Organic geochemistry and petrology of barren and Mo–Ni–PGE mineralized marine black shales of the Lower Cambrian Niutitang Formation (South China)

Marine black shales of the Lower Cambrian Niutitang Formation in southern China host Mo–Ni–platinum group elements (PGE) mineralization confined to a phosphate- and pyrite-rich stratiform body (max. 20-cm thick). The H/C atomic ratio, carbon isotopic composition, FTIR spectra of bulk organic matter, and spectra of extractable part of organic matter indicate similar sources and thermal evolution of organic matter in barren and mineralized black shales.The morphology and relative abundance of organic particles in barren and mineralized shales are different. In barren black shales, organic particles comprise only elongated bodies and laminae 2–10 μm across or elongated larger bodies (> 10 μm) with R_max = 2.96–5.21% (Type I particles). Mineralized black shales contain Type I particles in rock matrix (90–95 vol%), small veinlets or irregular organic accumulations (Type II particles, 1–5 vol%) that display weak to well developed mosaic texture and a variable reflectance (R_max = 3.55–8.65%), and small (< 1 to 5 μm) rounded or irregular Type III organic particles (1–4 vol%) distributed within phosphate nodules and sulphide rip-up clasts. Type III particles show similar reflectance as particles of Type I in rock matrix. Type I particles are interpreted as remnants of in situ bacterially reworked organic matter of cyanobacteria/algal type, Type II as solidified products or oil-derived material (migrabitumen), and Type III particles as remnants of original organic matter in phosphatized or sulphidized algal/microbial oncolite-like bodies. Equivalent vitrinite reflectances of Type I and III particles in barren and mineralized rocks are similar and correspond to semi-anthracite and anthracite. Micro-Raman spectra of organic particles in rocks display a wide belt in the area of 1600 cm^− 1 (G belt) and approximately the same belt in the area of 1350 cm^− 1 (D belt). The ratio of integrated areas of the two belts correlate with R_max values.The Mo–Ni–PGE mineralized body is interpreted as to represent a remnant of phosphate- and sulphide-rich subaquatic hardground supplied with organic material derived from plankton and benthic communities as well as with algal/microbial oncolite-like bodies that originated in wave-agitated, shallow-water, nearshore environment.     

库区蓄水型人工增雨效果评估及其应用

通过对降水影响系统分型,给出了以同一影响天气系统下的降水时段为评估单元,对降水前后目标区和控制区的流域面雨量、入库流量和作业前后雷达回波参量进行评估,并对2005年夏季增雨作业个例进行了计算,结果表明,雷达回波参量在作业前后有明显的变化,平均增雨率为19.61%,投入产出比为1:37,经济效益显著。     

武乡区块山西组泥页岩孔隙结构及分形特征研究

沁水盆地东部煤系伴生泥页岩广泛发育,页岩气资源潜力大,开展该区泥页岩孔隙结构特征的研究对页岩含气性评价及实现煤层气、页岩气合探共采具有重要意义。本文以盆地内武乡区块Y井二叠系山西组泥页岩为研究对象,通过XRD、高压压汞和低温液氮吸附等实验手段对泥页岩孔隙结构特征及分形特征进行了研究。结果表明,Y井山西组泥页岩的矿物组成以黏土矿物和石英为主;泥页岩中小于50 nm的孔隙大量发育,结构形态上以狭缝平板型孔隙和"细瓶颈"孔隙为主;泥页岩样品吸附曲线呈倒S型,属于Brunauer分类方案中的Ⅱ型曲线,其脱附曲线属于IUPAC分类方案中的H2型(兼具H1型及H3型),属De Boer分类方案中的B型(兼具E型及C型); Y井山西组泥页岩分形维数接近3,非均质性较强,矿物成分、总孔体积、平均孔径和TOC含量是影响泥页岩分形维数的重要因素。     

黔西北地区龙马溪组页岩有机质和脆性矿物的控缝机制

页岩"甜点"层段中有机质和脆性矿物对裂缝的发育具有极为重要的控制作用，揭示并把握裂缝萌生、发育和演化的机理与规律，对于压裂目标层段的优选以及页岩气增产和稳产具有极为重要的工程实践价值。以黔西北地区龙马溪组页岩为例，通过地化测试、岩石力学实验以及扫描电镜，深入剖析和揭示了"甜点"层段中与有机质和脆性矿物相关的控缝机制，并结合数值模拟实验展现了"甜点"层段中裂缝的形成和演化的完整过程。研究结果表明，有机质和脆性矿物的同步富集为裂缝的发育和演化提供了重要的物质基础，其中裂缝趋向于沿着有机质形成的结构面传播，有机质的孔隙结构对裂缝具有较为明显的诱导机制。在外力作用下，内在积累的能量转化为脆性矿物的变形和变位，脆性矿物含量越高者裂缝发育能力越强，裂缝发育程度越高。数值模拟实验呈现了一种由于有机孔隙和脆性矿物所导致的应力集中从而诱发裂缝萌生和演化的整个过程。该研究成果可为深化认识裂缝的成因机理以及压裂施工过程中相关压裂参数的调整提供一定的借鉴与参考。     

Migration and dispersion of trace elements in the rock–soil–plant system in areas underlain by black shales and slates of the Okchon Zone, Korea

The Okchon black shale in Korea provides a typical example of natural geological materials enriched with potentially toxic elements. The Chung-Joo, Duk-Pyung, Geum-Kwan, I-Won, Bo-Eun and Chu-Bu areas are underlain by these black shales and slates of the Guryongsan Formation or the Changri Formation, which are parts of the Okchon Group in the central part of the southern Korean Peninsula. In order to investigate the enrichment levels and dispersion patterns of potentially toxic elements in the rock–soil–plant system, environmental geochemical surveys were undertaken in the above six study areas in the Okchon Zone. After appropriate preparation, rock and soil samples were analyzed for potentially toxic elements by instrumental neutron activation analysis (INAA) and inductively coupled plasma atomic emission spectrometry (ICP-AES), and plant samples by atomic absorption spectrometry (AAS). In particular, Ba, Cd, Mo, V and U in Okchon black shales are highly enriched, and their mean concentrations are significantly higher than those in black slates. These elements are geochemically associated, and might be enriched simultaneously. The highest mean concentrations of 42.0 μg g⁻¹ As, 2100 μg g⁻¹ Ba, 10.9 μg g⁻¹ Cd, 213 μg g⁻¹ Mo, 83 μg g⁻¹ U, 938 μg g⁻¹ V and 394 μg g⁻¹ Zn are found in black shales from the Duk-Pyung area. Mean concentrations of As, Mo and U in soils overlying black shales occurring in the Duk-Pyung area (30 μg g⁻¹ As, 24 μg g⁻¹ Mo and 50 μg g⁻¹ U) and Chu-Bu area (39 μg g⁻¹ As, 15 μg g⁻¹ Mo and 27 μg g⁻¹ U) are higher than the permissible level. Enrichment index values of the six study areas decrease in the order of Duk-Pyung > Chu-Bu > Bo-Eun > Chung-Joo > Geum-Kwan = I-Won areas. Relationships between trace element concentrations in soils and plants are significantly correlated, and the biological absorption coefficients (BAC) in plants are in the order of Cd > Zn = Cu > Pb, which suggests that Cd is more bioavailable to plants than the other elements. Cadmium concentrations in plant species decrease in the order of chinese cabbage > red pepper > soybean = sesame > rice stalk > corn > rice grain. From the result of sequential extraction analysis of soils, relatively high proportions of Cu, Pb and Zn are present as residual fractions, and that of Cd as non-residual fractions. Cadmium occurs predominantly as exchangeable/water-acid soluble phase in soils, and this is in agreement with the findings of high Cd concentrations in plants.     

湘黔地区中奥陶世海平面上升的沉积响应

中奥陶世克拉道克阶(Caradocian)在全球范围内为海侵期,体现在全球范围广泛的黑色页岩沉积及笔石动物的大规模繁盛,湘黔地区这一时期地层发育完全,从碳酸盐台地-斜坡-外陆架盆地均有不同程度的响应。在台地区表现为碳酸盐台地的淹没,斜坡区表现为碳酸盐重力流及黑色页岩、粉砂岩沉积,形成碳酸盐与陆源碎屑的混合沉积,而在外陆架盆地区表现为黑色岩系大规模发育及笔石的大量繁盛。     

Swelling Behaviour of Expansive Shales from the Middle Region of Saudi Arabia

Severe and widespread damage in residential buildings, sidewalks and pavements in various parts of the middle region of Saudi Arabia is caused by the development of heave and swelling pressure in the expansive shales in the region. This paper presents the problems and the geotechnical and physicochemical properties of the tested shales. The swelling potential was determined using various methods. Swell tests were conducted under different loading conditions and following different procedures to quantify the amount of vertical swell and swelling pressure. The conventional one-dimensional oedometer swell tests were performed using three different procedures, namely, free swell, constant volume swell and swell overburden. In addition, swell tests were performed in the stress path triaxial apparatus. Tests under different vertical stresses and confinements were conducted. Vertical swell and swelling pressure obtained from the various methods were compared. The reliability of the different methods for estimation of swelling potential is discussed.     

Computer modeling and simulation of coalbed methane resources

Coal seam gas reservoirs are complex both geologically and in the mechanism of gas production. Understanding these naturally fractured reservoirs for two-phase (gas–water) flow conditions is often limited by a lack of data. This paper illustrates that reservoir simulation is a powerful tool which can be used to determine key data requirements, and how variability in reservoir properties and operating practices affect performance at the field level. The paper presents examples of how reservoir simulation can be used to assess the efficiency of well completions (fracturing or cavitation), identify candidate wells for remedial treatment, examine methane drainage in advance of mining, and assess the impact of errors in measured data on long-term gas production forecasts.     

利用变参数回归方法反演泥质岩裂缝密度

本文利用变参数回归分析建立了多口井的泥质岩储层裂缝密度模型。该模型的平均相对误差为１３．５％,较常系数回归分析、ＢＰ网络模型进行裂缝预测的精度高（平均相对误差分别为３８．７％、１７．９％）。通过实际资料处理认为该油田在纵向上随时代变老,深度加深,裂缝密度降低。即从Ｎ２２、Ｎ１２到Ｎ１,平均裂缝密度从０．７８条／ｍ、０．５条／ｍ降低到０．３条／ｍ。在平面上,沿构造轴部裂缝最发育,平均裂缝密度Ｎ２２、Ｎ１２、Ｎ１层分别为０．５８条／ｍ、０．６条／ｍ、０．３条／ｍ。     

Determination of characteristics of steam reservoirs by Radon-222 measurements in geothermal fluids

The authors conducted a Rn²²² survey in wells of the Larderello geothermal field (Italy) and observed considerable variations in concentrations. Simple models show that flow-rate plays an important part in the Rn²²² content of each well, as it directly affects the fluid transit time in the reservoirs. Rn²²² has been sampled from two wells of the Serrazzano area during flow-rate drawdown tests. The apparent volume of the steam reservoir of each of these two wells has been estimated from the Rn²²² concentration versus flow-rate curves.List of symbols Q Flow-rate (kg h^–1) - Decay constant of Rn²²² (=7.553×10^–3 h^–1) - Porosity of the reservoir (volume of fluid/volume of rock) - ₁ Density of the fluid in the reservoir (kg m^–3) - ₂ Density of the rock in the reservoir (kg m^–3) - M Stationary mass of fluid filling the reservoir (kg). - E Emanating power of the rock in the reservoir (nCi kg _rock ^–1 h^–1). - P Production rate of Rn²²² in the reservoir: number of atoms of Rn²²² (divided by 1.764×10⁷) transferred by the rock to the mass unit of fluid per unit time (nCi kg _fluid ^–1 h^–1). - N Specific concentration of Rn²²² in the fluid (nCi kg^–1) - Characteristic time of the steam reservoir at maximum flow-rate (=M/Q)