2020 Vol. 26, No. 2

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2020, 26(2): .
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Progress on strike-slip fault research and its significance
XIAO Kunze, TONG Hengmao
2020, 26(2): 151-166. doi: 10.12090/j.issn.1006-6616.2020.26.02.015
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Since the emergence of the strike-slip fault concept, the importance of strike-slip fault in geological science research has gradually been realized. Understandings of strike-slip faults in terms of geometry, kinematics, dynamics and tectonic significance have accelerated the study on strike-slip fault. However, there are still some limitations in its classification and mechanism analysis. Based on the literature review of strike-slip fault, the principle, concept and related terms are summarized, then the displacement characteristics, identification marks, mechanical mechanism, strike-slip derived or associated structures, characteristics of strike-slip basins, classification and examples of strike-slip faults are analyzed. Combined with the mechanical mechanism of strike-slip fault, a new classification method of strike-slip fault is proposed, and a brief analysis of typical faults is made using the new classification method, such as the San Andreas fault on the west coast of the United States, the Alpine fault in New Zealand, the Tanlu fault and the Altyn Tagh fault in China.
Integrated determination of principal stress and tensile strength of rock based on the laboratory and field hydraulic fracturing tests
WANG Chenghu, GAO Guiyun, WANG Hong, WANG Pu
2020, 26(2): 167-174. doi: 10.12090/j.issn.1006-6616.2020.26.02.016
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The compliance of the drilling-rod hydraulic fracturing in-situ stress measurement can affect the determination accuracy of the maximum horizontal principal stress. Utilizing tensile strengths based on the hollow cylinder hydraulic fracturing test to replace reopening pressures to calculate maximum horizontal principal stresses is a very promising option to cut down the negative effects from the drilling-rod test system. Eight hydraulic fracturing in-situ stress measurement tests were conducted in a 65 m-deep borehole in an under-construction railway tunnel in Fujian Province. Seventeen hollow cylinders made from the cores recovered from the same borehole were fractured hydraulically in laboratory. The average tensile strength based on the hollow cylinder hydraulic fracturing test is 8.40 MPa, which is close to 8.22 MPa, that determined by the classic hydraulic fracturing in-situ stress measurement. For the 8 in-situ stress measurements within a very narrow depth range of 20 m, the average value of the minimum horizontal principal stress is 8.41 MPa, and the average value of the maximum horizontal principal stress based on the hollow-cylinder tensile strength is 16.88 MPa, which is close to 16.70 MPa, the average value that calculated by the reopening pressure. The relationship between the three major principal stresses is σH > σV > σh, which is favorable for the strike-slip faulting. Based on the comparative analysis, for the drilling-rod hydraulic fracturing test system, when the test depth is shallow and the system compliance is minor, there are no marked differences in the calculated maximum principal stresses between based on the reopening pressures and the hollow-cylinder-test tensile strengths, which proves that the tensile strengths based on the hollow-cylinder test can be utilized to calculate the maximum horizontal principal stress during the hydraulic fracturing in-situ stress measurement; at the same time, the tensile strength of rock mass in the test interval, determined by the field hydraulic fracturing test with minor test system compliance, is definitely reliable for use.
Research progress of interaction of fluid with rock in the ductile shear zone
LIU Gui
2020, 26(2): 175-186. doi: 10.12090/j.issn.1006-6616.2020.26.02.017
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The jointly controlling mechanism of tectonic deformation process and fluid mineralization is one of the hot issues of mineral deposits. As a strain localization zone in the continental lithosphere, a large amount of fluid is generally permeated in the shear zone. In the ductile shear zone, the interaction between fluid and rock, the localization of its chemical and physical effects lead to chemical unbalances and component migrations of minerals, causing re-adjustment of chemical composition of rocks. The action of the fluid, the change of composition and volume in the shear zone, the deformation and mineralization simulation experiments in the shear zone are summarized and analyzed. The mechanical-chemical action during shear deformation and the behavior of shear structural stresses and fluids during the process of tectonogenesis are discussed. Therefore, comprehensive research on the influence of tectonic forces on temperature, petrophysical properties, geochemical phase balance, and coherent parameters of water-rock systems should be strengthened.
Research on the genetic model and exploration progress of hot dry rock resources on the southeast coast of China
LI Tingxin, LIN Wenjing, GAN Haonan, YUE Gaofan, ZHANG Delong, WANG Guiling
2020, 26(2): 187-200. doi: 10.12090/j.issn.1006-6616.2020.26.02.018
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Hot dry rock (HDR) is an important geothermal resource, whose exploitation mostly centers on the heat contained in the intermediate-acid intrusive rock mass of the crust since the Mesozoic. The southeast coast is the main distribution area of highly radioactive granites in China, with a large area of developed Mesozoic acid granite intrusions, which makes it a target area for HDR prospecting. By studying the tectonic background of the southeast coast, regional terrestrial heat flow distribution, crustal thickness, buried depth of the curie surface and new structures, the occurrence background of HDR resources on the southeast coast and the existence of HDR resources in Fujian were analyzed and discussed. Based on the analysis of the heat-controlling structure, a genetic model of HDR resources on the southeast coast was proposed and a ternary heat accumulation model for HDR accumulation on the southeast coast was preliminary established. The exploration targeting at HDR resources in Zhangzhou, Huizhou, etc. was summarized. The progress and related research provide the basis for future exploration and evaluation of HDR resources on the southeast coast of China.
Advances in quantitative characterization of shale pore structure by using fluid injection methods
YU Yuxi, WANG Zongxiu, ZHANG Kaixun, CHENG Ming
2020, 26(2): 201-210. doi: 10.12090/j.issn.1006-6616.2020.26.02.019
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Shale is compact and has complex structure, which makes it hard to characterize its pore structure quantitatively; however, the pore structure of shale can provide important information for shale reservoir evaluation and sweet spot determination. The fluid injection methods, represented by the gas adsorption method and the mercury injection method, are the most commonly used techniques in shale pore structure characterization, but neither of them can provide the complete pore size range of shale. In this paper, the research results of previous studies were reviewed and summarized, and the key factors affect the test result of gas adsorption method and mercury injection method were analyzed. The problems and future directions in the combined characterization of shale pore structure in the complete pore size were pointed out. It is noted that the characterization results from the gas adsorption using particle samples do not match those from the mercury injection using bulk samples, which makes the data combination impossible. And the combined characterization results are hard to be verified. For mercury injection, the usage of particle samples can improve the data quality compared to the bulk ones, as well as the combined characterization results. The understandings about conformance correction, premium particle size and data compatibility are the key issues to improve the combined characterization of shale pore structure.
Research on the status quo of environmental geology impact of enhanced geothermal system and countermeasures
GAN Haonan, WANG Guiling, LIN Wenjing, ZHANG Wei, QIN Xianghui, ZHANG Chongyuan
2020, 26(2): 211-220. doi: 10.12090/j.issn.1006-6616.2020.26.02.020
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Enhanced geothermal system (EGS) is the hotspot of geothermal resource development and utilization. Its power generation is almost impervious to the external environment and it cause little pollution and damage to the environment. In recent years, it has been found that in the process of EGS development, the geothermal reservoir reconstruction and water injection operation can lead to a large number of microseismic events. The water injection processes of a few EGS projects are obviously related to the local earthquakes of magnitude 3 or above, causing close attention of researchers. This paper introduces the principle, technology and development and utilization status of the enhanced geothermal system. And the main EGS related environmental impact events at home and abroad are sorted out and analyzed. On this basis, the current research progress of EGS environmental impact is summarized, and the coutermeasures in the next step are put forward, which provide effective reference for the site selection and development of EGS projects in China.
Study on influence of construction precipitation on surface settlement and stratum stress on the ground fissure site
WANG Qingbing, HUANG Qiangbing, YAN Yufeng, YANG Zhao, HU Shiwei, LEI Jian
2020, 26(2): 221-231. doi: 10.12090/j.issn.1006-6616.2020.26.02.021
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Ground fissure is a typical urban geological disaster in Xi'an city, and the change of groundwater level is an important factor in inducing ground fissure activity. Taking construction precipitation in underground excavation section of Xi'an Metro Line 6 as the engineering background, based on the finite element numerical simulation, the surface settlement law and strata stress variation characteristics caused by construction precipitation on ground fissure site were analyzed. The research results show that when groundwater level falls, the surface settlement deformation of the hanging wall is greater than that of the footwall, and there is a phenomenon of differential settlement on both sides of the ground fissure zone. The maximum differential settlement is approximately in a linear relationship with the depth of the groundwater level decline. At different positions, the lateral surface settlement curve shows a "Z" shape. The differential settlement area changes with the position of ground fissures, and the curve shows quadratic function between differential settlement and lateral position. In addition, with the groundwater level falling, the vertical stress of the stratum increases with the decrease of the underground water level, and there is a sudden change in the stratum stress at the location of the ground fissure and curve shows cubic polynomial function between stress affected area and depth. Based on the layer-wise summation method, the analytical solution of the surface settlement when the groundwater level falls is calculated. By comparing the calculation results with that of the numerical simulation, it shows a basic consistency, and the empirical formula for calculating the maximum surface settlement is obtained. The research results can provide scientific guidance for the safe construction of underground tunnel and other underground projects on ground fissure sites.
Pan-lake during the late Pleistocene in the source area of the Yellow River and its significance
HAN Jian'en, LUO Peng, YU Jia, SHAO Zhaogang, MENG Qingwei, WANG Jin, ZHU Dagang
2020, 26(2): 232-243. doi: 10.12090/j.issn.1006-6616.2020.26.02.022
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According to the sedimentary characteristics and the results of ESR dating of the lacustrine strata profile in Maduo County, Qinghai Province, the pan-lake event had occurred in the source area of the Yellow River during the late Pleistocene period at about 130 kaB.P.. During the pan-lake period, the four lakes in Maduo County connected with each other, and formed one huge lake whose area was 4.1 times bigger than the total area of the present four lakes. The pan-lake event in the Maduo area coincided with the transition of deep sea oxygen isotope from MIS 6 to MIS 5, which shows that the climate change on the Qinghai-Tibet Plateau is closely related to the global climate change. As the lacustrine strata in the source area of the Yellow River were more sensitive to the global climate change, it recorded the climate change earlier than other areas did. The analysis of the grain size, carbonate and magnetic susceptibility of the sediments in the Maduo lacustrine strata profile shows 9 stages of the lacustrine sediments during the period of 132±10~128±12 ka, indicating a fluctuating and rising process of climate change on the Qinghai-Tibet Plateau in transition from MIS 6 to MIS 5. A large area of lacustrine sedimentation in the source area of the Yellow River ended at about 130 kaB.P. This may be the result of the regional tectonic activities of Gonghe Movement which cut through the Duoshixia gorge in the lower reaches, causing a suddenly leak out of the lake water.
Paleoclimatic and paleoenvironmental evolution recorded by the aeolian sand-paleosol sequence in the Zoigê basin
QI Lin, WANG Yan, CAI Yao, QIAO Yansong, YAO Haitao, YANG Shuaibin, BAI Wenbin
2020, 26(2): 244-251. doi: 10.12090/j.issn.1006-6616.2020.26.02.023
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The aeolian sand-paleosol sequence in the Zoigê basin is a sensitive record of paleoclimate change and paleoenvironmental evolution for the northeastern region in the Tibet Plateau. A typical aeolian sand-paleosol section, called Xiaman, was tested for its AMS C age, grain size, magnetic susceptibility and sporo-pollen. Then the paleoclimate and paleoenvironment evolution since the last deglacial period in this area was discussed. The results show that the land desertification in the Zoigê basin occurred at least in the last deglacial period of more than 16 ka years ago. Variations of the formation structure, grain size and magnetic susceptibility indicate that the paleoclimate has undergone many alternations of cold and warm, and the sandy land has also experienced many processes of fixation and activation. The climate tended to be relatively warm and wet during 16130~6460 aB.P., around 3445 aB.P. and 700 aB.P.. There was a very warm period during 8170~6460 aB.P.. Since 11.3 kaB.P., the sporo-pollen contents of warm-fitted trees in paleosol have decreased considerably, while that of herbaceous plants, especially swampy plants, such as Myriophyllum and Syperaceae, have increased obviously, indicating that the paleoenvironment has significantly changed and the swampy peats have begun to develop.
Study on the river network, geomorphological features and tectonic activity in the Danjiangkou reservoir and its surrounding areas
WEN Li, WEI Pengfei, LI Xuemin, SUN Xiaozhou, WANG Lixuan
2020, 26(2): 252-262. doi: 10.12090/j.issn.1006-6616.2020.26.02.024
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Owing to its sensitiveness to tectonics and climate, river records the relevant information about river system evolution, structural deformation and climate change. It is a breakthrough point in structural geomorphology research to elaborate on regional geomorphology and tectonic activities by studying the formation and evolution of the river, while the most direct and effective way to study formation and evolution of the river is through the spatial change of river morphology. Complex geomorphology, frequently-happened geological disasters, and strong tectonic activities make the Danjiangkou reservoir an ideal place for structural geomorphology research. In this paper, we researched on the river morphology, geomorphology and tectonic activities in the surrounding areas of the Danjiangkou reservoir. It is shown that the spatial characteristics of the river network fractal dimension values are highly consistent with the spatial distribution of the regional active faults. In and around the relatively active fault zones, the river networks are affected by tectonic activities in the process of development. The evolution of the river is immature and the river network fractal dimension values are relatively low (below 1.115). On the contrary, in and around the relatively inactive fault zones, the evolution of the river is mature, and the river network fractal dimension values are relatively high(above 1.25). Moreover, there is no significant correlation between the spatial distribution of river network fractal dimension values and geomorphological parameters, such as topographic slope and average elevation, which means the crucial factor affecting the spatial distribution of river network is the regional tectonic activity. Therefore, characteristics of river network fractal dimension can quantitatively reflect the strength and difference of regional tectonic activities, which provides reference for the studies on river formation and evolution, tectonic activity and prediction of geological disasters.
Information construction method of geological survey projects based on digital mapping technology
YANG Xingchen, YE Mengni, YE Peisheng, CAI Maotang, LOU Yuxing, ZHANG Xujiao, LIU Hao
2020, 26(2): 263-270. doi: 10.12090/j.issn.1006-6616.2020.26.02.025
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The informatization construction of geological survey project is one of the supporting systems to realize the effective service of geological survey to the national ecological civilization construction. Digital mapping technology is the key technology in the informationization construction of geological survey projects, which makes the whole process of field data acquisition, data processing and output of results informationized. In view of the technical difficulties in the informatization construction of geological survey projects, a set of concise and practical informatization construction methods for geological survey projects are summarized by applying the latest digital mapping system platform. Firstly, the data sources that meet the requirements of geological survey accuracy are selected, and the 2000 national geodetic coordinate system is adopted. Then, the selected data source images are downloaded and registered by DGSGIS tools in the digital mapping technology system as the geographic base maps. Finally, the spatial database of geological survey projects is constructed by using the digital mapping system. This method is simple and practical, and has certain guiding significance for the informatization construction of geological survey projects.
Permian very low-grade metamorphism and its potential for hydrocarbon generation in the Linxi-Wulanhaote Area, Inner Mongolia, China
LI Changhai, LI Gang, WANG Shijie, SHAO Xuefeng, WANG Ying, WEN Kai, LIU Zhenghong
2020, 26(2): 271-284. doi: 10.12090/j.issn.1006-6616.2020.26.02.026
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The very low-grade metamorphism has been the focus of research in recent years and has great significance for the study of structural evolution of young orogenic belt and petroleum exploration. The recent studies revealed that the Carboniferous Permian strata in the northeastern part of China mainly underwent very low-grade metamorphism and gradually became a new petroleum exploration layer. This paper launched studies on the illite crystallinity, illite polytype and illite b0 dimension of the Permian System in the Linxi-Wulanhaote Area. The illite crystallinity ranges from 0.175 to 0.47, mainly clustering between 0.25 and 0.35 with an average of 0.30. Illite b0 ranges from 9.0155 to 9.0316 Å, with an average of 9.0249 Å. Illite polytype is predominantly 2M1. Based on the above data, the Permian System in the study area mainly experienced the prehnite-pumpellyite facies very low-grade metamorphism under medium-pressure with metamorphic temperature at 200~370℃, indicating its potential for hydrocarbon generation. Together with the hydrocarbon generation history of the Permian strata and the widespread Cretaceous granites in the study area, the very low-grade metamorphism might occurred during the early-Cretaceous, related to the increase of geothermal gradient caused by the intrusion of granite.