Temporal variation of codaQ during Hualien earthquake of 1986 in eastern Taiwan

The May 20, 1986, Hualien earthquake sequence occurred on the northeastern coast of Taiwan. TheM=6.1 (GS mb) mainshock was followed by a large number of closely-clustered aftershocks with the largest being anM=5.5 event. One seismic station, TWD of the Taiwan Telemetered Seismographic Network, is located in the surface projection of the source region and provides excellent recordings of the entire earthquake sequence. These recordings, plus events occurring in the same source area preceding the mainshock, offer a unique opportunity to study the spatial and temporal variations of codaQ in a region of active subduction. A simple technique is devised that uses the envelope of the coda waveform to enable a quick determination of the codaQ from drum records. For recordings with a peak power at about 8 Hz, the following findings have been obtained: 1. The ambient codaQ near an active subduction region was as low as 145; 2. There was no significant decrease in codaQ within the period beginning one year and four months prior to the mainshock; 3. There was a significant drop of codaQ immediately after the mainshock; this drop lasted approximately two days before returning to the ambient level; 4. CodaQ values varied with focal depth.     

岩石颗粒度测量方法的研究及其应用

本文介绍了三种不同岩石颗粒度的测量方法,点计法,线计法,带计法及两种不同计算程序。颗粒度测量结果研究表明三种不同测量方法及两种不同计算程序之间存在着差別,其中结合野外的实例,其应用结果带计法为最好,线段长度百分比要比颗粒的频率百分比计算程序要好,前者能较客观地反映颗粒的实际搬运时水介质动力条件和沉积物的沉积环境。     

A numerical compaction model of overpressuring in shales

A one-dimensional model of sediment compaction is presented to relate pressure, porosity, permeability, and fluid and solid-particle velocities in an evolving sedimentary basin. The burial history of a sedimentary package is followed and incorporated into rate models for diagenetic reactions to predict clay compositions with depth. The governing set of nonlinear, partial differential equations constitutes a moving boundary problem and is solved by a finite difference scheme. Sedimentation rates and a permeability-porosity function for shales are required to implement the model. Additional factors are incorporated to mimic the effect of increased fluid volume generated by dehydration from clay mineral transformations and by thermal expansion. We demonstrate that the major cause of overpressuring in sediments accumulating along passive margins is nonequilibrium compaction. Sedimentation rates and strata permeability are the most important geologic factors in the formation of overpressured zones. Smectite dehydration and aquathermal pressuring play secondary roles in the development and sustenance of overpressures.     

结构性对上海软土渗透系数影响的试验研究

对在不同固结压力下原状土、重塑土的渗透系数进行试验研究，对比分析渗透系数的变化规律，研究上海软土结构性对渗透系数的影响。该试验的研究结果对上海软土渗透系数的确定有重要的工程指导意义。     

SARS疫情预测预报中的分段非线性回归方法

介绍了几种对累计SARS疫情预测预报中的非线性增长曲线模型，说明了Richards增长曲线在这次SARS疫情预测预报中合理性和可行性，由此建立了累计SARS疫情预测预报中的非线性回归点模型。并具体对北京SARS疫情进行了跟踪预测预报，包括整体和分时间段的预测预报，获得了北京SARS疫情随时间的预测预报结果，说明了北京4月底的一系列控制措施对北京SARS疫情所带来的影响，为进一步的后续研究打下了良好基础。     

铁路既有曲线整正测量方法

给出了全站仪任意点设站测量既有曲线上点的坐标的方法，对曲线整正中半径选择、缓和曲线长度选配、拨距计算方法进行了探讨，讨论的方法及推导的公式可以直接应用于既有曲线整正作业。     

Porosity, permeability, and fluid flow in the Yellowstone geothermal system, Wyoming

Cores from two of 13 U.S. Geological Survey research holes at Yellowstone National Park (Y-5 and Y-8) were evaluated to characterize lithology, texture, alteration, and the degree and nature of fracturing and veining. Porosity and matrix permeability measurements and petrographic examination of the cores were used to evaluate the effects of lithology and hydrothermal alteration on porosity and permeability. The intervals studied in these two core holes span the conductive zone and the upper portion of the convective geothermal reservoir. Variations in porosity and matrix permeability observed in the Y-5 and Y-8 cores are primarily controlled by lithology. Y-8 intersects three distinct lithologies: volcaniclastic sandstone, perlitic rhyolitic lava, and non-welded pumiceous ash-flow tuff. The sandstone typically has high permeability and porosity, and the tuff has very high porosity and moderate permeability, while the perlitic lava has very low porosity and is essentially impermeable. Hydrothermal self-sealing appears to have generated localized permeability barriers within the reservoir. Changes in pressure and temperature in Y-8 correspond to a zone of silicification in the volcaniclastic sandstone just above the contact with the perlitic rhyolite; this silicification has significantly reduced porosity and permeability. In rocks with inherently low matrix permeability (such as densely welded ash-flow tuff), fluid flow is controlled by the fracture network. The Y-5 core hole penetrates a thick intracaldera section of the 0.6-Ma Lava Creek ash-flow tuff. In this core, the degree of welding appears to be responsible for most of the variations in porosity, matrix permeability, and the frequency of fractures and veins. Fractures are most abundant within the more densely welded sections of the tuff. However, the most prominent zones of fracturing and mineralization are associated with hydrothermal breccias within densely welded portions of the tuff. These breccia zones represent transient conduits of high fluid flow that formed by the explosive release of overpressure in the underlying geothermal reservoir and that were subsequently sealed by supersaturated geothermal fluids. In addition to this fracture sealing, hydrothermal alteration at Yellowstone appears generally to reduce matrix permeability and focus flow along fractures, where multiple pulses of fluid flow and self-sealing have occurred.     

低渗透砂砾岩油层相对渗透率曲线的形态及其变化特征

以宝浪油田低渗透砂砾岩储层为例，主要分析了低渗透储层相对渗透率曲线的形态及变化特征和影响相对渗透率曲线形态变化的原因。分析结果表明，低渗透砂砾岩储层的非达西渗流使油相的相对渗透率增大，使水相的相对渗透率减小。孔隙结构的非均质性，特别是粘土矿物的含量和注入水水质对相对渗透率曲线的影响都很大。     

低产低渗裂缝油田吞吐采油试验研究

头台油田是构造—岩性油藏。裂缝型、特低渗透是其显著特点，常规注水开发后经常出现严重的油井水淹，造成油田开发低效。本文以头台油田研究为例，认为对于裂缝型特低渗透油田，采用注水吞吐采油技术，通过套管直接向地层注水，利用储层毛管力作用，进行油水置换，实现单井自注自采吞吐采油，可以改善油田开发效果，减缓产量递减。适合注水吞吐采油基本条件是岩石润湿性为弱亲水和岩石饱和非润湿相。影响注水吞吐采油效果的主要因素是储层吸水状况、微缝发育状况、储层非均质性、注入体积和关井压力等。吞吐采油技术可作为改善裂缝型特低渗透油藏开发效果的一种新的模式来研究和推广。