1,720,966 research outputs found
Geophysical Well-Log Analysis In Characterizing The Hydrology Of Crystalline Rocks Of The Canadian Shield
Get PDFA full suite of geophysical logs, including nuclear, electric, acoustic transit-time, acoustic waveform, and acoustic televiewer logs, and high-resolution flowmeter measurements have been used to investigate the lithologic and hydrologic properties of three igneous plutons located on the southern margin of the Canadian shield. Geophysical
logs were used to identify lithologic boundaries, determine the properties of unfractured
granitic or gabbroic rocks, interpret and calibrate the results of surface geophysical
surveys, and characterize permeable fracture zones that could serve as conduits
for fluid migration. Nuclear and acoustic transit-time logs provided good quantitative
correlation with changes in lithology. Electric logs yielded consistent qualitative
correlations, with lower resistivities associated with more mafic lithologies. Lithologic
contacts indentified on logs generally confirmed the results of surface electromagnetic,
seismic, and gravity surveys. All major fracture zones intersected by boreholes were
clearly indicated by the geophysical logs. Electric, epithermal-neutron, and acoustic
transit-time logs gave the most consistent indications of fracturing, but the lithologic
responses associated with some thin mafic intrusions were difficult to distinguish from
possible fractures, and some steeply-dipping fractures were not indicated by conventional
acoustic transit-time logs. Electric and neutron log response is attributed to
the effect of clay minearl alteration products in the vicinity of fractures. This alteration may be indirectly related to permebaility, but no direct relationship between
resistivity or neutron attenuation and permeability appears to exist. Tube-wave attenuation determined from acoustic waveform logs was related to the transmissivity
of equivalent infinite, plane fractures; these results agree qualitatively, and possibly
quantitatively with packer isolation and injection tests if the combined effects of differing scales of investigation and borehole enlargements in fracture zones are taken into account. Tube-wave attenuation in waveform logs also compares well with the permeability distributions determined from tube-wave generation in vertical seismic profiles. Comparison of conventional geophysical logs, acoustic televiewer images of the borehole wall, and fracture frequency distributions measured on core samples indicates
that many fractures are completely sealed and have no effect on log response, whereas
many more apparently sealed fractures have been slightly opened during drilling, and
do provide some log response. High resolution flowmeter meaurements of natural flow
in boreholes and comparison of packer isolation tests with log data indicate that a
relatively few individual fractures often provide a large proportion of fracture zone
transmissivity in the immediate vicinity of the borehole, and that the orientation of
these fractures may not coincide with fracture zone orientation. These results indicate
that the scale problem in relating borehole logs to regional configuration of fracture
flow systems may be the most important consideration in the appplication of geophysical
well logging to the characterization of ground water flow in crystalline rock
bodies
Modeling Borehole Stoneley Wave Propagation Across Permeable In-Situ Fractures
Get PDFThe characterization of hydraulic transmissivity of permeable fracture reservoirs is a
very important task in the exploration of water resources and hydrocarbons. Previous
studies that model the permeable structure as a single fluid-filled fracture failed to
explain the observed significant Stoneley wave attenuation across the permeable structure.
In this paper, the structure is modeled as a permeable fracture zone and synthetic
Stoneley wave seismograms in the vicinity of the structure are calculated. The results
show that Stoneley waves can be strongly attenuated or even eliminated without significant
reflection, because of the dissipation of wave energy into the permeable zone.
Several field cases are also modeled and the theoretical results are compared with the
field data. It is shown that low- and medium-frequency Stoneley waves (1 kHz data from
Moodus, Conneticut, and 5 kHz data from Monitoba, Canada) are very sensitive to the
permeability of the fractures and can be used to assess permeability from in-situ logging
data, if the fracture porosity and zone thickness can be measured. At high frequencies,
however, Stoneley waves are not very sensitive to permeability but are mainly affected
by the sum of the fracture openings expressed as the product of fracture zone thickness
and porosity in the fracture zone. This finding is demonstrated by a logging data set
(Monitoba, Canada) obtained using high-frequency Stoneley waves at 34 kHz.United States. Dept. of Energy (Grant DE-FG0286ER13636)Massachusetts Institute of Technology. Full Waveform Acoustic Logging Consortiu
Laboratory Studies Of The Acoustic Properties Of Samples From The Salton Sea Scientific Drilling Project And Their Relation To Microstructure And Field Measurements
Get PDFCompressional and shear wave velocities were measured at confining pressures up to
200 MPa for twelve core samples from the depth interval of 600 to 2600 m in the California State 2-14 borehole. Samples were selected to represent the various lithologies, including clean, heavily cemented sandstones, altered, impermeable claystones, and several intermediate siltstones. Velocities measured at ultrasonic frequencies in the laboratory correspond closely with velocities determined from acoustic waveform logs and vertical seismic profiles. The samples exhibit P-wave velocities around 3.5 km/sec at depths above 1250 m, but increase to nearly 5.0 km/sec at 1300 m in depth. Further increases with depth result in compressional wave velocity increasing to nearly 6.0 km/sec. These increases in velocities are related to systematic variations in lithology, microstructure and hydrothermal alteration of originally clay-rich sediments. Scanning electron microscope observations of core samples confirm that local core velocities are determined by the combined effects of pore size distributions, and the proportion of clays and alteration minerals such as epidote present in the form of pore fillings and veins.United States. Dept. of the Interior. Geological Survey (Grant 14-08-001A-0328)Elf-Aquitaine (Postdoctoral Fellowship
Fracture Characterization From Attenuation And Generation Of Tube Waves
No full textResults are presented from experiments carried out in conjunction with the USGS at
the Hubbard Brook Experimental Forest near Mirror Lake, New Hampshire. The study
focuses on our ability to obtain orientation and transmissivity estimates of naturally
occuring fractures. The collected dataset includes a four-offset hydrophone vertical
seismic profile, full waveform acoustic logs at 5, 15 and 35 kHz, borehole televiewer,
temperature, resistivity, and SP logs, and well-to-well pu,mp test data. While the basic
assumptions of the VSP generation model are found to be tenable, fracture aperture
estimates from VSP were generally one order of magnitude lower than corresponding
pump test or Stoneley wave attenuation results. A new model for tube wave generation
which makes use of fracture stiffnes (stress/length) is presented
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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