Simulation of paleotectonic stress fields and quantitative prediction of multi-period fractures in shale reservoirs: A case study of the Niutitang Formation in the Lower Cambrian in the Cen'gong block,South China

Reservoirs where tectonic fractures significantly impact fluid flow are widespread. Industrial-level shale gas production has been established from the Lower Cambrian Niutitang Formation in the Cen'gong block, South China; the practice of exploration and development of shale gas in the Cen'gong block shows that the abundance of gas in different layers and wells is closely related to the degree of development of fractures. In this study, the data obtained from outcrop, cores, and logs were used to determine the developmental characteristics of such tectonic fractures. By doing an analysis of structural evolution, acoustic emission, burial history, logging evaluation, seismic inversion, and rock mechanics tests, 3-D heterogeneous geomechanical models were established by using a finite element method (FEM) stress analysis approach to simulate paleotectonic stress fields during the Late Hercynian—Early Indo-Chinese and Middle-Late Yanshanian periods. The effects of faulting, folding, and variations of mechanical parameters on the development of fractures could then be identified. A fracture density calculation model was established to determine the quantitative development of fractures in different stages and layers. Favorable areas for shale gas exploration were determined by examining the relationship between fracture density and gas content of three wells. The simulation results indicate the magnitude of minimum principal stress during the Late Hercynian — Early Indo-Chinese period within the Cen'gong block is −100 ∼ −110 MPa with a direction of SE-NW (140°–320°), and the magnitude of the maximum principal stress during the Middle-Late Yanshanian period within the Cen'gong block is 150–170 MPa with a direction of NNW-SSE (345°–165°). During the Late Hercynian — Early Indo-Chinese period, the mechanical parameters and faults play an important role in the development of fractures, and fractures at the downthrown side of the fault are more developed than those at the uplifted side; folding plays an important role in the development of fractures in the Middle-Late Yanshanian period, and faulting is a secondary control. This 3-D heterogeneous geomechanical modelling method and fracture density calculation modelling are not only significant for prediction of shale fractures in complex structural areas, but also have a practical significance for the prediction of other reservoir fractures.     

Microscopic Pore characteristics and methane sorption capacity of the lower cambrian shales in yangtze platform北大核心CSCD

The lower Cambrian develops a set of organic-rich black shales in Yangtze Platform and is regarded as one of the key layers of shale gas exploration. The microscope pore structure characteristics and methane sorption capacity were investigated using scanning electron microscope, nitrogen adsorption and methane sorption experiments, and then their controlling factors combining with organic matter, mineral compositions were discussed for Niutitang shales in Zunyi area, Mufushan shales in Nanjing area and Huangboling shales in Chizhou area. The results show as below; ( I ) The pores in lower Cambrian shales are mainly dominated by organic pores, interlayer pores in clay minerals and micro-fractures, as well as containing some intergranular pores between brittle mineral grains, honeycomb poies formed by pyrite crystals falling out, and dissolution molds in fossils; ( 2) DKT pore size distributions show the pores is mainly concentrated in the range of less than 4 nm in lower Cambrian shales and kerogens, while a certain amount of pores are above 4 nm are also existed in lower Cambrian shales, which may be contributed by smectite; ( 3)The specific surface area, pore volume and Langmuir methane sorption capacity of the lower Cambrian shales are ranging from 5.58 to 31. 96 inVg, 0.026 to 0.088 mL/g and 1.36 to 5. 3 mL/g, respectively, which are mainly controlled by TOC and smectite contents, but the effect of TOC and smectite on physical properties are quite different for the lower Cambrian shales in different regions; ( 4)The specific surface area of two Niutitang kerogens are 7. 08 and 7. 92 times than that of the shales and methane sorp-Tion capacity of kerogens arc 5.81 and 7.09 times than that of the shales, suggesting that kerogen is a main carrier of methane gas occurrence in.     

贵州织金含稀土磷矿床稀土元素赋存状态研究

利用等离子质谱仪ICP-MS、扫描电镜配合能谱分析、电子探针分析方法,研究了贵州织金含磷岩系剖面稀土含量变化。结果表明,剖面上稀土含量与磷灰石含量变化呈正相关关系,说明稀土主要赋存于磷灰石矿物中;利用扫描电镜、电子探针分析方法对生物碎屑、白云石和胶磷矿进行单矿物微量元素分析研究表明,胶磷矿中稀土含量最高,生物碎屑和白云石稀土含量较低,说明织金含稀土磷矿床稀土元素赋存状态是以类质同象的形式存在于胶磷矿中;利用稀土元素化学物相分析研究同样表明只有少量的稀土元素被磷块岩中粘土矿物所吸附,大量的稀土元素以类质同相形式存在于胶磷矿中。     

寒武纪大爆发与动物树的成型

由“真动物”构成的动物界（不包括海绵）通常被划分为双胚层动物、原口动物和后口动物3个亚界。寒武纪大爆发经历了爆发的前奏—序幕—主幕3个阶段,其中后两个阶段处于早寒武世初期（依次以小壳化石的首次辐射和澄江动物群爆发为代表）,另一个则发生在“寒武前夜”（即前寒武纪末期）,以伊迪卡拉生物群为代表。这次独特的三幕式大爆发分步完成了动物形态演化谱系树（简写为TOA）的成型。已有化石证据显示,动物树的3大主体或3个亚界的起源及其早期辐射分别发生于寒武纪大爆发这3个主要阶段。澄江化石库中发现的早期后口动物亚界涵盖了该亚界中所有6大分支（棘皮类、半索类、头索类、尾索类、脊椎类和绝灭了的古虫类）的原始类群,澄江动物群时代标志着寒武纪大爆发的顶峰,完成了动物树框架的成型,从而宣告了寒武纪大爆发的基本终结。其学术重要性超越了中寒武世的布尔吉斯页岩,因为前者位于动物树形成的“源头”,而后者仅代表此后的“一段流程”。在动物演化历史上4个最具转折意义的重大创新事件（即多细胞动物起源、两侧对称动物起源、后口动物起源和脊椎动物起源）中,第一个发生在伊迪卡拉纪甚至更早的时期,其余3个则可通过梅树村化石群和澄江化石群观察到其完成的主体过程。已灭绝的古虫动物门,是初具鳃裂构造的原始分节动物,作为由原口动物向后口动物过渡的一个珍稀“缺环”,很可能代表着后口动物亚界的一个根。古囊类兼有两侧对称的古虫类和一些原始棘皮动物的镶嵌体征,最可能代表棘皮动物的一个根。在早寒武世动物演化谱系中,后口动物的＂顶端类群＂的代表是被誉为“第一鱼”的昆明鱼目,目前已知包括昆明鱼、海口鱼和钟健鱼,它们具对眼、脊索与串珠状脊椎软骨共存的原始脊椎,?