| 四川盆地东北部三叠系飞仙关组硫酸盐还原作用对碳酸盐成岩作用的影响 |
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| 引用本文： | 黄思静,Hairuo QING,胡作维,邹明亮,冯文立,王春梅,郜晓勇,王庆东.四川盆地东北部三叠系飞仙关组硫酸盐还原作用对碳酸盐成岩作用的影响[J].沉积学报,2007,25(6):815-824. |
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| 作者姓名： | 黄思静 Hairuo QING 胡作维 邹明亮 冯文立 王春梅 郜晓勇 王庆东 |
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| 作者单位： | 成都理工大学;成都理工大学;成都理工大学;成都理工大学;成都理工大学;成都理工大学;成都理工大学 |
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| 基金项目： | 国家自然科学基金项目(批准号:4067207240472068)资助 |
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| 摘 要： | 四川盆地东北部三叠系飞仙关组存在广泛的硫酸盐还原作用，同时地层中也存在锶含量异常高的成岩流体。研究表明:热化学硫酸盐还原作用（TSR）和（或）细菌硫酸盐还原作用（BSR）造成的SO42-离子的消耗对成岩孔隙流体中SrSO4溶解度的改变是三叠系中高Sr成岩流体的形成机制之一，该机制使得孔隙流体从白云石化作用和碳酸盐矿物的新生变形作用中获得的Sr在流体中以高浓度的Sr2+形式存在，并使之在流体中极度富集，这也是四川盆地东北部三叠系中大型和超大型天青石矿床的形成机制之一。H2S和CO2是硫酸盐还原作用的重要产物，不同温度条件下溶于水中的H2S和CO2，与不溶于水的气体分子之间的平衡反应H2S（aq）H2S(g)和CO2(aq)CO2(g)的平衡常数和吉布斯自由能增量计算表明，当温度从25℃升高至220℃时，两个反应的平衡常数分别大致从10增至240和从20增至500，两个反应的平衡常数都始终大于1，说明H2S和CO2更趋向于以气体形式存在，同时温度越高，系统中以气体形式存在的H2S和CO2会越多，溶解于水中的H2S和CO2会越少，因而在深埋藏的高温条件下，H2S和CO2对碳酸盐矿物的溶解能力可能相对很小。相对低温的成岩环境、高温流体的向上和侧向运移、构造抬升、富氧流体与含有H2S流体的混合以及金属硫化物的沉淀是提高含H2S和（或）CO2流体对碳酸盐矿物溶解能力的五个途径。因此，与较早成岩阶段相对浅埋藏环境的碳酸盐溶解作用有关的H2S和CO2流体可能与细菌硫酸盐还原作用（BSR）关系更为密切；断层或其它流体运移通道是高温含有H2S和CO2流体向上运移的基础条件，具有原生孔隙度和渗透率的礁、滩相高能沉积物也是流体发生侧向运移的先决条件；大幅度的构造抬升造成的地层温度降低是提高含H2S和（或）CO2地层流体对碳酸盐矿物溶解能力的重要因素，地壳抬升至近地表造成的古喀斯特作用也可以为H2S的氧化提供良好的地质环境。在有关的勘探中应注意:在断层等流体运移通道造成高温含H2S和CO2流体向上运移的条件下，与之有关的构造低点应该是主要的勘探目标；在燕山运动导致的地层抬升并导致深部热流体降温的条件下，与之有关的构造高点应该是主要的勘探目标，应分别对待。
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| 关 键 词： | 四川盆地东北部 三叠系飞仙关组 富锶成岩流体 TSR与BSR H2S与CO2 |
| 文章编号： | 1000-0550（2007）06-0815-10 |
| 收稿时间： | 2007-02-16 |
| 修稿时间： | 2007-03-26 |
Influence of Sulfate Reduction on Diagenesis of Feixianguan Carbonate in Triassic, NE Sichuan Basin of China |
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| HUANG Si-jing,Hairuo QING,HU Zuo-wei,ZOU Ming-liang,FENG Wen-li,WANG Chun-mei,GAO Xiao-yong,WANG Qing-dong.Influence of Sulfate Reduction on Diagenesis of Feixianguan Carbonate in Triassic, NE Sichuan Basin of China[J].Acta Sedimentologica Sinica,2007,25(6):815-824. |
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| Authors: | HUANG Si-jing Hairuo QING HU Zuo-wei ZOU Ming-liang FENG Wen-li WANG Chun-mei GAO Xiao-yong WANG Qing-dong |
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| Institution: | State Key Laboratory of Oil/Gas Reservoir Geology and Exploitation, Institute of Sedimentary Geology, Chengdu University of Technology, Chengdu 610059 |
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| Abstract: | Sulfate reduction has been recognized recently as a process of geologic significance, and is common and widespread in the Feixianguan of Triassic, NE Sichuan Basin of China. The widespread distribution of calcite cements with extremely high strontium concentrations (more than 3 000×10-6) indicate that the digenesis of Feixianguan carbonate have been strongly influenced by an unconventional strontium-rich pore fluids. The interstitial fluid with strontium concentration much higher than normally encountered is resulted by bacterial and (or) thermochemical sulfate reduction which removed the SO42- from the system and therefore, changed the solubility of celestite (SrSO4). The strontium in diagenetic pore fluids is original from the recrystallization of metastable aragonite and high Mg calcite to diagenetic low magnesium calcite and dolomite. This mechanism must be related to the large and super large scale celestite deposits of Triassic, NE Sichuan Basin of China. Both H2S and CO2 are the common products of bacterial and thermochemical sulfate reduction. The increment of Gibbs free energy (ΔG) and equilibrium constants (K) for the reactions of H2S(aq)H2S(g) and CO2(aq)CO2(g) were calculated here. The results indicate that, in the temperature interval of 25℃ to 220℃, the equilibrium constants (K) for the two reactions increase from about 10 to 240 and from about 20 to 500, respectively, and always more than 1. Both H2S and CO2 are more preferable to gas than aqueous solution, and the solubility of H2S and CO2 drop down with the increase of temperature, so the lower ability of dissolution for carbonate of H2S and CO2 in the deeper burial environment should be expected. The lower temperature diagenetic setting, hydrothermal migration upward, the mixing of oxygenated groundwater and aqueous solution of H2S to form sulfuric acid，and metal sulfide precipitation are the four ways to enhance the ability of dissolution of CO2 and (or) H2S for carbonate. The carbonate dissolution by H2S and CO2 during earlier diagenesis is closer relation to bacterial sulfate reduction rather than thermochemical sulfate reduction. The presence of faults is an important condition for the path of H2S and CO2 fluid flow upward. The facies such as bank margin lime grainstones or reef limestones with more primary porosity and permeability are the preferential sites for lateral fluid flow and carbonate leaching. The uplift of the crust and karstification can provide a geologic setting for the oxidation of H2S in order to enhance the leaching ability. We hope that the research conclusion here is helpful for the prediction of good quality reservoir in the Feixianguan carbonate of Triassic, NE Sichuan Basin of China. |
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| Keywords: | NE Sichuan basin Feixianguan Formation of Triassic strontium-rich diagenetic fluids TSR and BSR H2S and CO2 |
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