【作者】 陈玲；

【导师】 马昌前； 凌文黎；

【作者基本信息】 中国地质大学 ， 矿物学、岩石学、矿床学， 2010， 博士

【摘要】 在华南黔中—雪峰-江南隆起带北侧以及南盘江-十万大山地区分布着大量的古生界—中生界古油藏。古油藏的存在说明,在地质历史上这些地区曾存在大规模的油气运移及聚集,尽管这些油藏后来遭受了明显的破坏。位于贵州省东南的麻江古油藏是华南地区最大的海相古油藏之一,属构造圈闭—岩性遮挡复合型油藏,原始面积2450 km2,现残存800km2,估算的原始石油储量超过15亿吨,现残存的沥青约为3.5亿吨。该古油藏储层主要为下奥陶统红花园组白云岩和中下志留统翁项群砂岩、粉砂岩,沥青主要赋存于溶蚀孔、洞、层间裂缝以及粒问孔、缝中。显然,弄清这类古油藏的形成和演化历史对促进华南海相油气的勘探和认识华南陆块主要沉积盆地显生宙的构造演化性质具有重要的意义,但对这些古油藏的许多重要基础地质问题仍缺乏了解,如该古油藏聚集成藏和遭受破坏的时代等。妨碍对这些基础地质问题深入了解的重要原因之一是缺乏对有机物质进行同位素定年的有效方法。近年来,随着同位素分析样品制备技术水平和质谱测定精度的提高,以及对有机物质中Re-Os同位素体系属性认识的深入,在国外Re-Os同位素体系已被成功地运用于油气成藏年代学研究,并已取得了突出的成果,而在国内相关研究尚未见相关报道。主要是与油气成藏有关的有机质样品中,其Re、Os的含量极低(多数为分别为ng/g和Pg/g的数量级),限制了Re-Os同位素技术的应用和方法的推广。因此,建立和优化富有机质物质的Re-Os同位素分析测试技术,对油气藏成藏年代学的研究具有重要意义,也能更好地限定古油藏的破坏时代。本论文以贵州省东南地区麻江古油藏为主要研究对象,在系统的野外调查和样品采集的基础上,对古油藏中的沥青样品进行了Re-Os同位素分析,并对储层样品进行了流体包裹体测温、测盐分析,进而对油气藏成藏和破坏时代进行探讨。取得了如下进展和主要认识：(1)在国内首次建立了富有机质物质——沥青的Re-Os同位素分析测试方法在总结和吸收国内外多家实验室Re-Os同位素测试方法技术的基础上,结合本研究中样品的特殊性以及中国地质大学“地质过程与矿产资源”国家重点实验室(GPMR)所具备的实验条件,建立了富含有机质沥青样品的Re-Os同位素分析测试方法。分析测试方法主要包括以下重要步骤：样品的溶解、分离纯化Os、分离纯化Re、Re-Os同位素的质谱测定等。样品的溶解在实验中占有重要地位,本方法采用Carius管反王水法溶解样品,根据本研究中设计的Carius管的尺寸,称样量控制在200mmg以内(先加Os稀释剂),溶样温度控制在190℃左右(采用阶段升温,从室温升至80℃,稳定1h；再升温至120℃,再稳定1-2h；最后直接由120℃升至190℃左右,稳定24h)；溶解后样品呈淡红色,对大多数样品溶解后出现的针状物质,进行了物相研究；溶解后的样品采用CCl4萃取-HBr反萃取的方法分离Os,采用微蒸馏方法纯化Os,采用阴离子交换树脂法分离纯化Re。制备好的Os样品采用Pt带作为点样带引入离子源,在具备负离子电离状态下用热电离质谱仪Triton完成Os同位素比值分析；离子流信号的接收采用电子倍增器动态跳峰的方式；样品电离前采用真空还原技术对样品进行还原处理,以提高质谱测定精度,并对质谱测量过程中的最佳电离温度和最佳通氧量进行了优化。Re的同位素分析采用同位素稀释法进行样品制备,并用电感耦合等离子质谱仪(ICP-MS)进行比值测定,为校正ICP-MS测量过程中的质量分馏,在分析过程中采用了标样-样品-标样的“三明治”式测量方式；样品测量间隔采用5%HNO3和高纯水反复清洗进样管以防止样品间的交叉污染。质谱测量获得的Os同位素数据需采用专门编制的离线处理程序进行脱氧和质量分馏校正。Re同位素数据经过分馏校正后,结合同位素稀释公式,计算出样品的Re含量和同位素组成。数据的分析质量由已知样品和国际仪器标样控制,分析结果表明其与国际文献值或推荐值相符。(2)麻江古油藏沥青Re-Os同位素特征及其对古油藏形成和破坏时间的指示根据储层岩石、矿物的流体包裹体分析测试,结合麻江古油藏构造演化史以及储层埋藏史-温度史曲线,确定了麻江古油藏成藏时代主要为印支期。应用本研究建立的沥青Re-Os同位素分析测试方法,对麻江古油藏沥青的Re-Os同位素组成进行了分析,分析结果表明,层间裂缝中的沥青具有相对较高的Re含量(21.12-373.9 ng/g)和极低的Os含量(0.1086-0.9081 ng/g),187Re/188Os比值变化范围为777.0-3587,对应的187Os/188Os比值为1.313-4.913,显示出高放射成因Os同位素特征。据此特征,采用类似于高Re低Os硫化物矿物的计算方式,获得了古油藏沥青样品87.0±3.3 Ma的Re-Os等时线年龄。研究认为该年龄代表了沥青物质的形成时代,即古油藏被破坏的时间。所获得的破坏年龄同区内与麻江古油藏密切相关的丹寨汞金矿床的成矿时代(晚白垩世早期)相当,对应于沥青大量沉淀的时期,与区域流体活动事件相对应。通过应用本次研究所建立的沥青物质Re-Os同位素分析方法对麻江古油藏沥青样品进行测试的结果表明,该方法的应用有效,获得的年龄与区域构造以及流体活动事件相符合。本次研究的结果表明,麻江古油藏主要成藏期为印支期,而其发生破坏的时间为87Ma左右的燕山晚期。本次研究的成果还表明,Re-Os同位素方法在对油源单一、后期构造作用较弱、油气成藏充注期次明确的油藏的原油、油砂年代学研究中具有十分重要的应用潜力,并将会对油气勘探工作产生有意义的指导作用。本研究工作的特色和创新之处：(1)在国内首次报道了古油藏沥青物质的Re-Os同位素等时线年龄,为了解华南麻江古油藏发生破坏作用的时代提供了直接的年代学数据；(2)国内首次建立了富有机质物质——沥青的Re-Os同位素分析测试方法。更多还原

【Abstract】 There are a lot of Paleozoic-Mesozoic paleo-oil reservoirs which are mainly distributed at the northern margin of the central Guizhou-Xuefeng-Jiangnan uplift and the Nanpanjiang-Shiwandashan area in South China. The existence of these paleo-oil reservoirs demonstrate that there was large-scale oil-gas accumulation and migration in geological history, but later suffered destruction. Majiang Paleo-oil reservoir is one of the largest marine Paleo-oil fields, which is a structural traps-block complex lithology reservoir, and the original area was of 2450 km2, but the current area is only 800 km2. It has been estimated that the original oil reserves were more than 1.5 billion tons, but the remnants are only 350 million tons of bitumen. The main reservoir beds are the Lower Ordovician Honghuayuan formation and Middle-Lower Silurian Wengxiang group, and the bitumen mainly occurs in dissolved holes, holes, cracks, interlayer cracks and intergranular pores and crevices. Obviously, the understanding of the formation and evolution history for theses paleo-oil reservoirs has great importances not only for the marine oil and gas exploration, but also for the comprehension of tectonic evolution of sedimentary basins in South China. Nevertheless, there are still a lot of important basic geological issues need to be resolved, eg. the accumulation and destruction age of these paleo-oil reservoirs. The most important barrier is the lack of dating of organic substances that are related to paleo-oil reservoirs.Recently, with the development of analysis test and mass spectrum technology, and the understanding of pro-organic attribute for Re-Os isotope system, Re-Os isotope has been successfully applied in geochronology of hydrocarbon accumulation. However, because of the low concentrations of Re and Os (from ng/g to pg/g in the order of magnitude), analytical method of the pros and cons have important implications for the experiment results, which limit the development of this method. Therefore, the establishment and development of organic rich material Re-Os isotope analytical techniques is of great importance to the chronology of oil and gas reservoir, also this method can provide constraints on the destruction time of paleo-oil reservoir.Majiang paleo-oil reservoir was selected as the main study area, based on thorough field survey and related sample analyses, the time of hydrocarbon accumulation and destruction are discussed. New developments are achieved in the following two aspects:(1) A Re-Os isotope analytical method suitable for organic rich materials like bitumen is established for the first time in ChinaBased on a comparison and evaluation of the documented Re-Os isotope techniques, combined with the special nature of the bitumen samples and the facility available in the State Key laboratory of Geological Processes and Mineral Resources (GPMR), the Re-Os isotope analytical method suitable for organic rich materials like bitumen is established.This analytical method includes the following important steps:sample digestion, separation and purification of Os, separation and purification of Re, and Re-Os isotope measurement with mass spectrometry. The sample digestion plays an important role in the whole processes, employing the Carius tube method, no more than 200mg samples were dissolved and equilibrated with a known amount of185Re and 190Os spikes, in inverse aqua regia (2:1 14N HNO3 and 12 N HCl,9mL) for 24h at 190℃with the stage heating method; The dissolved samples are always presented in light red color with a large amount of needle like material, and the phase of this material has been studied. Osmium was separated using solvent extraction (CCl4 and HBr) and purified using micro-distillation method, Rhenium was separated and purified using anion chromatography techniques. The purified Os was loaded onto Pt filaments and measured using negative ion thermal ionization mass spectrometry (NTIMS) using an electron multiplier in peak-hopping mode, the reduction technique in vacuum condition is of great importance for improving the measuring accuracy. The purified Re was measured using inductively coupled plasma mass spectrometry (ICP-MS) method, in order to correct the mass fractionation during the analysis processes, the standard sample-sample-standard sample "sandwich-like" sequence was employed during the measurement; 5% HNO3 and purified water were employed to wash the pipe to avoid cross-contamination. The measured Osmium isotope data should be processed with mass fractionation correction and oxygen isotope interference correction. After the mass fractionation of the original Re isotope data, combined with the isotope dilution formula, the Re isotope data was obtained. The quality of the data was controlled by the known sample and international standard sample. Following the above method, the data show good consistence with the documented and recommended value.(2) The Re-Os isotope features of the bitumen from Majiang paleo-oil reservoir and its indication for the timing of hydrocarbon accumulation and destructionBased on the fluid inclusion analysis of reservoirs rocks, combined with the tectonic evolution of Majiang paleo-oil pool and the reservoir burial history-temperature history curve, the hydrocarbon accumulation time was limited at Indosinian period. Employing the bitumen Re-Os isotope analytical method which is established by this research, the bitumen in the interlayer was analyzed, and showed high concentration of Re (21.12-373.9 ng/g) and low concentration of Os (0.1086-0.9081 ng/g), the 187Re/188Os ratio ranges from 777.0 to 3587, 187Os/188Os ratio ranges from 1.313 to 4.913, exhibiting highly radiogenic Os isotopic signature. According to these features, the data processing method of the low level and highly radiogenic sulfide was employed, and a Re-Os isochron age of 87.0±3.3 Ma is obtained. This age is reckoned as the formation time of this bitumen, which is been reckoned as the destruction time of Majiang paleo-oil reservoir and the mineralization age of Danzhai mercury-golden deposit, which corresponding with the regional fluid flow events.Employing the bitumen Re-Os isotope analytical method which established by this study, we obtained meaningful data. The results showed that the hydrocarbon was accumulated at Indosinian period, and the reservoir was damaged at Late Yanshanian period ca.87 Ma. The research also showed that the Re-Os isotope method may have great importance in crude oil and oil sandstone with single sourced, weak tectonic movements influenced petroliferous basins.The features and innovations of this research:(1) the first report of Re-Os isotope isochron age for bitumen from paleo-oil reservoir, which provided the direct chronological information for the destruction of Majiang paleo-oil reservoir; (2) the Re-Os analysis method for organic rich material like bitumen was first established in China.更多还原