Theoretical study on the reactivity of sulfate species with hydrocarbons   总被引：2，自引：0，他引：2  

Qisheng Ma  Alon Amrani  Yongchun Tang 《Geochimica et cosmochimica acta》2008,72(18):4565-4576

The abiotic, thermochemically controlled reduction of sulfate to hydrogen sulfide coupled with the oxidation of hydrocarbons, is termed thermochemical sulfate reduction (TSR), and is an important alteration process that affects petroleum accumulations in nature. Although TSR is commonly observed in high-temperature carbonate reservoirs, it has proven difficult to simulate in the laboratory under conditions resembling nature. The present study was designed to evaluate the relative reactivities of various sulfate species in order to provide greater insight into the mechanism of TSR and potentially to fill the gap between laboratory experimental data and geological observations. Accordingly, quantum mechanics density functional theory (DFT) was used to determine the activation energy required to reach a potential transition state for various aqueous systems involving simple hydrocarbons and different sulfate species. The entire reaction process that results in the reduction of sulfate to sulfide is far too complex to be modeled entirely; therefore, we examined what is believed to be the rate limiting step, namely, the reduction of sulfate S(VI) to sulfite S(IV). The results of the study show that water-solvated sulfate anions are very stable due to their symmetrical molecular structure and spherical electronic distributions. Consequently, in the absence of catalysis, the reactivity of is expected to be extremely low. However, both the protonation of sulfate to form bisulfate anions () and the formation of metal-sulfate contact ion-pairs could effectively destabilize the sulfate molecular structure, thereby making it more reactive.Previous reports of experimental simulations of TSR generally have involved the use of acidic solutions that contain elevated concentrations of relative to . However, in formation waters typically encountered in petroleum reservoirs, the concentration of is likely to be significantly lower than the levels used in the laboratory, with most of the dissolved sulfate occurring as , aqueous calcium sulfate ([CaSO₄]_(aq)), and aqueous magnesium sulfate ([MgSO₄]_(aq)). Our calculations indicate that TSR reactions that occur in natural environments are most likely to involve bisulfate ions () and/or magnesium sulfate contact ion-pairs ([MgSO₄]_CIP) rather than ‘free’ sulfate ions () or solvated sulfate ion-pairs, and that water chemistry likely plays a significant role in controlling the rate of TSR.  相似文献   

Effect of indigenous bacteria on geochemical behavior of arsenic in aquifer sediments from the Hetao Basin, Inner Mongolia: Evidence from sediment incubations   总被引：5，自引：0，他引：5  

Huaming Guo  Xiaohui Tang  Suzhen Yang  Zhaoli Shen 《Applied Geochemistry》2008,23(12):3267-3277

Incubation studies were carried out using 5 freshly collected sediments from shallow aquifers of the Hetao Basin, Inner Mongolia. The aquifer sediments covering a range of redox conditions, as indicated by their deep grey to yellow color were mixed with degassed artificial As solution or degassed deionized water at a ratio of solid to water of about 1:10 (wt./wt.). Suspensions which were either amended with glucose or autoclaved, were incubated in parallel with unamended suspensions. Five microcosm cultures of unamended sediments gradually release the equivalent of 0.03–0.30 μg/g As to the dissolved phase. The addition of glucose as a potential electron donor results in a marked stimulation in the mobilization of As (0.71–3.81 μg/g) in the amended incubations for all sediments. The quantity of As released accounts for 60–70% of As bound to Fe/Mn oxides in the original sediments. The microbially mediated mobilization of As with the organic nutrient as an electron donor is strongly associated with the As bound to Fe/Mn oxides, as well as the exchangeable As. During the incubations amended with glucose, 2–4% of the sediment Fe is released. The results suggest that the introduction of labile dissolved organic C into the yellowish sediment aquifers with As-free groundwater would reduce a significant proportion of the Fe(III) oxyhydroxides mediated by anaerobic bacteria respiration and increase groundwater As concentrations.  相似文献   

Iodine in Chinese coals and its geochemistry during coalification     

Daishe Wu  Haiwen Deng  Baoshan Zheng  Wuyi Wang  Xiuyi Tang  Huayun Xiao 《Applied Geochemistry》2008,23(8):2082-2090

To determine the I distribution in Chinese coals, a nationwide survey was undertaken based on the distribution, periods of formation, rank and production yields of various coal deposits. A total of 305 coal samples were collected and their I contents were determined by catalytic spectrophotometry with pyrohydrolysis. The geochemistry of I during coalification (including both peat diagenesis and coal metamorphism) was assessed. It was found that the I contents of Chinese coals range from 0.04 mg kg^–1 to 39.5 mg kg^–1 and exhibit a lognormal distribution, with a geometric mean of 1.27 mg kg^–1. Statistical correlation analysis and the observation that I contents increase with coal rank indicate that coal I is chalcophile in nature, and not generally organically bound. When peat developed into lignite through diagenesis, 95–99.9% of the original I was lost. The composition and structure of clay minerals present in the coal were controlled by the original depositional environment. The higher the I content of coals, the more likely the original sediments were affected by a marine environment. Iodine contents increased from lignite through sub-bituminous and bituminous coals to anthracite. This indicates that coal absorbed excess I from hydrothermal fluids during metamorphism (including geothermal metamorphism and telemagmatic metamorphism). The telemagmatic metamorphism was caused by magmatic activities that depended on the specific geological structure of the region. In China, most high-rank coals were formed by telemagmatic metamorphism.  相似文献   

Extreme oxygen isotope signature of meteoric water in magmatic zircon from metagranite in the Sulu orogen, China: Implications for Neoproterozoic rift magmatism   总被引：4，自引：0，他引：4  

Jun Tang  Yong-Fei Zheng  Bing Gong  Tian-Shan Gao  Fu-Yuan Wu 《Geochimica et cosmochimica acta》2008,72(13):3139-3169

Unusual ¹⁸O depletion, with δ¹⁸O values as negative as −10‰ to −4‰ relative to VSMOW, was reported in zircons from ultrahigh-pressure eclogite-facies metamorphic rocks in the Dabie-Sulu orogenic belt, China. But it is critical for the negative δ¹⁸O zircons to be distinguished between magmatic and metamorphic origins, because the ¹⁸O depletion can be acquired by high-T eclogite-facies metamorphism of meteoric-hydrothermally altered low δ¹⁸O rocks. While zircon O diffusion kinetics has placed a reasonable constraint on this, zircon trace element compositions can provide a straightforward distinction between the magmatic and metamorphic origins. This paper reports our finding of unusual ¹⁸O depletion in zircon from granitic gneiss in the northeastern end of the Sulu orogen. Zircon δ¹⁸O values vary from −7.8‰ to −3.1‰ along a profile of 50 m length at Zaobuzhen. They are close to extremely low δ¹⁸O values of −9.0‰ to −5.9‰ for metagranite at Qinglongshan and adjacent areas in the southwestern end of the Sulu orogen. CL imaging suggests that the low δ¹⁸O zircons at Zaobuzhen are primarily of magmatic origin, but underwent different degrees of metamorphic modification. Zircon U-Pb dating yields middle Neoproterozoic ages of 751 ± 27 to 779 ± 25 Ma for protolith crystallization and Triassic ages of 214 ± 10 to 241 ± 33 Ma for metamorphic resetting. However, no metamorphic modification occurs in zircon REE patterns that only indicate magmatic recrystallization and hydrothermal alteration, respectively. Thus, the negative δ¹⁸O zircons are interpreted as crystallizing from negative δ¹⁸O magmas due to melting of meteoric-hydrothermally altered negative δ¹⁸O rocks in an active rift setting at about 780 Ma. The variation in zircon δ¹⁸O values indicates considerable O isotope heterogeneity in its granitic protolith. Zircon Lu-Hf isotope analyses give positive ε_Hf(t) values of 1.6-4.1 and Hf model ages of 1.18-1.30 Ga. This suggests that the granitic protolith was derived from the mid-Neoproterozoic reworking of late Mesoproterozoic juvenile crust. The metagranites at Zaobuzhen and Qinglongshan, about 450 km apart, are two known occurrences of the unusually low δ¹⁸O zircons below −6‰ so far reported in the Sulu orogen. They are similar to each other in both protolith and metamorphic ages, so that they share the same nature of both Neoproterozoic protolith and Triassic metamorphism. Therefore, the locally negative δ¹⁸O zircons may register centers of low δ¹⁸O magmatism during the supercontinental rifting.  相似文献   

Refertilization of ancient lithospheric mantle beneath the central North China Craton: Evidence from petrology and geochemistry of peridotite xenoliths     

Yan-Jie Tang  Hong-Fu Zhang  Ji-Feng Ying  Jin Zhang  Xiao-Ming Liu 《Lithos》2008,101(3-4):435-452

The petrology and geochemistry of peridotite xenoliths in the Cenozoic basalts from Fanshi, the central North China Craton (NCC), provide constraints on the evolution of sub-continental lithospheric mantle. These peridotite xenoliths are mainly spinel-facies lherzolites with minor harzburgites. The lherzolites are characterized by low forsterite contents in olivines (Fo < 91) and light rare earth element (LREE) enrichments in clinopyroxenes. In contrast, the harzburgites are typified by high-Fo olivines (> 91), high-Cr# spinels and clinopyroxenes with low abundances of heavy REE (HREE). These features are similar to those from old refractory lithospheric mantle around the world, and thus interpreted to be relics of old lithospheric mantle. The old lithospheric mantle has been chemically modified by the influx of melts, as evidenced by the Sr–Nd isotopic compositions of clinopyroxenes and relatively lower Fo contents than typical Archean lithospheric mantle (Fo > 92.5). The Sr–Nd isotopic compositions of harzburgites are close to EM1-type mantle, and of the lherzolites are similar to bulk silicate earth. The latter could be the result of recent modification of old harzburgites by asthenospheric melt, which is strengthened by fertile compositions of minerals in the lherzolites. Therefore, the isotopic and chemical heterogeneities of the Fanshi peridotite xenoliths reflect the refertilization of ancient refractory lithospheric mantle by massive addition of asthenospheric melts. This may be an important mechanism for the lithospheric evolution beneath the Central NCC.  相似文献   

The geochemical characteristics and origin of crude oils in the Kekeya Oilfield,Xinjiang, China   总被引：2，自引：2，他引：0  

Youjun Tang  Ling Zan  Dujie Hou  Zhongyao Xiao 《中国地球化学学报》2008,27(4):420-423

GC/MS and GC/MS/MS techniques were employed to describe the characteristics of biomarker assemblages in two sets of hydrocarbon source rocks, Jurassic and Permian, in southwestern Tarim, and the parameters for the classification of the two sets of hydrocarbon source rocks have been established. It is found that diahopane and C30-unknown terpane are abundant in Permian samples, the contents of diahopane in Jurassic samples are relatively low, and terpenoids have been detected in Jurassic samples but not in Permian source rock samples. Kekeya crude oils are abundant in diahopane and C30-unknown terpane. The results of fine oil-rock correlation indicated that Kekeya crude oils were derived mainly from the Permian hydrocarbon source rocks. However, a small amount of diterpenoid was detected in the crude oils, indicating that the Jurassic hydrocarbon source rocks also made a certain contribution to Kekeya crude oils.  相似文献   

Dynamical downscaling of regional climate over eastern China using RSM with multiple physics scheme ensembles     

Peishu  Zong  Jianping  Tang  Shuyu  Wang  Lingyun  Xie  Jianwei  Yu  Yunqian  Zhu  Xiaorui  Niu  Chao  Li 《Theoretical and Applied Climatology》2017,129(3-4):1263-1277

Theoretical and Applied Climatology - The parameterization of physical processes is one of the critical elements to properly simulate the regional climate over eastern China. It is essential to...  相似文献   

中印城镇化区域差异及城镇体系空间演化比较   总被引：3，自引：1，他引：2  

李佳洺  杨宇  樊杰  金凤君  张文忠  刘盛和  傅伯杰 《地理学报》2017,72(6):986-1000

中国和印度作为两个正在崛起的大国,发展历程较为相似,但发展路径和模式差异较大。两个国家政治制度、经济体系、发展环境等的显著差异已经吸引了学者的广泛关注,本文将从地理学视角出发,重点关注两国城镇化及城镇体系的区域差异和空间演化过程。以人口普查和联合国城市人口数据为基础,采用空间分析、参数估计、非参数估计等多种方法,对中印两国城镇化和城镇体系的空间特征进行系统的比较分析,结果表明：① 20世纪90年代以来,中国城镇化的区域差异由南北差异转变为沿海—内部差异,而印度南北差异的格局则基本稳定;② 从省（邦）级空间尺度来看,中国和印度的人口密度和城镇化率都呈现正相关关系,当城镇化率超过50%后,两者的相关性更为显著,但是近年来中国人口密度与城镇化率的相关性不断增强,而印度则呈现降低的趋势;③ 现阶段中印两国以大中城市为主的城镇体系符合位序—规模分布的特征,但是经济改革对于两个国家城镇体系空间演化的影响差异明显,改革使得中国城镇发展的主要驱动力由地理历史因素向经济系统空间结构转变,而印度城镇发展的驱动力始终是地理历史因素,经济改革甚至降低了经济系统空间结构对城镇发展的影响。  相似文献   

A peak-cluster assessment method for the identification of upland planation surfaces     

Li-Yang Xiong  Guo-An Tang  Ye-Qing Qian 《International journal of geographical information science》2017,31(2):387-404

Residual upland planation surfaces serve as strong evidence of peneplains during long intervals of base-level stability in the peneplanation process. Multi-stage planation surfaces could aid the calculation of uplift rates and the reconstruction of upland plateau evolution. However, most planation surfaces have been damaged by crustal uplift, tectonic deformation, and surface erosion, thus increasing the difficulty in automatically identifying residual planation surfaces. This study proposes a peak-cluster assessment method for the automatic identification of potential upland planation surfaces. It consists of two steps: peak extraction and peak-cluster characterization. Three critical parameters, namely, landform planation index (LPI), peak elevation standard deviation, and peak density, are employed to assess peak clusters. The proposed method is applied and validated in five case areas in the Tibetan Plateau using a Shuttle Radar Topography Mission digital elevation model (SRTM DEM) with 3 arc-second resolution. Results show that the proposed method can effectively extract potential planation surfaces, which are found to be stable with different resolutions of DEM data. A significant planation characteristic can be obtained in the relatively flat areas of the Gangdise–Nyainqentanglha Mountains and Qaidam Basin. Several vestiges of potential former planation areas are also extracted in the hilly-gully areas of the western part of the Himalaya Mountains, the northern part of the Tangula–Hengduan Mountains, and the northeastern part of the Kunlun–Qinling Mountains despite the absence of significant topographical features characterized by low slope angles or low terrain reliefs. Vestiges of planation surfaces are also identified in these hilly-gully upland areas. Hence, the proposed method can be effectively used to extract potential upland planation surfaces not only in flat areas but also in hilly-gully areas.  相似文献   

HBV相关肝病患者外周血NK细胞PD-1、Tim-3表达及意义     

赵小瑜  周妮  汤永志  林希  陈华忠  朱坚胜 《寒旱区科学》2017,9(5):51-54,59

目的 了解HBV相关肝病患者外周血NK细胞表面PD-1、Tim-3的表达情况,探讨PD-1和Tim-3的表达与血清HBV-DNA载量的相关情况。方法 选择HBV感染相关肝病患者74例,其中CHB患者30例,LC患者24例,HCC患者20例,健康对照18例。应用流式细胞术检测NK细胞表面PD-1、Tim-3表达,荧光定量PCR检测HBV-DNA量,ELISA法检测细胞因子分泌水平。统计各组患者PD-1和Tim-3的表达率,比较各组差异,分析其与病情的相关性。结果 CHB、LC、HCC组外周血NK细胞表面PD-1和Tim-3的表达率分别为34.46%±7.31%、59.09%±12.35%、61.49%±15.26%和19.18%±6.05%、28.64%±11.20%、31.24%±11.85%,均高于对照组（P<0.01）,LC组和HCC组明显高于CHB组（P<0.01）,LC组和HCC组比较无统计学差异。在CHB组,PD-1的表达率与HBV-DNA呈负相关关系（R=-0.437,P=0.033）。CHB、LC、HCC各组血清中细胞因子TNF-α和IFN-γ水平分别为0.66±0.63、0.75±0.66、0.85±0.71和1.76±0.88、1.83±1.23、1.60±0.53,均低于健康对照组（P<0.01）。结论 HBV相关肝病患者NK细胞表面PD-1、Tim-3表达均增加,且与病情严重程度有关,增加表达的PD-1与血清HBV-DNA载量存在负相关性,HBV肝病各组血清TNF-α、IFN-γ分泌减少。  相似文献