水压致裂法原地应力测量及初步结果

水压致裂法是直接测量地壳较深部应力的有效方法.本文介绍了水压致裂法原地应力测量的基本原理、技术方法和主要的仪器设备;给出了1980年在河北省易县和1981年在江苏省新沂县两次野外实测试验结果;对所测得的原地应力的大小和方向及诱发裂缝形态进行了初步讨论;并将水压致裂法测量结果与套芯法结果做了对比.     

缝长,尺度对水压致裂应力测量结果的影响规律

本文从弹性力学、断裂力学的基本理论出发,结合室内实验和野外观测结果研究了尺度、缝长对水压致裂应力测量结果的影响规律。研究结果表明,室内实验样品的孔径比不应大于四分之一,最好小于十分之一,较大的绝对尺度可以使实验结果变得稳定。野外实际测量除了满足上述要求外,裂缝单翼长度不应小于十倍的钻孔半径,否则测不到可靠的封闭压力。据此,进行大尺度水压致裂室内模拟实验对于提高压裂技术,完善水压致裂应力测量理论是非常必要的。     

水压致裂压裂裂缝的扩展及其力学特性

引言 近几年来,我们对水压致裂法应力测量在室内外作了一些工作,并结合发现的问题做了水压致裂室内模拟实验。 实验发现,钻孔加压率对岩石表观破坏强度有相当大的影响,加压率大,破坏强度也大。其结果,必然影响水压致裂应力测量的精度。本文探讨和分析了造成这种影响的原因和规律。提出:水压致裂过程中的裂缝扩展的动力学特性是造成上述结果的主要原因。     

套芯法、水压致裂法原地应力测量、钻孔崩落及震源机制解分析所得结果的对比

我国已积累了大量震源机制解资料,近年来为各种目的开展了套芯法及水压致裂法原地应力测量,并从一些深钻井的测井资料中获得了一批钻孔崩落数据,为地壳应力状态的研究提供了十分有用的资料.为了进行区域构造应力场的研究,笔者对上述各种方法的测量结果进行了对比研究.在同一个钻孔中用不同的方法进行原地应力测量,如在同一个钻孔中用套芯法及水压致裂法进行观测;用水压致裂法的测量结果与同一钻孔中发现的钻孔崩落资料进行对比.还在相距不远的钻孔中用同样的或不同的方法进行原地应力测量;还将同一地区各种方法所得的资料进行了对比,发现其差异并不很大.这就使我们有可能利用上述各种方法提供的资料来进行区域构造应力场及地壳应力状态的研究.     

套芯法、水压致裂法原地应力测量、钻孔崩落及震源机制解分析所得结果的对比

我国已积累了大量震源机制解资料,近年来为各种目的开展了套芯法及水压致裂法原地应力测量,并从一些深钻井的测井资料中获得了一批钻孔崩落数据,为地壳应力状态的研究提供了十分有用的资料.为了进行区域构造应力场的研究,笔者对上述各种方法的测量结果进行了对比研究.在同一个钻孔中用不同的方法进行原地应力测量,如在同一个钻孔中用套芯法及水压致裂法进行观测;用水压致裂法的测量结果与同一钻孔中发现的钻孔崩落资料进行对比.还在相距不远的钻孔中用同样的或不同的方法进行原地应力测量;还将同一地区各种方法所得的资料进行了对比,发现其差异并不很大.这就使我们有可能利用上述各种方法提供的资料来进行区域构造应力场及地壳应力状态的研究.     

三峡工程原地应力测量及蓄水诱发地震探讨

为了研究三峡拟建水库蓄水诱发地震的可能性,1988年在三峡拟建坝址三斗坪附近的茅坪镇花岗岩体中进行了水压致裂应力测量.钻孔深度800m,在154—791m 深度中的16个深度段进行了水压致裂     

考虑系统柔度影响的水压致裂法测量深部岩石应力

为了有效测量水压致裂方法中的重张压力,必须使用具有足够小柔度的试验设备,否则无法从重张压力估计垂直钻孔平面的最大水平应力.仅通过替换水压致裂系统中的某一部件来大幅度降低系统柔度是很难的.但如果流量计尽可能安装在靠近跨接式封隔器隔离出的钻孔测试区.那么系统柔度就会大大降低.为此,我们研制出配有井下流量计的试验系统,并在野...     

在同一钻孔中水压致裂法地应力测量与套钻孔应力解除法测量成果的比较

本文叙述了在同一钻孔中水压致裂法地应力测量和套钻孔应力解除法进行对比测量，获得基本一致实测成果的两个实例。     

唐山地区深部应力测量

在唐山东约20公里的东矿区黄坨苗圃356米深钻孔中,在300米以上深度成功地进行了11次水压致裂应力测量,取得了主应力大小及其方向随深度变化的资科。测量结果表明,现在唐山地区的应力水平很低,在接近300米的深度上最大水平主应力仅7.8兆帕,最大水平剪应力值也仅1兆帕。最大主应力方向在180米以上变化较大,180米以下的三次测量结果一致性很好,最大主应力方向为北81°西到北86°西,与华北地区应力测量的总体方向是一致的。文中还将水压致裂应力测量的结果与应力解除与用声发射凯塞效应法测得的结果作了对比。     

我国水压致裂法首次试验喜获成果

水压致裂法应力测量是近年来发展起来的一种测量地壳深部应力的新方法。由于这种方法不需要套芯和复杂灵敏的井下仪器,所以可以在深井中测量应力。它还具有不需精确了解岩石的弹性参量且在具有高的差应力的地区仍能测量等优点,因此愈来愈受到人们重视。 美国用水压致裂法进行了大量的深部应力测量,西德,日本也相继开展了水压致裂应力测量工作,取得了令人鼓午的结果。     

Quench rates in air, water, and liquid nitrogen, and inference of temperature in volcanic eruption columns

We apply a geospeedometer previously developed in this lab to investigate cooling rate profiles of rhyolitic samples initially held at 720–750°C and quenched in water, liquid nitrogen, and air. For quench of mm-size samples in liquid nitrogen and in air, the cooling rate is uniform and is controlled by heat transfer in the quench medium instead of heat conduction in the sample. The heat transfer coefficient in ‘static’ air decreases with increasing sample size. For quench of mm-size samples in water, heat transfer in water is rapid and the cooling rate is largely controlled by heat conduction in the sample. Our experimental results are roughly consistent with previous calculations for cooling in air and in water (although constant heat transfer coefficients were used in these calculations), but cooling rate in liquid nitrogen is only 1.8–2.3 times that in ‘static’ air, and slower by a factor of 2 than calculated by previous authors. Cooling rate in compressed airflow is about the same as that in liquid nitrogen. The experimental results are applied to interpret cooling rates of pyroclasts in ash beds of the most recent eruptions of the Mono Craters. Cooling rates of pyroclasts are inversely correlated with sample size and slower than those in air. The results indicate that the hydrous species concentrations of the pyroclasts were frozen in the eruption column, rather than inside ash beds or in flight in ambient air. From the cooling rates, we infer eruption column temperature in a region where and at a time when hydrous species concentrations in a pyroclast were locked in. The temperature ranges from 260 to 570°C for the most recent eruptions of Mono Craters. These are the first estimates of temperatures in volcanic eruption columns. The ability to estimate cooling rates and eruption column temperatures from eruptive products will provide constraints to dynamic models for the eruption columns.     

Comparison of liquefaction potential of loess in Lanzhou, China, and Memphis, USA

This paper presents an evaluation of the liquefaction potential of loess in Lanzhou, China, and Memphis, USA. The topography, stratigraphy, and genesis of loess in these two areas were investigated and compared. Several loess samples in each study area were taken and their physical indices were determined. In addition, the microstructures of these loess samples were investigated using an electron microscope, and dynamic triaxial tests were performed using an artificial seismic wave. The results of this investigation indicated that both Lanzhou loess and Memphis loess have a potential for liquefaction, but Memphis loess is less susceptible to liquefaction. Furthermore, Lanzhou loess and Memphis loess behave differently during ground shaking.     

Deposition and fate of reactive Fe,Mn, P,and C in suspended particulate matter in the Bay of Biscay

Hydrographic structure of the water column, dissolved nutrient concentrations and the distribution of suspended particulate matter were recorded from CDT measurements and Niskin bottles sampling on the continental slope of the Bay of Biscay and on the axis of Capbreton canyon. Ascorbate extraction was applied here for the first time on marine suspended particles to determine the content of reactive Fe- and Mn-oxides, and P associated with Fe-oxides. Hydrographic structure of the south-eastern part of the Bay of Biscay did not change during the last three decades. Particulate organic carbon (POC) contents dropped strongly with depth, showing that organic matter mineralization was efficient in the water column. Organic matter mineralized in the water column had a Redfield N:P ratio. POC percent of particles collected at depth were higher during a bloom period, suggesting that some new organic matter reached the bottom. Contents of Fe and Mn extracted with the ascorbate leaching solution showed that suspended particles originated from the Gironde estuary, one of the major sources of particles in the Bay of Biscay. Intermediate and deeper nepheloid layers occurred in the Capbreton canyon. Particles of nepheloid layers were enriched in Mn- and Fe-oxides because they originated from resuspension of surface sediment.     

Attenuation of P,S, and coda waves in Koyna region,India

The attenuation properties of the crust in the Koyna region of the Indian shield have been investigated using 164 seismograms from 37 local earthquakes that occurred in the region. The extended coda normalization method has been used to estimate the quality factors for P waves and S waves , and the single back-scattering model has been used to determine the quality factor for coda waves (Q _c). The earthquakes used in the present study have the focal depth in the range of 1–9 km, and the epicentral distance vary from 11 to 55 km. The values of and Q _c show a dependence on frequency in the Koyna region. The average frequency dependent relationships (Q = Q ₀ f ⁿ) estimated for the region are , and . The ratio is found to be greater than one for the frequency range considered here (1.5–18 Hz). This ratio, along with the frequency dependence of quality factors, indicates that scattering is an important factor contributing to the attenuation of body waves in the region. A comparison of Q _c and in the present study shows that for frequencies below 4 Hz and for the frequencies greater than 4 Hz. This may be due to the multiple scattering effect of the medium. The outcome of this study is expected to be useful for the estimation of source parameters and near-source simulation of earthquake ground motion, which in turn are required in the seismic hazard assessment of a region.     

Determination of nitrophenols,diaminotoluenes, and chloroaromatics in ammunition wastewater

Methods for the determination of three compound classes, i. e. diaminotoluenes, nitrophenols, and chloroaromatics in groundwater of a former ammunition plant are reported. Diaminotoluenes were extracted by discontinuous liquid/liquid-, nitrophenols by continuous liquid/liquid-extraction using dichloromethane, and chloroaromatics by solid-phase extraction. These compound classes may be analyzed by gas chromatography (GC) or gas chromatography coupled to mass spectrometry (GC/MS) without derivatization or after derivatization with N-methyl-bis(trifluoroacetamide) (MBTFA) or heptafluorobutyric anhydride (HFBA) in the case of diaminotoluenes and HFBA or acetic anhydride in the case of nitrophenols. An atomic emission detector (AED) coupled to a gas chromatograph may be employed for the analysis of chloroaromatics. High selectivity can be achieved using the characteristic wavelengths of chlorine. A variety of these compounds were identified and quantified in a groundwater sample from the former ammunition plant Elsnig (Saxony, Germany). Concentrations were in the lower ppb range. Thus, dichlorobenzenes which may have been used as substituents at the end of World War II could be identified in groundwater samples at this site.     

Spatial and temporal variations in source,diagenesis, and fate of organic matter in sediments of the Netravati River,India

Organic matter (OM) such as organic nitrogen plays a substantial role in the global biogeochemical cycling of bio‐reactive components—amino acids (AA) in aquatic environments. Spatial and temporal variations in source, diagenesis, and fate of organic nitrogen such as AA in sediments of small tropical rivers and the role of oxbow/meandering loops under changing climatic conditions are poorly investigated. This study assessed the spatial and seasonal variations in OM composition, source, and diagenesis of a tropical small mountainous river—Netravati River, India, for 1 year. Water samples were determined for suspended particulate matter, and surface sediments were examined for bulk parameters, surface area (SA), and the L‐ and D‐enantiomers of AA. The L‐ and D‐enantiomers of AA displayed subtle seasonal variations in composition and depicted varying degrees of diagenesis. The concentration of D‐enantiomer of AA was high and showed substantial contributions from bacteria, terrestrial source, and in situ production. The D‐arginine was the most abundant D‐enantiomer of AA in the study area, possibly due to extracellular secretion by bacterial species and adsorption onto sediments, and thus, it was protected from degradation. Degradation index was more negative at the oxbow and meandering loop stations during the dry season suggesting that local geomorphologic settings steer the diagenesis of OM within the river. A negative relationship between gamma‐aminobutyric acid and organic carbon:surface area (OC:SA) ratio and a positive correlation between tyrosine and OC:SA ratio suggested accelerated loss of OM. Furthermore, the concentrations of most bulk parameters were higher in the lower reaches during monsoon and premonsoon seasons. Taken together, changes in seasons have an operational control in distinguishing the composition, source, and diagenesis of spatial OM distribution. Moreover, oxbows and river meandering loops influence the diagenetic processes in small tropical river systems.     

Characteristics,origins, and significance of pyrites in deep-water shales

As important metal sulfides in the geochemical cycle of sulfur, the characteristics and formation processes of pyrites can provide useful clues regarding their environment. Based on previous findings, shale pyrites were divided into three major classes(euhedral pyrites, framboidal pyrites(framboids) and metasomatic pyrites) and six sub-classes in this study. At the microscopic scale, each type of pyrite is associated with a different formation process. Framboids are formed by burst nucleation in...     

Cadmium,zinc, copper,and barium in foraminifera tests

The concentrations of cadmium, zinc, copper and barium have been determined on 2-mg samples of single-species foraminifera populations. Cleaning techniques were tested using North Atlantic core tops, and followed by a detailed downcore study for the last 30,000 years in South Atlantic core V22-174. Raw foram tests cleaned by crushing followed by ultrasonic removal of fine-grained material, and dissolved in a pH 5.5 acetate buffer, contain appreciable amounts of trace elements associated with ferromanganese and alumino-silicate contaminants. A reductive/complexing cleaning treatment reduces ferromanganese contamination by 1–2 orders of magnitude. Acetate buffers at pH 5.5 complex iron and raise the solubility of ferromanganese oxides; these buffers are unsuitable for separating carbonate lattice-bound trace elements from the fraction associated with ferromanganese phases. Improved mechanical and ultrasonic reductive cleaning combined with a mild dissolution in distilled water under 1 atm.P_CO2 reduces contaminant levels another order of magnitude. The Cd and Zn concentrations (order 10^?8 mole Cd/mole Ca and 10^?5 mole Zn/mole Ca) of species with low surface area show an increase with decreasing isotopic temperatures. This increase is consistent with the increasing concentrations of these metals from low values in surface waters to higher values at depth. The variance of Cd and Zn over the last 30,000 years in the central South Atlantic is consistent with the probable variability of the dissolved trace elements at the calcification levels of the species analyzed. Cu and Ba are irreproducible and probably sensitive to residual contaminant phases. The trace element content of the tests differs from levels observed in a recent coprecipitation study. Foraminifera may be a significant vector in zinc cycling in the ocean.