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Zhang J.,Wuhan University | He S.,Wuhan University | Yi J.,Sinopec | Zhang B.,Sinopec | And 4 more authors.
Shiyou Xuebao/Acta Petrolei Sinica

Shales of Lower Paleozoic marine strata in the western middle Yangtze area are considered to be of a high degree of thermal evolution. It is, however, very difficult to accurately determine their thermal maturities (vitrinite reflectance, Ro) due to the lack of vitrinite in organic macerals in marine shales of these Lower Paleozoic formations. The objective of the present study is to restore the maximum paleogeotemperature experienced by these shales and then to reconstruct their thermal evolutionary histories using the basin modeling technology with the data obtained from thermo-acoustic emission experiments and kerogen FTIR (Fourier transform infrared spectroscopy) analysis. The results of thermo-acoustic emission experiments illustrated that Lower Paleozoic marine shales have a good thermal Kaiser effect and the rock thermo-acoustic emission signal varies with geotemperatures remarkably. For instance, the maximum paleogeotemperature experienced by the Lower Cambrian Shuijingtuo Formation ranges from 293°C to 324°C, while the maximum paleogeotemperature of the Upper Ordovician Wufeng Formation and Lower Silurian Longmaxi Formation ranges from 210°C to 256°C. Furthermore, the sensitivity of the thermal Kaiser effect was tested by reheating experiments, which suggested that the thermo-acoustic emission could be applied to the measurement of maximum paleogeotemperatures experienced by marine shales. Considering the measured maximum paleotemperature as a constraint, in typical well simulation of the thermal maturity modeling of Lower Paleozoic marine shales, the calculation results of the thermal maturity modeling demonstrated that the simulated values of vitrinite reflectance (Ro) for the Lower Cambrian and Upper Ordovician-Lower Silurian marine shales range from 4.0% to 4.5% and 2.6% to 3.2%, respectively. Therefore, the organic matter maturities of marine shales in the Lower Cambrian Shuijingtuo Formation, Upper Ordovician Wufeng Formation and Lower Silurian Longmaxi Formation are all in a high-maturity to overmature stage of thermal evolution, which is consistent with the data obtained from the kerogen FTIR analysis of the Lower Paleozoic marine formations. Source

Shi W.,Chinese Academy of Geological Sciences | Shi W.,TU Bergakademie Freiberg | Dong S.-W.,Chinese Academy of Geological Sciences | Ratschbacher L.,TU Bergakademie Freiberg | And 5 more authors.
International Geology Review

Based on detailed structural data and available tectonic chronological data from the Dangyang Basin, the authors propose that the north-central Yangtze craton experienced three stages of tectonic evolution since Late Triassic time. In the Late Triassic to Early Jurassic (T3-J1), due to the Indosinian orogeny, nearly N-S compression and shortening occurred, which initiated the Dangyang Basin as a foreland basin of the Qinling-Dabie orogen. During the Late Jurassic-Early Cretaceous (J3-K1) period, the Yanshanian intracontinental orogeny caused contemporaneous NE-SW and NW-SE shortening, which resulted in intense folding of the foreland basin; contraction formed a brush structure diverging in a SE direction and strongly converging in a NWdirection around the Huangling anticline. In the Late Cretaceous to Palaeogene, the Yuan'an and Hanshui grabens were separated from other parts of the Dangyang Basin due to post-orogenic ENE-WSW extension. Finally, at the end of the Palaeogene, ENE-WSW shortening led to inversion and deformation of the grabens. © 2013 Taylor & Francis. Source

Shi W.,Key Laboratory of Neotectonic Movement and Geohazard | Shi W.,Chinese Academy of Geological Sciences | Li J.,Chinese Academy of Geological Sciences | Tian M.,Chinese Academy of Geological Sciences | And 3 more authors.
Geoscience Frontiers

The Dabashan orocline is situated in the northwestern margin of the central Yangtze block, central China. Previous studies have defined the orthogonal superposed folds growing in its central-western segment thereby confirming its two-stage tectonic evolution history. Geological mapping has revealed that more types of superposed folds have developed in the eastern segment of the orocline, which probably provides more clues for probing the structure and tectonic history of the Dabashan orocline. In this paper, based on geological mapping, structural measurements and analyses of deformation, we have identified three groups of folds with different trends (e.g. NW-, NE- and nearly E-trending folds) and three types of structural patterns of superposed folds in the eastern Dabashan foreland (e.g. syn-axial, oblique, and conjunctional superposed folds). In combination with geochronological data, we propose that the syn-axial superposed folds are due to two stages of ∼N-S shortening in the west and north of the Shennongjia massif, and that oblique superposed folds have been resulted from the superposition of the NW- and NE-trending folds onto the early ∼E-W folds in the east of the Shennongjia massif in the late Jurassic to early Cretaceous. The conjunctional folds are composed of the NW- and NE-trending folds, corresponding to the regional-scale dual-orocline in the eastern Sichuan as a result of the southwestward expansion of the Dabashan foreland during late Jurassic to early Cretaceous, coeval with the northwestward propagation of the Xuefengshan foreland. Integration of the structure and geochronology of the belt shows that the Dabashan orocline is a combined deformation belt primarily experiencing a two-stage tectonic evolution history in Mesozoic, initiation of the Dabashan orocline as a foreland basin along the front of the Qinling orogen in late Triassic to early Jurassic due to collisional orogeny, and the final formation of the Dabashan orocline owing to the southwestward propagation of the Qinling orogen during late Jurassic to early Cretaceous intra-continental orogeny. Our studies provide some evidences for understanding the structure and deformation of the Dabashan orocline.© 2013, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. All rights reserved. Source

Yu W.-X.,Nanjing University | Yu W.-X.,Wuxi Research Institute of Petroleum Geology | Lu J.-L.,Wuxi Research Institute of Petroleum Geology | Zhang Q.-L.,Nanjing University | And 2 more authors.
Bulletin of Mineralogy Petrology and Geochemistry

Carbonate mineral is an important mineral component in the YingCheng formation volcanic reservoir of the Changling rift, and calcite is the main authigenic carbonate mineral. On the basis of isotopic analyses of C and O in the calcite, the genesis of authigenic carbonate mineral in this volcanic reservoir was studied. The results show that the δ 13C V-PDB values of calcite in samples collected from the volcanic reservoir of the Changling rift range from - 12.7‰ to 0.4‰; that these samples are characterized by high δ 18O values of from 3. 8‰ to 12‰; and that the calculated δ 13C values of CO 2 gas equilibrium with calcite range from -16.0‰ to 2.2‰. The large variation of carbon and oxygen isotope compositions indicates that mineral-forming material may derive from multiple sources. The δ 13C-δ 18O diagram of calcite suggests that the calcite-forming CO 2 gas originated from both inorganic and organic sources, mantle and magma are major sources and sedimentary organic matter is the secondary source. The inorganic and organic CO 2 gases and organic acids produced by the thermal evolution of organic matter dissolved in the fluid to form an acidic fluid. Finally, this fluid reacted with silicate mineral in the volcanic reservoir to form carbonate mineral. Source

Ma Z.,Sinopec | Ma Z.,Wuxi Research Institute of Petroleum Geology | Zheng L.,Sinopec | Zheng L.,Wuxi Research Institute of Petroleum Geology | And 4 more authors.
Xinan Shiyou Daxue Xuebao/Journal of Southwest Petroleum University

According to the presence of aalt lake sediments of the Tertiary in the east of China, we make use of hydrocarbon generation and expulsion of pore hot simulation instrument to carry out the simulation under the conditions of formation of salt and no salt argillaceous source rock hydrocarbon generation and expulsion simulation experiments, through the analysis of hydrocarbon products of the salts in hydrocarbon source rocks in the process of hydrocarbon generation and expulsion. The results have shown that:(1)the presence of salts accelerated the evolution of hydrocarbon generation, and promoted oil and gas generation.(2)the presence of salt reduces the adsorption capacity of organic matter, accelerated the process of transformation and dehydration of clay, and promoted the initial operation of oil and gas shift easy cleavage and other reasons, the source rocks in the development of micro-pores and apertures in source rocks.(3)Although there exist a large number of stranded oil resources, salt-free zones in shale source rocks has little value of commercial exploitation because of the difficulties in fracturing. But they may be favorable of shale rock gas exploitation when reaching maturing. Although it is easy to discharge oil and gas generated in the process of evolution of salt rocks, 20% of oil resources were still stuck, when Ro=1.28%a large number of salts rich in minerals and low brittleness with clay minerals, are conducive to creating cracks, and are easy for fracturing, which makes salt rock areas favorable shale zones for reservoir exploration. Source

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