compress air which is stored in sealed underground caverns and back-produced when required with energy recovered in a gas turbine. Compare to other large-scale energy storage technologies, CAES has advantages of low construction cost, small land occupation,technology maturation, fine sealing, high reliability, and high safety, it is the only one of the large-scale energy storage technologies that considered to be a mature technology as well as one that is commercially viable (Mei S et al., 2017). A large-scale CAES can achieve an output of hundreds to thousands MW, and regulate the power grid of an urban agglomeration. Currently, the two major CAES in commercial use both adopt natural gas for post-combustion, so problems such as fuel dependence and carbon emission existed. To address these issues, researches on unfired CAES has been a hot topic globally in recent years (Budt M et al., 2016).

The research and development of CAES systems in China started relatively late, mostly focusing on theoretical and small-scale experimental levels. There are no CAES plants that have been put into commercial operation in China. The Institute of Engineering Thermophysics of the Chinese Academy of Sciences built 15 kW and 1.5 MW class advanced CAES experimental systems in 2013 and 10 MW class advanced CAES experimental systems in 2016. In 2015,the 500 kW class A-CAES power generation demonstration system jointly developed by Tsinghua University and other research institutions achieved the milestone of 100 kW power generation in Wuhu City, Anhui Province. China has a large abundance of salt cave resources, with a volume of 130×106m3, and most of them are unused. Due to its advantages such as high bearing pressure, the salt cavern is well suited for the construction of gas storage.

Underground gas storage is an important part of the largescale CASE power station project. However, not all rock formations are suitable for underground gas storage construction, considering the technical feasibility and economic benefits of the project (Mei SW et al., 2017). In 2018, China’s first salt cavern advanced adiabatic compressed air energy storage (SC-AA-CAES) project was launched in Changzhou, Jiangsu. The project proposes to build a 60 MW class SC-AA-CAES system, which will be built into a CAES plant with an installed capacity of 1×106kW.

3.3. Key minerals

3.3.1. Raw materials needed for the energy transition

Fig. 20. Pilot test of carbon dioxide flooding and geological storage in Cainan Oilfield, Xinjiang (a) and CO2 industrial burial experiment (b)(Source from Internet).

Fig. 21. Principle of compressed air.

The low-carbon future will be “very” intensive in minerals, because clean energy technologies require more material resources than fossil fuel-based power generation technologies. In the era of fossil energy, energy acquisition mainly relies on mineral mining, while the production of renewable energy mainly relies on technology, using solar photovoltaic panels, wind turbines, and other equipment to convert resources into usable energy. Therefore, energy production has shifted from mineral mining to equipment manufacturing (Li JF and Jiang SY, 2020). In addition, the raw materials required for the energy transition also include elements necessary for new energy transmission and storage.The American Institute of Physics proposed the concept of Energy Critical Elements in 2011, using chemical elements that describe a class of important driving and catalytic effects for the development of energy technology. They are indispensable elements for advanced energy production,transmission, and storage, mainly including rare earth,lithium, cobalt, nickel, graphite, etc (Fig. 22). China has been at the forefront of the world in the detection and research of the distribution of key elements (including key energy elements) on the earth. It has drawn 78 element geochemical distribution maps across China, and has drawn 30% of the Earth’s land surface geochemical reference map of the world in collaboration with more than 20 countries around the world(Wang XQ, 2020).

Rare earth is called “industrial vitamins” and has irreplaceable excellent magnetic, optical, and electrical properties, which are critical to the development of new energy and high-tech industries. The reserves of rare earth resources themselves are not scarce and are widely distributed. China’s reserves are the world’s largest,accounting for 36.7% of the world’s total reserves, and are much higher than the second-ranked Russia (10%) (USGS,2019). The appearance of rare earth resembles “soil”, their distribution is scattered and extraction is extremely difficult,but China has 85% of the world’s rare earth production capacity. The breakthrough of “reflux cascade extraction”technology has put China’s rare earth extraction and refining industry chain in a leading and dominant position in the world. China has less than 40% of the world’s rare earth resources, but it supplies more than 90% of the world’s rare earth demand. Regarding the distribution data of rare earth elements (REE) nationwide, some progress has been made recently. Wang XQ et al. (2020) gave the background values of ΣLREE, ΣHREE, and ΣREE in rocks nationwide.Considering the characteristics of rare earth elements, a total of 35 geochemical anomalies were delineated across the country. Among these anomalies, 26 anomalies are consistent with the known rare earth minerals or rare earth metallogenic belts, and 9 anomalies in rare earth hyper-enrichment centers were newly discovered. The anomalies show potential targets for the follow-up exploration of the REE deposits of Bayan Obo type, carbonite-alkali-related type, ion-adsorbed type,granite pegmatite type, sedimentary clay type, and sedimentary phosphate type. In particular, the newly discovered mudstone is a rare earth-rich layer, with an average rare earth content of more than 400 μg/g, which is three times the Clarke value of the crust. For example, the Neogene Mangbang Formation mudstone in the Tengchong block has extraordinary enrichment of rare earth and may have the potential to form rare earth deposits (Liu DS et al.,2020).

Fig. 22. Some key minerals supporting carbon emission reduction. a–lithium ore (kunzite), b–rare earth ore, c–tungsten ore (scheelite), d–copper ore (Source: Journal of China University of Mining and Technology).

With the large demand for the use of new energy batteries,the demand for lithium and cobalt ore will greatly exceed its reserves, which has become a hot spot for investigation and research of key resources (Giurco D et al., 2019). China occupies a prominent position in the cobalt industry chain.More than half of the world’s finished cobalt and nearly threequarters of the chemical cobalt required for the production of lithium batteries in the world are produced in China (Cui SJ et al., 2020). In recent years, Chinese scholars have made important breakthroughs in the study of lithium and cobalt.Wang XQ et al. (2020) have circled a total of 31 geochemical anomalies based on the national watershed sediment geochemical data and classified them into 19 lithium geochemical provinces (Extraordinary enrichment areas). In particular, the newly discovered lithium-enriched areas related to argillaceous rocks and brine-type lithium anomalies related to arid basins have important guiding significance for lithium ore prospecting (Wang XQ et al., 2020). Based on the data of the China Geochemical Benchmark Program (CGB), Dongsheng Liu and others calculated the benchmark value of China’s rock cobalt at 6.4 mg/kg, and the benchmark value of sediments in the catchment area of 10.99 mg/kg. This benchmark will play an important reference role in the anomaly evaluation of cobalt resources (Liu DS et al., 2020).

On the other hand, the demand for high-nickel ternary batteries produced by nickel mines with price advantages in the new energy automobile industry has gradually increased,and even nickel has gradually replaced cobalt in battery materials. At present, China has identified 339 nickel ore deposits (points), of which 4 are super large, 14 are large, 26 are medium, 75 are small, and 220 are mineralized (chemical)sites; They are mainly distributed in 19 provinces (regions), of which the total reserves of 11 provinces (regions) including Gansu, Xinjiang, Qinghai, Yunnan, Sichuan, Jilin, Shaanxi,Guizhou, Jiangxi, Inner Mongolia, and Henan Provinces account for more than 90% of the country’s nickel resource reserves. Deposits are mainly concentrated in relatively active tectonic units such as orogenic belts or cratonic edges, such as the Tianshan orogenic belt, the Xingmeng-Jiling-Heilongjiang Orogenic Belt, the Qinling-Qilian-Kunlun Orogenic Belt, the North China Plate, the Yangtze Plate, and the edge of the Tarim Plate (Sun T et al., 2014).

Graphite is also one of the important raw materials for producing a battery. Since the early 20th century, the graphite mining industry has developed rapidly. According to the existing exploration and research of Chinese geology, it is found that graphite deposits are widely distributed in China,and most of the deposits are medium-sized deposits, and the resources are relatively concentrated in a few metallogenic areas. By the end of 2016, about 150 crystalline graphite deposits were discovered with reserves of 300 Mt.Heilongjiang, Inner Mongolia, Sichuan, Shanxi, and Shandong Provinces accounted for nearly 90% of the total resources, of which Heilongjiang Province accounted for nearly 43% of the national resources (Fig. 23).

3.3.2. Carbon reduction minerals: exploitation and utilization of serpentine ores and other minerals

Fig. 23. Pie chart of the distribution of crystalline graphite resources in China (Sun L et al., 2018).

In recent years, the study of carbon dioxide adsorption has made rapid progress, among which the method of mineral fixation is closely related to geologists. Ore carbonization is to use the basic oxides, such as magnesite (MgCO3) and calcite (CaCO3), existing in natural silicate ores (such as olivine), to convert CO2into stable inorganic carbonate,mainly to imitate the weathering process of calcium/magnesium silicate minerals in nature, to achieve CO2carbonization of ore.

In the natural environment, there are abundant minerals used in the carbonation of minerals, such as serpentine.Serpentine is a high magnesium mineral, which is mainly composed of MgO, SiO2, H2O, FeO, Fe2O3, NiO, and other components. Through treatment, the serpentine absorbs CO2and is stored as carbonate with a mild environment and stable chemical properties (Paulo et al., 2021). China is rich in serpentine mineral resources (Fig. 24), with proven reserves of more than 500×106t (Peng XY et al., 2019). In addition, a large number of industrial wastes (such as abandoned asbestos and tailings) need to be processed every year. Using the magnesium-containing components in a scrap of serpentine and its waste to fix CO2can not only recycle waste but also be a new method to slow down the greenhouse effect, which has a broad application prospect (Liu ZM and Wu YH, 2015).

Compared with solid materials, an aqueous solution rich in Mg2+/Ca2+can save the operation cost of Mg2+and the Ca2+leaching process. Therefore, mineralization through an aqueous solution rich in Mg2+/Ca2+may become another promising method to solve the CO2problem (Long C et al.,2019). Seawater/concentrated seawater in particular is very attractive for the use of CO2because it can solve both the problem of CO2fixation and the problem of seawater pretreatment or brine waste from desalination plants.

4. Future development

4.1. Problems and challenges

Fig. 24. Distribution of serpentine deposits in China (Dong FQ et al., 2015).

Whether in the world or China, the proportion of fossil fuels in energy consumption is still an absolute advantage.The utilization rate of fossil fuel combustion is low, and it pollutes the environment. The carbon dioxide and other gases released by combustion will easily cause the “greenhouse effect”, which will make the earth’s temperature rise year by year, cause climate anomalies, and have a serious impact on the sustainable development of the social economy. Although China’s energy consumption structure has been gradually improved, there is still a distance from the carbon-neutral target (Fig. 25). Geoscience plays an important role in the process of carbon neutrality, but there are still some problems and challenges.

Fig. 25. China’s energy consumption structure from 2002 to 2018(Liu MP, 2021).

First of all, in recent decades, China has made great progress in eight areas of carbon reduction, including natural gas hydrate, geothermal, hot dry rock, nuclear energy,hydropower, wind energy, solar energy, and hydrogen energy,but the relevant technologies are still immature. For example,in the exploration and utilization of natural gas hydrate, the overall investigation level is still low, which is far from finding out China’s overall resource status, predicting geological reserves, and meeting the needs of ensuring scale development (Wu NY et al., 2010). In terms of theoretical research, due to the uneven degree of exploration, the theoretical research of hydrate mineralization in the sea area is relatively weak and lagging behind, which affects the scientific evaluation of hydrate resource potential and the effective prediction of the metallogenic area (Wang X et al.,2014; Su PB et al., 2010); Hydrate production equipment and technology are faced with the problems of deep-sea shallow occurrence, complex reservoir geological conditions and so on. The traditional offshore oil and gas production equipment is difficult to use directly, so it is necessary to develop a complete set of special equipment from drilling and completion to production testing (Sha ZB et al., 2019).

There is still a big gap between China’s current mining technology and large-scale, long-term, and commercial development, so it is still necessary to further improve or innovate the trial production technology. In addition, due to the complex storage conditions, shallow burial, and severe tropical storms, the safe development, and utilization of marine hydrate still face many challenges (Gan HY and Wang JS, 2004; Wei HL et al., 2016); Compared with natural gas,coal-bed gas, and shale gas, the conditions of hydrate exploitation are more complex, which requires “separation of methane and water molecules” to achieve continuous and stable gas production. The objective conditions determine that the cost of hydrate exploitation is higher, which is not economical at present (Li JF et al., 2018; Ryu BJ et al., 2013).Therefore, on the whole, the problems faced by China in the field of carbon reduction include distribution of resource to be clarified, exploration and mining technology and equipment to be improved, mining technology and methods to be innovated, environmental safety prevention and control to be deepened, and mining economic benefits to be improved.

In the field of sequestration technologies including carbon capture, sequestration, and compressed air energy storage, the main problem is the need for strategic investment. Mature technologies and equipment are used to systematically obtain rock characteristic data. The storage of CO2and other gases is suitable for carbon sequestration only under certain geological conditions. Data on the properties of rocks such as salt or sandstone needs to be collected systematically to store CO2in areas where decarbonization may take place. Geological sites for permanent storage of CO2or seasonal storage of gas require detailed rock characterization. In addition, a combination of core data, well logging data, and seismic image data is often used to describe the characteristics of underground reservoirs, forming the basis of economic decisions on how to use these underground storage spaces.The problem of compressed air energy storage is the lack of underground gas storage (a 100 MW CAES power station requires 100000 m3of gas storage equipment), which is also one of the main factors restricting the promotion of CAES technology in China (Guo CB et al., 2019).

Key minerals needed to support carbon neutrality such as rare earth, lithium, cobalt, nickel, graphite, and serpentinite,etc. are essential for the energy transition. Although the exploration and research of these minerals have made good progress in China, there is still a lack of specific spatial distribution data and reserve data, which is still the focus of future research. It is also worth noting that the competition for control of the raw materials required for the energy transition is largely similar to oil-led geopolitics. Uneven geographical distribution, unbalanced supply and demand, and the difficulty of mining largely implicate that key energy elements are the focal point to future geopolitical competition for new energy (Cui SJ et al., 2020).

Zhong-li Ding, a Chinese academician on climate change,proposed three approaches to achieve carbon neutrality. First is the energy supply systems, it is important to use non-carbon energy to replace fossil fuel for electricity generation,hydrogen production, and develop new electricity system or energy supply system; second is energy consumption, try the best to replace fossil fuels with non-carbon energy in the household, transportation, industry, agriculture, and buildings;third is human carbon fixation, which removes the inevitable carbon emission from combing the measures of ecological restoration and conservation, soil carbon sequestration, and carbon capture and storage.

4.2. Opportunities for geoscience and geological technologies

The setting of China’s carbon neutrality target can inspire other countries to increase their confidence in coping with climate change, strengthen the establishment of national independent contribution targets, and effectively support the Paris Agreement. For a long time, geoscience has been considered an important part of the decarbonization solution.China has the best universities and research institutions, as well as the research bases of oil and gas companies, and has excellent research and development capabilities. China’s active promotion of carbon neutrality can help stimulate the research and creativity of these institutions. Geosciences are increasingly focusing on seasonal storage (such as hydrogen,air). Through the development of geoscience research and technological progress, it can integrate surface renewable energy such as solar energy and wind energy to promote current China’s energy system to achieve carbon neutrality as a reality. The research results of carbon neutrality and carbon peak by experts in geosciences fields can not only greatly increase the disciplinary influence of geoscience, but also give play to the social and ecological value of geoscience. In the process of promoting carbon neutrality, geosciences can help decision-makers understand the mechanism and value of carbon neutrality, promote the implementation of relevant policies, and the sustainable development of the entire“integrated system of man and nature”.

5. Discussion

The development of China’s geosciences and geologists can do a lot in carbon peak and carbon neutrality. Geoscience and geological technologies can not only contribute to carbon emission reduction and sequestration, raw materials needed for exploration and development of new energy, and serving the development of new energy, but also in the fields of underground space energy storage and natural disaster response. Considering the current status and development direction of China’s geoscience and carbon neutrality, the following four aspects still need to be further explored:

(i) The research and practice of carbon neutrality in China’s geosciences involve many fields, including three major aspects: carbon emission reduction and sequestration technology, and key minerals needed to support carbon neutrality. Hope to help carbon neutrality in many ways.However, the effects of various fields on carbon neutrality still need to be further evaluated, and it is still unknown which field has the highest benefits for China’s carbon neutrality.

(ii) The development of green energy such as natural gas,geothermal energy, hydropower, and hot dry rock is the main battlefield of geological work. Whether it is research or practice, China’s geoscience community has made important progress. However, the development of green energy involves multiple underground fluid phases, reactive rocks, fractures,and rock heterogeneity. Geological work requires complex imaging and detection for monitoring and verification. In addition, energy development also involves different types of land use on the surface, and even protected areas, which may have potential impacts on biodiversity and community residents. Geological work needs to be further evaluated and weighed against the pros and cons.

(iii) Geological work can provide geological support for new energy site selection. In reality, geological conditions are often unstable or unpredictable. Therefore, it is necessary to conduct in-depth geotechnical feasibility and mitigation measures, and form the basis of relevant economic decisions.Such as wind farm and solar energy site selection,hydropower station, pipeline layout, etc. all has special requirements on the geological environment. In particular, the location of offshore wind farms should fully consider the geological structure of the seabed and the depth of the seabed,which is beneficial to construction, reduces costs, and prevents geological disasters. Besides, the carbon trading market should be actively developed. The national carbon trading system initiated in 2017 which using economic measures to reduce the carbon emission of companies.

(iv) Supporting the carbon peak and carbon neutrality target also requires a lot of geological survey work. For example, the establishment of a complete carbon neutrality technology support system; actively participate in international organizations to enhance international exchanges and cooperation; carry out territorial and spatial carbon sequestration zoning, carry out nationwide CO2sequestration potential evaluation, and delineate potential areas; strengthen the innovative research on scientific and technological problems of geological artificial carbon sequestration, and gradually solve a series of geological scientific problems from carbon emission reduction to carbon sequestration; carry out CO2geological storage demonstration projects in typical areas, etc.

6. Conclusions

(i) Carbon neutrality is a global issue that requires participation and interdisciplinary research from all fields and disciplines. In the process of participating in research and practical work, the geosciences should give full play to its disciplinary advantages and use unique methods and technologies, such as remote sensing technology, exploration,and monitoring methods, to help achieve China’s carbon neutrality goal. In addition, all relevant departments within geosciences should also coordinate the development and organize research on natural resources strategies. Guided by the theory of earth system science, conduct theoretical system research on global climate change and other issues, and coordinate cutting-edge scientific information and advanced technology tools in various disciplines.

(ii) The Chinese geological science community has carried out a lot of work, in natural gas hydrate, geothermal, hot dry rock, nuclear energy, hydropower, wind energy, solar energy,hydrogen energy, and other unconventional energy fields; and carbon capture and storage, compressed air energy storage and other storage technology fields; as well as rare earth,lithium, cobalt, nickel, graphite, serpentine and other key minerals needed to support carbon neutrality. And important research results have also been achieved. The goal of carbon neutrality provides new opportunities and challenges for geoscience research. In the future, it is still necessary to provide theoretical and technical support from the above aspects. Enhance climate adaptability and support the achievement of carbon peak and carbon neutrality goals.

(iii) The Chinese government has issued a series of supporting policies and practical work to accelerate the realization of carbon neutrality industrialization and realize the sustainable development of clean energy. For example,accelerate the construction of a new power system that adapts to the development of a high proportion of renewable energy;adjust the energy structure. Increase the proportion of lowcarbon energy and non-carbon energy in the energy consumption structure; steadily promote hydropower development; safe development of nuclear power; speed up the development of photovoltaic and wind power; and the implementation of special financial support policies for green and low-carbon development and so on.

CRediT authorship contribution statement

Yao Wang conceived of the presented idea. Chi-hui Guo and Shu-rong Zhuang developed the theory and wrote the original draft. Xi-jie Chen, Li-qiong Jia and Ze-yu Chen modified the manuscript. Zi-long Xia and Zhen Wu collected the data and provided figures and tables in the manuscript. All authors discussed the results and contributed to the final manuscript.

Declaration of competing interest

The authors declare no conflicts of interest.

Acknowledgment

This study was supported by the project of China Geological Survey on a systematic assessment of ecological protection and natural resources utilization (DD20211413)