1,720,972 research outputs found
Imaging Geometry And Growth Rate Of A Hydraulic Fracture Zone By Locating Induced Microearthquakes
Full text linkThe hydraulic fracturing technique has become an important tool in the enhancement
of hydrocarbons recovery, geothermal energy extraction, and solid waste disposal. The
characterization of geometry parameters and growth rate of a hydraulic fracture zone
is an important task for monitoring and assessing subsurface cracks. In this paper,
we develop a location approach to determine the precise hypocenter locations for a
cluster of seismic events induced by hydraulic fracturing. Two techniques were used
in our location scheme: waveform correlation and grid search methods. The waveform
correlation method allows us to obtain more accurate differential arrival times among
events within in a cluster.. The grid search method is suitable when dealing with a
nonlinear location problem.
We applied our method to seismic waveform data from a hydraulic fracturing experiment
at the Los Alamos Hot Dry Rock geothermal site and determined hypocenter
locations for 157 induced microearthquakes. The maximum absolute and relative location
errors were estimated to be 30-39 meters and 3-9 meters, respectively. Among the
157 events, 147 microearthquakes occurred in a tight cluster of a dimension of 40 meters,
roughly defining a vertical hydraulic fracture zone. The length, height, and width
of the hydraulic fracture zone were measured to be 40, 35 and 5 meters, respectively.
The orientation of the fracture zone is estimated at about N400W. Analysis of the
temporal-spatial pattern of the induced microseismicity revealed that the fracture zone
grows significantly in a two-hour period during the hydraulic injection. Using seismicity
distribution in time and space in this period, we determined that the fracture zone
grows toward the northwest along the fracture zone strike with a growth rate of 0.1-0.2
meters per minute.Massachusetts Institute of Technology. Borehole Acoustics and Logging ConsortiumUnited States. Dept. of Energy (Grant DE-FG02-86ER13636
Source Characterization Of Microearthquakes Induced By Hydraulic Fracturing With Empirical Green's Function
Full text linkIn this paper, we retrieved relative source time functions (RSTF) and estimated the
source parameters for microearthquakes (M= -1.9 to -2.6) induced by hydraulic injection
at Fenton Hill, New Mexico, using an empirical Green's function (EGF) method.
Seismic waveform of a small event in seismic doublets or multiplets (Gelle and Meuller,
1980), defined as co-located events with similar focal mechanisms, within a hydraulic
fracture zone, is treated as the EGF and is deconvolved from that of a larger event in the doublets or multiplets to retrieve the relative source time function. Time domain analysis of the RSTFs reveals the source complexity of the induced microearthquakes. The
azimuthal variation of the RSTF indicates that the rupture propagates to the northwest,
which is consistent with the growth direction of the hydraulic fracture zone determined
by Li and Cheng (1995) with a seismicity temporal-spatial distribution pattern. The
source duration of the induced events ranges from 2 to 8 ms and the source radii are
estimated to be 4 to 12 meters. Values of stress drops are from 1 to 19 bars. Significant
variation of the stress drops may reflect the heterogeneity of the stress field in the
hydraulic fracture zone and its vicinity and indicate that the stress field heterogeneity
extends down to a few meters.Massachusetts Institute of Technology. Borehole Acoustics and Logging ConsortiumUnited States. Dept. of Energy (Contract DE-FG02-86ER13636
Imaging Hydraulic Fractures: Source Location Uncertainty Analysis At The UPRC Carthage Test Site
Full text linkHydraulic fracturing is a useful tool for enhancing gas and oil production. High-resolution seismic imaging of the fracture geometry and fracture growth process is the key in determining optimal spacing and location of wells and in improving reservoir performance for increased production rate. In this paper, we address how accurately the
sources along a fracture zone at different depths can be determined for given velocity
models, geophone array geometry configurations, and location of monitor wells. We apply
a theory of uncertainty analysis to estimate microearthquake location uncertainties
in both relative and absolute senses. To estimate the location uncertainties, we used
the velocity models, two geophone arrays in two monitor wells, and the location of the
fracture well, and an assumed fracture orientation of an upcoming hydraulic fracturing
experiment by Union Pacific Resources Company (UPRC) and its partners at Carthage Field, Panola, Texas.
We calculated the 95% confidence regions, in both absolute and relative senses, for
five hypothetical sources along an assumed strike of a target fracture zone at three
different depths. The semimajor and semiminor axes of the relative error ellipses for
these epicenters are typically estimated to be 12 and 5 ft, respectively, and the relative depth uncertainty is derived at about 6 ft. The absolute location uncertainties are at least 3 to 10 times larger than the relative location uncertainties. The high-precision relative source locations result in a relative measurement error about 4-15% in measuring the fracture length. The location ambiguity from two-station locations is discussed and arrival azimuthals is proposed to to be used for removing such location ambiguity. The location uncertainty analysis is expected to be generalized as a practical tool in optimal designing of a two-well seismic monitoring system for high-resolution imaging of hydraulic fractures.Massachusetts Institute of Technology. Earth Resources Laboratory. Reservoir Delineation
ConsortiumUnited States. Dept. of Energy (Contract DE-FG02-86ERI3636
Location Of Microearthquakes Induced By Hydraulic Fracturing
Full text linkThis paper examines the problem of locating microearthquakes induced by hydraulic
fracturing using seismic arrival time data. In addition to the use of absolute arrival
times measured for individual events, we consider the use of differential arrival times
amongst a set of two or more seismic events as a means of constraining their locations
relative to one another. Differential arrival times can be measured very accurately
using cross-correlation techniques and are less sensitive than absolute arrival times to
subsurface velocity structure. We have developed an algorithm which combines relative
event location techniques with conventional absolute location techniques and applied
it to a set of 19 microearthquakes recorded during a hydraulic fracturing experiment
conducted as part of the Los Alamos Hot Dry Rock project. We find that the events,
except for a few outliers, delineate a planar zone 30 meters in dimension, presumably a
fracture plane. This example shows that the use of differential arrival times improves the accuracy of locating microearthquake clusters and that the relative locations of events within the cluster are better determined than their absolute locations. The results also suggest the need for directional data from three-component stations or better station geometry to further improve location accuracy
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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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