According to the actual demands of petroleum exploration and development, this paper describes the research progress and application of artificial intelligence technology in the field of petroleum exploration and development, and discusses the applications and development directions of artificial intelligence technology in the future. Machine learning technology has preliminary application in lithology identification, logging curve reconstruction, reservoir parameter prediction and other logging processing and interpretation, and has shown great potential. Computer vision is effective in the seismic first breaks picking, fault identification and other seismic processing and interpretation. Deep learning and optimization technology has been applied to reservoir engineering, and realized the real-time optimization of waterflooding development and prediction of oil and gas field production. The application of data mining in drilling and completion, surface engineering and other fields has formed intelligent equipment and integrated software. The potential development directions of artificial intelligence in the field of petroleum exploration and development are intelligent production equipment, automatic processing interpretation and professional software platform. The focus of development is digital basin, fast intelligent imaging logging tool, intelligent node seismic acquisition system, intelligent rotary steering drilling, intelligent fracturing technology and equipment, real-time monitoring and control engineering of separate layer injection and production.

Carbon dioxide is an important medium of the global carbon cycle, and has the dual properties of realizing the conversion of organic matter in the ecosystem and causing the greenhouse effect. The fixed or available carbon dioxide in the atmosphere is defined as “gray carbon”, while the carbon dioxide that cannot be fixed or used and remains in the atmosphere is called “black carbon”. Carbon neutral is the consensus of human development, but its implementation still faces many challenges in politics, resources, technology, market, and energy structure, etc. It is proposed that carbon replacement, carbon emission reduction, carbon sequestration, and carbon cycle are the four main approaches to achieve carbon neutral, among which carbon replacement is the backbone. New energy has become the leading role of the third energy conversion and will dominate carbon neutral in the future. Nowadays, solar energy, wind energy, hydropower, nuclear energy and hydrogen energy are the main forces of new energy, helping the power sector to achieve low carbon emissions. “Green hydrogen” is the reserve force of new energy, helping further reduce carbon emissions in industrial and transportation fields. Artificial carbon conversion technology is a bridge connecting new energy and fossil energy, effectively reducing the carbon emissions of fossil energy. It is predicted that the peak value of China’s carbon dioxide emissions will reach 110×10⁸ t in 2030. The study predicts that China's carbon emissions will drop to 22×10⁸ t, 33×10⁸ t and 44×10⁸ t, respectively, in 2060 according to three scenarios of high, medium, and low levels. To realize carbon neutral in China, seven implementation suggestions have been put forward to build a new “three small and one large” energy structure in China and promote the realization of China's energy independence strategy.

The development of natural gas in China has entered a golden and leap-forward stage, which is a necessary bridge to clean energy. This in-depth study on the status quo, theory, technology and prospect of natural gas development shows: (1) The global remaining proven recoverable reserves of natural gas are 186×10¹² m³, and the reserves-production ratio is 52.4, indicating a solid resource base for long-term and rapid development. (2) Ten formation and distribution laws of conventional and unconventional natural gas reservoirs have been proposed. In terms of exploration geology, the theory of conventional “monolithic” giant gas fields with different gas sources, and an unconventional gas accumulation theory with continuous distribution of “sweet spots” in different lithologic reservoirs have been established; in terms of development geology, a development theory of conventional structural gas reservoirs is oriented to “controlling water intrusion”, while a development theory of unconventional gas is concentrated on artificial gas reservoirs. (3) With the geological resources of 210×10¹² m³ (excluding hydrates) and the total proven rate of the resources less than 2% at present, the natural gas in China will see a constant increase in reserve and production; by 2030, the proven geological reserves of natural gas are expected to reach about (6 000-7 000)×10⁸ m³, the production of conventional and unconventional natural gas each will reach about 1 000×10⁸ m³, and the gas consumption will reach 5500×10⁸ m³. The dependence on imported natural gas may be 64% by 2030, and 70% by 2050. (4) Ten measures for future development of natural gas have been proposed, including strengthening exploration in large-scale resource areas, increasing the development benefits of unconventional gas, and enhancing the peak adjusting capacity of gas storage and scale construction of liquified natural gas.

As an important type of “conventional–unconventional orderly accumulation”, shale oil is mature oil stored in organic-rich shales with nano-scale pores. This paper analyzes and summarizes elementary petroleum geological issues concerning continental shale oil in China, including sedimentary environment, reservoir space, geochemical features and accumulation mechanism. Mainly deposited in semi-deep to deep lake environment, shale rich in organic matter usually coexists with other lithologies in laminated texture, and micron to nano-scale pores and microfractures serve as primary reservoir space. Favorable shale mainly has typeⅠand ⅡA kerogens with a Ro of 0.7% –2.0%, TOC more than 2.0%, and effective thickness of over 10 m. The evolution of shale pores and retained accumulation pattern of shale oil are figured out. Reservoir space, brittleness, viscosity, pressure, retained quantity are key parameters in the “core” area evaluation of shale oil. Continuously accumulated in the center of lake basins, continental shale oil resources in China are about 30×108–60×108 t by preliminary prediction. Volume fracturing in horizontal wells, reformation of natural fractures, and man-made reservoir by injecting coarse grains are some of the key technologies for shale oil production. A three step development road for shale oil is put forward, speeding up study on “shale oil prospective area”, stepping up selection of “core areas”, and expanding “test areas”. By learning from marine shale breakthroughs in North America, continental shale oil industrialization is likely to kick off in China.

The origin of grain dolomite in M₅⁵ Member of Ordovician Majiagou Formation in northwestern Ordos Basin was studied by geochemical and petrological tests on core samples. Observation of cores, thin sections and casting thin sections, analysis of cathodoluminescence, X-ray diffraction, microscopic sampling of trace elements, laser sampling δ¹⁸O and δ¹³C, and fluid inclusion homogenization temperature were conducted. The results show that the dolomite is the product of recrystallization of micritic to crystal powder dolomite rather than the product of dolomitization of grain limestone. In the spherical grains are residual gypsum and halite pseudo crystals identical with those in the host micritic dolomite. The spherical particles of dolomite has similar trace elements and δ¹⁸O and δ¹³C characteristics to micritic dolomite. Furthermore, Mn/Sr ratio of the fine-medium dolomite between the dolomite grains is about 5-8, while Mn/Sr ratios of calcite in limestone, micritic dolostone in micritic dolomite, and micritic and powdery dolomite are about 0-2, indicating that the dolomite experienced strong diagenesis. Homogenization temperature of inclusions of fine-medium dolomite is about 148. 19 ℃, higher than that of inclusions in micritic to crystal powder dolomite (about 122.60 ℃), which also supports the conclusion that the grain dolomite experienced burial diagenesis and negative shift of δ¹⁸O and δ¹³C. The δ¹⁸O, δ¹³C values of micritic to crystal powder dolomite match with the negative migration, but those of calcite in limestone don’t. It is of great significance to elucidate the genesis of “dolomite recrystallization” for the prediction of such dolomite reservoirs.

Great changes of the global energy industry have been caused by the rapid development of unconventional oil and gas. It is necessary to deeply consider the profound influence of the unconventional oil and gas revolution on the classical petroleum geological theory and to review geological conception of oil and gas accumulation elements and theoretic framework of petroleum system, giving the petroleum geology a new academic connotation. The author summarizes the significant progresses of global unconventional oil and gas exploration and development, and points out that the unconventional oil and gas revolution not only has a significant economic significance of oil and gas resource increment, but also brings great innovation to the theory of petroleum geology, thus having important scientific significances. This paper summarizes the core contents of four aspects of hydrocarbon generation, reservoir, distribution and development in classical petroleum geology, and comprehensively reviews the five important nodes in the developmental history of petroleum geology, which include anticline and trap theory, hydrocarbon generation from organic matter and petroleum system theory, continental petroleum geology, marine deepwater petroleum geology, continuous hydrocarbon accumulation and unconventional oil and gas geological theory. Unconventional oil and gas has made a great breakthrough to classical petroleum geology on the basic theoretical concepts such as trap, reservoir, caprock, resource distribution, and enrichment, thereby promoting the basic research on petroleum geology to transform into the whole process of hydrocarbon generation, whole type of reservoir, and whole genetic mechanism, deepening unconventional petroleum geology theory, promoting the development and reconstruction of petroleum geology system, representing great significances to the strategic development from conventional to unconventional oil and gas in China or even in the world.

With Sichuan Basin as focus, this paper introduces the depositional environment, geochemical and reservoir characteristics, gas concentration and prospective resource potential of three different types of shale in China: marine shale, marine-terrigenous shale and lacustrine shale. Marine shale features high organic abundance (TOC: 1.0%-5.5% ), high-over maturity (Ro: 2%-5%), rich accumulation of shale gas (gas concentration: 1.17-6.02 m3/t) and continental shelf deposition, mainly distributed in the Paleozoic in the Yangtze area, Southern China, the Paleozoic in Northern China Platform and the Cambrian-Ordovician in Tarim Basin; Marine-terrigenous coalbed carbonaceous shale has high organic abundance (TOC: 2.6%-5.4%) and medium maturity (Ro: 1.1%-2.5%); Lacustrine shale in the Mesozoic and Cenozoic has high organic abundance (TOC: 0.5%-22%) and mid-low maturity (Ro: 0.6-1.5%). The study on shale reservoirs in the Lower Paleozoic in Sichuan Basin firstly indicated that Cambrian and Silurian marine shale developed lots of micro- and nanometer-sized pores, which is quite similar to the conditions in North America. Through comprehensive evaluation, it is thought that several shale gas intervals in Sichuan Basin are the practical targets for shale gas exploration and development, and that the Weiyuan-Changning area in the Mid-South of Sichuan Basin is the core area for shale gas exploration and development, which is characterized by high thermal evolution degree (Ro: 2%-4%), high porosity (3.0%-4.8%), high gas concentration (2.8-3.3 m3/t), high brittle mineral content (40%-80%) and proper burial depth (1 500-4 500m).

Based on field geological survey, interpretation of seismic data and analysis of drilling and logging data, the evolution of geological structures, stratigraphic sedimentary filling sequence and sedimentary system around the Bogda Mountain were analyzed according to the idea of "structure controlling basin, basin controlling facies and facies controlling assemblages". The tectonic evolution of the basin around the Bogda Mountain can be divided into nine stages. The Middle-Late Permian-Middle-Late Triassic was the development stage of intracontinental rift, foreland basin and inland depression basin when lake, fan delta and braided river delta sedimentary facies developed. Early intracontinental rifting, late Permian tectonic uplift, and middle-late Triassic tectonic subsidence controlled the shape, type, subsidence rate and sedimentary system evolution of the basin. The Bogda Mountain area was the subsidence center and deposition center of the deep water lake basin in the Middle Permian with mainly deep-water deposition and local gravity flow deposition. This area had tectonic inversion in the Late Permian, when the Bogda Mountain uplifted to form a low bulge and a series of fan delta sand bodies. In the Middle-Late Triassic, subsidence occurred in the Bogda low uplift, characterized by extensive development of braided river delta deposits.

Through reviewing the development history of tight oil and gas in China, summarizing theoretical understandings in exploration and development, and comparing the geological conditions and development technologies objectively in China and the United States, the progress and stage of tight oil and gas exploration and development in China have been clarified, and the future development orientation of theory and technology, process methods and development policy for tight oil and gas in China have been envisaged. In nearly a decade, relying on the exploration and development practice, science and technology research and management innovation, huge breakthroughs have been made in the exploration and development of tight oil and gas in China. The laws of formation, distribution and accumulation of tight oil and gas have been researched, the development theories such as “multi-stage pressure drop” and “man-made reservoirs” have been established, and several technology series, including enrichment regions selection, well pattern deployment, single well production and recovery factor enhancement, and low cost development, have been innovated and integrated. All those promote the rapid rise of both reserves and production of tight oil and gas. However, limited by the sedimentary environment and tectonic background, compared with North America, China’s tight oil and gas reservoirs are worse in continuity, more difficult to develop and poorer in economic efficiency. Moreover, there are still some gaps in reservoir identification accuracy and fracturing technology between China and North America. In the future, boosting the rapid development of tight oil and gas, Chinese oil and gas companies should further improve the resource evaluation method, tackle key technologies such as high-precision 3D seismic interpretation, man-made reservoir, and intelligent engineering, innovate theories and technologies to enhance single well production and recovery rate, and actively endeavor to get the finance and tax subsidy on tight oil and gas.

The potential resource of CBM in China is huge and prospective resource is 27.3×1012m3. Energy basket in China is extremely irrational: the CBM quantity emitted to atmosphere during coal production per year approaches 194×108m3, close to the Chinese yearly nature gas output, equal to one-third of the CBM quantity emitted to atmosphere during coal production in the world and 27% of the artificial emission CBM quantity in China. Therefore it is extremely important and instant to make a middle and long term planning of taking advantage of and developing Chinese CBM.This paper predicts the CBM utilization and development in 2005, 2010 and 2025 in China by studying the latest CBM exploration and development progress, combined with Chinese and foreign developing situation and Chinese energy strategy programme.

Water shut-off and profile control is an important technology for improving water flooding efficiency of seriously heterogeneous reservoir, especially for the mature reservoir with higher water-cut. New methods have been put forward and applied during the past years to meet the production demand, which made significant contribution to the mature reservoir development. This paper reviews the traditional techniques, indicates the problems need to be solved, and proposes the related tendency. For the mature reservoir chartered by higher water-cut and serious heterogeneity, the research of desirable water shut-off and profile control technologies should put emphasis on the development of depth water divert materials with lower cost and higher quality, simultaneously take efforts to investigate the corresponding mechanisms and assistant on the base of reservoir re-understanding. With such efforts the overall disadvantageous water distribution in depth reservoir can be disrupted and the improvement of water-flooding efficiency can be achieved.

The Anyue Sinian-Cambrian giant gas field was discovered in central paleo-uplift in the Sichuan Basin in 2013, which is a structural-lithological gas reservoir, with 779.9 km2 proven gas-bearing area and 4 403.8×108 m3 proven geological reserves in the Cambrian Longwangmiao Formation in Moxi Block, and the discovery implies it possesses trillion-cubic-meter reserves in the Sinian-Cambrian Formations in Sichuan Basin. The main understandings achieved are as follows: (1) Sinian-Cambrian sedimentary filling sequences and division evidence are redetermined; (2) During Late Sinian and Early Cambrian, “Deyang-Anyue” paleo-taphrogenic trough was successively developed and controlled the distribution of source rocks in the Lower-Cambrian, characterized by 20-160 m source rock thickness, TOC 1.7%-3.6% and Ro 2.0%-3.5%; (3) Carbonate edge platform occurred in the Sinian Dengying Formation, and carbonate gentle slope platform occurred in the Longwangmiao Formation, with large-scale grain beach near the synsedimentary paleo-uplift; (4) Two types of gas-bearing reservoir, i.e. carbonate fracture-vug type in the Sinian Dengying Formation and dolomite pore type in the Cambrian Longwangmiao Formation, and superposition transformation of penecontemporaneous dolomitization and supergene karst formed high porosity-permeability reservoirs, with 3%-4% porosity and (1-6)×10-3 μm2 permeability in the Sinian Dengying Formation, and 4%-5% porosity and (1-5)×10-3 μm2 permeability in the Cambrian Longwangmiao Formation; (5) Giant paleo-oil pool occurred in the core of the paleo-uplift during late Hercynian—Indosinian, with over 5 000 km2 and (48-63)×108 t oil resources, and then in the Yanshanian period, in-situ crude oil cracked to generate gas and dispersive liquid hydrocarbons in deep slope cracked to generate gas, both of which provide sufficient gas for the giant gas field; (6) The formation and retention of the giant gas field is mainly controlled by paleo-taphrogenic trough, paleo-platform, paleo-oil pool cracking gas and paleo-uplift jointly; (7) Total gas resources of the Sinian-Cambrian giant gas field are preliminarily predicted to be about 5×1012 m3, and the paleo-uplift and its slope, southern Sichuan Basin depression and deep formations of the high and steep structure belt in east Sichuan, are key exploration plays. The discovery of deep Anyue Sinian-Cambrian giant primay oil-cracking gas field in the Sichuan Basin, is the first in global ancient strata exploration, which is of great inspiration for extension of oil & gas discoveries for global middle-deep formations from Lower Paleozoic to Middle-Upper Proterozoic strata.

Through analysis of the problems in the production of Gulong shale oil in the Songliao Basin and the scientific exploration of the preliminary basic research, the special characteristics of Gulong shale oil in terms of reservoir space, phase distribution, flow pattern and mineral evolution are proposed, and six basic scientific problems currently faced are concluded, including: (1) The source of organic matter, mechanism of hydrocarbon generation and expulsion, and key factors affecting shale oil abundance; (2) The types and structural characteristics of effective reservoir space and their contribution to porosity and permeability; (3) The genesis and evolution of minerals and their control on reservoir availability, sensitivity and compressibility; (4) The rock mechanical characteristics and fracture propagation law; (5) The shale oil products, phase change law and main control factors of adsorption and desorption conversion; (6) The shale oil-liquid solid-liquid gas interaction mechanism and enhanced oil recovery mechanism. Three key research suggestions are proposed for realizing the large-scale economic utilization of the Gulong shale oil: (1) Deepen research on the mechanism of oil and gas generation and discharge, storage and transportation, to guide the selection of geological sweet spots of shale oil; (2) Deepen research on the compressibility and fracture initiation mechanism to support the selection of engineering sweet spots and optimization of engineering design; (3) Deepen research on the fluid action mechanism under formation conditions, to guide the optimization of development schemes and the selection of technologies for enhancing oil recovery.

Through detailed analyses of the distribution characteristics of organic-rich shale, appearance features of high-quality shale, microscopic characteristics of shale reservoir rocks, fracturabilities, and the relationship between preservation conditions and shale gas enrichment in Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation in Sichuan Basin, theoretical understandings and specific suggestions with respect to the exploration and development of shale gas in China are summarized and proposed respectively. Successful experiences in the exploration and development of shale gas of the Wufeng Formation-Longmaxi Formation in the Sichuan Basin can be summarized into the following aspects: depositional environment and depositional process control the distribution of organic-rich shale; high quality shale in “sweet spot segments” are commonly characterized by high content of organic carbon, high brittleness, high porosity and gas content; organic pores are important storage space for the enrichment of shale gas; preservation conditions are the key factor for the geological evaluation of shale gas in structurally complex regions; shale gas can be considered as “artificial gas reservoirs” and the fracturability assessment is essential for high-production; nanoscale storage space and the mode of occurrence control the special seepage characteristics of shale gas. The following suggestions are proposed for the development of China’s shale gas industry: (1) focus more on fundamental research to achieve new breakthrough in the geological theory of shale gas; (2) emphasize exploration practices to have all-round discoveries in multiple strata; (3) study the regularities of development and production to establish new models of shale gas development; (4) think creatively to invent new technologies to tackle key problems; (5) explore the management innovation to create new mechanisms in shale gas development.

Based on the theoretical study and field application of volume stimulation in horizontal wells over the past 10 years, the core connotation of volume stimulation was further interpreted. The implementation methods, design models and key issues were analyzed, and the future development direction was put forward. The research shows that the multi-cluster limited entry technique can achieve homogenous growth of multiple fractures. The hybrid stimulation of “breaking rock by gel stimulation + carrying proppant by slick water” plus small-particle proppant can reduce the fracture complexity near the well bore and increase stimulated reservoir volume (SRV) in the far-field. The requirement of fracture conductivity in unconventional formations can be met by shear-sustained fractures and proppant-transporting slick water. The optimum well spacing between a child well and a parent well should be determined by the stimulation modes, injection volume and pressure drawdown. Reconstructing seepage field, stress field and stimulation targets is crucial for improving the stimulation results in a horizontal well. Reducing cluster spacing and well spacing is the basis for establishing development modes of fracture-controlled reserves. Fracturing-design decision system based on “spatial-mode stimulation” and geology-engineering integration is an important research direction for volume stimulation techniques.

Continental shale oil has two types, low-medium maturity and medium-high maturity, and they are different in terms of resource environment, potential, production methods and technologies, and industrial evaluation criteria. In addition, continental shale oil is different from the shale oil and tight oil in the United States. Scientific definition of connotations of these resource types is of great significance for promoting the exploration of continental shale oil from "outside source" into "inside source" and making it a strategic replacement resource in the future. The connotations of low-medium maturity and medium-high maturity continental shale oils are made clear in this study. The former refers to the liquid hydrocarbons and multiple organic matter buried in the continental organic-rich shale strata with a burial depth deeper than 300 m and a R_o value less than 1.0%. The latter refers to the liquid hydrocarbons present in organic-rich shale intervals with a burial depth that in the "liquid window" range of the Tissot model and a R_o value greater than 1.0%. The geological characteristics, resource potential and economic evaluation criteria of different types of continental shale oil are systematically summarized. According to evaluation, the recoverable resources of in-situ conversion technology for shale oil with low-medium maturity in China is about (700-900)×10⁸ t, and the economic recoverable resources under medium oil price condition ($ 60-65/bbl) is (150-200)×10⁸ t. Shale oil with low-medium maturity guarantees the occurrence of the continental shale oil revolution. Pilot target areas should be optimized and core technical equipment should be developed according to the key parameters such as the cumulative production scale of well groups, the production scale, the preservation conditions, and the economics of exploitation. The geological resources of medium-high maturity shale oil are about 100×10⁸ t, and the recoverable resources can to be determined after the daily production and cumulative production of a single well reach the economic threshold. Continental shale oil and tight oil are different in lithological combinations, facies distribution, and productivity evaluation criteria. The two can be independently distinguished and coexist according to different resource types. The determination of China's continental shale oil types, resources potentials, and tight oil boundary systems can provide a reference for the upcoming shale oil exploration and development practices and help the development of China’s continental shale oil.

In this review on the exploration and development process of the Shunbei ultra-deep carbonate oil and gas field in the Tarim Basin, the progress of exploration and development technologies during the 13th five-year plan has been summarized systematically, giving important guidance for the exploration and development of ultra-deep marine carbonate reservoirs in China and abroad. Through analyzing the primary geological factors of “hydrocarbon generation-reservoir formation-hydrocarbon accumulation” of ancient and superposed basin comprehensively and dynamically, we point out that because the Lower Cambrian Yuertusi Formation high-quality source rocks have been located in a low-temperature environment for a long time, they were capable of generating hydrocarbon continuously in late stage, providing ideal geological conditions for massive liquid hydrocarbon accumulation in ultra-deep layers. In addition, strike-slip faults developed in tectonically stable areas have strong control on reservoir formation and hydrocarbon accumulation in this region. With these understandings, the exploration focus shifted from the two paleo-uplifts located in the north and the south to the Shuntuoguole lower uplift located in between and achieved major hydrocarbon discoveries. Through continuing improvement of seismic exploration technologies for ultra-deep carbonates in desert, integrated technologies including seismic acquisition in ultra-deep carbonates, seismic imaging of strike-slip faults and the associated cavity-fracture systems, detailed structural interpretation of strike-slip faults, characterization and quantitative description of fault-controlled cavities and fractures, description of fault-controlled traps and target optimization have been established. Geology-engineering integration including well trajectory optimization, high efficiency drilling, completion and reservoir reformation technologies has provided important support for exploration and development of the Shunbei oil and gas field.

The discovery of the giant Anyue gas field in Sichuan Basin gives petroleum explorers confidence to find oil and gas in Proterozoic to Cambrian. Based on the reconstruction of tectonic setting and the analysis of major geological events in Mesoproterozoic-Neoproterozoic, the petroleum geological conditions of Proterozoic to Cambrian is discussed in this paper from three aspects, i.e. source rocks, reservoir conditions, and the type and efficiency of play. It is found that lower organisms boomed in the interglacial epoch from Mesoproterozoic-Neoproterozoic to Eopaleozoic when the organic matters concentrated and high quality source rocks formed. Sinian-Cambrian microbial rock and grain-stone banks overlapped with multiple-period constructive digenesis may form large-scale reservoir rocks. However, because of the anoxic event and weak weathering effect in Eopaleozoic-Mesoproterozoic, the reservoirs are generally poor in quality, and only the reservoirs that suffered weathering and leaching may have the opportunity to form dissolution-reconstructed reservoirs. There are large rifts formed during Mesoproterozoic-Neoproterozoic in Huabei Craton, Yangtze Craton, and Tarim Craton in China, and definitely source rocks in the rifts, while whether there are favorite source-reservoir plays depends on circumstance. The existence of Sinian-Cambrian effective play has been proved in Upper Yangtze area. The effectiveness of source-reservoir plays in Huabei area depends on two factors: (1) the effectiveness of secondary play formed by Proterozoic source rock and Paleozoic, Mesozoic, Cenozoic reservoir rocks; (2) the matching between reservoirs formed by reconstruction from Mesoproterozoic- Neoproterozoic to Eopaleozoic and the inner hydrocarbon kitchens with late hydrocarbon generation. As for Tarim Basin, the time of Proterozoic and the original basin should be analyzed before the evaluation of the effective play. To sum up, Proterozoic to Cambrian in the three craton basins in China is a potential exploration formation, which deserves further investigation and research.

The latest advancement of CO₂ flooding and sequestration theory and technology in China is systematically described, and the future development direction is put forward. Based on the geological characteristics of continental reservoirs, five theories and key technologies have been developed: (1) Enriched the understandings about the mass transfer characteristics of components between CO₂ and crude oil in continental reservoirs, micro-flooding mechanism and sequestration mechanism of different geological bodies. (2) Established the design method of reservoir engineering parameters, injection-production control technology and development effect evaluation technology of CO₂ flooding, etc. (3) Developed a series of production engineering technologies such as separated layer CO₂ injection technology, high efficiency lifting technology, on-line wellbore corrosion monitoring and protection technology. (4) Innovated a series of surface engineering technology including CO₂ capture technology, pipeline CO₂ transportation, CO₂ surface injection, and production gas circulation injection, etc. (5) Formed a series of supporting technologies including monitoring, and safety and environmental protection evaluation of CO₂ flooding reservoir. On this basis, the technological development directions in the future have been put forward: (1) Breakthrough in low-cost CO₂ capture technology to provide cheap CO₂ gas source; (2) Improve the miscibility technology between CO₂ and crude oil to enhance oil displacement efficiency; (3) Improve CO₂ sweeping volume; (4) Develop more effective lifting tools and technologies; (5) Strengthen the research of basic theory and key technology of CO₂ storage monitoring. CO₂ flooding and sequestration in the Jilin Oilfield shows that this technology has broad application prospects in China.

Through a comprehensive review of the development status of workover technology of PetroChina Company Limited (PetroChina), this paper presents the connotation of workover operation under the background of the new era, the latest progress of workover operation in the respects of equipment, tools, technology and the construction of information and standardization. The gaps between PetroChina and foreign counterpart in workover technology are as follows: the level of automation and intellectualization of tools and equipment is relatively low, the snubbing operation in gas wells characterized by HT/HP and high H₂S is lagged behind; water plugging in the long horizontal wellbore needs to be further developed, coiled tubing and its relevant equipment for ultra-deep well operation has to be optimized; informationization, standardization and big data application of workover operation need to be started. Based on this as well as the development status of workover technology in China and the technical difficulties faced in the future, eight suggestions for future development are put forward: (1) strengthen the dynamic understanding of reservoir and improve the pertinence of workover schemes; (2) develop the general overhaul technology in a systematical way to tackle issues of seriously problematic wells; (3) put more efforts into the research of horizontal well workover operation and develop relevant technology for long horizontal section operation; (4) improve the snubbing technology and extend its applications; (5) expand the capacity of coiled tubing operation and improve the level of special operations; (6) develop automatic workover technology into the field of artificial intelligence; (7) promote clean operation in an all-round way and build green oil and gas fields; (8) perfect the informationization construction to realize the sharing of workover resources.

To supplement missing logging information without increasing economic cost, a machine learning method to generate synthetic well logs from the existing log data was presented, and the experimental verification and application effect analysis were carried out. Since the traditional Fully Connected Neural Network (FCNN) is incapable of preserving spatial dependency, the Long Short-Term Memory (LSTM) network, which is a kind of Recurrent Neural Network (RNN), was utilized to establish a method for log reconstruction. By this method, synthetic logs can be generated from series of input log data with consideration of variation trend and context information with depth. Besides, a cascaded LSTM was proposed by combining the standard LSTM with a cascade system. Testing through real well log data shows that: the results from the LSTM are of higher accuracy than the traditional FCNN; the cascaded LSTM is more suitable for the problem with multiple series data; the machine learning method proposed provides an accurate and cost effective way for synthetic well log generation.

The Ordovician Wufeng Formation-Silurian Longmaxi Formation organic-rich shales distributed widely and stably in Southern Sichuan Basin were investigated based on drilling data. Geological evaluation of wells show that the shale reservoirs have good properties in the Yibin, Weiyuan, Zigong, Changning, Luzhou, Dazu areas, with key parameters such as TOC, porosity, gas content similar to the core shale gas production zones. Moreover, these areas are stable in structure, good in preservation conditions and highly certain in resources. The shale reservoirs have a burial depth of 4 500 m or shallow, a total area of over 2×10⁴ km² and estimated resource of over 10×10¹² m³, so they are the most resource-rich and practical areas for shale gas exploitation in China. Through construction of the Changning-Weiyuan national demonstration region, the production and EUR of shale gas wells increased significantly, the cost of shale gas wells decreased remarkable, resulting in economic benefit better than expected. Moreover, the localized exploration and development technologies and methods are effective and repeatable, so it is the right time for accelerating shale gas exploitation. Based on the production decline pattern of horizontal wells at present and wells to be drilled in the near future, at the end of the 13th Five Year Plan, the production of shale gas in southern Sichuan Basin is expected to reach 10 billion cubic meters per year. The resources are sufficient for a stable production period at 30 billion cubic meters per year, which will make the South Sichuan basin become the largest production base of shale gas in China.

The remaining onshore hydrocarbon resources in China, which are distributed in lithostratigraphic reservoirs of low and medium abundance, have great potential for exploration. Aimed at the exploration of the lithostratigraphic reservoirs in four types of prototype basins (onshore terrestrial rifts, depressions, forelands and marine kratons) and in glutenites， volcanics and fracturevug carbonate rocks, significant results are achieved on geological theory, technological innovation and production efficiency through five years of systematic study. (1) Establish the geological theory about the lithostratigraphic reservoirs in the fourtype basins; (2) Establish the largearea accumulation theory of lowmedium abundance lithostratigraphic reservoirs; (3) Innovate systematic exploration procedures and series of technologies for the lithostratigraphic reservoirs. Twentyone core patents are of independent innovation; (4) Push forward the significant exploration transformation from structural reservoirs to lithostratigraphic reservoirs, leading to great success in exploring largescale lithostratigraphic reservoirs by PetroChina Company Limited.

Continental shale oil is a general term for liquid hydrocarbons and many kinds of organic matter in continental organic-rich shale series with vitrinite reflectance of more than 0.5% at buried depth of more than 300 m, and is an important type of source-rock oil and gas. Based on the evolution model of oil generation and expulsion in organic-rich shale series controlled by maturity, continental shale oil is divided into two types: medium-high maturity and medium-low maturity. (1) The continental shale series in China develop high-quality source rocks of freshwater and saltwater lacustrine facies, as well as multiple types of reservoirs, including clastic rocks, carbonate rocks, diamictite, tuff and shale, forming a number of "sweet sections" and "sweet areas" of continuous distribution inside or near source rocks, which have large scale resources. (2) Experimental analysis of organic rich shale samples shows that the shale samples with wavy and horizontal beddings have good storage conditions, and the horizontal permeability of shale is tens to hundreds of times of its vertical permeability, which is conducive to the lateral migration and accumulation of shale oil in the source rocks. (3) After evaluation, the geological resources of medium-high maturity shale oil are about 10 billion tons, which can be effectively developed by horizontal drilling and volumetric fracturing, and will be a practical field of oil exploration in recent years. Shale oil with medium and low maturity has huge resource potential, and technological recoverable resources of (70-90) billion tons, making it a strategic alternative resource of oil industry. However, economic development of this type of shale oil needs in-situ conversion technology breakthroughs. Continental shale oil is an inevitable choice in the process of Chinese continental petroleum exploration from "outside source" to "inside source". Making breakthroughs in the core technologies such as "sweet area" evaluation and optimization, horizontal well volume fracturing and in-situ conversion technology and equipment is the key to realizing scale development of continental shale oil economically.

As technologies advance in oilfield development, mature oilfields are able to keep sustainable production and complex oilfields difficult to produce in the past are put into production efficiently. In this work, new progresses of main development technologies for medium-high permeability and high water cut, low permeability, heavy oil, complex faulted block and special lithology reservoirs in the past decade, especially those international achievements made in enhanced oil recovery, were summarized, the key problems and major challenges that different oilfields are facing were analyzed, and the development route and direction of three-generation technologies were proposed as “mature technology in industrialized application, key technology in pilot test and innovative technology for backup”. The key research contents should focus on: (1) Fine water flooding and chemical flooding for mature oilfields, improving oil recovery after chemical flooding, and gas flooding for low permeability reservoirs must be researched and tested in field further. (2) Study on subversive technologies like nanometer smart flooding, in-situ upgrading and injection and production through the same well should be strengthened. (3) EOR technologies for low oil price, new fields (deep sea, deep layer, unconventional reservoirs etc.) and highly difficult conditions (the quaternary recovery after chemical flooding, tertiary recovery in ultra-low permeability reservoirs) should be stocked up in advance. The development cost must be lowered significantly through constant innovation in technology and reservoir management to realize sustainable development of oilfields.

The source rock quality, organic pore structure, occurrence state and sealing mechanisms of shale gas in the Ordovician Wufeng-Longmaxi Formation (O₃w-S₁l), Fuling region, Sichuan Basin were studied using ultra-microscopic organic maceral identification, FIB-SEM, high temperature/pressure isothermal adsorption and isotopic age dating of noble gas. The results show that: (1) O₃w-S₁l organic-rich shale was mainly formed in a sedimentary environment with high productivity in surface water and hypoxia in bottom water, it can be divided into two sections according to TOC, of which the lower section (TOC≥3%) is mainly composed of graptolite, phytoplankton, acritarch, bacteria and solid bitumen, among them, graptolite is the main contributor to TOC, but the shale gas is mainly derived from phytoplankton, acritarch and other hydrogen-rich organic matter, as well as the pyrolysis of liquid hydrocarbons produced by this kind of organic matter. (2) Organic pores, as principal reservoir space for shale gas, exist in hydrogen-rich organic matter and solid bitumen. The graptolites and plenty of other organic matter stacking distribution in lamina provide more reservoir space for shale gas, and effective pathways of connected pores for fluid flow. (3) Shale gas in Fuling region is in supercritical state and dominated by free gas; the match of formation time of closed shale gas system and gas-generation peak, as well as slight alteration degree of sealing conditions in the later stage, are key factors controlling the retention and accumulation of shale gas in the regions with high thermal maturity and complex structural areas; adsorption, capillary sealing and slow diffusion of shale are the main microscopic mechanisms for the retention and accumulation of shale gas. It thus can be seen that the generation and accumulation of marine shale gas with high thermal maturity in complex structure areas is controlled jointly by anoxic depositional environment, excellent hydrocarbon rock quality, superior reservoir space and favorable sealing conditions.

By analyzing geological characteristics of shale gas in Southern China and the United States, main factors controlling the accumulation and key issues in the exploration and development of shale gas in China have been examined. The geological characteristics of shale gas in China include multi-stages of tectonic evolution, complex structure types, abundant faults, small continuous distribution area of shale formations, and no corresponding relationship between current thermal evolution degree and current burial depth of two main sets of shale formations (the Cambrian and Silurian). According to the analysis of the factors affecting shale gas enrichment such as fracture, tectonic type, shale gas migration, and gas content etc, the enrichment mechanisms of shale gas in China are: “sedimentary facies and preservation condition” are the main reservoir-controlling factors affecting the accumulation of shale gas, and “structure types and tectonism” are the main factors controlling the enrichment of shale gas in China; the former factors define shale gas plays, and the latter ones determine the position of sweet spots. The future research directions of shale gas in China are: firstly, contrary to the shale gas development in the United States, shale gas exploration and development in China should extend from the overpressure to normal pressure, and even low pressure areas; secondly, shale gas exploration in the Sichuan basin should extend from middle-deep to deep formations, studies should be done on the shale gas enrichment mechanism and accumulation models in formations more than 4 000 m deep, and horizontal well fracturing technology for these formations; thirdly, the development of transitional facies and continental facies shale gas should be brought along by drawing on exploration and development experience of marine shale gas.

Based on the main geological features and technical breakthroughs made in tight oil exploration, the major challenges facing tight oil development are analyzed, and the key technical trend for tight oil development is discussed in this paper. Mainly found in continental deposits, tight oil reservoirs in China feature small area, poor physical properties, big differences in geological characteristics between different basins, but low porosity, low permeability and pressure in general. In contrast to marine tight oil, tight oil in continental deposits faces such challenges as low production and recovery, and poor economics. Through nearly three years of research and pilot test, an integrated development mode with repeated fracturing of horizontal wells as the principal technique has been proposed, which includes integrated design, platform long horizontal well drilling, massive volume fracturing, re-fracturing stimulation, controlled production, factory-like operation, concentrated surface construction etc. It is recommended that study be strengthened on basic tight oil development theory, practical development technologies, and economic evaluation of tight oil development over the whole life cycle.

This paper deals with the main scientific problems, academic connotation, progress and prospects of reservoir development geology. The reservoir development geology involves the key scientific problems of reservoir connectivity, flow ability, and changeability through time. Its research focus on the forming mechanism and distribution model of geological factors controlling the reservoir development, the control mechanism of geological factors to oil and gas production, the rule of reservoir dynamic evolution during development, and the reservoir characterization and modeling technology. Important progress has been made on theory and technology of reservoir development geology in high water-cut reservoirs, low permeability and tight shale reservoirs, fracture-cavity reservoirs, which makes the reservoir development geology grow as an independent academic subject already. With the development expansion in areas of deep-strata, deep-water, and unconventional hydrocarbon reservoirs, and the increasing difficulties of high water-cut reservoir development, the theory and technology of reservoir development geology remain to be developed in order to support efficient and economic development of hydrocarbon fields with a sustainable growth.

Energy is the basis of human development and the impetus of society progress. There are three sources of energy: energy of celestial body outside the Earth, the Earth energy and energy of interaction between the Earth and other celestial bodies. Meanwhile, there are three scales of co-evolution: the evolution of the Sun-Earth-Moon system on an ultra-long time scale has provided energy sources and extra-terrestrial environmental conditions for the formation of the Earth system; the evolution of the Earth system on a long time scale has provided the material preconditions such as energy resources and suitable sphere environment for life birth and the human development; on a short time scale, the development of human civilization makes the human circle break through the Earth system, expanding the extraterrestrial civilization. With the co-evolution, there are three processes in the carbon cycle: inorganic carbon cycle, short-term organic carbon cycle and long-term organic carbon cycle, which records human immoderate utilization of fossil energy and global sphere reforming activities, breaking the natural balance and closed-loop path of the carbon cycle of the Earth, causing the increase of greenhouse gases and global climate change, affecting human happiness and development. The energy transition is inevitable, and carbon neutrality must be realized. Building the green energy community is a fundamental measure to create the new energy system under carbon neutrality target. China is speeding up its energy revolution and developing a powerful energy nation. It is necessary to secure the cornerstone of the supply of fossil energy and forge a strong growing pole for green and sustainable development of new energy. China energy production and consumption structure will make a revolutionary transformation from the type of fossil energy domination to the type of new energy domination, depending on a high-level self-reliance of science and technology and a high-quality green energy system of cleaning, low-carbon, safety, efficiency and independence. Energy development has three major trends: low-carbon fossil energy, large-scale new energy and intelligent energy system, relying on the green innovation, contributing the green energy and constructing the green homeland.