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Luo S.,Wuhan Center | He S.,Wuhan University | Jin Q.,China National Offshore Oil Corporation | Yang R.,Wuhan University | Zhang J.,Wuhan University
Jilin Daxue Xuebao (Diqiu Kexue Ban)/Journal of Jilin University (Earth Science Edition) | Year: 2015

Bonan sag is a typical overpressured sag with abundant hydrocarbon resources, and present-day overpressures commonly occur in the Eocene third and fourth members of Shahejie Formation (Es3 and Es4) at depths between 2 300 m and 4 200 m. By assessing present-day pressure distribution and response from drilling stem test (DST), wire logging and geological date, the characteristics of overpressure and geological factors affecting abnormal pressure are discussed in detail. Sonic transit times of mudstones deviate from the normal compaction trend line to the overpressured area revealed by drilling, but density has no obvious response. On the whole, three overpressure systems have been identified, including an upper system distribution in Es1, a middle reservoir overpressure with main part in lower Es3, and a lower reservoir overpressure in the upper part of Es4. The second member in which sand contents are more than 20% generally shows normal pressure. This study indicates that sourced rocks, low permeability sealing rocks, and fault structure are the three major factors controlled the range of overpressure and its structure. Multiphase fluid from mud-rich sources rock composes material basis of an overpressured system. Compacted mudstone within Es1, and cemented sandstone interbeded with mudstone in Es3, as well as mudstone and gypsum beds distribution in the upper part of Es4, formed respectively barrier of each system, can also control the distribution and construction change of overpressures system. Fault structures, which has great influence on formation pressure and distribution of oil, show a complex and duality fault-fluid flow behavior. The optimized and calibrated seismic intervai-velocity data, in conjunction with measured pressure, have been used with considerable success in overall recognition of large-scale overpressured system in Bonan sag. ©, 2015, Jilin University Press. All right reserved. Source


Yang P.,Chengdu Center | Xie Y.,Chengdu Center | Li X.-B.,Wuhan Center | Bai D.-Y.,Geological Survey of Hunan Province | And 2 more authors.
Geology in China | Year: 2012

Based on systematic observation, sampling and organic geochemical studies of Sinian Doushantuo Formation source rocks on the western side of the Xuefeng Mountain, this paper summarizes source rocks distribution, organic matter types, formation of source rocks and sedimentary environment, maturity of organic matter and hydrocarbon-generation history. The platform-basin deposition model of Sinian Doushantuo Formation has a close relationship with black shale distribution and organic carbon content. The source rocks are mainly distributed in northern Guizhou, eastern Guizhou, and southeastern Upper Yangtze plate. Black shale in northern Guizhou and eastern Guizhou is from 20m to 70 m in thickness, and high-value areas of organic carbon (2.0%) are mainly distributed in northern Guizhou, eastern Guizhou, and southeastern Upper Yangtze plate such as Shimen - Taoyuan - Annua area. Organic macerals suggest that organic matters of the black shale are of Type I. The mass fraction of group elements is characterized by saturated hydrocarbon> non-hydrocarbon > aromatic hydrocarbon. The ratio of saturated hydrocarbon and aromatic hydrocarbon in basins and slopes is generally higher than that in the restricted platform, which suggests that the black shale series of Doushantuo Formation is sapropelitic source rock and that the deposition of parent materials was somewhat related to the depositional environment throughout the depositional period. Kerogen δ 13Corg values in different depositional environments of Doushantuo Formation imply that there existed remarkable differences in the abundances of organic matters and sources of marine plankton, maritime bacteria and marine algae. For the specific sedimentary organic matter (marine plankton, maritime bacteria and marine algae), the deeper the water, the lower the kerogen δ 13Corg value, and the higher the organic matter content, indicating that the organic carbon content of source rocks was decided by the organic matter productivity, the formation of source rocks and the sedimentary environment. The reflectance of equivalent vitrinite (Rc) varies from 1.78% to 3.05% in the study area, and the Rc of Doushantuo Formation can be calculated by methylphenanthrene index. The Rc is 1.96% in Songlin, and from 2.06% to 2.10% in Meiziwan of Meitan, suggesting that most of the samples have reached the overmature stage, and a minor part of samples have reached the higher mature wet gas stage. The modeling results of hydrocarbon - generating history show that the source rocks of Doushantuo Formation at Zhangjiajie entered into the oil - generation stage in late early Silurian period (434 Ma), entered into the oil-generation peak stage in early Middle Triassic period (244 Ma), and entered into the condensed oil and wet oil stage in late Middle Triassic, when the Ro (%) reached 1.3. The results show that the source rocks of Doushantuo Formation were deposited in the late rift basins characterized by higher paleogeothermal gradient, lower threshold depth of oil generation and earlier oil generation, which was in favor of the accumulation of Sinian Dengying Formation oil and gas in the early time. Source


Xu Z.,China University of Geosciences | Zhang J.,Wuhan Center | Junliang J.,China University of Geosciences | Kexin Z.,China University of Geosciences
Acta Geologica Sinica | Year: 2015

The northeastern Tibetan Plateau is located at the convergence of the Asian winter and summer monsoons and westerlies; thus, this area has witnessed historic climate changes. The Xunhua basin is an intermontane basin on the northeastern margin of the Tibetan Plateau. The basin contains more than 2000 m of Cenozoic fluvial-lacustrine sediments, recording a long history of climate and environmental changes. We collected the mid-Miocene sediments from the Xunhua basin and used palynological methods to discuss the relationship between aridification in the interior of Asia, global cooling, and uplift of the Tibetan Plateau. Based on the palynological analysis of the Xigou section, Xunhua basin, the palynological diagram is subdivided into three pollen zones and past vegetation and climate are reconstructed. Zone I, Ephedripites-Nitraridites-Chenopodipollis-Quercoidites (14.0-12.5 Ma), represents mixed shrub-steppe vegetation with a dry and cold climate. In zone II, Pinaceae-Betulaepollenites-Ephedripites-Chenopodipollis-Graminidites (12.5-8.0 Ma), the vegetation and climate conditions improved, even though the vegetation was still dominated by shrub-steppe taxa. Zone III, Ephedripites-Nitrariadites-Chenopodipollis (8.0-5.0 Ma), represents desert steppe vegetation with drier and colder climate. The palynological records suggest that shrub-steppe dominated the whole Xigou section and the content gradually increased, implying a protracted aridification process, although there was an obvious climate improvement during 12.5-8.0 Ma. The aridification in the Xunhua basin and surrounding mountains during 14.0-12.5 Ma was probably related to global cooling induced by the rapid expansion of the East Antarctic ice-sheets and the relatively higher evaporation rate. During the 12.5-8.0 Ma period, although topographic changes (uplift of Jishi Shan) decreased precipitation and strengthened aridification in the Xunhua basin on leeward slopes, the improved vegetation and climate conditions were probably controlled by the decrease in evaporation rates as a result of continuous cooling. From 8.0 to 5.0 Ma, the rapid development of the desert steppe can be attributed to global cooling and uplift of the Tibetan Plateau. © 2015 Geological Society of China. Source


Xiong S.,Wuhan University | Yao S.,Wuhan University | Gong Y.,Wuhan University | Tan M.,Wuhan Center | And 2 more authors.
Diqiu Kexue - Zhongguo Dizhi Daxue Xuebao/Earth Science - Journal of China University of Geosciences | Year: 2016

The Wusihe lead-zinc deposit, hosted in the Dengying Formation, is a large lead-zinc deposit in the Sichuan Province, China. The previous research noted the Wusihe deposit was classified as a sediment-hosted stratiform lead-zinc deposit. However, our field survey result suggests that hydrothermal ore-forming processes are crucial to lead-zinc mineralization. In this paper, we present a detailed petrographic, microthermometric and laser Raman spectroscopy study of fluid inclusions from the Wusihe deposit reveals the characteristics of ore-forming fluids and mineralization mechanism. Primary fluid inclusions (FIs) in dolomite, quartz, calcite, fluorite and sphalerite are mainly two phases (L+V type). Microthermometric data show the homogenization temperatures range from 120℃ to 260℃, and the average of salinity is 10.0% NaCl eqv. The estimated trapping pressures are 32 MPa to 68 MPa. The laser Raman spectroscopy shows that the gas components have a certain amount of CH4, H2S, C2H6, C2H2, N2 and NH3. The mixed ore-forming fluids offer heat, SO4 2-, and Mg2+ to provoke the thermochemical sulfate reduction (TSR). The TSR could be a key factor for sulfur source and H+. The change of pH value leads to the precipitation of metallogenic elements. © 2016, Editorial Department of Earth Science. All right reserved. Source


Wang N.,Wuhan Center | Shi T.,China Three Gorges University | Li Y.,Wuhan Center | Lian Z.,Wuhan Center | Ke P.,Wuhan Center
Environmental Earth Sciences | Year: 2016

Rainfall is one of the main inducing factors of landslide disaster. Based on many years of landslide monitoring data and rainfall data of Jianshi County, 66 landslides occurred from 2002 to 2008 were chosen, which is about 52.38 % of the total 126 landslides in the whole area. There are 13 landslides with deformation or displacement over twice, this is about 19.70 % of 66 landslides chosen. According to analysis the correlation between rainfall and landslides with the geostatistics method, the critical rainfall and effective rainfall are determined. Using the Bayes statistical inference model to improve the probability model, the probabilities of landslide early warning system zones are determined. The landslide early warning model is established on basis of the result of landslide susceptibility, rainfall model and probabilistic model with ArcGIS software. The probability value (T) is from 0.002168 to 0.909062. The whole county is divided into four grades of landslide early warning system. The data of second deformation or displacement of 13 landslides induced by the rainfall are used to validate the model. Totally, the result of landslide early warning model is scientific and reliable. The rainfall data of eight landslides are in line with the model and in the range of level IV/V. The accuracy is about 61.54 % according to the relationship between landslide and rainfall. The distributions of 11 landslides are located in the level V zone and the accuracy is 84.62 % according to the relationship between landslide early warning result. © 2015, Springer-Verlag Berlin Heidelberg. Source

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