Onset voltages of atmospheric corona discharges on coniferous trees

In this article, the phenomenon of generation of corona discharges on the tops of trees and plants is described. In the first part of the text, the conditions for generation of this electric field which leads to formation of corona discharge and transfer of electric charge between atmosphere and Earth, are discussed. Experimental results of the onset voltage and its dependence on the discharge parameters are presented. The coincidence between released species from corona burning point and surrounding atmosphere is also discussed. Equation for the calculation of critical intensity of the electric field and onset voltage in dependence on radius of the tip are also discussed and compared with experimental data and equations for current–voltage characteristics are described. The attempt to explain differences between theory and measured data is proposed.     

Detection of seepage paths in earth dams using self-potential and electrical resistivity methods

Earth and rockfill dams are designed to operate under steady state seepage. Anomalous seepage may be a threat to the integrity of the structure. In spite of advances made in the fields of geotechnical engineering, it is not possible to have 100% leak-proof structure. Any excessive and unplanned seepage may lead to the failure of the dam, especially in unconsolidated or fractured terrains. Geophysical methods play an important role in mapping seepage paths and monitoring the changes of the seepage with time, enabling to plan technically and economically worthwhile remedial measures. In the present paper, utilisation of electrical methods for delineation of seepage zones at two of the four Saddle dams of the Som-Kamla-Amba project, Rajasthan State, India; which is founded on heterogeneous rock mass, is discussed. Electrical resistivity method was used to delineate zones favourable for seepage, whereas, self-potential (SP) method was used to delineate the seepage paths. SP measurements have shown negative anomaly of the order of 10–20 mV in amplitude, indicating low seepage, coinciding with the seepage measurements made by the project authorities.     

高分辨率中子俘获伽马能谱测井

叙述了NCGS测井的原理及元素含量计算方法;解决了现场测井中计算元素含量时必须得到的参数,如等效相对探测效率曲线的刻度、探管和井液中干扰(Fe、Ti、H)份额的扣除。用自己研制的仪器经山东几个煤田钻孔实测资料验证.计算的元素含量与岩芯化学分析对照结果,其精度不低于美国PGT公司和Schlumberger公司制造的仪器。此外,还介绍了连续测量获得的谱,经处理绘制成连续曲线,首次推出S_(511)、S_B、S_H/S_B等曲线,提供多种有用地质信息。     

高温高压下上地幔岩石电导率实验研究

为了建立具有普遍适用性的上地幔电性结构,本文利用Kawai-1000t压机和Solartron IS-1260阻抗/增益-相位分析仪,在4.0~14.0 GPa、873~1673 K的条件下,采用交流阻抗谱法（频率范围10^-1~10⁶Hz）测量了不含水的地幔岩电导率.实验结果显示,岩石的电导率随温度升高而大幅度的增大;在较大的温度范围内岩石的导电机制发生了变化,中低温时为小极化子导电,此时激活焓为0.94 eV （±0.13） eV,激活体积为0.11（±0.92） cm³·mol^-1,高温时为和镁空穴相关的离子导电,此时激活焓为1.6~3.17 eV,激活体积为6.75（±7.43） cm³·mol^-1;本次测量的电导率比低压下岩石的电导率要高,比矿物的电导率也要高.用本次的实验结果回归计算得到Fennoscandian地区的上地幔的一维电导率剖面,发现200 km以上本次实验计算的结果和大地电磁测深的电导率剖面吻合的比较好,在200 km以下本次实验得到的要比野外测量的电导率稍稍高一点,可能是因为实验过程中没有完全避免水的影响.本次的实验结果比用有效均匀介质方法计算得到的pyrolite矿物模型的电导率要高出两个数量级,这样的结果显示只用一种矿物的电导率或是几种矿物理论计算的结果有一定的不合理性.     

测井资料在碳酸盐岩洞—裂缝型储层产能评价中的应用

介绍了一种基于测井资料来预测双孔结构碳酸盐岩储层产能的新方法。首先根据碳酸盐岩剖面中双孔结构储层的地质和测井特征,提取与储层产能密切相关的多个测井和地质参数,考虑到这些参数与产能的非线性相关关系以及产能数据的变化特点,采用BP神经网络技术建立其储层产能的预测模型,由此处理了轮南地区的多口井测井资料。所预测的储层段产能与试油产能较为一致,效果良好。     

Reliability of dipole-dipole electrical resistivity tomography for defining depth to bedrock in covered karst terranes

 Sinkhole collapse is one of the main limitations on the development of karst areas, especially where bedrock is covered by unconsolidated material. Studies of sinkhole formation have shown that sinkholes are likely to develop in cutter (enlarged joint) zones as a result of subterranean erosion by flowing groundwater. Because of the irregular distribution of pinnacles and cutters on the bedrock surface, uncertainties arise when "hit-or-miss" borehole drilling is used to locate potential collapse sites. A high-resolution geophysical technique capable of depicting the details of the bedrock surface is essential for guiding the drilling program. Dipole-dipole electrical resistivity tomography (ERT) was used to map the bedrock surface at a site in southern Indiana where limestone is covered by about 9 m of clayey soils. Forty-nine transects were conducted over an area of approximately 42,037 m². The electrode spacing was 3 m. The length of the transects varied from 81 to 249 m. The tomographs were interpreted with the aid of soil borings. The repeatability of ERT was evaluated by comparing the rock surface elevations interpreted from pairs of transects where they crossed each other. The average difference was 2.4 m, with a maximum of 10 m. The discrepancy between interpreted bedrock-surface elevations for a transect intersection may be caused by variations in the subsurface geology normal to the transect. Averaging the elevation data interpreted from different transects improved the ERT results. A bedrock surface map was generated using only the averaged elevation data at the transect junctions. The accuracy of the map was further evaluated using data from four exploratory boreholes. The average difference between interpreted and actual bedrock surface-elevations was less than 0.4 m. The map shows two large troughs in the limestone surface: one coinciding with an existing sinkhole basin, while the other is in alignment with a small topographic valley. Because sinkholes were observed at the same elevation interval in similar valleys in the vicinity, the delineated trough may have implications for future land use at the site. Received: 4 January 1999 · Accepted: 8 March 1999     

测井数据标准化方法研究及软件设计

在油藏描述中必须对测井数据进行标准化处理,其目的是使研究区的所有同类测井数据具有统一的刻度。这里详细介绍了各种测井数据标准化的方法原理,并给出了相应的实例。此外,针对油藏描述中测井数据标准化处理的流程,设计了相应的软件,为精确油藏描述作好了准备。     

测井曲线判识构造软煤技术预测煤与瓦斯突出

基于构造软煤与硬煤的物性差异,分析构造软煤分层在测井曲线上的响应特征;根据煤层段测井曲线的形态特征,将揭露区钻孔测井曲线初步判识的结果同钻孔邻近巷道煤壁观测的结果进行对比、验证,形成了一套测井曲线判识构造软煤技术。利用该技术获取了研究区的构造软煤资料,对研究区的煤与瓦斯突出危险性区域进行了预测。     

利用多元地震属性预测测井特性

通过寻找井旁地震数据与测井曲线的关系,将这一关系应用到远离井的区域(只有地质数据,但无测井)来预测测井的有关特性,其方法有单属性分析和多属性分析[1]。本文通过实例描述了多属性分析的特点及预测结果。从单属性回归到多属性预测、再到神经网络预测过渡时,预测能力持续提高。同时对地震属性的选择和有效性进行了讨论,将结果应用到整个二维地震剖面上,能更好地确定井以外区域的测井特性。     

Regional geoelectric structure beneath Deccan Volcanic Province of the Indian subcontinent using magnetotellurics

Understanding deep continental structure and the seismotectonics of Deccan trap covered region has attained greater importance in recent years. For imaging the deep crustal structure, magnetotelluric (MT) investigations have been carried out along three long profiles viz. Guhagarh–Sangole (GS), Sangole–Partur (SP), Edlabad–Khandwa (EK) and one short profile along Nanasi–Mokhad (NM). The results of GS, SP and NM profiles show that the traps lie directly over high resistive basement with thin inter-trappean sediments, where large thickness of sediments, of the order of 1.5–2.0 km, has been delineated along EK profile across Narmada–Son–Lineament zone. The basement is intersected by faults/fractures, which are clearly delineated as narrow steep conducting features at a few locations. The conducting features delineated along SP profile are also seen from the results of aeromagnetic anomalies. Towards the southern part of the profile, these features are spatially correlated with Kurduwadi rift proposed earlier from gravity studies. Apart from the Kurduwadi rift extending to deep crustal levels, the present study indicates additional conductive features in the basement. The variation in the resistivity along GS profile can be attributed to crustal block structure in Koyna region. Similar block structure is also seen along NM profile.Deccan trap thickness, based on various geophysical methods, varies gradually from 1.8 km towards west to 0.3 km towards the east. While this is the general trend, a sharp variation in the thickness of trap is observed near Koyna. The resistivity of the trap is more (150–200 Ω m) towards the west as compared to the east (50–60 Ω m) indicating more compact or denser nature for the basalt towards west. The upper crust is highly resistive (5000–10,000 Ω m), and the lower crust is moderately resistive (500–1000 Ω m). In the present study, seismotectonics of the region is discussed based on the regional geoelectrical structure with lateral variation in the resistivity of the basement and presence of anomalous conductors in the crust.