上扬子北缘晚二叠世大隆组有机质类型、分布规律及赋存控制因素

发布时间：2018-01-09 22:03

本文关键词：上扬子北缘晚二叠世大隆组有机质类型、分布规律及赋存控制因素　出处：《中国地质大学》2017年博士论文　论文类型：学位论文

【摘要】：随着中国经济腾飞,对能源的需求也持续增长。至2016年中国有35%的天然气依靠进口。近年来,页岩气(shale gas)作为资源潜力巨大的新能源领域,受到世界各国高度重视。随着美国页岩气开采技术的突破,美国已经从天然气纯进口国转变成天然气纯出口国。中国从早古生代至新生代发育有多套黑色页岩,页岩气地质资源储量与美国相当。经过不断努力,中国南方早古生代地层黑色页岩中获得工业气流,但是中国页岩气基础理论研究还非常薄弱,一系列地质问题认识不足始终制约着中国页岩气发展。加强中国南方黑色页岩的页岩气地质特征研究是页岩气开发的当务之急,研究黑色页岩中有机质分布状态与控制因素对页岩气勘探开发更是具有指导意义。因此,本文以扬子北缘上二叠统深水相沉积大隆组为研究目标,选取上寺和甘溪两条具有连续沉积记录的剖面,通过扫描电子显微镜(SEM)、孢粉有机质观察大隆组赋存有机质类型和分布状态,并结合高精度微量元素地球化学数据探讨古环境因素对有机质保存的影响,在此基础上,结合前人资料总结出大隆组有机质沉积模式,以此对页岩气评价提供理论依据。首先,笔者总结了现代海洋沉积物和地质历史时期黑色页岩中有机质保存控制因素,发现不论是现代沉积物还是地质历史时期沉积岩,影响赋存其中的有机质保存的因素是一致的:有机质类型(有机质物质组成)、生产力和保存环境以及粘土矿物吸附保护作用。这为后期工作提供了理论基础和指导思想。笔者选取上寺剖面31个样品、甘溪剖面21个样品,利用SEM观察赋存其中的原位有机质类型和分布状态。二次电子(SE)图像和背散射电子(BSE)图像中有机质亮度、形貌及能谱分析是有机质赋存类型鉴别的重要依据。结果显示大隆组有机质分为形态有机质、弥散有机质和沥青三种类型。在背散射图片中所有类型有机质均为黑色,但是形态有机质是具有生物结构的高稳定性颗粒有机质,保留了有机体原始信息,在二次电子图片中发亮;弥散有机质是粘土矿物与有机质相互作用的产物,在二次电子图片中为片状矿物聚合体,在背散射模式下为黑色斑块,具有高C,低O、Si、Al的特征;块状沥青经运移储集在样品孔缝系统中,二次电子图像下可见棱角及断口,能谱数据显示沥青C质量分数高,Si和Al极少。SEM结果还显示成岩作用对有机质保存和分布的影响主要体现在弥散有机质和沥青上,对靠自身稳定性保存的形态有机质没有明显作用。成岩作用深的区域(甘溪剖面)样品中弥散有机质粘土矿物形态明显、C含量少,样品中沥青含量高。而且部分沥青的成分和形态也会受成岩作用影响。为了与SEM结果进行对比,笔者还对上寺、甘溪剖面样品进行孢粉有机质处理。在透射光下,有机质被分为形态有机质和无定形有机质两种形式组成。形态有机质是保留有生物形态的有机质颗粒,由孢型(包括孢粉化石、疑源化石以及其他各种藻类)和结构有机质(包括植物碎屑和动物碎屑)组成,无定形有机质主要由海绵无定形和颗粒无定形组成。其中,笔者识别出保存完好的球形、椭球型疑源化石Dictyotidium、Leiosphaeridia,链状疑源化石Reduviasporonites,孢粉化石Cycadopites、Lundbladispora以及有孔虫衬膜,还有一些藻类孢子和植物管胞。形态有机质结构在透射光与SEM下十分相似,可以直接与SEM下的形态有机质对应;海绵无定形有机质是弥散有机质的主体,薄片中往往以聚合物形式存在,这可能是有机质缩聚的结果,其定量结果在纵向上与TOC变化趋势一致,这些特征可以与弥散有机质对应,也说明海绵无定形有机质(弥散有机质)是TOC的主体成分;薄片下颗粒无定形有机质可以单独存在,也可以与海绵无定形有机质聚合在一起,但是这种有机质的颗粒形态往往具有三维属性,可以与沥青对应。前人研究已经得出还原的水体以及高生产力是影响大隆组有机质保存的重要因素,但是二者具体如何作用却没有详细描述。笔者综合考虑高精度微量元素地球化学、生物学及海平面变化数据,将上寺剖面分为四个阶段、甘溪剖面分为五个阶段,并详细讨论各阶段生产力与氧化还原环境对有机质保存的影响。还原的水体环境可以促进有机质保存,上寺剖面第Ⅱ阶段、甘溪剖面第I、III阶段,有机质保存的重要层段(TOC平均值大于3%)均沉积于还原的水体环境。当水体持续处于缺氧状态时,水体氧化还原环境对有机质保存的影响力会降低,此时生产力才是控制TOC含量变化的关键因素,如上寺剖面第Ⅱ阶段、甘溪剖面第III阶段,TOC与生产力指标有极好的相关性(R2≥0.79),与氧化还原环境指标相关性则要弱些(R2≤0.58);而当水体环境为氧化—次氧化时,如上寺剖面第IV阶段,甘溪剖面第IV、V阶段,TOC水平较低,平均值不足1%,这种条件下,古海洋因素对有机质的影响需要视情况而定,若形态有机质含量高,那么生产力对有机质保存的控制作用更明显,如甘溪剖面第Ⅱ、IV阶段,反之则水体氧化还原环境是主要控制因素,如上寺剖面第I、IV阶段。最后笔者综合所有数据,总结大隆组沉积模式如下:大隆组古生产力提高主要由晚二叠世两次海侵事件引起,中上扬子地区中二叠世末期开始火山活动频繁,风化作用加剧。火山活动和风化作用导致大量营养元素和粘土堆积在陆架低地,晚二叠世海平面迅速上升,堆积的营养物质进入海洋系统导致邻海盆地生产力增加,耗氧量也随之增加并形成分层海水。缺氧环境往往由海水中部开始扩散,随着海水溶氧量进一步减少,氧气最小带扩大至底层水体形成稳定的缺氧环境,此时维持氧气消耗之外剩余的有机质与海水中的粘土矿物相互作用迅速沉降保存,形成大量弥散有机质,因此表层海水生产力是控制有机质保存的主要因素。缺氧环境一直持续到第二次海侵末期,第一次海侵期间大部分营养元素已经被消耗,因此第二次海侵中期开始生产力已经逐渐降低,水体环境在次氧化至缺氧环境之间波动,此时TOC受水体环境和生产力共同控制,有机质类型受生产力和粘土矿物含量控制,弥散有机质含量与粘土矿物含量成正比,形态有机质与沥青也广泛存在。在低海平面时期,粘土含量减少,大量有机质由于缺乏粘土矿物的吸附保护而被分解,样品中剩余少量耐降解的形态有机质,几乎没有弥散有机质保存。充分了解泥质烃源岩中有机质赋存类型有助于理解成岩过程中形成的油气资源,更有利于烃源岩评价以及非常规油气勘探开发工作。形态有机质是孢粉或疑源化石的外壁,自身具有高稳定性,但是由于其含量较少,与TOC没有很好的线性关系;弥散有机质是无定形有机质的主要成分,而且与TOC具有相同的变化趋势,因此,笔者认为弥散有机质才是富有机质硅质泥岩段TOC的主体,弥散有机质具有作为生烃母质的潜力,也说明硅质泥岩中TOC可以反映原生有机质保存情况;块状沥青是有机质经过运移的结果,当沥青大量存在时样品TOC不能准确反映海洋的生产力水平,但是残留沥青在深埋条件具有裂解生气的能力。笔者认为大隆组有机质具有产烃的潜力,但是广元地区成熟度相对较低,湖北建始地区大隆组是更好的页岩气勘探层位。
[Abstract]:Chinese with economic growth, the demand for energy continues to grow. China to 2016 35% of natural gas imports. In recent years, shale gas (shale gas) as a resource potential of the new energy field, attracted worldwide attention. With the U.S. shale gas mining technology breakthrough, the United States has become pure natural gas exports in the transition from a net importer of natural gas. Chinese from early Paleozoic to Cenozoic development with several sets of black shale, shale gas geological reserves and the United States. After continuous efforts, the early Paleozoic strata in South China black shale obtained industrial gas shale gas, but Chinese basic theory research is still very weak, a series of geological problems lack of knowledge always restricts the development of shale gas China. Strengthen shale gas geological characteristics of Chinese southern black shale is a pressing matter of the moment of shale gas development, research in black shale Organic matter distribution and controlling factors of shale gas exploration and development is a guiding significance. Therefore, based on the northern margin of the Yangtze plate two Permian deep-water sedimentary facies formation as the research object, the selection of temple and Gan Xi two with continuous sedimentary records section, by scanning electron microscope (SEM), organic pollen qualitative observation Dalong formation exists in organic matter types and distribution, combined with high precision trace element geochemical data to discuss the effects of environmental factors on the preservation of organic matter, on this basis, combined with previous data summarized Dalong formation organic matter deposition pattern, provides the theoretical basis for shale gas assessment. Firstly, the author summarizes the organic quality control factors of modern marine sediments and preserve the geological history in black shale, found that both the geological history of modern sediments or sedimentary rocks, which influence occurrence of organic matter preservation The factor is the same: the type of organic matter (organic matter composition), productivity and preservation of the environment and the protective effect of clay mineral adsorption. It provides a theoretical basis and guidance for later work. The author selects the temple on the profile of 31 samples, 21 samples of Ganqi profile, the in situ observation of the occurrence and the type of organic matter the distribution by SEM. Two electron (SE) images and backscattered electron (BSE) organic matter image brightness, morphology and energy spectrum analysis is an important basis for identification of organic occurrence types. The results showed that dalongformation organic matter is divided into organic form, dispersed organic matter and three types of asphalt. On the back scattering picture all types of organic matter are black, but the form of organic matter is high stability of particulate organic matter with biological structure, retain the original information in the organism, shiny two electronic images; dispersion of organic matter is clay mineral With the interaction of organic products, in the two electronic picture for flaky mineral polymer in the back scattering mode for the black patch, with high C, low O, Si, Al; bulk asphalt by migration in the reservoir samples aperture system, the two electronic image under visible edges and fracture and the spectrum data show that the asphalt content of C, Si and Al.SEM showed little influence of diagenesis on the preservation of organic matter and the distribution is mainly reflected in the diffusion of organic matter and asphalt, has no obvious effect on the morphology of the preservation of organic matter on its own stability. With the deep diagenetic region (Ganqi profile the dispersion of clay minerals) organic matter form significantly in the sample, C content, high asphalt content in the sample. And the composition and form part of the asphalt will be affected by diagenesis. In order to compare with the results of SEM, the author of the temple, Ganqi profile samples were from there Organic matter processing. In the transmission light, the organic matter is divided into forms of organic matter and amorphous organic matter two forms. Form of organic matter is preserved particulate organic matter biological form, the spore type (including sporopollen fossils, fossils and other suspected source algae) and organic matter (including plant debris structure and animal debris), amorphous organic matter is mainly composed of amorphous and amorphous sponge particles. Among them, the author identifies spherical well preserved, ellipsoid type fossil Dictyotidium Leiosphaeridia, suspected source, suspected source of fossil Reduviasporonites chain, Cycadopites Lundbladispora and fossil foraminifera, lining film, and some algae spores and plant cell form of organic matter. The structure is very similar in the transmission light and SEM, can be directly corresponding forms of organic matter and SEM sponge; amorphous organic matter is the main diffusion of organic matter, slice into Go in the form of a polymer, which may be the result of organic condensation, the quantitative results in the vertical and TOC trends, these features can correspond to the dispersion of organic matter, also shows that the sponge amorphous organic matter (dispersed organic matter) is the main component of TOC sheet; granular amorphous organic matter can exist alone also, no amorphous organic matter in the polymerization with the sponge, but the particle morphology of organic matter has three-dimensional attributes, and can. Previous studies have reached the corresponding asphalt reduction and high water productivity is an important factor affecting the preservation of organic matter in group long, but the two is not described in detail how the role of the author. Considering the high precision trace element geochemistry, biological data and sea level changes, the temple section is divided into four stages, Ganqi profile is divided into five stages, and a detailed discussion of each order Effect of productivity and redox environment on the preservation of organic matter. The reduction of water environment can promote the preservation of organic matter, on the temple section in the second stage, Ganqi profile I, III stage, organic matter preservation important layer (TOC average value is greater than 3%) were deposited on the water. When the water continues to restore in a hypoxic state, water redox environment will reduce the influence on the preservation of organic matter, the productivity is the key factor to control the change of the content of TOC, as the temple section in the second stage, Ganqi profile phase III, the correlation between TOC and productivity index has an excellent (R2 = 0.79), reduction of environmental indicators associated with oxidation some are weak (R2 < 0.58); and when the water environment is oxidation and oxidation, as the temple section phase IV, Ganqi profile IV, V stage, TOC level is low, the average value of less than 1%, the conditions of ancient marine factors on organic matter The impact depends on the situation, if the shape of the organic content is high, then the productivity effect on the preservation of organic matter is more obvious, such as Ganqi Profile II, IV stage, whereas the water oxidation reduction environment is the main control factor, such as the temple section I, IV stage. Finally the writer integrated all data. The following summary of Dalong formation sedimentary model: Dalong group of ancient productivity is mainly caused by the Late Permian two transgression events in Yangtze area since Late Permian volcano activity, weathering intensified. Volcano activity and weathering caused large amount of nutrient elements and clay accumulation in the continental shelf of the lowlands, the late Permian sea level rose rapidly, nutrition the accumulation of material into the ocean system leads to increased productivity of adjacent sea basin, the oxygen consumption is increased and the formation of layered water. The anoxic environment often by seawater at the middle of diffusion, with dissolved oxygen in seawater To further reduce the amount of oxygen, the minimum zone extended to the bottom water formation of anoxic environment, clay minerals and organic matter at this time to maintain the water remaining oxygen consumption outside the interaction in the rapid settlement preservation, the formation of a large number of dispersed organic matter, so the surface water productivity is the main factor to control the preservation of organic matter. The anoxic environment continued until second the end of the period of the first transgression most nutrient elements have been consumed, so the second transgression started in the middle of productivity has been gradually reduced, the water environment in the suboxic anoxic environment to fluctuations between the TOC by the water environment and productivity jointly control the type of organic matter is controlled by the productivity and the content of clay minerals, organic matter and clay dispersion the mineral content is proportional to the form of organic matter and asphalt are also widespread. In the low sea level period, clay content reduced, a large number of Organic matter decomposition due to the adsorption of clay minerals and the lack of protection, the residual resistance degradation morphology of organic matter in the sample, almost no diffusion preservation of organic matter. To fully understand the occurrence of organic matter types in muddy source rock is helpful in understanding the formation of rock in the process of oil and gas resources, more conducive to the evaluation of hydrocarbon source rocks and unconventional oil and gas exploration and development work. The organic matter is the form or suspected source of fossil pollen, itself has the advantages of high stability, but its content is less, not a good linear relationship with TOC diffusion; organic matter is the main component of amorphous organic matter, and TOC has the same trend, therefore, the author thinks that the diffusion of organic matter is the main organic rich siliceous mudstone TOC, dispersion with organic matter as hydrocarbon source rock potential, also shows that TOC can reflect the primary siliceous mudstone organic matter preservation; massive drain Green is the organic matter after the migration, when there are a lot of asphalt samples TOC does not accurately reflect the marine productivity level, but the residual asphalt with cracking ability of deep buried condition. The author thinks that the Dalong formation with organic matter hydrocarbon producing potential, but the maturity of Guangyuan area is relatively low, the Hubei area of Jianshi Dalong group shale gas exploration horizon better.

【学位授予单位】：中国地质大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P618.13

【相似文献】