Power is an important perspective to better understand and analyze energy geopolitics, energy security, international energy cooperation and global energy governance. Based on the geographical attributes analysis of energy, the geopolitical attributes of energy are discussed and a connotation power system is constructed, including the resources power, trade and transportation power, capital power and technology power. Then, a geographical framework for the study of energy geopolitics and energy power is carried out. In the framework, resources power and trade power are considered as the core of traditional energy geopolitics, technological control and capital control are taken as the new focus of energy power. Economic globalization, regional integration and global energy governance expand the extension of energy power. Geographical distribution, changes of energy power from place space to flow space, interrelationship between energy actors and global energy governance, and the study of decision-making service for energy security are the four fundamental parts of energy geopolitics and energy power research.

Technology change is the material foundation of energy geopolitics transition. Different from the traditional view that "energy politics is equal to resource politics", this article argues that resource endowment and technology breakthrough are equally important in determining energy geopolitics dynamics. Energy technology can be divided into two categories, namely competence-enhancing technology and competence-destroying technology. For example, shale oil and shale gas extraction technology belongs to the first category and renewable energy technology belongs to the second, while the breakthrough in renewable energy technology will significantly reconstruct global energy structure. Tracing the history of technological transition, the dominant energy resource evolved from wood to coal, to oil and gas and then to renewables. The energy technology innovation cycles are closely intertwined with great powers' geopolitical competition, while major technology shift triggers the upgrade of energy utilization. The technology leading state could always exert its geopolitical advantages in each energy transition process, and the success of challenging state in replacing hegemonic state is always being supported by new energy technology innovation. With the arrival of the fourth industrial revolution, renewable energies, such as wind power, solar power and controllable nuclear fusion will substantively transform and reshape global energy geopolitics. Currently, two geopolitical consequences in new energy transition could be observed. (1) Accessibility and availability to critical elements, especially the rare earth, cobalt and lithium in renewable energy sector, will become the new battle fields of energy geopolitics. (2) Disruptive technology will be the linchpin in leading energy industry upgradation. Global powers such as China, US and EU have set up their roadmaps in promoting renewable energy development. Geopolitical competition among great powers will accelerate the evolution of the present round of energy transition. The progress of new energy technology will substantively affect energy security. On the one hand, the structure of major powers game and the implementation of energy diplomacy will largely differ from the past. On the other hand, the oil and gas related geopolitical conflicts will be largely decreased. In the meanwhile, the cut-off of grids will be a new weapon in global geopolitical game.

To date, there are two significant issues including the "shale gas revolution" in the US and the rise of China, which have restructured greatly the distribution and hierarchies of international energy power system. On the basis of two theories of power interdependence and balance in international politics and geopolitics, this paper constructs the theoretical framework and models of energy power, and portrays spatial dynamics of energy power territories and balance areas between the US and China. Results are obtained as follows: First of all, with the rapid evolution of international energy power system and energy trade network, the energy power space of China and the United States has undergone tremendous changes. Secondly, the coal power and natural gas power spaces between China and the United States have basically formed relatively stable regional groups. China's crude oil power space maintains a strong global expansion trend, while the US crude oil power space faces transformation and reconstruction. Thirdly, the balance areas of energy power between China and the United States are constantly fragmented and relatively concentrated in most parts of Europe, Southern Africa and East Asia. According to the characteristics of energy resources and geopolitics, they are divided into five types, namely, the resource endowment type, the resource consumption type, the geographical channel type, the political and economic separation type, and the third-country controling type. Finally, focusing on these types, we suggest some policies. It is necessary to enlarge energy trades and investments with resource endowment countries, to strengthen energy technology cooperation with resource market-oriented countries, to ensure the security and fluent flows of energy transport channels, to strengthen economic cooperation with the political-economic separation countries to influence their diplomatic policies, and to reasonably arrange energy cooperation with the third-country controlling countries. These conclusions are expected to play a guiding role in China's energy trade cooperation, which is of great significance to this country's energy security.

Under the background of economic globalization, the internationalization of national energy security issues has become increasingly prominent. Since the beginning of the 21st century, along with the acceleration of world multi-polarization, the study on the evolution characteristics of global energy security's pattern and its driving mechanism has become one of the key issues in the field of energy geopolitics. Based on this understanding, this paper systematically evaluates the energy security status of 124 countries since 2000, reveals the evolution characteristics and its mechanism, and identifies the major geopolitical threats. The results show that: (1) Since the beginning of the 21st century, the evolution of the global energy security pattern has been continuously optimized, but it has shown obvious phase characteristics. Since 2010, the optimization trend has become more significant. (2) The global energy security pattern is basically consistent with the international order, that is, energy-safe countries are concentrated in economically developed regions of Western Europe and North America, and the relatively safe countries are mainly distributed in Central Europe, Latin America, and high-income regions in Asia. The countries with transitional energy system are mainly distributed in the developing regions of Middle East, Southeast Europe, and East Asia, while countries with dangerous or relatively dangerous energy system are economically underdeveloped regions in Africa and South Asia. (3) In the past 20 years, the world's energy security level has improved significantly, which is mainly driven by climate-friendly green technologies and the continuous downturn in oil price. For this reason, the level of energy security in developed economies has increased significantly. However, due to the low innovation capacity, backward productivity, and low disposable income of residents, developing countries have less room for improvement in energy security. (4) In the context of the rise of populism, the intensification of trade barriers and the strategic contraction of the United States in the Middle East, the global energy security pattern in the future will be affected by the changes in China-US relation, the increasing urgency to promoting the energy transition, and the polarized political climate.

The security of crude oil supply plays an important role in China's national security, so quantitative assessment for it can provide some policy references for risk prevention. The event data analysis model was employed to quantitatively measure the bilateral relations between China and 21 major crude oil suppliers. The results show that the relations between China and most of its crude oil trading partners are at medium and low levels, but the overall trend has been rising in recent more than ten years, which indicates that crude oil import has a certain risk of political relations but tends to decline. Eleven indexes from five aspects of resources, politics, economy, transportation and military were selected, and the weights of the indexes were determined by combination weighting method. The set pair analysis model was used to evaluate the supply security degree of 21 source countries of China's crude oil import and then the main obstacle factors were identified. The results show that there are significant differences in the supply security degrees of the 21 countries. Some of the Middle East countries, Russia, Venezuela and Kazakhstan have a high degree of supply security, while most African and Asia-Pacific countries have a low degree of supply security. Crude oil resource status, transportation risks and political risks of the suppliers are the main obstacles to the supply security of most suppliers. To prevent risks, China should take policy measures such as pursuing multilateral energy diplomacy and expanding strategic petroleum reserves.

In order to assess the situation of natural gas security in major countries, this study introduces and revises APERC's 4A Energy Security to construct a scientific and quantifiable natural gas security indicator system by using the Analytic Hierarchy Process (AHP) and Delphi method. The study draws the following conclusions. (1) The countries ranking at the top of natural gas security list are natural gas exporters with excellent performance in four dimensions (Availability, Accessibility, Acceptability, and Affordability). (2) The indicators of recoverable reserves of natural gas and affordability of consumers are more important than the other six indicators. (3) Compared with importers, natural gas export countries have obvious advantages in Availability, Affordability and Accessibility. Finally, according to the main findings in this research, China should make efforts to develop its natural gas industry, improve market mechanism, diversify its import sources, and efficiently utilize natural gas resources.