Application and Development Countermeasures of CCUS Technology in China’s Petroleum Industry

: Greenhouse gas emissions cause many global problems. Under the strong promotion of the government’s two-carbon goals policy, China’s petroleum industry is actively carrying out the application of carbon capture, utilization, and storage (CCUS). The energy consumption and carbon emissions in China are reviewed, and the importance of the petroleum industry in the process of carbon emission reduction is clariﬁed. The applications, advantages, and disadvantages of carbon capture, carbon utilization, and carbon sequestration technologies in China’s petroleum industry are summarized, respectively. The current challenges and risks faced by China’s petroleum industry in the operation of CCUS projects are analyzed, and corresponding suggestions are provided. This article aims to systematically provide references and help for the application of CCUS in China’s petroleum industry.


Introduction
Climate change affects human' survival and social development, and is a global issue that has attracted international attention. In September 2020, the Chinese government proposed two-carbon goals at the United Nations General Assembly; that is, the goals of "carbon peaking" in 2030 and "carbon neutrality" in 2060 [1][2][3]. According to the China Carbon Dioxide Capture, Utilization and Storage (CCUS) Annual Report (2021) issued by the Environmental Planning Institute of the Ministry of Ecology and Environment of the People's Republic of China, by the end of 2020, about 40 CCUS demonstration projects had been put into operation or were under construction in China [4][5][6][7]. These mainly focus on small-scale oil capture and displacement demonstrations in petroleum, coal chemicals, and power industries; and on the development of the carbon dioxide-enhanced oil recovery (CO 2 -EOR) project. As typical energy-intensive industries, the oil, gas, and coal industries have become the main experimental and research objects of CCUS technology when it was first proposed. The natural storage environment of oil and gas fields also provides new ideas for CO 2 storage. CO 2 injection proved to positively impact the production from near-abandoned oil and gas wells at a lower cost than conventional refract. The research results have also greatly stimulated the enthusiasm of the oil and gas industries to promote the further development of CCUS technology [8]. China's three major state-owned oil companies (PetroChina, Sinopec, and CNOOC), which are the main controllers of China's petroleum industry, are also actively promoting the two-carbon goals.
China attaches great importance to the basic research and technology development of CCUS. In 2003, China funded the first CCUS-related research funded by the National Science and Technology Program through the National Natural Science Foundation. In 2011 alone, 36 studies were supported by the National Science and Technology Program. By the end of the "Twelfth Five-Year Plan" period, more than 140 research projects had been funded by the National Science and Technology Program, mainly in capture and Atmosphere 2022, 13, 1757 2 of 9 storage technologies. In 2021, the National Natural Science Foundation of China launched the research on major basic scientific problems and countermeasures for national carbon neutrality; and will carry out special funding work for CCUS theory, technology, database, risk assessment, and other aspects [9][10][11][12][13][14].
CCUS technology is an internationally recognized carbon emission reduction technology. The early construction and operation costs of carbon capture and storage (CCS) were high, and only capital input had no output benefits, which limited the development of CCS technology. Later, CCUS technology strengthened the research and development of CO 2 utilization. Converting CO 2 into energy or substance has realized carbon cycle rebalancing, increased the economic benefits of CCUS, and made it the most practical and feasible technical solution to reduce carbon emissions on a large scale [15][16][17]. In China, CCUS still has a large development space and funding gap. According to the technology development roadmap of the Ministry of Science and Technology, it is necessary to realize the extensive deployment of CCUS and new regional formats in 2050, with the carbon dioxide utilization and storage capacity reaching 800 Mt/a [18,19]. This paper will first summarize China's energy consumption and carbon emissions to illustrate the urgency and necessity of developing CCUS technology. Then, we will talk about the application of capture, utilization, and storage in China's petroleum industry at this stage; and analyze the effects, challenges, and policy prospects.

Energy Consumption and Carbon Emissions in China
Since China joined the WTO in 2003, as the world factory, it has produced a large number of daily necessities for most countries in the world. However, rapid economic development and extensive industrial production have resulted in large energy use (Figure 1) [20] and a huge amount of carbon emissions ( Figure 2) [21][22][23]. At the same time, it can also be seen that the growth rate of total carbon emissions in recent years has been significantly slower than that of energy consumption, which indicates that the intensity of carbon emissions has decreased significantly. The growth rate of China's energy consumption will slow down further and the elasticity coefficient of energy consumption will also decline, which is lower than the level at the beginning of the 21st century. After 2035, China's energy consumption will enter a low growth period of about 2% [24,25]. Clean, low-carbon, and efficient energy consumption has become an inevitable trend in China [26].
CCUS technology is an internationally recognized carbon emission red nology. The early construction and operation costs of carbon capture and st were high, and only capital input had no output benefits, which limited the d of CCS technology. Later, CCUS technology strengthened the research and d of CO2 utilization. Converting CO2 into energy or substance has realized car balancing, increased the economic benefits of CCUS, and made it the most p feasible technical solution to reduce carbon emissions on a large scale [15-1 CCUS still has a large development space and funding gap. According to the development roadmap of the Ministry of Science and Technology, it is necessa the extensive deployment of CCUS and new regional formats in 2050, with dioxide utilization and storage capacity reaching 800 Mt/a [18,19]. This paper will first summarize China's energy consumption and carbo to illustrate the urgency and necessity of developing CCUS technology. Then about the application of capture, utilization, and storage in China's petroleum this stage; and analyze the effects, challenges, and policy prospects.

Energy Consumption and Carbon Emissions in China
Since China joined the WTO in 2003, as the world factory, it has prod number of daily necessities for most countries in the world. However, rap development and extensive industrial production have resulted in large ener ure 1) [20] and a huge amount of carbon emissions ( Figure 2) [21][22][23]. At the can also be seen that the growth rate of total carbon emissions in recent ye significantly slower than that of energy consumption, which indicates that of carbon emissions has decreased significantly. The growth rate of China's sumption will slow down further and the elasticity coefficient of energy consu also decline, which is lower than the level at the beginning of the 21st century China's energy consumption will enter a low growth period of about 2% [2 low-carbon, and efficient energy consumption has become an inevitable tre [26].  As China's economic development has gradually entered a new normal stage optimization and adjustment of the industrial structure, the demand for energy, and environmental protection requirements have promoted the development of China' ergy in a cleaner, more efficient, more intensive, lower carbon, and more diversifie rection. At this stage, China is in an important period of energy transformation. The stitution effect of low-carbon and clean energy on coal has been significantly enhan and the policy of energy conservation and consumption reduction will continue to be moted. In the past, China's economic development relied too much on the consump of carbon energy. Coal is a major component of China's energy consumption [27]. Ov the proportion of coal consumption has gradually decreased, while the proportion of ural gas, primary electricity, and other energy sources has gradually increased (Figu [20]. Economic development plays a leading role in the growth of natural gas consu tion demand. According to this trend, natural gas use will continue to grow stea While the total amount of carbon emissions increases and the emission intensity grad decreases, carbon capture, utilization, and storage of CO2 are important means to ach carbon neutrality [7,[28][29].  As China's economic development has gradually entered a new normal stage, the optimization and adjustment of the industrial structure, the demand for energy, and the environmental protection requirements have promoted the development of China's energy in a cleaner, more efficient, more intensive, lower carbon, and more diversified direction. At this stage, China is in an important period of energy transformation. The substitution effect of low-carbon and clean energy on coal has been significantly enhanced, and the policy of energy conservation and consumption reduction will continue to be promoted. In the past, China's economic development relied too much on the consumption of carbon energy. Coal is a major component of China's energy consumption [27]. Overall, the proportion of coal consumption has gradually decreased, while the proportion of natural gas, primary electricity, and other energy sources has gradually increased ( Figure 3) [20]. Economic development plays a leading role in the growth of natural gas consumption demand. According to this trend, natural gas use will continue to grow steadily. While the total amount of carbon emissions increases and the emission intensity gradually decreases, carbon capture, utilization, and storage of CO 2 are important means to achieve carbon neutrality [7,28,29]. As China's economic development has gradually entered a new normal stage, the optimization and adjustment of the industrial structure, the demand for energy, and the environmental protection requirements have promoted the development of China's energy in a cleaner, more efficient, more intensive, lower carbon, and more diversified direction. At this stage, China is in an important period of energy transformation. The substitution effect of low-carbon and clean energy on coal has been significantly enhanced, and the policy of energy conservation and consumption reduction will continue to be promoted. In the past, China's economic development relied too much on the consumption of carbon energy. Coal is a major component of China's energy consumption [27]. Overall, the proportion of coal consumption has gradually decreased, while the proportion of natural gas, primary electricity, and other energy sources has gradually increased (Figure 3) [20]. Economic development plays a leading role in the growth of natural gas consumption demand. According to this trend, natural gas use will continue to grow steadily. While the total amount of carbon emissions increases and the emission intensity gradually decreases, carbon capture, utilization, and storage of CO2 are important means to achieve carbon neutrality [7,[28][29].

Progress of CCUS Technology in China's Petroleum Industry
In recent years, international oil companies have actively announced the carbon peak and carbon neutral targets under the national level of vigorously promoting greenhouse gas emission reduction measures. Among them, the oil company alliance represented by the Oil and Gas Industry Climate Initiative (OGCI) has set an example, and actively set emission reduction targets and scope [30]. Some well-known international oilfield technology service companies, such as Schlumberger, Halliburton, Baker Hughes, and National Oilwell Varco, have carried out corresponding new energy business [31], setting 2050 as the deadline for achieving net zero carbon emissions. Chinese oil companies are also vigorously promoting the application of CCUS.

Carbon Capture
From the perspective of the capture process, it mainly includes capture after combustion, capture before combustion, and capture by oxygen-enriched combustion. In terms of capture methods, they mainly include the chemical absorption method, physical adsorption method, membrane separation method, low-temperature distillation method, etc. [32][33][34]. Among them, the chemical absorption method is the most commonly used capture method for Chinese oil companies. For example, chemical absorption method is used for CO 2 capture in the refinery tail gas capture project of Zhongyuan Oilfield and the high carbon natural gas capture project of Songnan Gas Field.
The main reason for the high cost of carbon capture is a large amount of energy consumption in the capture process. Therefore, reducing the energy demand in the process of carbon capture is the main research direction of carbon capture development at this stage [35].

Carbon Utilization
In the petroleum industry, it is mainly divided into two aspects: geological utilization and geological storage. CO 2 geological utilization refers to the technology of injecting CO 2 into the reservoir to improve the recovery efficiency. It can be subdivided into the following categories: CO 2 enhanced oil recovery (CO 2 -EOR), CO 2 enhanced coalbed methane recovery (CO 2 -ECBM), CO 2 enhanced natural gas recovery (CO 2 -ENGR), CO 2 enhanced shale gas recovery (CO 2 -ESGR), CO 2 enhanced saline water recovery (CO 2 -ESWR), and CO 2 storage in a depleted reservoir (CO 2 -SDR) [36][37][38]. CO 2 geological utilization technology can reduce the CO 2 utilization cost by replacing CO 2 with formation resources, which is conducive to large-scale industrial promotion and application. CO 2 -EOR can be used and stored synchronously. At present, a large number of projects have been applied and certain economic benefits can be achieved [39]. As of 7 August 2022, PetroChina Jidong Oilfield has applied CO 2 huff and puff, and CO 2 oil displacement technology in the reservoir; in addition, it has achieved a significant production increase. The accumulated comprehensive utilization of CO 2 exceeds 108 × 10 4 t; a cumulative oil increase of 98 × 10 4 t. On 29 August 2022, Sinopec announced that the "Qilu Petrochemical Shengli Oilfield Million ton CCUS Project", China's largest demonstration base for carbon capture, utilization, and storage of the whole industrial chain, was officially put into operation. This marks that China's CCUS industry has entered the middle and late stage of technology demonstration-mature commercial operation. The project covers more than 25 million tons of ultra-low permeability reservoir reserves and 73 injection wells are deployed. It is estimated that the cumulative injection of more than 10 million tons in 2015 will increase oil by nearly 3 million tons and the recovery factor will increase by more than 12%. The primary storage rate of CO 2 can reach 60% to 70%.

Carbon Storage
With the significant reduction of CCUS technology cost and energy consumption, CO 2 storage technology is used as a supplement to CO 2 geological utilization. Carbon storage technology is mainly used to inject captured CO 2 into deep salt water layers, deep coal Atmosphere 2022, 13, 1757 5 of 9 seams and oilfields without commercial exploitation value, depleted natural gas fields, etc. [40][41][42]. The deep salt water layer is widely distributed in the inland and marine sedimentary basins of China. Because of its huge CO 2 storage space and long CO 2 injection duration, it is conducive to the implementation of large capacity CO 2 geological storage projects. Therefore, CO 2 deep salt water layer storage technology is considered as one of the technologies with the most CO 2 storage potential.
The China Shenhua Coal to Liquid Deep Salt Water Layer CO 2 Capture and Storage (CCS) Demonstration Project has accumulatively injected 3 × 10 5 t CO 2 ; it is currently the largest CO 2 saline water layer storage project in Asia [43]. However, in order to ensure the feasibility and safety of geological storage, and prevent potential environmental risks, such as fault activation and earthquake events that may be induced, the pollution of freshwater aquifers caused by carbon dioxide escape, and leakage endangering human health and local ecosystems nearby, a large number of geological surveys, sampling, and analysis have been carried out in the early stages of the project, as well as multiple fracturing treatments [44]. After injection, several sets of detection systems were installed for continuous monitoring. These have greatly increased the project cost. China's oil companies have also carried out CO 2 storage for many years. The storage area varies from 1.2 km 2 to 60.8 km 2 . The total injection amount also ranges from 1 × 10 4 t to 30 × 10 4 t.

Challenges Faced by Large-Scale Applications
China's CCUS technology started later than that in Europe and the United States. Capture technology: the pre-combustion capture technology is relatively mature and some of them have commercial capabilities. The post-combustion capture technology is at the primary application stage; especially, the post-combustion chemical absorption method has a large gap with its international leading commercial application. The second generation capture technology is still in the development stage [45][46][47]. Transportation: land transportation and inland ship transportation technologies have been relatively mature. However, the design of the supporting land transmission pipeline and pipe network is still in the early stage. For the development of submarine pipeline transportation technology, it is still in the conceptual design stage [48,49]. Utilization: CCUS-EOR and other projects are still in the stage of industrial demonstration research and development. Storage: the demonstration project of seabed CO 2 storage has not been carried out yet. The volume of other storage projects is significantly different from that of Europe, America, and other regions [35].
At present, local governments and oil enterprises have shown high enthusiasm for CCUS; however, once the project is approved or implemented, it is difficult to promote it. The large-scale application of CCUS in China's petroleum industry faces many challenges, including technology, environment, capital, and policy [50][51][52][53]: (1) High investment cost. The investment subjects of CCUS technology are basically state-owned energy enterprises. The initial investment and maintenance costs of the whole process are high, and the payback period is long. The high investment cost is the main reason hindering the large-scale industrialization of CCUS.
(2) Lack of CO 2 gas sources. The scale of available CO 2 sources in major Chinese oil companies is small and scattered. The lack of matching bridges between oil fields and carbon sources also makes it difficult for oil companies to start large-scale CO 2 flooding and storage projects.
(3) The technical level of CCUS still needs to be developed. Generally speaking, China's CCUS technology is in the stage of industrialization and testing; and there is still a gap between it and the international advanced level. At present, there are still a lot of technical problems that need to be solved or improved in the application of CCUS technology in China's petroleum industry.
(4) Environmental safety. There are certain environmental risks in the process of CO 2 capture, transportation, utilization, and storage.
(5) Low market participation. At present, China's CCUS applications are mainly government-driven projects; and private enterprises are less involved in the research and development, and promotion of this technology. Therefore, Chinese oil companies should effectively promote diversified market players to enter the CCUS cooperation and competition.
(6) Lack of collaborative cooperation. The application and promotion of CCUS requires the joint cooperation of multiple industries and multiple parts. Except for a small amount of cooperation in the power and oil industries, there is currently less cross-industry cooperation.
(7) The standards and specifications are not clear. Due to the small number of operating projects, there is a lack of clear industry standards and operating specifications, which in turn limits the large-scale application of CCUS.
(8) Insufficient policy coordination. The advancement of the CCUS project depends on the government's financial and policy support. Support should highlight not only economic benefits, but also social benefits. At present, the policies introduced by various departments are relatively independent and lack corresponding coordination.

Development Strategy
The development of technology is not achieved overnight. The government, society, and enterprises need to coordinate and cooperate from various aspects. In the face of these challenges, the following development strategies are proposed [54][55][56]: (1) Strengthen key technology research. It is suggested that the government should coordinate enterprises and research institutions to jointly tackle key problems and promote collaborative innovation. Focusing on key links, such as carbon dioxide capture, industrial utilization, sequestration, and carbon sink measurement, we will tackle key problems in core technology and promote the technological upgrading of CCUS's entire industrial chain.
(2) Methods and standard system construction. This is an important link to realize the standardization of CCUS industrial development. CCUS standard specification systems and management systems need to be established; establish a series of standards and specifications covering CO 2 capture, transmission, storage, monitoring and evaluation, emission reduction verification, etc.
(3) Establish a good CCUS financial ecology. CCUS is a technology with a high investment risk. Reasonable and effective CCUS investment and financing channels play a vital role in industrial development. Building a good CCUS financial ecology can accelerate the sound development of its industry.
(4) Accelerate CCUS pipeline network layout and cluster infrastructure construction; increase the investment in relevant infrastructure and strengthen the construction of a transport network; to form a CCUS industrial center based on pipe network facilities and storage sites.
(5) Incorporate CCUS into the carbon emission trading system; formulate supporting systems and methods; reasonably allocate quotas; and clarify emission reduction throughout the life cycle. Thus, it will bring certain economic income to enterprises applying CCUS technology and absorb some carbon sequestration costs.
(6) The government should improve the fiscal and tax incentive policies, and laws and regulations system. CCUS should enjoy the same supporting policy support as renewable energy and other low-carbon clean energy technologies. Industry norms, the system and regulatory framework, and technical specifications should also be improved.

Summary and Recommendations
Chinese oil companies mainly use the most promising chemical absorption method for CO 2 capture. CO 2 oil displacement technology can realize storage and utilization simultaneously; and Sinopec and PetroChina have both carried out large-scale application. CO 2 storage technology has greatly improved the CO 2 emission reduction capacity, which has been carried out by Chinese oil companies for many years and has achieved good results. The large-scale application of CCUS in China's petroleum industry is facing many challenges. These include technology, environment, capital, market, standards, policies, and other aspects. The government, enterprises, and research institutions shall make overall plans for development and collaborative innovation; promote the development of CCUS core technology; establish a good ecology, reasonable standards, and norms; accelerate the construction of a CCUS pipeline network and infrastructure; incorporate CCUS into the carbon emission trading system; improve the fiscal and tax incentive policies, and laws and regulations system; improve the core competitiveness of CCUS technology in an all-round way; control greenhouse gas emissions; and improve energy and resource utilization efficiency.
Author Contributions: Conceptualization, X.C. and X.Y.; methodology, X.Y.; investigation, X.C. and Z.Z.; writing-original draft preparation, X.C.; writing-review and editing, X.C.; visualization, Y.Z.; supervision, X.Y. All authors have read and agreed to the published version of the manuscript.
Funding: This research received no external funding.

Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.

Conflicts of Interest:
The authors declare no conflict of interest.