Based on analyzing the history of shale revolution in the United States and the differences in geological and engineering characteristics of shale oil between continental basins in China and marine basins in the United States, the paper proposes ten noteworthy issues on continental shale oil revolution in China, including the application and evolution of the nomenclatures of shale oil and tight oil in U.S., the development process of shale oil/tight oil in U.S., the proposal and connotation of shale revolution, and the experience in system and mechanism that can be learned from successful shale revolution in U.S., the work pattern of shale oil in U.S., the relationship between the profit model of shale oil and investment channels, the relationship between production declines of shale oil, the concrete time when a breakthrough is made in shale oil exploration in China, the principles and standards for classification of shale oil, and the continental shale oil revolution in China. Research suggests that the concepts of shale oil and tight oil in North America are identical to some extent. The core of "shale revolution" in U.S. is to improve drilling and completion efficiency, reduce well construction costs, and increase single well production; the development stages of its work pattern is divided according to the changes in both well type and horizontal section length of horizontal well, as well as the development of hydraulic fracturing. The number of drilled and completed wells is an important indicator reflecting shale oil exploration and development. The profit models and investment channels of shale oil extraction are closely related. American companies’ pursuit of recovering investment as soon as possible to obtain profits leads to the general adoption of a production model based on pressure release, with a rapid decline in yield and an L-shaped production curve. In terms of system and mechanism, we should draw on the experience from the application of market mechanisms, the project operation model of "oil companies+lean management", as well as the establishment of shared and open databases. From the perspective of resource base, engineering and technological capabilities, and production expectations, China has the basic conditions for the success in the continental shale oil revolution. All efforts should be made to promote the marketization, technological and management transformation of shale oil exploration and development, highlight the "qualitative development and quantitative breakthrough" of shale oil, and effectively transform resources into reserves and then into beneficial production, which can ensure the victory of shale oil revolution.

Currently, sweet spot evaluation plays an important role in unconventional oil and gas exploration and development, which is of great significance to the large-scale efficient development of unconventional oil and gas. The concept connotation of sweet spot has been increasingly expanded and more diversified and regional the corresponding evaluation parameters and standard values are more diversified and regionally distinctive. At present, the commonly-used sweet spot evaluation and prediction methods include the contour map semi-quantitative plane superimposition evaluation method, the sweet spot quantitative and semi-quantitative evaluation method based on multi-parameter co-constraint, the radar graphic method, and the sweet spots quantitative evaluation method established based on the geological anomaly theory. In the practical application, the applicability evaluation and prediction method should be developed according to the basic data such as tectonic depositional settings, lithological association and resource type of the basin, and the principle of superposed progressive discrimination. Continental shales in China are highly heterogeneous, and there is a significant difference in the enrichment laws and main controlling factors of different types of shale oil. Both interlayer and hybrid shale oil have experienced migration and accumulation in the source. The main lithology of the reservoir is sandstone (siltstone) and carbonate rock (hybrid sedimentary rock). The reservoir property, hydrocarbon potential and brittleness of reservoirs are the key indicators. The pure shale oil intervals in the thick and ultra-thick layers is generally oil-bearing, and the oil is mainly retained in the source. The source rocks are the reservoirs. It is suggested to use the trichotomy method to divide hydrocarbon enrichment layers into Type I, Type II and Type III using 5~8 key parameters based on the data of sedimentary cycle, laminated texture type, lithological association, hydrocarbon potential, reservoir property, compressibility, mobility and recoverability. During the optimization of enrichment layers, zoning should be planned according to the thermal evolution maturity of different basins and zones. In the medium-low maturity zone, the medium-high TOC content shale interval (felsic laminae develop) adjacent to the high TOC content shale interval should be optimized; in the medium-high maturity zone, the high TOC content shale interval should be optimized. As the "gold target layer", Type I oil reservoir should be developed and produced initially, and progressively exploited according to technological maturity, so as to realize the maximum development and utilization of China's continental shale oil resources, and effectively serve to guarantee the national energy security.

As a type of unconventional oil and gas resources, shale oil and gas are self-generated and self-preserved. Divided according to the thermal maturity, medium-high maturity and medium-low maturity shale oil can be obtained; when divided according to the depositional environment of shale, marine, transitional and lacustrine facies shale gas are obtained. China is one of the most successful countries that have achieved large-scale commercial development of continental shale oil in the world. Significant discoveries of continental shale oil have been made successively in the Ordos Basin, Junggar Basin, Songliao Basin and Bohai Bay Basin. The marine shale gas industry has achieved breakthroughs and rapid scale development in the Sichuan Basin and surrounding areas. By the end of 2021, a total of 8 shale gas fields had been found in southern China, with the proved geological reserves totaling 2.74×10 ¹²m ³. In 2021, the annual production capacity of shale gas was 230×10 ⁸m ³, bringing the total production capacity to 924×10 ⁸m ³. The shale oil and gas resources in China have great potential, but there are many challenges during the large-scale exploration and beneficial development. Based on the development experience of shale oil and gas in foreign countries and relevant inspirations, it is suggested that the state takes the lead in evaluating and implementing the technologies that can convert black shales or high-carbon coals into oil and gas, estimating the total amount of economic resources involved, and formulating corresponding development plans. Additionally, national pilot test areas should be set up for in-situ conversion of black shales and high-carbon coals into oil and gas, and fiscal incentives and tax support policies for the conversion of shales and coals into oil and gas should be introduced and implemented to promote the maturity and conversion of underground shales and the heated conversion of underground coals into oil and gas. Moreover, national top-level design and coordinated investment should be implemented to establish the base of "worldwide super energy basins" represented by Ordos Basin and Sichuan Basin, so as to achieve the collaborative and integrated development of underground and overground resources such as renewable energy sources on the ground and oil, gas, coal, heat, lithium and uranium resource under the ground, involving CO ₂ capture and storage (CCS) and CO ₂ capture, utilization and storage (CCUS).

China has a complete range of coalbed methane (CBM) resources, which are extremely rich and relatively reliable. The resource foundation can completely form an emerging industry with an annual gas production of hundreds of billions of cubic meters. With strong national support, after 30 years of arduous efforts, China has made significant progresses in the exploration and development of coalbed methane, forming an industry with an annual production of 10 billion cubic meters. However, this is too far from the goal of 100 billion cubic meters of coalbed methane annually, and the national task has not been completed for three consecutive Five-year plans. At the same time, China CBM industry has lost its clear development direction. Only a small contribution can be made to the urgently needed natural gas industry in China. The fundamental reason is that the theory and technology of CBM exploration and development established domestically and internationally over the past 30 years can not fully reflect the composition and pore structure characteristics of coal, as well as the occurrence state of methane mainly in an adsorbed state, which is not fully in line with the mechanism of CBM production, of which applicability is too small to be universal. On the basis of in-depth analysis of the mechanism of coalbed methane production, it is proposed that only the integration of coal mine gas and natural gas development disciplines can establish scientific and practical theories and technologies for CBM exploration and development. Then, four types of CBM resources are divided. Moreover, each CBM resource can be established with scientific and practical theories and technologies to achieve efficient exploration and effective development. This article discusses the possibility and implementation path of building a 100 billion-cubic-meter-scale CBM industry in China from aspects such as the status of CBM resources, progress in oil and gas exploration and development technology, occurrence and migration laws of methane in coal. This article proposes to rely on the cross integration of coal and oil and gas industries, strengthen basic research, establish a theoretical and technical system suitable for efficient exploration and effective development of various types of coalbed methane reservoirs, generate a new discipline (direction), form a new production, technology, and industry field, and build a path of a large industry, To achieve the development strategy of forming an emerging coalbed methane industry supported by original theories and technologies of coalbed methane exploration and development, and to ensure the rapid formation of China's annual production of a 100 billion-cubic-meter-scale CBM industry, in order to significantly reduce China's dependence on external natural gas.

Archean buried-hill zone in the western section of Bonan low salient of Bohai Bay Basin has good conditions for hydrocarbon accumulation. Bozhong26-6 oilfield is an Archaean integrated oilfield with proven reserves of crude oil exceeding 100 million tons. Based on a large number of core, thin section, well logging and geochemical data, a systematical study was performed on Bozhong26-6 oilfield. The analysis suggests that the Archean buried-hill reservoirs can be vertically divided into weathered conglomerate zone, weathered fracture zone and bedrock zone, among which the weathered fracture zone is the key reservoir development zone. The superimposed fractures formed by the Indosinian, Yanshanian and Himalayan movements provided the foundation for the development of Archaean buried-hill reservoirs. The Indosinian compression and collision and the Yanshanian strike-slip thrust were the main driving forces for the formation of fractures, and the south-north extension of the Himalayan epoch maintained the validity of earlier fractures. Under the communication of fractures, a wide area of high-quality buried-hill reservoirs is formed by the dissolution of atmospheric fresh water, and the high-quality reservoirs are developed in the zone within 420 m away from the unconformity. The mudstone of Dongying Formation with weak overpressure and strong stability overlying buried hill provides good sealing conditions for the preservation of large-scale oil reservoirs. The Archean buried hills are in direct contact with the source rocks of Huanghekou sag in the south, and are connected with the source rocks of Bozhong sag in the north by the unconformity, thus forming a multi-dimensional oil-gas migration and charging mode. In conclusion, the above findings provide a guidance for the efficient exploration of Archean high-abundance oil reservoirs in Bozhong26-6 oilfield, further improve the hydrocarbon accumulation and reservoir mode of deep Archean buried hills in Bohai Bay Basin, and are of important guiding significance for the oil and gas exploration of the Archean buried hill zone around the southwest Bozhong sag.

Oil and gas are generated from organic matters in the rocks of sedimentary basins. Through an intensive and systematic study of global petroliferous basins, it is recognized that the distribution of global oil and gas fields is highly uneven, and most of oil and gas are enriched and accumulated in a few strata of sedimentary rocks. The distribution of oil and gas is significantly controlled by source rock, so that it is necessary to search for the source rocks initially before discovering new petroliferous basins. The nutrients required for biological growth in the sedimentary basins primarily come from rivers, and the nutrients flowing from rivers into the sedimentary basins control the degree of biological reproduction, and then control the abundance of organic matters in the source rocks, which decides the amount of oil and gas generated and the degree of enrichment of oil and gas resources in the sedimentary basins. Oil and gas are mainly distributed in the three systems on the earth, i.e., the river-lake system, river-gulf system and river-delta system. Specifically, the river-lake system is an important oil-bearing area on the earth. Lacustrine oil is mainly produced by sedimentary organic matters from the algae died in lakes. The growth of algae depends mainly on the nutrients that come from the rivers and flow into the lakes, and these nutrients can facilitate the growth of algae in the rift period and provide a guarantee for the formation of high-quality source rocks. The river-gulf system is the main distribution location of global marine oil. Gulfs are the estuary of rivers, which brings abundant minerals for rivers to promote the growth and proliferation of algae and other aquatic organisms; moreover, the gulfs are relatively isolated, which are conducive to the preservation of organic matters. In fact, boasting of the biggest reserves, the coal-type gas generated from coal-measure source rocks is the most widely distributed in the world and is mainly distributed in the river-delta system. The sediments brought by the river provide fertile soil for the growth of higher plants, and the native higher plants on the river-delta plain provide a solid material basis for the formation of coal-measure gas source rocks. The delta stratum reservoir is well developed with good reservoir-caprock configuration, which is beneficial for natural gas enrichment and accumulation.

Shale reservoirs are characterized by their nanometer pore size. At the nanoscale, fluid flow mechanisms and phase behaviors are significantly influenced by the size and surface effects, resulting in deviations from classical fluid theories. Conventional oil and gas reservoir engineering theory is not fully applicable to shale reservoirs, restricting the efficient development of shale oil and gas. It is thus of both scientific significance and engineering value to clarify fluid transport and phase properties at the nanometer pore scale of shale. Nanofluidics, with the capabilities of precisely manufacturing pore structure and observing in-situ fluid behaviors at the nanoscale, gives new experimental insights into microscopic seepage and phase behavior of shale oil and gas, and provides essential validation for theoretical studies. This paper reviews recent research progress on the nanofluidic study of the nanoscale single- and two-phase flow of oil, gas and water, phase behavior of single- and multi-component hydrocarbons, diffusion and mixing process, as well as microphysical model of shale reservoirs. We focus on introducing nanofluidic methods to detect fluid characteristics, and the differences between experimental results and theoretical descriptions. The current limitations of nanofluidic studies of shale reservoir fluids are discussed in the end, and future directions in this field are foreseen.

The evaluation of oil and gas resources is to predict the potential of oil and gas resources in the future based on the understanding and judgement of the geological conditions of hydrocarbon accumulation,which is of great significance for oil companies to implement the internationalization strategy.According to the evaluation methods,petroleum geological theories,exploration technologies,and types of discovered traps,the development history of global oil and gas resources evaluation can be divided into four stages:start-up (1900-1957),rapid development (1958-1985),stable development (1986-2007) and participation by China (2008-).The evaluation results of global oil and gas resources are affected by the evaluation methods used at different stages,the evaluation scope of resources,petroleum geological theories,exploration technologies such as geophysics and drilling,as well as oil price,and hydrocarbon production.After comparing and analyzing the evaluation or statistical results of global oil and gas resources of China National Petroleum Corporation (CNPC) in 2020,the United States Geological Survey (USGS) in 2012 and the International Energy Agency (IEA) in 2019,it is considered that the evaluation results of CNPC (2020) is more comprehensive,and the evaluation results of recoverable resources to be discovered are lower than those of IEA (2019).With the development of petroleum geological theories and the progress of science and technology,oil and gas resources will be continuously transformed into petroleum reserves and production in the future.The evaluation methods of global oil and gas resources will gradually focus on the overall evaluation of source rock as the core object,the evaluation results will be presented in a three-dimensional way,the evaluation objects will continuously expand to deep water,deep play and unconventional resources,the evaluation process will highlight the requirements in terms of "economy" and "low carbon" ;big data and artificial intelligence technology will also play an important role in the future evaluation of global oil and gas resources.

Continental lacustrine shale developed in the Lower Jurassic of Sichuan Basin has high-quality source rock, high-abundance organic matter, and rich shale oil resources. Previous studies mainly focused on the Da'anzhai Member of Ziliujing Formation, and less on other horizons. The geological characteristics and resource potential of lacustrine shale oil in the Lower Jurassic were determined by analyzing the geochemical characteristics of Jurassic shale such as depositional environment, organic matter abundance, type, and maturity, as well as the geological conditions such as shale reservoir properties and reservoir space types. The results show that for the three sets of lacustrine shales in Dongyuemiao Member and Da'anzhai Member of Ziliujing Formation and Lianggaoshan Formation developed in Sichuan Basin, TOC content is generally greater than 1.0%; the organic matter of type Ⅱ ₁-Ⅱ ₂ indicate that these three sets of shale have good hydrocarbon potential; R _o is within the range of 1.00% to 1.82%, indicating a medium to high degree of thermal evolution. The shale is thick and widely distributed, with an average porosity of 4% -9% and the development of shale bedding fractures. Dongyuemiao Member has a gentle broad basin still-water deposit environment; Da'anzhai Member was formed in the largest lake flooding period in the Jurassic System, shown as a deep basin deep-water environment; Lianggaoshan Formation is dominated by a broad basin shallow-water environment. There are three combination patterns of shale development:pure shale type, shale-carbonate rock interbedding type and shale-sandstone interbedding type. Based on the evaluation of enriched intervals, five sweet spots are clearly divided vertically and the zones of thin oil, light oil and condensate oil and gas are divided horizontally. In particular, major discoveries such as Well Ping'an 1 have demonstrated that there is great exploration and development potential for shale oil in the Jurassic System of Sichuan Basin.

In terms of the"dual carbon"target, green, pollution-free and high-energy density hydrogen energy has become an important trend for the future development of energy industry. Underground hydrogen storage is a promising technology for large-scale hydrogen storage. This paper describes the concept, field practice and theoretical research status of underground hydrogen storage. A deep analysis is performed on the modes and characteristics of hydrogen storage in the salt cavern, aquifer, depleted oil and gas reservoirs, as well as abandoned coal mine, of which the advantages and disadvantages are compared from multiple perspectives. Underground natural gas storage provides technical experience for hydrogen storage, but there are obvious differences between the both. Further, the paper systematically analyzes the feasibility of underground hydrogen storage, and elaborates the difficulties and challenge in terms of caprock, wellbore integrity and chemical reaction in reservoirs. Based on the above research and analysis, the difficulties in the development of underground hydrogen storage technology are clarified; the future development prospects of underground hydrogen storage have been predicted; the corresponding countermeasures and suggestions are also put forward, such as strengthening the research on the geomechanical integrity of caprock and the integrity of wellbore, and facilitating the assessment of the geochemical and microbial reactions of reservoir rocks, fluids and hydrogen, which provide a significant reference for the underground hydrogen storage in China.

The production measures of oil and gas field development is severely restricted by the degree of understanding of subsurface reservoirs and fluids; reservoir description plays an important role in oil and gas field development business, and the main goal of reservoir description is to construct the digital twin system of reservoirs. Based on analyzing the current research status and development trend of oil and gas field development and the demands for digital transformation-based production, the paper proposes the digital twin theory of oil and gas reservoir, which defines the reservoir digital twin as "building a digital twin simulation model of oil and gas reservoirs to maximize the quantitative approximation of the real reservoir, characterizing the dynamic changes of the whole life cycle of reservoirs in a timely and accurate manner, and simulating the development behavior of reservoir entities from the physical world in a real environment". This points out the direction for the integrated research of reservoir description and reservoir engineering. Further, the paper presents the key directions and contents of smart oil and gas field construction based on the digital twin system of oil and gas reservoirs, and it is pointed out that by establishing a digital copy of oil and gas reservoir development system, i.e., the digital twin system of oil and gas reservoirs, as a basis for optimal development and scientific management of oil and gas fields in the cloud, a new technological revolution in the field of oil and gas field development will emerge, and the digital twin system of oil and gas reservoirs will give new connotation to the construction of smart oil and gas fields.

Analyzing the successful experience of the shale gas revolution in the United States is of great significance for promoting the development of China’s shale gas industry. A comparative study is performed on the exploration and development history, geological conditions for accumulation, development and utilization conditions and resource development status of shale gas in China and the United States. The results show that although both China and the United States have abundant shale gas resources, China’s shale gas output is far lower than that of the United States due to late beginning of exploration and development, low proved resource rate, and low development degree. The shale gas exploration and development in China is still in the early stage of rapid development. The United States has unique geological conditions for shale gas accumulation, superior geological conditions for development, and complete development infrastructure. Moreover, the United States has such advantages as strong technological innovation capability, world-leading process technology, and industrial policy support, which jointly promote the leap in shale gas production. Compared with the United States, China has several disadvantages such as multiple stages of tectonic evolution, multiple types of sedimentary basins, and three types of shales developing in marine, transitional and continental facies. Different types of shales varies greatly in quality. In addition, due to the strong tectonic transformation in the late period, the shale gas preservation conditions are very different in various structural units. The main distribution areas of shale gas in China have complex landforms and subsurface geological conditions, and relatively weak development infrastructure. At present, China is still far behind the United States in terms of key technologies and processes such as three-dimensional and efficient development. As the main body of natural gas production growth in China and the United States and an important field of natural gas production growth in China in the future, this paper makes the following suggestions. (1) The exploration and development of shale gas in Wufeng-Longmaxi formations in Sichuan Basin should be further accelerated to increase reserves and production. (2) Public oil and gas survey should further play a leading role, strengthen the geological survey and evaluation of shale gas in new areas and new strata, and set up new shale gas production bases. (3) It should strengthen independent innovation, enhance theoretical research on shale gas accumulation, tackle key technologies suitable for China’s landform and geological conditions, and promote low-cost and effective development of deep, normal pressured, continental and transitional shale gas. (4) Policy support should be continued to promote the rapid development of shale gas industry.

The genetic method with basin modeling as the core has been widely used in hydrocarbon exploration and production. China’s basin modeling theory and research are in the front ranks of countries of the world, but the application software development lags far behind other countries. According to statistics, 75 % of the 39 pieces of basin modeling software or algorithms available in China are developed by foreign companies, and 100 % of the popular software on the international market are developed by overseas companies. At present, the main challenge faced by basin modeling research is that the classical petroleum system theory widely applied in the past cannot effectively evaluate unconventional oil-gas resources. In this study, whole petroleum system theory is adopted to address the current challenges. Firstly, the basic characteristics, genetic mechanism and distribution regularities for the joint coexistence of conventional and unconventional oil-gas resources are elaborated based on the whole petroleum system theory, providing theoretical and methodological guidance for the prediction and assessment of conventional and unconventional oil-gas resources. Secondly, key technologies for predicting and assessing conventional, tight and shale oil-gas resources have been developed by establishing a combined genetic model for conventional and unconventional oil-gas reservoirs and a material balance relationship between total hydrocarbon generation and hydrocarbon resources. Thirdly, this paper establishes five sets of material balance equations between the total hydrocarbon production and the evolution and productivity of the whole petroleum system, analyzes the key geological parameters such as primitive hydrocarbon production ratio, migration-accumulation coefficient, movable hydrocarbon ratio and oil recovery, and proposes 12 key technologies of three categories for basin modeling. The new generation basin modeling system based on the whole petroleum system theory and modern information technology is expected to achieve quantitative, automated and intelligent assessment of oil-gas resources, increase the total amount of resources as the study objects by 5 to 8 times, deepen the research of predicted and assessed resources by more than 3 times, significantly improve the reliability of the predicted and assessed results, and solve the existing bottleneck problem.

Large tight sandstone gas reservoirs in Tianfu gas field of Sichuan Basin were discovered in the Member 2 of Shaximiao Formation in 2019 and the Member 1 of Shaximiao Formation in 2021, respectively. The proven reserves are 1 349×10 ⁸m ³ and the production is 15.7×10 ⁸m ³ in 2022. Based on the core and geochemical analysis data, the paper investigates the sedimentary reservoir characteristics, natural gas geochemical characteristics, gas reservoir types and gas reservoir formation conditions of Shaximiao Formation in Tianfu gas field. In the study area, shallow-water deltaic and lacustrine deposits are found in the Member 1 of Shaximiao Formation, while fluvial deposits are found in the Member 2 of Shaximiao Formation. The lithologies of the reservoir are mainly composed of feldspathic litharenite and lithic arkose, and the reservoir spaces are mainly occupied by residual intergranular pores, followed by feldspar dissolution pores. The natural gas source of reservoir is mainly from the Triassic Xujiahe Formation. The natural gas in the Member 1 of Shaximiao Formation and the 6th, 8th and 9th sand groups of 1st submember of Member 2 of Shaximiao Formation is dominated by coal-type gas with a small amount of mixed gas, while the gas in the 7th sand group of 1st submember of Member 2 of Shaximiao Formation is characterized by the occurrence of both mixed gas and oil-type gas. The gas reservoir in Shaximiao Formation of Tianfu gas field is a large lithologic gas reservoir with accumulation regularity of dual-source and multi-phase charging, fault and sandbody transport, accumulation around the source, and differential enrichment at the channel. A series of key exploration and development technologies have been developed by tackling the key exploitation problems of large tight sandstone gas reservoirs in Shaximiao Formation of Tianfu gas field, i.e., (1) technology of precisely choosing layers under the constraint of high-precision isochronous stratigraphic framework, (2) technology of finely characterizing sand bodies and precisely predicting target based on 3D seismic survey, (3) supporting technology to accelerate exploration and production based on horizontal well and volume fracturing, (4) processing technology of exploitation and transportation on the ground for the purpose of fast construction, investment, optimization and simplification, (5) integrated technical and economic template for scale and cost-effective development. The discovery of Tianfu gas field has improved the exploration and development of tight sandstone gas in China, and enriched the exploration methods of tight sandstone gas, and effectively promoted the exploration and development process of tight sandstone gas in Sichuan Basin.

China's deep coalbed methane (CBM) resources, with the burial depths exceeding 1 500 m, are abundant and coexist with adsorbed and free gases. The occurrence state, accumulation characteristics, and development laws of deep CBM differ significantly from those of mid-shallow CBM, and the unclear evolution patterns have restricted its efficient exploration and development. Taking the No.8 deep coal seam in Daning-Jixian block on the eastern margin of Ordos Basin for example, this study finely characterizes the accumulation characteristics of deep CBM and simulates the burial evolution history, thermal evolution history, and hydrocarbon generation history of deep coal seams, thus improving the deep CBM enrichment and accumulation laws and patterns; moreover, the targeted exploration and development strategies are proposed. The results show that the No.8 deep coal seam is widespread in Daning-Jixian block, with high organic matter thermal maturity and Type III kerogen. This indicates significant hydrocarbon generation potential, with the total hydrocarbon intensity of (20.2-34.7) ×10 ⁸m ³/km ². The deep coal reservoir develops cleats, fractures, texture pores, cell pores, gas pores, intergranular pores, and dissolution pores, providing favorable conditions for the accumulation of deep free-state CBM. The structural-lithologic-hydrodynamic coupling closure is favorable for the preservation of deep CBM. The evolution stages of hydrocarbon accumulation in deep coal seams in the study area include the initial hydrocarbon generation stage (Stage I, 306-251 Ma), the first thermal hydrocarbon generation stage (Stage II, 251-203 Ma), the decreasing stage of organic matter thermal evolution (Stage III, 203-145 Ma), the hydrocarbon generation peak stage (Stage IV, 145-130 Ma), and the final formation stage of the oil/gas accumulation pattern (Stage V, 130 Ma to present). The deep CBM under free and adsorbed states coexist in the study area. On this basis, the paper proposes the hydrocarbon enrichment and accumulation pattern of "wide covering hydrocarbon generation, box-type closure, microstructure adjustment, self-generation and self-storage, and blanket-type accumulation", and establishes three types of deep CBM accumulation models:microfold and physical property coupling control (Type I), microfault monocline and hydrodynamic force coupling control (Type II), and physical property and hydrodynamic force coupling control (Type III) on reservoir accumulation. These understandings can effectively guide the selection of favorable areas for deep CBM exploration in Daning-Jixian block, establish an evaluation index system for favorable areas in deep coal reservoirs, propose differentiated development plans for exploration areas with different accumulation models, and help achieve the truly efficient and low-cost development of deep CBM in the study area. The research findings have important reference significance for carrying out deep CBM exploration and development in other blocks in China.

Heavy oil is an important type of oil resources. Sustainable and efficient development of heavy oil resources have great significance to national energy security. The main characteristics of thermal recovery of heavy oil in China are summarized as below:as viewed from geological and oil-reservoir characteristics, China boasts various types of heavy oil reservoirs with deep burial, thin bed, strong heterogeneity and complex oil-water system; as for composition, the spatial reticular structure formed from the interaction between colloid and asphaltene molecules leads to high viscosity of heavy oil; as for rheological properties, there is a critical temperature. When the temperature is higher than the critical temperature, heavy oil displays the properties of Newtonian fluids; when the temperature is lower than the critical temperature, heavy oil displays the rheological properties of Bingham fluids with yield value; as for percolation characteristics, heavy oil possesses the properties of underground non-Darcy flow, with a starting pressure gradient, and it is subject to the influences of temperature, reservoir permeability, crude oil viscosity and asphaltene content. This paper summarizes the status quo of heavy oil development technology at home and abroad, and elaborates the main mechanism, applicable conditions, application examples, current problems and development direction of steam huff and puff, steam flooding, steam assisted gravity drainage (SAGD), in situ combustion and thermal composite development. Steam huff and puff is still the main method for thermal recovery of heavy oil and steam flooding is one of the effective substituted techniques to steam huff and puff; SAGD has made important progress in technology introduction and absorption; in situ combustion has become an important technology of greatly improving recovery efficiency; thermal composite development technology has realized efficient production of the marginal heavy oil. It is indicated that heavy oil requires high-quality and efficient thermal recovery technology in the future. In line with the maximization of "double objectives" for recovery efficiency and oil steam ratio, it is required to continuously strengthen reservoir description, dynamic monitoring and injection-production regulation, and actively explore the transformation of heat generation mode, so as to realize efficient development of heavy oil and green low-carbon development.

Deep coalbed methane (CBM) will become an important field for China to increase the large-scale natural gas reserves and production in the future. It is of great significance to review the history and progress of the geological research on deep CBM propose and evaluate the existing problems and exploration directions, which can provide a reference for developing applicable exploration and development technologies. Analyses reveal that China has made three major advances in the geological research of deep CBM in the past 20 years. First, the basic concept and its scientific connotation of deep CBM have been defined. It is found that there is a critical depth for the absorbed gas content of deep coalbeds, which mainly depends on the coupling relationship between geothermal gradient and geo-stress gradient, and other geological factors can adjust the critical depth. A decrease in the adsorbed gas content may lead to an increase in free gas content, resulting in the orderly accumulation of CBM in the depth sequence and the formation of highly to super saturated reservoirs with abundant free gas in the deep coal. Second, remarkable progress has been made in research of the geological properties of deep coal reservoirs, and it has been recognized that the weakening adsorption of deep coal reservoirs and the increase of free gas content are resulted from the dynamic equilibrium between the positive effect of pressure and the negative effect of temperature. Moreover, it has been found that there is a "highly permeability window" of coal reservoirs near the transition zone of geo-stress state on the depth profile, and the formation temperature and pressure indices related to the reconstruction of deep coal reservoirs may have a threshold property, and the temperature compensation and variable pore compressibility effects may significantly lower the decay rate of permeability for deep coal reservoirs. Third, an in-depth research is gradually implemented on the accumulation and geological evaluation of deep CBM reservoirs, and the exploration on accumulation mechanism focuses on CBM gas-bearing property formed by buried depth changes, vertical permeability distribution and its geological control, thus initially revealing the "depth effect" for CBM reservoir formation. Through on-site case analysis, the relevant understandings have been deepened and expanded from basin to favorable zone, then to sweet spot and from reservoir control to production control. The analyses suggest that the organic connection and deep coupling of basic geology (reservoir-forming process), exploration geology (evaluation optimization) and development geology (dynamic process) are key directions for the geological-engineering integration in deep CBM exploration and development. Therefore, it is suggested future research should focus on "depth effect", including the systematic description of deep CBM reservoir and the characterization of gas reservoir engineering responses to geological conditions.

The natural gas resources in Sichuan Basin rank first in China, with the proven rate of only 18.8 % , indicating enormous potentials for exploration and development. In recent years, significant breakthroughs have been made in oil and gas exploration in new fields, new strata, and new types of marine carbonate rocks, unconventional marine gas, continental tight gas, and continental shale oil in deep to ultra-deep layers of Sichuan Basin, demonstrating tremendous resource prospects. Despite of the low degree of exploration, the marine carbonate gas reservoirs in deep to ultra-deep layers in the western and central Sichuan Basin display a 3D accumulation pattern in multiple series of strata with hydrocarbons supplied from excellent source rocks, vertically stacked and horizontally connected high-energy mound-beach reservoirs in many series of strata, good source reservoir configuration and developed fault conduit systems, which are expected to form a new trillion cubic meter scale reserve zone. The foreland subbasin-slope is a favorable area for the enrichment of continental tight gas in central-western Sichuan Basin, and two sets of petroleum accumulation systems are formed, i.e., Xujiahe Formation and the Jurassic Shaximiao Formation, in which Xujiahe Formation is the major source rock. A giant gas field of 100 billion cubic meters has been discovered with the cumulative produced geological reserves exceeding 10 ¹²m ³, and has become a new growth pole for natural gas production in Sichuan Basin. Unconventional hydrocarbon-bearing strata series such as Permian and Jurassic shale, mudstone, and coal are continuously and stably distributed. Oil and gas are widely enriched and accumulated, and most abundant in central and eastern Sichuan Basin, and moreover exploration breakthroughs have been achieved. In the favorable exploration area for unconventional natural gas, the resources in the Permian reservoirs amount to nearly 8×10 ¹²m ³; in the favorable exploration area for Jurassic shale oil, the resources are estimated to be 16.96 ×10 ¹²m ³. The marine carbonate gas and continental tight gas in deep to ultra-deep layers in the western and central Sichuan Basin have been the main area for increasing reserves on a large scale in Sichuan Basin. Unconventional natural gas and continental shale oil are important resource replacement areas.

After nearly 40 years of exploration in Kaiping sag of Pearl River Mouth Basin, a medium to large light oil field has been discovered in deep-water Paleogene strata of Kaiping11-4 structure. To further guide oil-gas exploration in Kaiping sag, the paper deeply investigates the petroleum geological conditions such as hydrocarbon sources, reservoirs, traps, preservation and migration conditions in Kaiping11-4 structure, and summarizes the oil and gas accumulation mode. The geological structure of Kaiping sag is a detachment-type compound half-graben with faults in the north and overlaps in the south. In Kaiping sag, Wenchang Formation develops high quality semi-deep to deep lacustrine source rocks with great hydrocarbon generation potential, and the shallow-water braided delta front deposits of Enping Formation develop a favorable reservoir-cap assemblage. The traps formed under the early tectonic activities are various, including faulted block, faulted anticline and plunging anticline, while the weak tectonic activity in the late period is conducive to oil and gas preservation. The inheritance faults that cut through the source rocks provide vertical migration channels so that oil and gas can be transported through the "source-fault-reservoir" system. The reservoirs in Kaiping11-4 structure have undergone multi-phase continuous charging since 17 Ma, presenting a hydrocarbon accumulation mode with the characteristics of "hydrocarbon supplying from high-quality lacustrine sources, strongly charging through near-source faults, and enriching in multiple stages and levels". The discovery of medium to large light oil field in Kaiping11-4 structure is not only a breakthrough of the new area exploration in Kaiping sag, but also a breakthrough of the Paleogene crude oil exploration in the eastern deep-water area of the South China Sea. It shows that the deep-water area of Pearl River Mouth Basin has a broad prospect for oil and gas exploration, and is of great significance to the exploration of petroliferous basins in the northern deep-water area of the South China Sea.

Compared with marine shale oil in North America, continental shale oil in China has such characteristics as complex mineral composition, strong heterogeneity, thin single-layer thickness, and rapid vertical changes of lithologies and lithofacies. Thus, there are great difficulties in logging lithology identification, accurate calculation of rock mechanical parameters and fine division of reservoir qualities, which bring great challenges for the well logging evaluation of sweet spots in shale oil reservoirs. In view of the difficulties encountered in the logging evaluation of shale oil exploration areas in Songliao, Ordos, Junggar, and Bohai Bay basins, this paper mainly explores the new methods for shale rock physical experiment, represented by four-dimensional digital core, laboratory multi-state two-dimensional NMR spectroscopy, and onsite movable full-diameter rock core NMR spectroscopy; the new well logging technologies, represented by high-precision calculation of mineral components based on elemental logging, identification of sedimentary structure based on image logging, horizontal well interpretation, and fracturing evaluation.A complete technical system for well logging evaluation of continental shale oil has been formed, which shows the innovation and development of well logging evaluation technology of shale oil in recent years.