With the continuous deepening of oil and gas exploration and development, unconventional oil and gas resources, represented by tight oil, have become research hotspots. However, few studies have investigated tight oil potential in any systematic way in the shell limestone reservoir of the Sichuan Basin. Herein, we used thin section analysis, X-ray diffraction (XRD), high-pressure mercury intrusion, low-pressure N2 and CO2 adsorption experiments, low-field nuclear magnetic resonance (NMR), focused ion beam–scanning electron microscopy (FIB-SEM), and nano-CT to characterize multi-porous media. The reservoir space controlled by nonfabric, shell, and matrix constitutes all the reservoir space for tight oil. The interconnected porosity was mainly distributed in the range of 1% to 5% (avg. 2.12%). The effective interconnected porosity mainly ranged from 0.5% to 2.0% (avg. 1.59%). The porosity of large fractures was 0.1% to 0.5% (avg. 0.21%). The porosity of isolated pores and bound oil–water pores was 0.2% to 0.8% (avg. 0.44%). The dissolved pores adjacent to fractures, the microfractures controlled by the shell, the microfractures controlled by the matrix, the isolated pores, and the intracrystalline pores constitute five independent pore-throat systems. The development of pores and fractures in shell limestone reservoirs are coupled on the centimeter–millimeter–micron–nanometer scale. Various reservoir-permeability models show continuous distribution characteristics. These findings make an important contribution to the exploration and exploitation of tight oil in shell limestone.

In the mid-21st century, natural gas will enter its golden age, and the era of natural gas is arriving. This paper reviews the development stages of global natural gas industry and the enlightenment of American shale gas revolution, summarizes the development history and achievements of the natural gas industry in China, analyzes the status and challenges of natural gas in the green and low-carbon energy transition, and puts forward the natural gas industry development strategies under carbon neutral target in China. The natural gas industry in China has experienced three periods: start, growth, and leap forward. At present, China has become the fourth largest natural gas producer and third largest natural gas consumer in the world, and has made great achievements in natural gas exploration and development theory and technology, providing important support for the growth of production and reserves. China has set its goal of carbon neutrality to promote green and sustainable development, which brings opportunities and challenges for natural gas industry. Natural gas has significant low-carbon advantages, and gas-electric peak shaving boosts new energy development; the difficulty and cost of development are more prominent. For the national energy security and harmonious development between economy and ecology under the carbon neutral goal, based on the principle of “comprehensive planning, technological innovation, multi-energy complementarity, diversified integration, flexibility and efficiency, optimization and upgrading”, the construction of the production-supply- storage-marketing system has to be improved so as to boost the development of the natural gas industry. First, it is necessary to strengthen efforts in the exploration and development of natural gas, making projects and arrangement in key exploration and development areas, meanwhile, it is urgent to make breakthroughs in key science theories and technologies, so as to increase reserve and production. Second, it should promote green and innovative development of the natural gas by developing new techniques, expanding new fields and integrating with new energy. Third, there is a demand to realize transformation and upgrading of the supply and demand structure of natural gas by strengthening the layout of pipeline gas, liquefied natural gas and the construction of underground gas storage, establishing reserve system for improving abilities of emergency response and adjustment, raising the proportion of natural gas in the primary energy consumption and contributing to the transformation of energy consumption structure, realizing low-carbon resources utilization and clean energy consumption.

The main controlling factors, genetic types, distribution characteristics, influence on water injection development and technical strategies of bioclastic limestone interlayers in MB2-MC1 section of lower Mishrif Formation in H Oilfield, Iraq, were studied using core ananlysis, casting thin section, analytical test, seismic data, logging, production performance and numerical simulation. The results indicate that the shoal front slope and intershoal deposits during relative sea-level rise cycles, marsh and incision filling deposits during relative sea-level fall cycles, and the lower part of the bioclastic shoal deposits during high-frequency cycles are the material basis for the development of interlayers. Superimposed destructive diagenesis is the primary controlling factor, affecting the lower part of shoal, intershoal, shoal front slope, marsh and incision filling types. The main permeability ranges from（0.05 to 1.50） ×10 -3 μm~2 with a pore throat radius of 0.05～0.5 μm. The barriers are located at the top of MB2-1 and MB2-2 layers, the bottom of MC1-1 layer and MC1-3 layer, and the baffles are mainly developed inside MB2-1 and MB2-2 layers. Water injection at the bottom of the continuous barrier has a slow effect, with the oil-water interface slowly and evenly uplifted, and a large formation pressure deficit. In contrast, water at the bottom of the discontinuous barrier experiences coning, resulting in rapid increase in the water cut of the well. The bottom water flow around the baffle is significant, and the pressure gradient of the upper and lower formations changes. During development, it is crucial to make full use of the characteristics of the barrier and baffle, adhere to the separated development units, and adopt the mode of bottom injection top production and peripheral injection top production. According to the types and distribution characteristics of the barrier and baffle, the well location deployment is optimized to ensure the maximum recovery degree in the low water cut period.

The essence of energy system transition is the “energy revolution”. The development of the “resource-dominated” energy system with fossil energy as the mainstay has promoted human progress, but it has also triggered energy crisis and ecological environment crisis, which is not compatible with the new demands of the new round of scientific and technological revolution, industrial transformation, and sustainable human development. It is in urgent need to research and develop a new-type energy system in the context of carbon neutrality. In the framework of “technique-dominated” new green and intelligent energy system with “three new” of new energy, new power and new energy storage as the mainstay, the “super energy basin” concepts with the Ordos Basin, NW China as a representative will reshape the concept and model of future energy exploration and development. In view of the “six inequalities” in global energy and the resource conditions of “abundant coal, insufficient oil and gas and infinite new energy” in China, it is suggested to deeply boost “China energy revolution”, sticking to the six principles of independent energy production, green energy supply, secure energy reserve, efficient energy consumption, intelligent energy management, economical energy cost; enhance “energy scientific and technological innovation” by implementing technique-dominated “four major science and technology innovation projects”, namely, clean coal project, oil production stabilization and gas production increasing project, new energy acceleration project, and green-intelligent energy project; implement “energy transition” by accelerating the green-dominated “four-modernization development”, namely, fossil energy cleaning, large-scale new energy, coordinated centralized energy distribution, intelligent multi-energy management, so as to promote the exchange of “two 80%s” in China's energy structure and construct the new green and intelligent energy system.

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.

Unconventional oil and gas reservoirs have broad exploration and development prospects. Fracture parameters and effectiveness evaluation are two of the key tasks for the evaluation of these types of reservoirs. Array acoustic logging can be used for fracture evaluation to compensate for the deficiencies of the image logging fracture evaluation method. Therefore, to develop acoustic logging evaluation methods as well as nondestructive testing methods for fractures, experiments were conducted to study the shear wave transmission in fractured media. Experiment data demonstrate a good correlation between the shear wave attenuation coefficient and fracture width, and the shear wave attenuation coefficients rise logarithmically with the increase in the fracture width for all models with different porosities and distinct dip angles of fractures. The shear wave attenuation coefficient changes relatively faster with the fracture width when the fracture width is within 250 μm. In addition, the shear wave attenuation is affected by the core porosity and fracture dip angle. When the fracture width is constant, the shear wave attenuation caused by the 0° fracture is relatively larger and is obviously greater than that of the fractures at other angles, which is consistent with the existing experimental results. The results of this study can be used to guide further research on amplitude compensation methods for sonic signal transmission in fractured media and fracture evaluation methods.

Global climate change caused by geological processes is one of the main causes of the 5 global mass extinctions in geological history. Human industrialization activities have caused serious damage to the ecosystem, the greenhouse effect of atmospheric CO2 has intensified, and the living environment is facing threats and challenges. Carbon neutrality is the active action and common goal of mankind in the face of the climate change crisis, therefore, probing into its theoretical and technological connotation, scientific and technological innovation system has far-reaching significance and broad prospects. Studies indicate that (1) Carbon neutrality reflects the theoretical connotations of “energy science” and “carbon neutrality science”, including technical connotations of carbon emission reduction, zero carbon emission, negative carbon emission, and carbon trading. (2) Carbon neutrality spawns new industries such as carbon industry centering on CO2 capture, utilization, and storage (CCUS, or CO2 capture and storage CCS), and hydrogen industry centering on green hydrogen. “Gray carbon” and “black carbon” are the two application attributes of CO2. “Carbon+”, “Carbon−”, and “Carbon=” are three carbon-neutral products and technologies. (3) China faces three major challenges in achieving the goal of carbon neutrality: first, energy transition is large in scale and the cycle is short; Second, there are many problems in the process of energy transition, such as security uncertainties, economic utilization, and unpredictable disruptive technologies; Third, after transition, we may face new key techno-logical “bottlenecks” and “broken chain” of key mineral resources. (4) Based on current knowledge to predict the top 10 disruptive technologies and industries in the energy field: underground coal gasification, in-situ conversion process of medium and low-mature shale oil, CCUS/CCS, hydrogen energy and fuel cells, bio-photovoltaic power generation, space-based solar power generation, optical storage smart micro-grid, super energy storage, controllable nuclear fusion, wisdom energy Internet. Five strategic projects will be implemented, including energy conservation and efficiency improvement, carbon reduction and sequestration, scientific and technological innovation, emergency reserve and policy support. (5) In the future, different types of energy will have different orientations. Coal will play the role of ensuring the national energy strategy “reserve” and “guarantee the bottom line”. Petroleum will play the role of ensuring national energy security “urgent need” and the “cornerstone” of raw materials in people's livelihood. Natural gas will play the role in ensuring national energy “safety” and “best partner” of new energy. New energy will play the role in ensuring the “replacement” and “main force” of the national energy strategy. (6) Carbon neutrality is a major practice of the green industrial revolution, carbon reduction energy revolution, and ecological technology revolution, which will bring new and profound changes to human society, the environment and the economy. (7) Carbon neutrality needs to follow the four principles of “disruptive breakthroughs in technology, guarantee of energy security, realization of economic feasibility, and controllable social stability”. We should rely on technological innovation and management changes to ensure the realization of national energy “independence” and carbon neutrality goal, and make China's contribution to the construction of a livable earth, green development, and ecological civilization.

中东白垩系碳酸盐岩生物碎屑滩储层地层厚,规模大,是该区主力产层;但是其多为局限台地相,单储层薄,相带变化快,有效预测有利相带储层的分布是油藏高效开发的关键.结合该地区沉积研究,以伊拉克美索不达米亚盆地油田Mishrif-B1组为例,针对局限台地潮道相储层开展3D雕刻技术,有效识别了潮道的空间展布,并用于地质模型相约束;针对台内滩储层,开展相控薄层反演技术,在提高纵向精度(3～5米)的同时,更好地利用了地震的横向信息.研究成果大幅度提高了单井产能.

The Lower Permian Fengcheng Formation,as favourable source rock in the Junggar Basin,has been the target for petroleum exploration.Due to its deep burial depth,complicated lithology and few global analogs,the evaluation of the petroleum potential of Fengcheng Formation is still at its rudimentary stage.This study discusses the characteristics of alkaline minerals,geological background,origin of alkaline lakes and its forming processes through methods including core description,thin section observa-tion,SEM,X-ray diffraction analysis,TOC content measurements,inclusion temperature test,geochemical analysis,etc.the results suggest:(1) the Fengcheng Formation can be categorized into five rock types,among which,alkaline rock is the most distinguished lithofacies type of alkaline lakes and reedmergnerite is generally related to volcanic eruption or hydrothermal activities;(2) five rock associations are recognized in the Fengcheng Formation.From near-source to lake center,they are type Ⅴ of alluvial-fluvial facies,type Ⅲ and Ⅳ of shallow shoreface to lacustrine facies,respectively;type Ⅰ and Ⅱ of deep-semideep lacustrine facies,respectively.Type Ⅰ and Ⅲ are typical alkaline rock associations with favourable source rock potential;(3) the formation of alkaline lake is primarily controlled by volcanic activities and climate,where the former supply the Na-rich fluids,and the latter salinized the freshwater lake and facilitate the final formation of alkaline lake.

Alkaline-lacustrine deposition and its evolution model in Permian Fengcheng Formation at the Mahu sag, Junggar Basin were investigated through core and thin-section observation, geochemical and elemental analysis, logging response and lithofacies identification. Six lithofacies are developed in the Fengcheng Formation. The Feng 2 Member（P1 f2） is dominated by lithofacies with alkaline minerals, while the upper part of the Feng 1 Member（P1 f1） and the lower part of the Feng 3 Member（P1 f3） are primarily organic-rich mudstones that are interbedded with dolomite and dolomitic rock. Paleoenvironment evolution of Fengcheng Formation can be divided into 5 stages, which was controlled by volcanic activity and paleoclimate. The first stage（the early phase of P1 f1） was characterized by intensive volcanic activity and arid climate, developing pyroclastics and sedimentary volcaniclastic rocks. The secondary stage（the later phase of P1 f1） had weak volcanic activity and humid climate that contributed to the development of organic-rich mudstone, forming primary source rock in the Fengcheng Formation. The increasing arid climate at the third stage（the early phase of P1 f2） resulted in shrinking of lake basin and increasing of salinity, giving rise to dolomite and dolomitic rocks. The continuous aird climate, low lake level and high salinity at the fourth stage（the later phase of P1 f2） generated special alkaline minerals, e.g., trona, indicating the formation of alkaline-lacustrine. The humid climate made lake level rise and desalted lake water, therefore, the fifth stage（P1 f3） dominated by the deposition of terrigenous clastic rocks and dolomitic rocks.

Based on the core, cast thin section, whole rock analysis, conventional physical properties and high pressure mercury intrusion test, the sedimentary diagenesis characteristics of rudist shoal in Cretaceous Mishrif Formation of H Oilfield, Iraq and its control on the reservoir were studied. The rudist shoal of the Mishrif Formation develops in the high-stand systems tract and is distributed in the high places of paleogeomorphology on the edge of platform with strong hydrodynamic force. According to the relative sea level changes, lithologic evolution and sedimentary structure characteristics of the rudist shoal, the single rudist shoal is divided into four lithologic sections: A, B, C and D, that is, low-angle cross-bedding pelletoids-rudist packstone, low-angle cross-bedding and parallel bedding arene-rudist grainstone, parallel bedding rudist gravel limestone, and horizontal bedding carbonaceous mudstone. The complete sedimentary sequence of a single rudist shoal is often disrupted. Several rudist shoals superimpose to form thick rudist shoal sediment. The single rudist shoal thickness and lithologic sections assemblage change regularly in vertical direction. The rudist shoal has the characteristics of "strong dissolution, weak cementation and strong compaction", forming pore-type reservoir with intergranular pores, intergranular dissolved pores, mold pores, and dissolved pores. With mainly coarse pore throats larger than 5 μm, the reservoir is of medium-high porosity and high permeability. There is lithological reverse cycles inside single shoals and between single shoals, with content of mud crystals decreasing from the bottom to the top, dissolution increasing, cementation decreasing in strength, pore throats getting larger, and physical properties turning better. The rudist shoal of MB2-1 at the top of the high-stand systems tract has the largest thickness, moreover, subject to the strongest atmospheric freshwater leaching, this layer has the most significant dissolution and the largest pore throat, so it is the best reservoir of the Mishrif Formation.

中东地区白垩系Mishirif组以生物碎屑灰岩为主,其形成于温暖潮湿的环境中.综合利用岩心、铸体薄片、全岩分析、常规物性及高压压汞等资料,以伊拉克HF油田Mishrif组为例,开展生物碎屑类型、分布特征、差异成岩及储集层特征等研究.Mishrif组灰岩中生物碎屑以底栖有孔虫、非固着类双壳类、厚壳蛤和棘皮动物为主,含少量苔藓动物、藻类与海绵动物,其含量、类型及大小对沉积环境有重要指示意义.沉积环境决定岩石组分与结构的差异,在此基础上成岩作用控制岩石的孔隙结构与物性特征.生物碎屑主要经历了不同程度海水环境的泥晶化和生物钻孔、大气淡水环境的溶蚀和胶结、埋藏环境的压实压溶和颗粒破裂作用.以底栖有孔虫和非固着类双壳类碎屑为主的低能沉积环境具有“弱溶蚀、强胶结、强压实”的成岩特征,主要发育微孔、晶间孔及粒内孔,孔喉分布呈偏细态细微喉单峰型,物性较差;以厚壳蛤和棘皮动物碎屑为主的高能沉积环境具有“强溶蚀、弱胶结”的成岩特征,主要发育铸模孔、粒间孔及粒间溶孔,孔喉分布呈偏粗态中粗喉极宽峰型,是Mishrif组最有利储集层.以HF油田Mishrif组为代表的白垩系生物碎屑灰岩在中东地区发育广泛,故上述成果对于该地区生物碎屑灰岩油气开发具有重要意义.