【作者】 腾格尔；

【导师】 刘文汇；

【作者基本信息】 中国科学院研究生院（兰州地质研究所） ， 地球化学， 2004， 博士

【摘要】 我国海相地层分布广，多具高演化、低有机质丰度的特点，尤其下古生界经历了漫长的热演化史，致使有机质丰度、质量等都产生了很大变化，给烃源岩评价造成了极大困难。因此，探索高演化海相有效烃源岩的判识仍是当前我国油气领域重要研究任务之一。不少学者试图通过降低有机碳下限值、对原始有机质丰度和质量的恢复等方法解决存在问题，但困难不少，分歧较大。本论文以“环境控源”为切入点，以鄂尔多斯下古生界典型剖面为解剖对象，综合研究受热演化影响小、具继承性、能表征有效烃源岩形成古环境的无机地球化学参数体系，结合必要的有机地球化学研究，系统探讨了海相沉积环境与有效烃源岩发育的关系，进而判识研究区奥陶系潜在有效烃源岩及其分布规律。主要成果和认识： 1．聚类、对应分析结果表明，以CaO、MgO、Zn、Zr、Ni、Al₂O₃、Rb、V、P和Ba等变量组合为特征的前四个因子（f₁～f₄）是研究区主控因素，反映不同沉积条件下元素丰度及其组合特征，可以反演高演化海相烃源岩发育环境。 2．研究区无机参数分布总体呈两种形式，①TOC≥0.2％的层段（西缘克里摩里组和乌拉力克组、旬邑地区马六段），其Zr／Rb＜1，Rb／K值高，Rb／K与δ¹⁸O呈同步变化趋势，指示水动力弱、盐度高；亲铁、亲硫元素和U含量相对于沉积岩平均值高，V／（V+Ni）＞0.50，表明当时水—沉积界面处于缺氧状态；通过稀土元素的分布模式推断出沉降速率的变化，富有机质层段的沉降速率倾向于缓慢，但在快速低密度浊流沉积下亦可富集有机质和发育烃源岩；P、Ba含量高，碳酸盐δ¹³C值正向偏移等暗示有机质埋藏量和保存率高，且δ¹³C_org＜-28‰，指示为Ⅰ—Ⅱ型母质，生烃潜力较高；②TOC＜0.2％的层段（西缘桌子山组和三道沟组、岐山地区马家沟组），其亲铁、亲硫和亲生物元素缺乏富集是底部水体不缺氧、有机质难以保存的强有力证据，Zr／Rb＞1，加之稀土元素特征均反映出快速沉积的高能环境，且δ¹³C_org值介于-24‰～-28‰，属Ⅱ—Ⅲ型，生烃潜力较差。 运用稀土元素分异程度及Zr／Rb、Ti／Al等元素比值可以有效恢复古沉降速率和水动力条件，对微量元素示踪及古环境研究具有重要的理论与应用价值。 上述无机参数在海相碳酸盐岩中，即使其有机质热演化程度已达高—过成熟阶段，仍可提供重要的碳酸盐岩沉积—早期成岩作用的信息，尤其它们作为控制碳酸盐岩中有机质聚集和保存过程的主因子的特征变量组合，可反映出原始沉积环境性质及其演化的主要特征。利用其组合，结合必要的有机参数，重塑烃源岩发育环境，进而判识海相有效烃源岩及其分布规律是可行、有效的，为高演化海相碳酸盐岩有效烃源岩的评价提供了新途径，对油气勘探开发有着特殊的意义。 3．沉积有机质的质量转化受控于生态及沉积环境。缺氧条件下，沉积有机质经历强烈微生物改造，不稳定部分被优先降解，使有机质向富氢、富脂质转化，形成类型好，生烃潜力高的油气母质，其碳同位素组成显示为富集’℃的趋势。 氧化环境中，有机质不易保存，即使有少量的有机质保存下来，因不存在“优先降解”过程，其质量不仅受控于腐殖化作用，还受原始富氢生源（贫’3C）与贫氢生源（富’3C）间竞争的影响，当有机质，，二/(有机质.:3c+有机质;:矽值增加时，有机质倾向于腐殖型、富集重同位素组成，反之亦然。 研究区占’3Cor，的纵横向分布特征不仅蕴涵着有机质类型的信息，还可结合其它指标追踪古环境，为研究海相烃源岩，尤其判识高过成熟海相有效烃源岩及其展布规律提供重要依据。 4.生物繁盛、适宜的沉积速率及底层水为缺氧、滞静、低能等无疑是海相有效烃源岩发育的关键性控制因子，可用微量元素和碳氧同位素等无机参数对其进行表征。本文建立了判识海相有效烃源岩及其分布规律的环境分析基本模式。 鄂尔多斯盆地存在三种利于烃源岩发育的环境:①大陆边缘滞流、低能、缺氧的半封闭性环境，泥质含量对有机质有显著影响，如西缘克里摩里组;②盆地内部蒸发、泻湖、局限环境，盐度可能起着关键性的作用，如旬邑地区马六段;③斜坡带低密度浊流沉积，与沉积速率密切相关，如西缘乌拉力克组。前两种属 “保存模式”;③第三种为“生产力模式”。 5.鄂尔多斯盆地奥陶系烃源岩发育不均匀。克里摩里组与乌拉力克组在桌子山地区连续沉积，具良好的有机质富集条件，有机碳含量较高，为腐泥型，生烃潜力高，可视为潜在有效烃源岩，结合其上、下层位的粗粒岩层和顶部溶蚀面考虑，是极具勘探潜力的生储盖组合。平凉地区乌拉力克组和旬邑地区马六段亦有较高的生烃潜力。西缘桌子山组和三道沟组、岐山地区马家沟组属非有效烃源岩。 6.碳酸盐岩碳、氧同位素组成忠实记录了研究区相对海平面的波动，二者具相似的变化趋势，其地层曲线可代表相对海平面变化曲线。克里摩里期，桌子山地区受贺兰裂谷强烈沉降，相对海平面上升幅度较大，导致浮游生物繁盛，底栖生物缺乏，盐跃层、低能、缺氧条件等形成，接受了有机碳含量较高、有机质类型又好的细粒碳酸盐岩及笔石相。在岐山地区，马家沟期相对海?更多还原

【Abstract】 Lower Paleozoic marine deposits that commonly displays high-over maturity （Ro ranging 1.3 %⁴.5%） and lower total organic carbon contents (TOC were widespread in China, where were further complicated to distinguish the efficient hydrocarbon source rocks because of TOC , H/C, etc. have been changed by a long thermal evolution. Currently, the accurate evaluation of validity for marine hydrocarbon source rocks is one of the pending important problem in oil and gas exploration and developments. Some scholars had discussed different restoring methods for hydrocarbon generation potential of high-over mature potential source rock by many methods of geochemistry, but those have some difficulties and differences.The developments of hydrocarbon source rocks are primarily controlled by sedimentary environment that including （ i） productivity in the surface waters, （ii） sediment accumulation rate, （iii） bottom-water oxicity, and （iv） organic-matter source, these can be accepted as key variables. The chemic stability of trace elements and carbon isotope composition are stronger than organic matters even in high-over mature stage. Therefore, the inorganic parameters can show original sedimentary environment reliably, and have more predominance to further differentiate efficient hydorocarbon source rock in high-over mature stage. The Ordovician strata distribute widely in the West-South area, Ordos Basin. The Majiagou Formation （O₁m） in this area is made up of a suite of platform carbonate sediments, whereas the Wulalike Formation （O₂w） consists of a suite of foreslope gravity-flow sediments including clastic rocks intercalated with mudstone and carbonate rocks. In this paper, the paleoenvironments of potential hydrocarbon source rock of these Formations is discussed using inorganic parameters. The aim of this study was to grope for new approach for distinguishing the efficient hydrocarbon source rocks in high-overmature marine deposits.1. The main oxides, trace elements, rare earth elements and carbon,oxygen isotope compositions display a regular temporal and spatial evolution. The cluster and correspondence analytical results show that geochemically the different formations in the researchful area are not only independent but also correlated. Vertically, the geochemical signatures of these strata also exhibit an episodic and cyclic pattern of evolution, i.e. the simultaneous increase or decrease in most of the elements and parameters. In this respect, the evidences in favour of the above-mentioned regular evolution in time and space are strongly supported by the macroscopic features and depositional environments of these strata.2. High contents of Barium, Positive 513Ccarb excursions have reflected a high paleo-productivity and burial amounts of organic matter in Oik, Oaw in West and Oim6 Formation of Well XT1 that contain 0.2% total organic carbon, and have a good type of organic matters, high hydrocarbon potential. So these Formations can be regarded as efficient hydrocarbon source rocks. However, in O\z, O\s in West and Dim4"6Formations of Qishan section, TOC<0.2%, Ba<25 （xlO’6） , 613Ccarbmost have negative values, which indicate a low burial quantity, unfavorable preserved conditions, and low-quality of organic matters. These suggest that carbonate rocks in such environments are poor hydrocarbon source rocks. Rare-earth elements and oganic matter, both have osculatory correlation, REE fractionating degree can reflect sedimentation rate. Poor source rocks are rapidly deposited in shallow water, but efficient hydrocarbon source rocks are slowly deposited in bottom-water anoxicity, stagnated, bathyal environment mainly, black shales also can develop the efficient hydrocarbon source rocks, which sedimentation rate is high part. Therefore, paleo-productivity, burial amounts of organic matter, and sedimentation rate can be rebuilded effectively using inorganic parameters ?Ba, stable carbon isotopic composition and rare-earth elements, etc, and can be applied in further estimate studies for the validity of更多还原