Advances in Resources Research

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Tight oil is the accumulation of oil trapped in the shale formation or transported to the interlayer in a very short distance. Tight oil has a broad prospect of exploration and development and has become an important replacement resource for conventional oil resources. The evaluation of structural characteristics of tight oil reservoirs is the hot spot and frontier of tight oil research. However, tight oil resources are formed uniquely, and their characteristics are different from those of conventional oil resources. The study on the structural characteristics of tight oil reservoirs is helpful to deepen the scientific understanding of tight oil reservoir systems. This paper reviews the main progress made in the evaluation of structural characteristics of tight oil reservoirs in recent years. The purpose of this paper is to deepen the systematic understanding of tight oil reservoir structure and enrich the understanding of the occurrence law and enrichment mechanism of tight oil resources, to promote the geological evaluation, exploration, and development of tight oil resources.

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Oilfield water drives through the injection of water into the reservoir, using water to drive out the crude oil in the reservoir. Unstable waterflooding is a method of water-drive development. Unstable waterflooding is one of the important means to improve oil recovery when continuous waterflooding is difficult to establish an effective displacement effect of the oil layer. At present, more and more oilfields have entered the middle and high water cut stage, and the proportion of reservoirs with low permeability and low abundance is getting higher and higher, which makes oilfield development more difficult. The research on the development mechanism of oil field water drives, including unstable waterflooding, is one of the research focuses of oil field water flooding development. This paper reviews the present situation of oil recovery technology for unstable waterflooding in recent years, including laboratory experiments and field applications. Furthermore, combined with the latest research progress in recent years, the development trend of unstable waterflooding technology is discussed. The purpose of this paper is to deepen the understanding of the oilfield waterflooding development system and enrich the understanding of the mechanism of unstable waterflooding to promote the effective development of oil resources.

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Shale oil is a kind of unconventional oil and gas, which is rich in reserves and has become an important strategic replacement resource for conventional oil and gas resources. However, the formation of shale oil resources is unique, and the characteristics of shale oil resources are different from those of conventional oil and gas resources. Shale oil is an unconventional oil resource occurring in reservoir rock series dominated by organic shale. Shale is not only the source rock of shale oil generation but also the reservoir that accumulates and preserves shale oil. Shale reservoirs formation is affected by many factors. This paper summarizes the research achievements on the main influencing factors of shale reservoirs formation at home and abroad in recent years, including (1) organic carbon content; (2) organic matter maturity; (3) organic matter type; (4) reservoir burial depth; (5) porosity; and (6) microscopic pore throat structure. This paper not only summarizes the previous research but also puts forward some suggestions for the future research direction. This paper has a certain reference value for a comprehensive understanding of shale reservoir formation.

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Shale gas is a kind of unconventional natural gas that mainly exists both adsorbed and free gas in shale. Many types of rich organic matter mud shale formations are extensively developed in China. According to the geological background of rich organic matter shale development and shale gas geology conditions, shale in China is divided into south, north (north China-northeast), northwest, and Qinghai-Tibet. Among them, south area shale has large monolayer thickness with Paleozoic marine deposits mainly, high thermal evolution degree, strong late tectonic, rich shale gas resources; north area shale’s enrichment conditions are diversified, Paleozoic-Mesozoic-Cenozoic shale being completely developed with obvious rolling migration sedimentary characteristics, frequently high thin interbedding changes and obvious sedimentary phase belt partition; northwest type centers on Paleozoic and Mesozoic, the sedimentary type being complete with high organic matter abundance and relatively low thermal evolution degree of organic matter. Yangtze Paleozoic, Ordos Basin Mesozoic, and Bohai Bay Basin Cenozoic are favorable areas of shale gas exploration and development. It is of great significance to explore China’s shale gas resources and exploration and development practice, which can not only provide guidance for the development direction of China’s shale gas but also provide a useful reference for the development of shale gas industry in other countries and regions.

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As an important unconventional resource, shale oil has attracted more and more attention and has become a hot spot for oil and gas exploration and development. Jiyang Depression of Bohai Bay Basin, located in Eastern China, is a shale oil development area worthy of great attention and is regarded as the focus of continental shale oil geophysical research and exploration and development practice. This paper summarizes the research results on the occurrence characteristics of shale oil reservoirs in Jiyang Depression in recent years. The main results are as follows: (1) on organic matter, the effective source rocks in Jiyang Depression are developed in salt-brackish water environment, and the third member of Shahejie Formation, the first member of Shahejie Formation, and the fourth member of Shahejie Formation are the main source rocks; (2) on lithofacies, organic-rich laminated lithofacies are the most favorable lithofacies for shale oil distribution in Jiyang Depression; (3) on pores, the micropores in Jiyang Depression are affected by mineral composition; (4) on the fractures, the existence of fractures in Jiyang Depression is mainly due to the high mineral content of carbonate rocks; and (5) on mineral composition, Jiyang Depression is generally rich in carbonate minerals and low detritus. The occurrence characteristics of reservoirs in Jiyang Depression are beneficial to the generation and preservation of shale oil.

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As one of the distribution areas of the oldest organic shale in China, Yanshan area contained a Middle-Upper Proterozoic sedimentary succession, in which the exploration of shale oil and gas resources is of great significance. To investigate shale oil and gas accumulation conditions and resources potential of the Middle-Upper Proterozoic strata, here we carried out total organic carbon (TOC) analysis, equal vitrinite reflectance (Ro) measurement, Porosity and permeability, and isothermal adsorption experiments on shale samples collected from Xinglong-Kuancheng area. Organic shale-bearing strata in this area include Chuanlinggou, Hongshuizhuang, and Xiamaling Formations, of which Hongshuizhuang and Xiamaling Formations develop organic shales better. Due to favorable sedimentary environments, Honghongzhuang and Xiamaling Formations have large shale thickness values, with ranges of 20-140 m and 100-300 m, respectively. A large number of oil seepages in the field outcrop provide direct evidence for hydrocarbon generation in this set of strata. Organic shales with TOC greater than 2.0% are widely distributed and have high hydrocarbon generation ability. The thermal evolution degree of shale organic matter is from low maturity to over maturity and Ro generally ranges from 0.6% to 2.2%. Especially, the maturity of organic matter in Xiamaling Formation varies greatly with the distance from diabase dikes. Hongshuizhuang and Xiamaling Formation shales are characterized by ultra-low porosity and permeability, indicating a good development potential. From the perspective of shale oil and gas accumulation conditions, this study demonstrates the good resources potential of Hongshuizhuang and Xiamaling Formations. The North Hebei Depression is a favorable area for shale oil and gas exploration.

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The Shaanbei Chang 7 shale oil members in the Ordos Basin develops vertically with multiple lithologic superimpositions. The interlayer stress of the sand-mud-shale thin interlayer is different, and the stress in the small layer is variable, resulting in high hydraulic pressure fractures and short extension distances. The effective retrofit volume did not meet expectations. According to the characteristics of 3 small reservoirs in Chang 7 Member in Xin’anbian area of Shaanbei, combined with the geological, structural, and sedimentary characteristics of the block, the in-situ stress distribution law of vertical multi-interbedded layers with different lithologies was obtained by finely interpreting the in-situ stress logging results of the single well, and the sand was simulated. A three-dimensional regional model of in-situ stress of mud-sheet multi-thin interbedded lithologic reservoirs. The calculation results show that the overall three-dimensional stress of the block is σ_V>σ_H>σ_h (the σ_V is vertical stress, the σ_H is horizontal maximum stress, and the σ_h is horizontal minimum ground stress), the stress value of sandstone in the lateral upper layer is greater than that of shale and that of mudstone, and the difference of horizontal stress in the vertical direction increases with the increase of depth. Combined with the hydraulic fracturing physical model experiment, the fracture initiation and vertical extension patterns of hydraulic fractures in shale oil reservoirs under different stress differences were analyzed. The experiment found that the perforation of the horizon with a large difference between the vertical stress and the minimum horizontal principal stress is preferred, which is beneficial to hydraulic pressure. The expansion of fractures through layers increases the volume of complex fractures and improves the effect of volume stimulation of shale oil reservoirs.

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Climate change has a serious impact on the food crop ecosystem. Rice is not only an important food crop for human beings, but also one of the food crops sensitive to climate change. The research progress on the effects of climate change on rice in China is reviewed in this paper. Climate change significantly shifted the planting boundary of rice to the north, which shortened the growth and development period of rice, and then decreased the overall planting yield and quality of rice. The adverse effects of climate change can be dealt with through the adjustment of planting distribution, variety improvement, and technological improvement. In the future, climate change will further affect rice production. It is still necessary to strengthen the research on the impact mechanism of climate change and countermeasures to promote and ensure the sustainable development of rice. The purpose of this paper is to provide a reference for the assessment of the impact of climate change on rice and the sustainable development of rice.

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Shale oil resources have great potential for exploration and development, and their potential resources far exceed the conventional oil and gas resources found at present, which plays an important role in the development of the oil industry in the future. Biyang Sag in Nanxiang Basin is a typical Meso-Cenozoic oil-rich sag in eastern China, which has certain shale oil development potential. Based on previous studies, this paper summarizes the research results of the main controlling factors and recoverable factors of shale oil enrichment in Biyang Sag in recent years from six aspects. The contents include (1) hydrocarbon generation basis, (2) hydrocarbon expulsion characteristics, (3) storage spaces, (4) reservoir reformability, (5) crude oil’s physical properties, and (6) mobility. This paper is expected to provide a reference for the exploration and development of shale oil in Biyang Sag.

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Wetland is one of the most important environmental resources for human beings. With economic development, the evolution of wetlands has become a global phenomenon, and wetland research is a research hotspot in the frontier field of international wetland science. People conduct in-depth research on the structure, function, process, dynamics, and other aspects of wetlands from different angles to explore effective ways to coordinate wetland development and protection. The Yellow River Delta wetland is the most complete, typical, and youngest coastal estuarine wetland in China, and it is also the latest delta wetland in the world. The study of wetlands in the Yellow River Delta is of great significance. This paper summarizes the research progress of wetlands in the Yellow River Delta in recent years from (1) natural wetland characteristics, (2) constructed wetland characteristics, (3) hydrological characteristics, (4) soil characteristics, (5) vegetation characteristics, and (6) animal characteristics. On this basis, the key research direction in the future is put forward. The purpose of this paper is to provide a reference for the protection and effective utilization of wetlands in the Yellow River Delta.

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Water drive development is the most widely used and mature oil field development technology. Water drive development includes water flooding (water injection) and water injection huff and puff. The main reasons for the broad application of water drive development include: (1) injected water can drive crude oil wells, (2) water can be injected into strata relatively easily to increase reservoir energy, and (3) water resources have lower investment and operation costs. The driving development of more and more oilfields in China has entered the middle and high water cut stage, and the proportion of low-grade reservoirs with low permeability and low abundance is getting higher and higher, which makes the development more difficult. How to improve the effectiveness of the water drive and improve the efficiency of water drive is the key problem to be solved in oilfield water drive development. At the same time, under the condition of complex injection-production relationships and frequent dynamic changes of the displacement field, it can effectively tap the potential of remaining oil and improve the development effect of water drive, which puts forward higher requirements for water drive development technology. This paper summarizes the present situation of water-drive development technology in Chinese oilfields and puts forward some suggestions for the future development trend.

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Climate change is seriously affecting the food crop ecosystem. Wheat is not only an important food crop for human beings, but also one of the food crops sensitive to climate change. Wheat is divided into winter wheat and spring wheat. China is dominated by winter wheat. This paper reviews the research progress on the effects of climate change on wheat in China from four aspects. The contents include: (1) the influence of planting boundary and planting area, (2) the influence of planting system and yield, (3) the influence of quality, and (4) the influence of agricultural input. Previous studies have shown that although climate change moves the planting boundary of wheat northward and expands the planting area as a whole, climate change affects the growth and development process of wheat, the change of suitable planting areas, and the aggravation of diseases and insect pests, which leads to the decrease of planting yield and quality. The adverse effects of climate change can be dealt with through adjustment of planting distribution, variety improvement, and technological improvement. In the future, climate change will further affect the ecology of wheat. It is still necessary to strengthen the research on the impact mechanism and countermeasures of climate change to ensure wheat’s sustainable development. This paper aims to provide a reference for the impact assessment of climate change on wheat and the sustainable development of grain.