text:
|Publication number
|Publication type
|Application number
|Publication date
|Dec 7, 1999
|Filing date
|Jan 29, 1998
|Priority date
|Jan 29, 1998
|Fee status
|Publication number
|Gordon Sorrells, Norman R. Warpinski
|Original Assignee
|Gas Research Institute
|Export Citation
|BiBTeX, EndNote, RefMan
|Patent Citations (19), Non-Patent Citations (2), Referenced by (69), Classifications (12), Legal Events (10)
|External Links: USPTO, USPTO Assignment, Espacenet
1. Field of the Invention
The present invention generally relates to the field of oil and gas production and, more particularly, to a system and method for the in situ determination of the distribution and orientation of natural fractures in subterranean formations.
2. Discussion of the Related Art
Planar flaws such as faults, fractures, joints, etc., exist in abundance in all subterranean rock formations. With the exception of certain sets found in so-called "naturally fractured" formations, most of these flaws remain closed under the conditions imposed by the in situ stress state. However, perturbations of this state, such as those caused by fluid injection, will result in renewed movement on those flaw sets which are favorably oriented with respect to the principal axes of the perturbed stress state. Theoretical studies predict that these movements will be characterized by both a deviatoric component (relative movement parallel to the fracture face) as well as a dilatant component (relative movement perpendicular to the fracture face) depending upon the orientation of the fracture with respect to the principal axes of the local stress state as well as upon the relative magnitude of these stresses. Dilatant movement on a given fracture will enhance its fluid conductivity relative to that of the surrounding matrix. Consequently, fluid flow will proceed in directions defined by the orientation and distribution of those fracture sets which are not only activated by the injection process but are also characterized by a significant dilatational component of relative movement. Therefore, in order to maximize the efficiency of fluid injection projects such as waterfloods and to aid in the resolution of fluid leak-off problems associated with hydraulic fracturing treatments, it is important not only to determine the orientation of the fractures activated by the injection process, but also to determine their capacity for dilatant movement under the conditions imposed by the existing stress state.
At the present time, data concerning the distribution and orientation of natural fractures is typically acquired from the analysis of oriented core data. This method has the following disadvantages:
It samples only a small fraction of the reservoir.
It undersamples the density of fractures whose dips are approximately normal to the axis of the core.
It undersamples the density of fractures whose dimensions are much larger than the core dimensions.
In order to compensate for these problems, data provided by cross-well seismic surveys has occasionally been used to supplement the core data. However, cross-well seismics will only detect fractures whose dimensions are greater than a few meters and then only if there is a significant contrast in elastic properties of the rock matrix across the fracture face. Geologic studies of reservoir outcrops have also been used to address this problem. However, there may be no accessible outcrops of the reservoir rock. Even if such outcrops exist, there is no guarantee that the fracture distribution observed at the surface is representative of the distribution in the production zone. Neither of these techniques listed above will identify those fracture sets which are likely to be activated by the injection process and they provide no information concerning the dilatant properties of the observed fracture sets.
Attempts have also been made to put seismic sensors in reservoirs for relatively long periods of time, to detect the induced microseismic activity and map the spatial continuity of the sources of such activity using standard microseismic analysis techniques. While this method will identify the fractures activated by the injection process, it provides no information about the orientation and dilatant behavior of the fractures and is time consuming and costly to implement. Thus, there is a need for a method which will not only identify fracture sets activated by fluid injection, but also discriminate between deviatoric and dilatant fracture trends in a timely and cost effective manner.
It is well known that the amplitudes of seismic waves are functionally dependent, not only upon the strength of the source, and the length of the ray-path between source and observation point, but also upon the orientation of the source fracture, the orientation of its slip direction, and the orientation of the ray path at its point of origin. Thus, augmentation of standard microseismic data processing procedures to include the processing and analysis of the P and S wave amplitude data will provide estimates of the orientation of the source fractures and their slip directions. While the combined output of both the standard microseismic analysis and fracture orientation processing procedures will discriminate between deviatoric and dilatant fracture trends activated by the injection process.
Standard microseismic analysis techniques locate the sources of the microseismic activity induced by fluid injection. There are two basic methods for the accomplishment of this task. If several sensors at widely distributed locations are available, then generalized triangulation techniques should be used to determine microseismic source locations. Generalized triangulation, requires the measurement of the initial arrival times of the elastic waves generated by the source at the distributed observation points, as well as an independently acquired model of the seismic wave velocity distributions between the source and the observations points. Generalized triangulation can provide highly accurate source locations under ideal circumstances. However, for most typical oil and gas applications, such as hydraulic fracturing, ideal circumstances are rarely attainable. The essential problem is that the strengths of the induced microseismic sources are relatively weak and their associated elastic waves are not usually detectable at ranges in excess of 1000-2000 feet. Since most oil and gas production is derived from formations at depths greater than 1000-2000 feet, it is generally not feasible to attempt to detect induced microseismic activity with sensors deployed on the earth's surface. Thus, microseismic sensor systems deployed to monitor oil and gas well stimulation or production processes must typically be placed in nearby offset wells or in the injection well itself. When only one observation well is available, distribution of the sensors is restricted and the generalized triangulation technique becomes ineffective.
Since the cost of furnishing more than one well for microseismic observations is usually prohibitive to the producer, a second method of microseismic source location has evolved for oil and gas well monitoring applications. This method is implemented by measuring the arrival times of the compressional waves (P waves) and shear waves (S waves) as well as the particle motion of the P wave with orthogonally oriented, three component sensors deployed at one or more points in the observation well. Then, assuming that the elastic wave velocity distributions in the rock formations are known, the distances between the sources and the observation points may be determined from the differences between the arrival times of the P and S waves; while the directions from the observation points to the sources may be inferred from the orientation of the P wave particle motion. Fairly precise source locations can be obtained through the application of this method when data are available from 4 or more observation points and the distance between source and observation points is less than 1000-2000 feet.
The system and method of the present invention was developed specifically to augment this latter standard microseismic analysis technique so that it is particularly well suited for applications to microseismic data acquired in a single observation well. The present invention measures, then determines the ratio of the amplitudes of the shear and compressional waves detected at multiple points in one or more observation wells for each source fracture. It then uses a forward modeling method which compares these ratios to theoretical values to determine the orientation of a vector normal to the source fracture plane and a vector parallel to the direction of relative movement of the two surfaces of the source fracture plane. The dilatant behavior of the source fracture, if any, is then determined by comparison of the orientation of these two vectors.
Certain objects, advantages and novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the advantages and novel features, the present invention is generally directed to a system for determining the distribution and orientation of natural fractures in the earth. In accordance with one aspect of the invention, a system comprises an injection well having a fluid reservoir beneath the earth's surface. A pressure source for pressurizing the fluid within the reservoir is also provided. In this way, pressurized fluid within the reservoir causes movement along natural fractures, which movement creates microseismic activity in the form of shear waves and compressional waves radiated from the fracture. This system further includes an observation well remotely disposed from the injection well, preferably within a distance of several thousand feet. Sensing means and evaluating means are disposed at the observation well for sensing seismic waves that emanate from the natural fracture, and for determining various wave characteristics.
In accordance with a preferred embodiment, the sensing means includes a plurality of sensors that are disposed in a vertical array in a single observation well. This represents a significant improvement over systems of the prior art, wherein sensors were disposed in multiple observation wells in order to obtain the necessary signals for computations. The preferred system further includes a data recorder and a signal processor that receive electrical signals generated by the plurality of sensors. The signal processor includes coded segments which perform various functions, including: analyzing sensed wave data to estimate coordinates of the sensed wave source, the sensed wave source being a natural fracture in the earth; determining an amplitude of a shear wave component produced by the natural fracture, determining an amplitude of a compressional wave component produced by the natural fracture; predicting a theoretical shear wave versus compressional wave amplitude ratio for point sources of arbitrary failure, and matching a determined and a predicted shear wave versus compressional wave amplitude ratio to determine a failure mechanism and an orientation of the natural fracture.
In accordance with another aspect of the invention, a method is provided for accurately determining the distribution and orientation of natural fractures in the earth by analyzing microseismic activity along said natural fractures induced by external stimuli. Preferably, the method includes the steps of: detecting the elastic waves generated by said microseismic activity and determining the source coordinates of said waves. The method further determines the amplitudes of the shear wave (S-wave) component and the compressional wave (P-wave) component of said waves and determines the ratio of said S-wave amplitude to said P-wave amplitude (S/P ratio). Then, using the source coordinates, the method predicts S/P ratios for point sources. Finally, the method matches the determined S/P ratio and the predicted S/P ratio to determine the failure mechanism and orientation of the natural fracture.
In this foregoing manner, the system and method of the present invention allows the distribution and orientation of natural fractures in the earth to be determined from microseismic data. The present invention compares the ratio of the amplitude of the shear waves and compressional waves detected during microseismic activity (the S/P ratio) with S/P ratios for theoretical failure mechanisms and orientations that are predicted based on the coordinates of the source of such microseismic activity. The actual and predicted S/P) ratios are matched using forward modeling techniques to determine the failure mechanism and orientation of the natural fractures that generated the microseismic activity.
The accompanying drawings incorporated in and forming a part of the specification, illustrate several aspects of the present invention, and together with the description serve to explain the principles of the invention. In the drawings:
FIG. 1 is a schematic representation of a system and method for determining the distribution and orientation of natural fractures in subterranean structures in accordance with the present invention;
FIG. 2 is a simplified flow chart of the functions of the signal processor depicted in FIG. 1;
FIG. 3 is a graph that illustrates the angles specifying the direction of a vector in the ENZ Cartesian Coordinate System;
FIG. 4 is a flow diagram of the inversion code developed to derive estimates of the orientation of the normal to the fracture plane and orientation of the movement of one fracture surface relative to the other;
FIGS. 5A and 5B are graphs illustrating simulated measured and predicted amplitude ratio profiles when a vertical array of observation points were separated by approximately 50 feet;
FIG. 6 is a graph illustrating the spatial configurations of a hypothetical microseismic source distribution and monitoring system;
FIG. 7 is a cross-sectional view of a dilatant fracture in an extensional stress regime;
FIG. 8A is a Rose Diagram of the distribution of a sample population of fracture normal bearings returned by the inversion code for a given test;
FIG. 8B is a Rose Diagram illustrating the distribution of the sample population of the fracture normal dip, for the same test as FIG. 8A;
FIG. 8C is a histogram of the distribution of the sample population of a Dilantancy Ratio Residuals calculated for the test of FIGS. 8A and 8B;
FIG. 8D is a data table;
FIG. 9 displays hypothetical P, Sv, and Sh spectra;
FIG. 10 is a flow diagram for an amplitude ratio estimation code;
FIG. 11 is a graph showing the estimated locations of actual microseismic events with respect to the actual observation and injection well used in a test to validate one embodiment of the invention;
FIGS. 12A and 12B illustrate the application of a code to determine the S/P amplitude ratios;
FIGS. 13A and 13B compare measured and predicted S/P amplitude ratio profiles for one event station pair in the first test;
FIG. 14 is a Rose Diagram of the calculated dip angles of the normal to the planes formed by the calculated fracture normal vector and the calculated slip vectors for the first test data;
FIG. 15 is a Rose Diagram illustrating the calculated fracture azimuths for a subset of events in the test data set;
FIG. 16A is a Rose Diagram of the distribution of dip angles for a subset of events in the test data set.
FIG. 16B illustrates the Dilatancy Ratio distribution for a subset of events in the test data set.
Having summarized various aspects of the present invention, reference will now be made in detail to the description of the invention as illustrated in the drawings. While the invention will be described in connection with these drawings, there is no intent to limit it to the embodiment or embodiments disclosed therein. On the contrary, the intent is to cover all alternatives, modifications and equivalents included within the spirit and scope of the invention as defined by the appended claims.
With reference now to the drawings, FIG. 1 illustrates a schematic diagram of a first embodiment of a system and method for determining the distribution and orientation of natural fractures in accordance with the present invention. A source 11 containing pressurized fluid is connected to the bore hole of an injection well 12. As illustrated, the injection well extends below the earth's surface, where the earth's surface is denoted by reference numeral 13. Beneath the earth's surface 13, the bore hole extends into a fluid reservoir, the surface of which is denoted as 14. In a manner that is known, fluid within the reservoir may be pressurized by the source 11 to expand and apply pressure to the surrounding earthen walls. This applied pressure causes movement along natural fractures which movement results in seismic activity.
More specifically as the movement occurs along the fractures seismic waves radiate outwardly therefrom. As is known in the prior art, these waves may be detected by sensors disposed in multiple observations wells and used by employing triangulation or other computation techniques to detect the origin and other information about the natural fracture.
In accordance with the preferred embodiment of the present invention, a single observation well 21 is used to obtain the same information. Advantageously, this eliminates the need for having multiple observation wells, and therefore lowers the overall system implementation cost. Preferably the observation well 21 is located within approximately several thousand feet of the injection well.
Rather than disposing multiple sensors in multiple observation wells, the preferred embodiment disposes multiple sensors 22 in a single observation well. Specifically, the preferred embodiment disposes a plurality of sensors 22 in a vertical array within the observation well 21. In operation, pressurized fluid 15 from the fluid source 11 is pumped into the bore hole of the injection well 12. As the pressurized fluid enters the fluid reservoir 14, the fluid causes movements along the surfaces of the natural fractures (not shown) in the surrounding formations. Such movements along the fracture surfaces generate elastic waves that travel outwardly from their source 17 in a spherical wavefront 18. These waves are detected by a multi-level monitoring system 22 located in the bore hole of the observation well 21. The monitoring system is connected by wiring or by telemetry 23 to a data recording device 24 and a signal processor 25. The signal processor functions are denoted as 20.
FIG. 2 is a simplified flow chart of the functions 20 of the signal processor 25. In step 101, the signal processor analyzes the input wave data to estimate coordinates of the wave source 17. Next, in step 102, the signal processor 25 measures the total amplitudes of the far-field, point source component of the detected compressional and associated shear waves. Using these wave amplitudes, in step 103, the signal processor 25 determines the ratio of the shear wave amplitude to the compressional wave amplitude (S/P ratio) using known methods.
Next, in step 104, the signal processor 25 uses the source location coordinates to predict S/P ratios for theoretical failure mechanisms and orientations. Next, in step 105, the signal processor 25 compares the S/P ratio of the detected waves to the theoretical S/P ratios. Then, in step 106, the signal processor 25 uses forward modeling techniques to match the experimental and predicted S/P amplitude ratios to determine the failure mechanism and the orientation of the natural fracture which generated the waves. Finally, in step 107, the signal processor 25 stores the source location, orientation, and failure mechanism data for any future analysis and interpretation that may be desired.
To provide a better understanding of the present invention, the following will present some mathematical models and simulations for a system constructed in accordance with the present invention,
Letting α and β represent the P wave and S wave speeds in a homogeneous, isotropic, elastic solid, suppose that relative movement occurs across a fracture plane surface of area, δA, which is presumed to be small compared to the wavelengths of the seismic waves of interest and which is located with respect to an arbitrarily selected observation point by the vector, v. Let n be the unit vector normal to the surface and let the vector, s, specify the magnitude and direction of the relative movement of the two fracture faces which is presumed to be constant over the surface area, δA. Let F(ω) be the spectrum of the time history of the relative movement of the two fracture surfaces, where ω is the angular frequency. Now assume that ##EQU1## Given this assumption, it can be shown that if UFP (ω,r) and UFS (ω,r) are respectively, the far field displacement spectra of the P and S waves generated by the relative movement, s, then ##EQU2## where ##EQU3## and the symbol, ∘, denotes the scalar(inner) product of two vectors. It can be seen by inspection of equation 2 that the particle motion of the P wave is parallel to the unit vector, r. Whereas: ##EQU4## which demonstrates that the particle motion of the S wave is perpendicular to r. Now let p be a unit vector which is perpendicular to r and which lies in a vertical plane. Similarly let q be a unit vector which is perpendicular to r, but which lies in a horizontal plane. The components of UFS (ω,r) which are parallel to p and q are ##EQU5## and are commonly referred to as the Sv, and the Sh components of the far field S wave spectrum. The corresponding P, Sv, Sh and total S displacement amplitude spectra provide the theoretical basis for the study whose results are reported in this document. These spectra are given by: ##EQU6## Let RSv, and RSh, RS be the ratios of the Sv, Sh amplitude spectra and total S amplitude spectra to the P amplitude spectra. Then ##EQU7## Notice that if the source location is presumed known then the parameters k,r,p, and q may also be presumed to be known . Therefore, the unknown vectors in equations 13, 14. and 15, may be obtained by inversion of experimental measurements of RSv, RSh and RS. However, it is important to note that n and s may be interchanged in equations 13 and 14 without affecting the values of RSv, RSh and RS. This is an ambiguity which is inherent to all seismic source mechanism inversion methods. Thus, the components of n and s cannot be uniquely determined from the measured data without the imposition of additional constraints. A simple constraint which allows the unique determination of the orientation of the horizontal component of n and s is identified and discussed below.
Choose a coordinate system such that the positive Z axis is directed vertically upward and the positive E and N axes are directed in the geographic east and north directions, respectively. As shown in FIG. 3 the direction of the unit vector, r, is specified in the ENZ coordinate system by the angle, θr and φr. Therefore:
r=sinθr cosφrεE +sinθr sinφr εN +cosθr εZ(17)
where the set {εE,εN,εZ } are the base vectors of the coordinate system. Similarly;
n=sinθn cosφn εE +sinθn sinφn εN +cosθn εZ(18)
s=sinθs cosφs εE +sinθs sinφs εN +cosθs εZ(19)
A principal objective of the invention is to develop a method for the estimation of n and s for a microseismic event, given its source coordinates and measurements of RSv, RSh and RS at J observation points whose coordinates are also known. Since the amplitude ratios are non-linear and oscillatory functions of n and s, the familiar linear or linearized inversion schemes are not applicable to this particular problem. Therefore, a simple non-linear strategy was adopted to address the inversion problem. The essential elements of this strategy are:
Calculate predicted values of RSv, RSh and RS for each observation point and for a large number of realizable combinations of n and s. Then:
Find the combination of n and s which minimizes the differences between the observed and predicted values of RSv, RSh and RS at all observation points.
A computer code has been written to apply this strategy, and a flow diagram identifying the functional modules of the computer code is shown in FIG. 4. The components contained within each module are briefly described in the following paragraphs.
It can be seen from FIG. 4 that a Data Entry module 110 contains three components 112, 114, 116. The coordinates of the source (E0, N0, Z0) are entered as a 3 element row vector and the coordinates of the J observation points(Ej, Nj, Zj) are entered as a JX3 matrix in one of the components. A second component is used for the entry of the values of amplitude ratios measured at the observation points and expressed in db. The final component in this module is used for the specification of the seismic velocity ratio,k, which characterizes the source region. This component is also used for the entry of the desired ranges of the variables θn, φn, θs, and φs, and the sample intervals that are to be used for the calculation of trial values for n and s.
A Prediction module 120 also contains three components 122, 124, 126. One component of this module is used for the calculation of the rj, pj and qj. Since the version of the code used for this invention assumes a constant velocity propagation model; ##EQU8## pj is derived from rj using the relationships
pj ∘rj =0 (22)
and ##EQU9## where yp Nj and yp Ej are the N and E direction cosines of pj. Then qj is computed from pj and rj using the relationship;
qj =rj �pj (24)
where the symbol, �, denotes a vector (cross) product A second component within this module uses information from the data entry module to calculate the data vectors θ and φs. The elements of these vectors are then used in equations 18 and 19 to calculate M2 values for both for n and s; where M is the product of the lengths of the θ and φ data vectors.
The third component of this module uses the previously created values of rj, pj and qj as well as the M2 values for both n and s in equations 13, 14, and 15 to generate 3 M2 XJ matrices containing the predicted values of RSv, RSh, and RS expressed in db for all observation points.
A Minimization module 130 contains three components 132, 134, 136. One component retrieves the J measurements of RSv, RSh and RN stored in the Data Entry module 110. It also retrieves the predicted values of these variables from the Prediction module 120. These data values are then used to calculate the elements of the 3XM2 Residual Matrix. Each column in this matrix is referred to as a Residual Vector. The elements of the mth Residual Vector (m=1���M2), are the median values of the absolute value of the differences between the observed and predicted values of RSv, RSh and RS for the mth model. A second module is used to calculate the length (magnitude) of the M2 Residual Vectors. An algorithm is then applied to find the column index of the minimum length Residual Vector. The third component of this module uses this index to find the model values of n and s associated with the minimum length Residual Vector. As shown by the loop in FIG. 4, the user may iterate the prediction and minimization processes at his discretion. This option is used when computer memory is inadequate to calculate and temporarily store the desired number of model values RSv, RSh and RS in one pass.
A Storage and Display module 140 contains two components 142, 144. One component 142 is used to save the results of the inversion processing in a file named mecs.mat. The other component 144 creates 2 graphics files which are used for the visual comparison of observed values of RSv, RSh and RS with those calculated for the model values of n and s associated with the minimum length Residual Vector. An example of the graphical output of the code is shown in FIG. 5 for a hypothetical dip slip source test case. The true values of θIP φIP θP and φs for the dip slip test case are compared with those found by the inversion code in Table 1.
In order to simulate conditions likely to be encountered during the microseismic monitoring of a fluid injection project, the observation points may be deployed in a single 9 element vertical array with a station separation of approximately 50 feet. Thus the aperture of the array is approximately 400 feet. The dip slip source was placed north north-east of the source at a depth near the depth of the midpoint of the array and at a range of approximately 379 feet. The results shown in FIGS. 5A and 5B and Table 1 indicate that the inversion code has the capability to yield accurate results under simulated ideal field conditions. Its behavior under more realistic constraints is examined in the following section.
TABLE 1______________________________________Comparison of the true bearing and dip angles of n and s with thoseestimated by the inversion code for the dip slip test case. θn φn θs φs______________________________________True 70� 55� 72� 139�Estimated 67� 56� 75� 140�Error 3� -1� -3� -1�______________________________________
Description of Test Procedures.
Numerical studies have been undertaken to evaluate the theoretical performance of the inversion code when applied to S/P amplitude ratio data acquired under simulated field conditions. The basic field problem addressed by these studies is the observation of microseismic activity stimulated by a hydraulic fracturing treatment. The observations are presumed to be made with a commercially available microseismic monitoring system which is deployed in a nearby well. The spatial configurations of the hypothetical microseismic source distribution and the monitoring system are shown in FIG. 6.
The monitoring system includes five elements which are deployed in a vertical well. The center element of this array is chosen to be the origin of the ENZ coordinate system used for these studies. The interval between the individual elements of the array is approximately 100 feet. Thus, the aperture of the array is approximately 401) feet. The hypothetical treatment well is located north of the monitor well. For the majority of the tests undertaken during these studies, the distance between the simulated treatment and monitor wells was taken to be equal to the aperture of the observation point array (400 feet.). However, for 3 tests, simulations were performed for distances of 200,800, and 1600 feet. These particular tests were undertaken to determine if plausible variations in this parameter would have a significant impact upon the estimation of the components of the fracture normal and slip vectors using the inversion code.
The base microseismic source distribution is simulated by a 7�7 vertically oriented array which strikes N70�W. The interval between elements of the array is approximately 50 feet and the coordinates of the center element are (0,L,0), where L is the distance between the hypothetical treatment and monitor wells. It is important to note that the vertical dimension of the observation point array overlaps the vertical dimension of the source array by approximately 50 feet in both the positive and negative Z directions.
With the exception of two tests, the microseismic sources used in the simulation studies were presumed to occur in an extensional stress regime. The maximum principal stress in this regime is vertically oriented and n and s are constrained to lie in the same vertical plane. Consequently, a failure at any given point in this regime can be fully described by the determination of three angles, the bearing, φIP and dip, θIP of the fracture normal,n, and the angle,ζ, between n and s. As shown in FIG. 7. ##EQU10## where sd is referred to as the dilatant component of s and D is defined to be the dilatancy ratio (i.e., the ratio of the length of the dilatant component of the slip to the total length of the slip). For the purposes of the simulation studies, the output of the inversion code was reconfigured to yield estimates of (φn,θIP and D.
To simulate a set of extensional fractures activated by fluid injection, the bearing and dip angles of the fracture normal were held constant for each point in the source array for a given test. The dilatancy ratio was then systematically varied at each point in the source array to simulate failure conditions ranging from pure shear (D=0) to pure tension (D=1). Theoretical values of RSv, RSh and RS were calculated for each failure condition, each source point and each observation point. The velocity ratio,k, was held constant at a value of 1.68 for all of these calculations. Random noise was added to each calculated amplitude ratio to simulate measurement errors. The simulated measurement errors were drawn from a uniformly distributed population whose maximum and minimum values were +3 db and -3db. respectively. The results of these calculations for a single test are three 5�294 matrices which simulate the experimentally derived values of RSv, RSh and RS for the 294 microseismic events in the activated fracture zone set and as seen at the 5 observation points in the monitoring array 22 (See FIG. 1). These data were reorganized into two hundred ninety four 3�5 matrices of amplitude ratios which were serially input to the Data Entry Module 110 of the inversion code.
Noise was also added to the azimuth, the range and elevation of each of the source points and for each failure conditions in order to simulate errors associated with the estimation of microseismic source coordinates. In this case, however, the magnitudes of the noise components were held constant, while their signs were randomly assigned for each source point and failure condition. For a plurality of numerical studies undertaken, the magnitudes of the azimuth, range, and elevation errors were assumed to be 2.5�, 15 feet, and 15 feet, respectively. These values characterize what would be termed "good" microseismic source locations. The perturbed coordinates were then calculated for each source point and each failure condition and were used as the estimated source coordinates by the inversion code. The coordinates of the observation points and the value of k were assumed to be known and were entered without added errors into the inversion code.
After some preliminary experiments, the inversion code was set to run for two iterations. The settings of the θIP φIP θN, and φs data vectors for each iteration are listed in Table 2. These settings were used for all tests.
TABLE 2______________________________________Test Settings for the θn, θn, θs, andφs Data vectors. Iteration #1 Iteration # 2Data Sample SampleVector Length Range Interval Range Interval______________________________________θn 12 30�:180� 12.5� (θnl) - 12.5�:(θ.sub. nl) + 2.1� 12.5�φn 15 0�:180� 12� (θnl) - 12.0�:(θ.sub. nl) + 1.6� 12.0�θs 12 30�:180� 12.5� (θsl) - 12.5�:(θ.sub. sl) + 2.1� 12.5�φs 15 0�:180� 12� (θsl) - 12.0�:(θ.sub. sl) + 1.6� 12.0�:______________________________________ note: the symbols (θn,sl),(φn,sl) indicate the values of θn,s and φn,,s estimated during the first iteration.
Discussion of Test Results
The random measurement and location errors incorporated into the simulated field data contributes a statistical variability to the estimates of θIP, φIP and D, produced by the inversion code. It should also be recalled that the simulated observations are acquired with a vertically oriented linear array 22. Therefore, the inversion process is unconstrained in the horizontal plane. This phenomenon coupled with the finite width of the sample intervals also will produce an unpredictable variability in these estimates. Therefore, the results of each test have been summarized in terms of statistical parameters characterizing the sample populations of the estimates of φn, θIP and D returned by the inversion code. Example of the distributions of these sample populations for a given test are shown in FIGS. 8A-8C.
FIG. 8A is a Rose Diagram of the distribution of the sample population of fracture normal bearings,φn, returned by the inversion code for test #8. The true value of φn for this test was 100�. The divergence of the sample population from its true value, as seen in this figure, is due primarily to absence of any data constraints in the horizontal plane. However, it is important to note that despite the dispersion of the sample population, its median value,94.4�, differs from the true value by less than 6�.
The Rose Diagram illustrating the distribution of the sample population of the fracture normal dip,θn, for test #8 is shown in FIG. 8B. The true value for θn for this test was 55�. Notice that for this variable, the sample population is tightly grouped about its true value. Its median value was found to be 57.1�, which differs from its true value by only 2.1�. These results indicate that the vertical linear array provides adequate data constraints in the vertical plane even though it contains only 5 elements.
A histogram of the distribution of the sample population of Dilatancy Ratio Residuals calculated for this test is shown in FIG. 8C. The Dilatancy Ratio Residual is defined to be the difference between the Dilatancy Ratio returned by the inversion code and its true value for a given source location and failure condition. Notice that the sample population clusters tightly about a near zero mean value. This observation implies that, in practice, extensional microfracture events with Dilatancy Ratios as low as about 0.2 can be classified as dilatant with a high degree of confidence, even with a single monitor array consisting of only 5 elements.
As documented by the data listed in the table depicted in FIG. 8D, the sample distributions generated during other tests show characteristics that are roughly similar to those associated with the test #8 sample populations. There are, some important differences which are identified and discussed in the following paragraphs.
A variety of different tests were performed during the simulation studies. The results of these tests were summarized in terms of the median,μ, and the dispersion,δ, of the θIP and φn sample populations, and in terms of the mean value of the residuals for the D sample populations. For a given sample population, δ is defined by ##EQU11## where yl is the lth sample of the population and L is the total number of samples.
Test #1 was performed under "no noise" conditions to isolate and investigate the errors that could be directly attributed to the inversion process. It can be seen from the results listed in the first row of Table 3, that apart from the dispersion of the φn population, these errors are negligible. As mentioned earlier, the dispersion of the φn population reflects the absence of data constraints in the horizontal plane. It should also be noted that the differences between the median and true values of the θIP and φn sample populations, as well as the mean value of the D population, are insignificant. This demonstrates that the bias introduced by the inversion process is inconsequential.
Tests #2 and #3 were performed to investigate the sensitivity of the inversion process to measurement errors(test #2) and to measurement plus location errors (test #3). Comparison of the results of these tests with the test #1 results indicate that the principal effects of random measurement and location errors are slight but acceptable increases in the dispersion of the θn, and φn sample populations. as well as the introduction of a small bias to their median values. On the other hand, the small differences between the mean values of the D residual populations for tests #1 and #2 indicates that measurement and location errors have little significant impact on the estimates of the Dilatancy Ratio.
Tests #4 and #5 were performed to investigate the sensitivity of the sample population statistics to changes in the fracture dip angle. The comparison of the results of these tests with the results of prior tests indicates that the only apparent effect of changing the fracture dip angle is to increase the dispersion of the θn population from about 3�-4� to about 7�-8�.
Tests #6 through #8 are part of a subset of tests that were performed to investigate the sensitivity of the sample populations to changes in the fracture normal bearing angle. The results of tests #6-#8 are examples of the maximum and minimum changes observed in the population statistics generated during the performance the subset of tests. Notice that the φn population and, to a lesser extent, the D population are significantly sensitive to changes in the fracture normal bearing angle. In the worst cases (Tests #6 and #7) it is seen that the median values of the φn population can differ as much as 18� from their true values and their dispersions can be as great as 42�. In addition, it is seen that the magnitudes of the mean value of the D population residuals may be as large as 0.05. On the other hand, it is found that for the best case (test #8) the population statistics of all the variables are comparable to those observed during the "no noise" test (Test #1).
Tests #9-#11 were performed to investigate the sensitivity of the population statistics to changes in the distance between the monitor and source arrays. Notice that as the distance is increased beyond 400 feet (Tests #9 and #10) the dispersion of the θIP and φn sample populations as well as the bias of their median values tend to increase. A small, but significant increase in the magnitude of the mean value of the D residuals is also observed to occur as the distance is increased. Conversely, the results of Test #11 indicate that with the possible exception of the dispersion of the φn population, a reduction of the distance between source and monitor arrays below 400 feet has no significant effect on the sample population statistics.
Tests #12 and #13 were performed to investigate the sensitivity of the population statistics to a change from an extensional to a compressional stress regime. In order to simulate "worst case conditions", it was assumed was that the intermediate principal stress axis was vertically oriented. In this case the fracture normal and the slip vector lie in a horizontal plane. In order to isolate the effects of a change in stress regimes, the results of Tests #11 and #12 should be compared to the Test #5 and #6 results which were performed with similar values of the fracture normal bearing angle. On the basis of these comparisons it can be seen that the primary effect of a change in the stress regime from extensional to compressional is to increase the magnitude of the mean values of the Dilatancy Ratio Residuals.
A method for the experimental measurement of S/P amplitude ratios was developed for microseismic applications as a part of this research project. The theoretical basis for the method is illustrated in FIG. 9. The curves shown in this figure are hypothetical P, Sv and Sh displacement amplitude spectra. In order to simulate conditions that could be encountered in the microseismic monitoring of fluid injection projects, the distance between the observation point and the active fracture was assumed to be 400 feet and the maximum dimension of the induced microfracture was assumed to be approximately 10 feet. Notice that the two vertical lines seen in FIG. 9 subdivide the spectra into 3 frequency bands.
In Band 1, the wavelengths of the P and S waves are comparable to or greater than the distance between the source and observation point. Consequently, the near and intermediate field components of the P and S waves are the dominant contributors to the observed spectra in this band. In Bands 2 and 3, the far field P and S components are the primary contributors to the observed spectra. However, in Band 2 their wavelengths are large compared to the maximum source dimensions; whereas in Band 3, their wavelengths are comparable to or less than the maximum source dimension.
Now, it should be recalled that the theoretical expressions for the S/P amplitude ratios were developed subject to the constraints that:
1. The wavelengths of the P and S waves must be short compared to the distance between the source and the observation point.
2. The wavelengths of the P and S waves must be large compared to the maximum dimension of the source.
It follows, then, that the experimental measurements necessary for the calculation of S/P amplitude ratios must be confined to Band 2 in order to insure agreement with the theoretical models. Band 2 is referred to as the "far field, point source" band in the following paragraphs.
An interactive computer code which allows the observer to identify and constrain amplitude measurements to this band has been written and a flow diagram identifying its functional modules is shown in FIG. 10.
A Data Entry module 410 contains 3 components 412,414,416. One component is used to enter information concerning the microseismic event whose records are to be used for the calculation of S/P amplitude ratio. This information may include:
1. the event name;
2. the coordinates of the estimated event location;
3. the coordinates of the stations which recorded the event;
4. the orientations of one of the horizontal axes of the 3-axis transducers deployed at the stations.
A second component loads the file containing the 3-axis seismograms recorded at the stations in the network. This file is loaded as a Px3J matrix where P is the number of points and J is the number of stations. A third component is used to enter the values of the parameters which will control the process. These include:
1. the sample rate;
2. the order and corner frequencies of a Butterworth bandpass filter;
3. the compressional and shear wave velocities for the medium;
4. the compressional and shear dissipation constants;
5. the lengths of the P and S data windows
6. the lengths of the P and S spectral amplitude averaging windows.
A Preprocessing module 420 contains two sequentially linked components 422, 424. The first component serially loads the 3-axis seismograms from each station. It then uses the source and station location data as well as the horizontal transducer axis orientation to numerically align the horizontal seismograms in each 3-axis set in directions radial and transverse to the direction from the source to the observation point. The second component acquires the appropriate data from the Data Entry Module 410 and computes, then applies a Butterworth bandpass filter to the rotated seismograms received from the first component.
A Spectral Estimation module 430 contains four sequentially linked components 432, 434, 436, 438. The first component receives the aligned and filtered seismograms from the Pre-Processing Module 420 for the selected station, then displays them on the monitor screen. The operator uses this display to pick the start points for the spectral estimation data windows for samples of Noise, and the P, Sh and Sv seismic phases. This is accomplished by sequentially positioning the cursor on the selected points on the seismograms, then pressing the left mouse button. After selection of the final start point process control is automatically shifted to the second component in the sequence. This component uses the 3-axis data in each of the spectral windows to calculate estimates of the relative P, Sv, Sh and Noise displacement amplitude spectra. For the purposes of these calculations, it is assumed that the frequency responses of the elements of the 3-axis transducers are identical and flat with respect to acceleration inputs. The following relationships are used to derive the spectral estimates. Let Zp (f) and Rp (f) be the power spectral density estimates derived from the vertical and radial seismograms in the P spectral window. If Up (f) is the relative P displacement amplitude spectra, then; ##EQU12## where f is the frequency.
Similarly, if USv (f) is the relative Sv displacement amplitude spectra. then; ##EQU13## were the Sv subscript indicates the use of the data in the Sv spectral window.
Now let TSh (f) be the power spectral density estimate derived from the transverse seismogram in the Sh spectral window. If USh (f) is the relative Sv displacement amplitude spectra, then ##EQU14## Finally, let Unr (f) and Unl (f) be relative Noise displacement amplitude spectra in the P-Sv plane and in the transverse direction, respectively, Then ##EQU15## After completion of the spectral estimations, P and S attenuation correction factors are calculated and applied to the relative P, Sv, and Sh displacement amplitude spectra. The attenuation correction factors, C.sub.α (f,rj) and C.sub.β (f,rj) are defined by; ##EQU16## where Q.sub.α and Q.sub.β are the compressional and shear dissipation constants, respectively.
The third component 436 in the linked series plots the estimated relative displacement amplitude spectra in two sequential screen displays. The corrected P displacement amplitude spectrum is compared to the spectrum of the noise in the P-Sv plane in the first screen. The observer uses this screen to identify "far field, point source" band at this station and to pick the start point for the P spectral amplitude averaging window. He does this by positioning the cursor on the selected point within the "far field, point source" band then pressing the left mouse button. This action results in the calculation of the average P spectral amplitude in the selected window. The second screen is activated by pressing any key. The corrected Sh, Sv and S displacement spectra are compared to the spectra of the noise in the P-Sv and Sh planes in this screen. The observer uses it to pick the start point for the Sh, Sv and S spectral amplitude averaging windows within the "far field, point source" band. He does this by sequentially positioning the cursor on the selected points, then pressing the left mouse button. This action results in the calculation of the average Sh, Sv and S spectral amplitudes in the selected windows. Control is passed to the next component in the sequence by pressing any key. This component is used to calculate the Sh/P, Sv/P and S/P amplitude ratios. After completion of this task, control is returned to the Pre-Processing Module 420 and processing is initiated on the seismo, rams from the next station. These procedures are repeated until amplitude ratios have been computed for all stations in the network which recorded usable data from the event.
After completion of the processing of all station data, the results are sent to a Storage and Display module 440, where one component 442 is used to store the measured amplitude ratios in a user-designated file together with the coordinates of the observation points. Another component 444 in this module generates a final screen which displays the stored data for review by the user.
Monitor Well Observations
A microseismic data set acquired during the execution of an injection experiment was used to test the application of the previously described methods to real data. After a review of the seismograms of 89 events comprising this data set, the records of 53 events were selected for the test. The events in the sample population satisfy the following criteria:
1. The P and S signal to noise ratios were greater than 6 db at 4 or more stations in the monitoring array.
2. The aperture formed by the "good" signal to noise ratio stations was equal to or greater than 300 feet.
The estimated locations of the events in this subset with reference to an ENZ coordinate system fixed in the monitor well arc shown in FIG. 11 as asterisks. The circles seen in this figure represent the locations of the 15 transducers in the monitor array that were used for this experiment. The position of the treatment well is shown by the vertical line.
FIGS. 12A and 12B illustrate the application of the code described above to determine the S/P amplitude ratios for a specific microseismic event in the sample population. The asterisks seen in FIG. 12A define the estimated relative displacement amplitude spectrum of the P phase detected at station 7 for event ai in the sample subset. The solid curve seen in this figure describes the estimated background noise spectrum in the P-Sv plane. The length of the solid horizontal line defines the approximate width of the "far field, point source" frequency band for this particular event-station pair. Its level identifies the mean relative P spectral amplitude in this frequency band. Similar estimates for Sh (asterisks), Sv (o's) and S (x's) are shown in FIG. 12B. The curves shown as solid lines in this figure are the estimated Sh and Sv background noise spectra. The solid horizontal lines identify the mean relative Sh, Sv, and S spectral amplitudes. The amplitude ratios for the ai-7 event-station pair are determined from the measured values of the mean Sh, Sv, S, and P spectral amplitudes seen in FIGS. 12A and 12B.
The measured values of the S/P amplitude ratios for event ai (points) are compared to the "best fit" values (solid lines) in FIGS. 12A and 12B. The magnitude of the minimum length Residual Vector was found be 2.5 db for this event which represents a good fit between measured and predicted amplitude ratios. The orientation angles and Dilantancy Ratio for the pair of unit vectors which provided the "best fit" for the ai amplitude ratio data set are listed in Table 4. Notice that these vectors are identified only as V1 and V2. It will be recalled that n and s cannot be identified without ambiguity unless additional constraints are imposed upon the results of the inversion of the amplitude ratio data. Plausible constraints which should be applicable to the majority of microseismic events generated by fluid injection into oil and gas bearing formations are identified in the following paragraph.
TABLE 4______________________________________Orientation angles and the Dilatancy Ratio for the unit vectorsassociatedwith the minimum length Residual Vector for event ai.orientation angle V1 V2 Dilatancy Ratio______________________________________θ 22.9� 41.7�φ 157� 182� 0.5______________________________________
In most regions where fluid injection is used to stimulate or enhance the recovery of oil and gas, it is generally safe to assume that one of the principal stress axes is vertically oriented. If it can be further assumed that the vertical stress is not the intermediate principal stress, and that the microfracturing induced by fluid injection is essentially a two dimensional process, it follows that n and s must lie in the same vertical plane. Let f denote the unit vector normal to the plane of n and s. Then;
f=n�s=sinθf cosφf εE +sinθf sinφf εN +cos θf εZ (34)
where, as before, θaf is measured clockwise with respect to the positive Z axis and φf is measured counterclockwise with respect to the positive E axis. Therefore, if the foregoing assumptions are valid
θf ≅90� (35)
φf ≅φn �90� (36)
The applicability of these assumptions to the microseismic events acquired during the 7 B stimulation experiment was tested by calculating θf for the pairs of unit vectors (V1,V2) returned by the inversion code for the sample population.
As shown in FIG. 14, the angular distribution of θf is characterized by a sample mean of 89.5� and a standard deviation of 26.7�. These results imply that while the assumption of verticality is applicable to the majority of events in the sample population, small scale heterogeneity in local stress state may cause the plane defined by n and s to be rotated as much as 45� for some events. It can also be seen from equation 36 that for those events whose n-s planes are nearly vertically oriented, φf is approximately equal to the strike of the microfracture plane referenced to the positive E axis. The distribution of φf for those events whose values of θf satisfy the constraint that:
|θf -90�|≦standard deviation(θf) (37)
is shown by the Rose Diagram seen in FIG. 15. The dashed line shown in this figure is the nominal azimuth of the hydraulic fracture created by the stimulation referenced to the positive E axis. The histogram of the distribution which is shown in red identifies a set of 34 microfracturcs whose strike angles are approximately given by:
φf =88.9��32.3� (38)
referenced to the positive E axis or
φf =-71.1��32.2� (39)
when referenced to the nominal direction of the hydraulic fracture created by the stimulation experiment.
The distribution of the microfracture dip angles for the subset of microseismic events with near vertical n-s planes is shown in the Rose Diagram seen in FIG. 16A. Notice that the distribution is bimodal with a primary peak near 30� and a secondary peak near 60�. These are dip angles which are often associated with shear fracturing. However, as shown by the histogram of the Dilatancy Ratio distribution seen in FIG. 16B, the majority of the events in this subset are not the result of pure shear failures. In fact, most are also characterized by statisitically significant dilatant components of relative movement.
The foregoing description has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obvious modifications or variations are possible in light of the above teachings. As an example, the microseismic data may be obtained by sensors located on the surface of the earth or in the injection well itself.
The embodiment or embodiments discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they arc fairly and legally entitled.
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|U.S. Classification
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|International Classification
|Cooperative Classification
|European Classification
|May 15, 1998
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Comment Minority Report (Score 1) 81
If facebook makes storing bio metric data and also sharing that data with its partners part of the terms of use then people would potentially be allowing the use of that bio metric data to be tracked and advertised to. Legally it is obvious that governments will want to have a legal handle on this sort of behavior before it is widely exploited. If this kind of marketing behavior is found to be legally acceptable then a whole new market would be opened. Who holds the patent rights to this business process I wonder?

subset: commoncrawl


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Riverside hosts Pokemon MSO show, complete with Pokemon Go, on Sept. 30
For those of you out there hunting around the city for Pokémon, the Riverside Theater just announced your next big event. On Friday, Sept. 30, the Riverside will host Pokémon: Symphonic Evolutions, a live video game concert event - with an exclusive Pokémon Go meet-up.
Milwaukee Public Museum hosts first ever adult sleepover on Sept. 23
On Friday, Sept. 23, the Milwaukee Public Museum will host its first ever adult sleepover. Exclusively for adults 21 and older, the sleepover will feature tours, curator chats, Dome Theater films and exhibit-based programming.
Tagged with: Milwaukee Public Museum sleepover events
Pierluissi presents 52 poppy pantings
Adrienne Pierluissi, who owns The Sugar Maple in Bay View, will display 52 paintings at Lakeshore State Park on Sunday, July 17, from 3 to 7 p.m. It is the fourth and final installation of the show.
Foundation's Nohl Fund grants $338,000 toward area arts programs
Twenty visual arts and arts education programs in the community were recently awarded $338,000 in funding from the Greater Milwaukee Foundation's Mary L. Nohl Fund.
Holton Street bridge swing park is still one of Milwaukee's hidden gems
During my last few years in Milwaukee, I've found that this city has a number of interesting nooks and crannies just waiting to be discovered. My latest adventure was to the famed, yet hidden, Holton Street bridge swing park.
Milwaukee author Ellie Cahill talks about the local flavor in her latest book
Born and raised in Milwaukee and Wauwatosa and now living in Brookfield, Liz Czukas is the definition of a lifelong Milwaukeean. So it only makes sense that her latest novel, written as Ellie Cahill, is set in Milwaukee and features many familiar sights.
Milwaukee's Jeremy Novy to paint first street art in Black Cat Alley
Jeremy Novy, a Peck School of the Arts grad and a nationally-renowned street artist behind the colorful koi fish that have been swimming around the city for years, will paint the first street art in the East Side's new Black Cat Alley.
Milwaukee Public Museum's Science on Tap talks evolution and ... the pelvis?
At the MPM's upcoming Science on Tap event on Thursday, June 16, Dr. Caroline VanSickle from the University of Wisconsin - Madison will share with us her findings on human evolution based on her studies of the human pelvis.
"Harry Potter and the Sorcerer's Stone"
in concert with the MSO
For the first time ever, experience the entire film of "Harry Potter and the Sorcerers Stone" featuring live accompaniment by the Milwaukee Symphony Orchestra. This ultimate Harry Potter fan experience comes to the Riverside Theater for three shows Dec. 16-17.
Riverwest's Jazz Gallery Center preps for Night of the Arts local showcase
On Friday, May 27, The Jazz Gallery Center in Riverwest hosts LV & LV Night of the Arts, where up-and-coming local artists will be able to perform and display their creative works.
Insomnia Cookies serves up cookies for a cause on June 7
There's never a bad reason to indulge in some free cookies, but next month, Insomnia Cookies and the United Performing Arts Fund (UPAF) will give you a particularly good one with a free cookie giveaway on Tuesday, June 7.
Tagged with: cookies UPAF Insomnia Cookies
Museum preps new public health perspective for Streets of Old Milwaukee
The Milwaukee Public Museum's Streets of Old Milwaukee changes its theme twice a year, with the next change coming on July 1 as the Streets will offer a new, public health perspective in the beloved exhibit.
Come party with us this Friday at MAM After Dark: MKE Icons
Join in the fun at MAM After Dark: MKE Icons Friday night. We'll be there, as a proud sponsor, with coloring pages, fun LocaMoji's, temporary tattoos and more!
Tagged with: mam after dark mke icons locamojis emojis milwaukee art museum klassik
Louis C.K. returns for Aug. 1 BMO Harris Bradley Center show
The "Louie" and "Horace and Pete" mastermind will perform at the BMO Harris Bradley Center on Monday, Aug. 1 at 8 p.m.
Tagged with: Louis C.K. comedy BMO Harris Bradley Center
Cirque Italia returns to Milwaukee in June
Cirque Italia - the first traveling water circus in the United States - will make a second splashdown in Milwaukee this summer, returning to the Italian Community Center the weekend of Friday, June 3 through Sunday, June 5.
Tagged with: Cirque Italia circus events arts and entertainment
Baumgartners make historic endowment gift to Milwaukee Art Museum
The Milwaukee Art Museum today announced that Donna and Donald Baumgartner will make an $8 million gift to the Museum's endowment. Their gift is dedicated to support the position of Museum Director, whose title will be named the Donna and Donald Baumgartner Director of the Milwaukee Art Museum. This is the largest gift made to the Museum's growing endowment fund in the institution's history.
Black Cat Alley mural corridor on East Side announces roster of artists
The Black Cat Alley, a major new arts destination, will be a corridor of world-class murals created by a diverse group of professional and student artists. This "outdoor gallery" will be located in an alleyway between Farwell and Prospect.
Tagged with: art East Side murals Black Cat Alley MTO public art Jim Plaisted
MPL launches Stories from the Stacks video series
Milwaukee Public Library has launched a new video series called "Stories from the Stacks," and the segments offer a mix of interesting stories about the library, including a powerful one about an author that wrote a book at the Central Library while she was homeless.
Milwaukee Art Museum launches new Family Access Membership program
The Milwaukee Art Museum announced the launch of the Family Access Membership, a $20 year-long family membership to the museum for families who qualify for specific forms of public assistance.
Tagged with: Milwaukee Art Museum MAM arts families education Family Access Membership
5 reasons you should see David Sedaris at The Riverside on Saturday
David Sedaris, award-winning humorist, essayist and radio personality, returns to Milwaukee this Saturday as part of his current book tour for "Let's Celebrate Diabetes with Owls." Here are five reasons you should go to the show.
Tagged with: David Sedaris Riverside dentists colonoscopies pet peeves laughter comedy owls book tours authors
Rock the Green hosts Earth Day Celebration
If you're looking for something to do for lunch this Friday, be sure to stop by the CityCenter building, 735 N. Water St., Downtown, for food, live music, and a sneak peak at what Milwaukee is doing to make the Earth a better place.
David Cross takes on politics at Super Tuesday Pabst performance
Comedian David Cross was not scared to voice his liberal viewpoints at The Pabst last night in appearance that was part of his "Make America Great Again" tour.
Tagged with: comedy concerts David Cross Pabst Theater politics
"Marvel Universe Live" swoops into Milwaukee
Spider-Man, Iron Man, Black Widow, Hulk and more deliver live performances this weekend in "Marvel Universe Live," described as "the most technically advanced live show ever."
Tagged with: Marvel Universe Live Spider Man iron Man superheroes
Shorewood plans "Ghost Train" public art project
The Shorewood Public Art Committee announced that it's begun planning a new public art project, an "artistic sensory experience" called "The Ghost Train."
Tagged with: Shorewood public art art Ghost Train
Pink's "Dorian Gray" receives national praise from Huffington Post
Michael Pink, the artistic director at Milwaukee Ballet has once again proven that his unique and individual style continues to gather high-level praise on a national level from the Huffington Post.
Tagged with: Milwaukee Ballet Huffington Post Michael Pink Carol Escoda Dorian Gray


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Happy holiday shopping! In honor of all the giving to come this holiday season, the PopSugar editors are sharing our present picks for the year. We've got 100 great ideas from home goods and shoes to accessories and bags, but that's not all — also check out our finds under $200!
Around The Web
Great Ideas! Im doing gift guides all week on my blog The Very Thought of You. So far ive done for the special lady and for the men here is the link: www.verythoughtofyou.com
If you're looking for eco-friendly jewelry, check out http://bynataliefrigo.com She designed our wedding rings and uses only recycled metals and conflict free gems. Her jewelry is so beautiful and unique!
Lovely gift ideas! Although I love the Hermes bracelet, I'll probably be asking for the nail polishes of star-shaped earbuds instead :(
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Posted by ESPN.com's Matt Mosley
Ralph Vacchiano of the New York Daily News is reporting that the Giants' hopes of trading for Browns wide receiver Braylon Edwards are "all but dead." A recent Yahoo! Sports report indicated that a deal was "imminent," but now it appears the Browns' asking price (reportedly first- and third-round picks) is too steep for Giants general manager Jerry Reese's liking.
Vacchiano reports that the Giants have offered second- and fifth-round picks for Edwards. I'm not quite ready to put this thing to bed, though, because things could change if the Browns take Michael Crabtree in the first round Saturday. Maybe they come down on their asking price if they feel like Crabtree can immediately be a No. 1 wide receiver. We'll keep you posted on this.
Right now, I have to break away to write a column about what the Eagles are going to do at running back in this draft. Check back here in about two hours or so.


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The application for early career scientist travel funds is now open.
We encourage early career scientists to participate in the ASC and travel funds are available. To be eligible, the applicant must meet these requirements:
Applications will be assessed on the following criteria:
Online application for travel funds will open after successful contributors have been informed. The full accepted abstract, a CV, and a brief motivation letter is required. The deadline is 19 June.
Photo: Imagebureauet.dk


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TORONTO, Canada—After competing against a wide range of companies nationwide to win the Canada's Best Managed Companies (Best Managed) award in 2011 and 2012, Toronto, ON-based commercial real estate services firm Avison Young requalified in 2013 to maintain its status as a Best Managed company.
The prestigious national award is sponsored by Deloitte, CIBC, National Post, Queen's School of Business and MacKay CEO forums. The announcement was made this week by the national sponsors and in a special report in the National Post daily newspaper.
Canada's Best Managed companies, spanning every region across the country and an array of industries, have demonstrated business excellence through a rigorous and independent process that evaluates the calibre of their management abilities and practices.
"On behalf of the board of directors of Avison Young, our employees, our clients and our partners, we are truly honoured to have been named one of Canada's Best Managed Companies for the third consecutive year," comments Avison Young chair and CEO Mark Rose. "This award recognizes our commitment to strategy and to our Principal-led collaborative culture, which creates a workforce that is aligned with and focused on superior long-term results for clients. We are proud that this is a Canadian award administered by some of Canada's most highly regarded companies. It is shared by our staff across North America, who serve our clients day-in and day-out."
Avison Young is the world's fastest-growing commercial real estate services firm. Over the past five years, the company has grown from 11 to 54 offices and from 300 to more than 1,500 real estate professionals across Canada and the U.S.
"The leadership of Avison Young is totally committed to being among the best managed businesses in the world," states Avison Young principal Arthur Mirante, based in New York. The growth strategy of this enterprise, which is the fastest-growing business in the global real estate services industry, is our culture – a culture of collaboration, trust and client service all based on a value system of honesty, integrity and investment in people."
According to John Hughes, National Leader of Canada's Best Managed Companies and Managing Partner, Growth Enterprises, Deloitte: "Over the past 21 years, Canada's Best Managed Companies program has recognized the most innovative and Best Managed Companies in Canada. We are delighted to celebrate the accomplishments of Avison Young."
Established in 1993, Canada's Best Managed Companies is a national awards program recognizing Canadian companies that have implemented world-class business practices and created value in innovative ways. Applications are reviewed by an independent judging panel that evaluates how companies address various business challenges, including new technologies, globalization, brand management, leadership, leveraging and developing core competencies, designing information systems, and hiring the right talent to facilitate growth.


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Bryan Archer: Young, Gay and Gorgeous - Scene 1
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DVD Title Bryan Archer: Young, Gay and Gorgeous
Category Hunks
Added August 03, 2014
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Duration 8m, 14s
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Brett Dimineo wants to introduce Bryan Archer to his mega wang, but hasn't had him alone and to himself long enough until now. Getting him naked and touching him all over in his bathroom, Bryan gets the idea pretty quickly and pulls Brett's meat-sledge out for a quick go with his tongue before getting him naked too so they can really play! A little rimming is in order after the sucking to get their sphincters good and wet and lubricated before they go balls deep in one another. Banging hard, the loads come fast, and get everywhere!
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Bryan Archer: Young, Gay and Gorgeous
August 03 2014
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- Scene 1 - Gay Blondes Banging and Blowing Big Balls
- Scene 2 - Gay Threesome in the Pool House
- Scene 3 - Hot Body Young Twink Bryan Gives Up His Ass To Black Dick
- Scene 4 - Bryan Archer Has Hot Dicksucking Fun With Ty Parks
- Scene 5 - Hardcore Gay Orgy With Cody Scott Bryan Archer
- Scene 6 - Gay Garage Guys Give Oral Oil Change
- Scene 7 - Three Way Gay Triangle Gets Hot And Heated
- Scene 8 - Two Young Twinks Gangbanged By Bunch Of Horny Factory Workers
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No abstract available.Full Article | PDF Article
No abstract available.Full Article | PDF Article
OSA participates in Crossref's Cited-By Linking service. Citing articles from OSA journals and other participating publishers are listed here.
Alert me when this article is cited.
The single tube potentiometer.
Characteristic curves for two tubes.
The double tube potentiometer.
Curve of impedance and inductance on lighting circuit.
Inductance plotted against impedance for 1,000 cycles.
Equations on this page are rendered with MathJax. Learn more.


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Red Day? This Must Be French
By TAMAR LEWIN
Published: February 25, 2002
Halfway through the school year, Michael Jones still carries his ninth-grade schedule around with him — one copy in the backpack, another in the binder — to keep track of where he's supposed to be when.
His school, Trevor Day of Manhattan, adopted a six-day rotating schedule this year: on "A Day," the first day of the cycle, Michael starts with a long assembly and an 80-minute English class. On B Day, he has history and geometry in the morning. On C Day, it's Spanish, biology and chemistry. D Day starts with a long English period and a short Spanish class, while E Day has a long Spanish and a short English. F Day begins with a short Spanish followed by a long chemistry lab. Then the cycle starts all over again.
"Every morning our advisers tell us what day it is," said Michael. "It's confusing, but I like it. Each day's different, and in an 80-minute English class, you can have a really good discussion, without the teacher saying, `We're out of time, we'll pick it up tomorrow.' "
Forget the high school schedules of yesteryear, the dreary progression of eight 45-minute periods, in the same sequence Monday through Friday.
In fact, forget Monday to Friday.
With many New York City private schools now operating on 6- to 10-day rotating schedules, people think more in terms of Orange Day, Week 2, Day 4 or C Day. In some schools, schedules are so complicated that no one can memorize them — and a tiny, laminated If-This-Is- Tuesday-Week-2-This-Must-Be-History chart is an absolute necessity.
Still, administrators, teachers and students alike say that the varying class lengths and rotating schedules open up a fresh new pedagogy.
"There are tremendous strengths in this schedule, which spreads the old five days over six, so most subjects meet five out of every six days," said Dr. John Dexter, the Trevor Day headmaster. "It gets around the problem of a teacher having the same sleepy kids every day first period. It means the Monday holidays aren't so disruptive. And it puts a little space into the schedule, so there's more spontaneous time to talk to teachers, or take on more activities. You do have to think about how you're going to use those long periods. I think lecturing for 80 minutes should be a capital crime."
Large public schools, for the most part, do not have as much flexibility; particularly if there are students leaving for vocational training or internships every afternoon, a rotating schedule is nearly impossible. But nationwide, over the last decade, thousands of public schools have moved to a "block schedule," in which students have four long periods a day, skipping some subjects, instead of eight short periods meeting each day in each subject. In some districts, students do four subjects one semester and the other four the next semester. Other districts alternate days.
And some schools are experimenting with hybrid systems: At Irvington High School in Fremont, Calif., for example, students have six 53- minute periods on Monday, Tuesday and Friday. On Wednesday, periods one, three and five each meet for an hour and a half, while periods two, four, and six have their long sessions on Thursday.
At Mamaroneck High School in Westchester, most days have six 52- minute periods, but one day a week has eight 40-minute classes. To prevent Monday holidays from always disrupting the same classes, the school ignores the day of the week, and rotates, instead, through Day 1, Day 2, Day 3, Day 4 and Day 5, which comes in four variants: Day 5a, 5b, 5c, and 5d.
"There is, perhaps, no greater mystery in the life of a Mamaroneck High School parent than that of the `day' of the week," says the school's Web site.
Many education policy experts applaud the experiments, for reducing the amount of time students spend changing classes, and making it possible for teachers to try more actively engaging projects than the old 45- minute period allowed.
"Historically, we've structured the school day as if kids always learn in the same chunks of time, a fairly medieval approach," said Paul Houston, executive director of the American Association of School Administrators. "So my hat's off to people who try to find a better way. Some of the most successful creative scheduling is in Alaskan Eskimo villages with high schools of only 60 kids, where they'll fly a chemistry teacher in for six weeks and do the whole year's worth. The problem for big public schools is that, when you crank a new idea through the politics and the bureaucratic realities of moving 2,000 kids through a day, you usually just end up with a different type of straitjacket."
Independent schools, with their smaller size, he said, can be more experimental. And it is unquestionably at independent schools in New York and nationwide where scheduling has reached a creative apex. Many New York private schools have had complicated schedules for years, and more are now adopting them. In Manhattan, Browning, like Trevor Day, moved from a traditional schedule to a rotating one just this year. Columbia Grammar and Preparatory School and Trinity have long since settled into their six-day rotations.


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The Fine-Dining Options At The Courthouse Have Gotten Slimmer
Tough times have hit the employees, the lawyers, the defendants and the hangers-on at the Harris County courthouse complex -- the cafeterias have been shut down.
On Monday, people strolled up to get their morning coffee and bagel and found only locked doors. On Tuesday there was a sign asking them to excuse the inconvenience and that -- joy of joys -- more vending machines would be provided to make up the slack.
It's been a boon for the guy who has the pushcart in front of one of the buildings, but otherwise it's been a pain in the ass.
Joe Stinebaker, spokesman for county judge Ed Emmett, tells Hair Balls the company that runs the facilities "abandoned its contractual obligations."
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"The head of Kuchenmeister just closed up shop and supposedly told the employees they needed to file for unemployment," he says.
Commissioners Court has scheduled an emergency meeting for Monday to try and get a substitute company "at least for the short term," he says.
The company that had ran the cafeterias, Kuchenmeister, hadn't exactly provided gourmet cuisine to the courthouse crowd, but it at least was an option that didn't involve (for the general public) having to leave the facility and then wait your way again through the security line.
Stinebaker notes that Kuchenmeister had cut back on its employees so much recently that lines had gotten to be annoyingly long at the cafeterias.
"I think a lot of people had gotten used to going elsewhere or, like me, bringing it from home in a plastic H-E-B sack," he says.
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