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Microearthquake Investigations to Reveal Anisotropic Behavior of Seismic Characteristics in the Barn

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shallow marine and brackish-water deposits (Cheney 1929) Contains silica, limestone, dolomite, anhydrite, and salt (Cheney 1929) Ellenberger Group ... – PowerPoint PPT presentation

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Title: Microearthquake Investigations to Reveal Anisotropic Behavior of Seismic Characteristics in the Barn


1
Microearthquake Investigations to Reveal
Anisotropic Behavior of Seismic Characteristics
in the Barnett Shale Newark East Field, Wise
County, Texas
  • Tomieka Searcy
  • University of Oklahoma

2
Outline
  • Introduction
  • Study Area
  • Objective
  • Geology Overview
  • Methodology
  • Analyzing Shear Wave Splitting
  • Developing Microearthquake Locations Scenarios
  • Results and Discussion
  • Preferential Direction of First Shear Wave
  • Scenarios for Microearthquake Locations
  • Conclusions
  • Future Research Recommendations
  • Acknowledgements
  • References
  • Questions and Any Further Discussion

3
Study Area
Study Well Locations
Regional map showing the areal extent of Barnett
Shale (modified from Williams, 2002).
4
Introduction
  • Currently, the Institute of Theoretical
    Geophysics at the University of Oklahoma is
    developing induced-fracture mapping tools to
    improve exploration for oil and gas within
    anisotropic layers such as shale reservoirs.

5
Principal Stages
(1) Determination of geophone horizontal
components orientation using the
recordings of controlled sources ( perforation
shots ) in the offset well. (2) Use
of a special-purpose seismic tomography
technique to find a best Cijkl
fit to P-, S-wave arrival times
from the recordings of the controlled
sources. (3) Development of the
efficient method / applications for locating
hydraulic fracture events ( frac events)
and determining anisotropy and
stress field related parameters.
6
Introduction
  • The two FORTRAN programs for microearthquake
    investigations are
  • Frac_Detect (an automated program)
  • SW_View (a visual/manual program)

7
Thesis Data
  • Perforation Shot records
  • Dipole Sonic Log
  • Three Component Seismograms
  • Micro-earthquake events generated by water
    injection

8
Introduction
  • From the recorded microearthquake seismograms, I
    used polarization diagrams to investigate shear
    wave splitting.

Assigning the two shear waves arrival times as
the moment of encountering fractures allowed the
imaging of fractures
The institute developed microearthquake scenarios
(locations over time and space) in accordance to
an anisotropic model.
9
Shear Wave Splitting Description
S1
Shear Wave
S2
S - Shear Wave S1 First S-Wave S2 Second
S-Wave
S1
S2
Schematic illustration of shear wave splitting
10
Geology Overview
11
Regional Setting
The Ouachita thrust belt is an east-west
Paleozoic overthrust trend in the southern United
States extending 1400 miles (2250km). The Fort
Worth Basin have very little structural
deformation from the Ouachita thrust. It is
essentially a ramp dipping into and under the
Ouachita thrusts.
Meckel et al.,1992
12
Fort Worth Basin
Study Area
(modified from Montgomery, et al 2005)
13
Stratigraphy
(Montgomery, et al 2005)
14
Lithology
  • Marble Falls Limestone
  • White to gray, crystalline, shallow water, shelf
    limestone
  • Upper limestone and a lower portion of consisting
    of interbedded dark limestone and gray-black
    shale, sometimes referred to as the Comyn
    Formation
  • Major unconformity overlies the top of the Marble
    Falls limestone
  • Upper Barnett Shale
  • Marine shelf deposits
  • siliceous shale, limestone, and minor dolomite
  • Forestburg Limestone
  • Carbonate unit
  • Typically dark gray to jet black petroliferous
    shales which are highly radioactive thus high
    gamma ray
  • Thins to the northwest over the Chappel shelf and
    to the south and west along the Llano uplift and
    Bend arch
  • Lower Barnett Shale
  • Marine shelf deposits
  • siliceous shale, limestone, and minor dolomite
  • Viola limestone
  • shallow marine and brackish-water deposits
    (Cheney 1929)
  • Contains silica, limestone, dolomite, anhydrite,
    and salt (Cheney 1929)
  • Ellenberger Group
  • massive sequence of cherty, crystalline
    limestones and dolomites

(Peppard-Souders, 1975 and Montgomery et al.,
2005)
15
Methodology
16
Borehole Acquisition for Study
Frac Well
Monitor Well
1499 feet
Forestburg Limestone
Perforation Shots
Three Component Geophones
Microearthquakes
17
Quality Three Component Data
Recording Stations
Time, milliseconds
Microseismic event file 34 from study well
18
Determining Shear Wave Arrival Times
Polarization diagram from microseismic event file
34 at station 2 showing first and second shear
wave polarizations
Polarization diagram from microseismic event file
34 at station 2 showing first shear polarization
Polarization diagram from microseismic event file
34 at station 2 showing onset of second shear
polarization
19
Quantity of Data Analyzed
  • To confidently reveal anisotropy, I examined
    10,000 microearthquake event files.
  • I chose quality event files for analyzing shear
    wave splitting.
  • I analyzed
  • 600 Microearthquake Event Files
  • 7200 Three Component Seismograms
  • 21,600 Recorded Signals

20
FRAC_DETECT Frac Event Data Processing System
Extracting frac events from raw data files
Shot records
Event files
Seismic tomography model in the framework of
anisotropic media
Seismic array horizontal component orientations
Determining frac event locations and the
associated parameters
Associated Parameters include size, energy, time,
Automated analysis and imaging of the resultant
micro-seismic event locations, including
generation of maps in 3 principal projections
Output files in standard graphical formats
(Abaseyev, March-2005)
21
Results and Discussion
22
Orientation of Horizontal Component of the First
Shear Wave(Visual Method Results)
Time
Legend Preferential Orientation
23
Orientation of Horizontal Component of the First
Shear Wave(Automated Method Results)
Time
Legend Preferential Orientation
24
Overlay of Results
25
Lets Highlight Similarities
Legend Preferential Orientation Automated Visual

Time
26
(No Transcript)
27
RESULTS OVERLAY
Legend Preferential Orientations Automated Visua
l
Level of Agreement
Match
Close Match
Match With Less Angles
Similar but More Angles
Differ
28
Statistics
29
Discussion
  • Totaling the ones that match, match closely, and
    match with less angles gives the level of
    precision to the Automated Program.
  • 66 of the Visual Program Results precisely
    corresponds to the Automated Program Results.
  • Adding the ones that match, match closely, match
    with less angles, and similar but with more
    angles gives the level of acceptance to the
    Automated Program. The accepted results may
    include the similar but more angles because these
    results have a recognizable difference that can
    be traced.
  • 95 of the Visual Results can be accepted to
    correspond to the Automated Program results.

30
Scenarios for Microearthquake Locations
  • According to Time and Space

31
-6600
P - wave S1 - wave S2 - wave
-6800
-7000
-7200
Depth, feet
-7400
-7600
-7800
Pwave (Vertical,
) Pwave (Horizontal,
) S1wave (Vertical, )
S2-wave (Horizontal,
) P-wave Anisotropy Coefficient S-wave
Anisotropy Coefficient
-6600
-6800
-7000
Depth, feet
-7200
-7400
-7600
-7800
Anisotropy Coefficient
10
20
30
40
32
(modified from Abaseyev 2005)
Likelihood surfaces of locating the oriented
shot. Isotopic model (upper panel) and
anisotropic model (lower panel). Cross hairs
annotate predicted location for perforation shot
location for each model.
33
Map View
Study Frac well 1
Study Frac well 1
Study Monitor well 1
Study Monitor well 1
Visual Program Results
Automated Results for All Frac Events
34
Side View
Visual Program Results
Automated Results for All Events
35
Energy Distribution for Visual Results
Total number of events located 552
36
Energy Distribution for Visual Results
Marble Falls Limestone
Upper Barnet Limestone
Upper Barnett Shale
Forestburg Limestone
Lower Barnett Shale
Viola Limestone
Ellenberger Limestone
37
Discussion
  • I analyzed quality three component seismograms to
    observe the arrival times S1 and S2 waves.
  • Using polarization diagrams, I observed and
    recorded the preferential direction of the first
    shear wave and the time delay between the two
    shear waves.
  • After comparing the preferential directions of
    the first shear waves, I interpreted that the
    Visual Method reasonably corresponds to the
    Automated Method.
  • Only 5 of the visual method results
    significantly differed from the automated program
    results.
  • Using a seismic tomography model of an
    anisotropic medium, my results accurately
    revealed the microearthquake locations over time
    and space.

38
Conclusions
  • Observing and recording shear wave splitting
    occurrences proved that anisotropy exist in the
    hydraulic fractured zones of the study well.
  • Two factors affect correlation between the two
    methods for determining shear wave splitting
  • Quality of seismograms
  • Time delay between first and second shear waves

39
Conclusions
  • - The manual procedure using the SW_View
  • program is a more precise procedure because
  • individual seismograms are analyzed.
  • - On the other hand, the Frac_Detect Program is
  • faster because it considers all of the data by
  • approximating the time arrivals from
    predetermined
  • good quality seismogram criteria.
  • - The manual procedure of the SW_View
  • program confirms the accuracy of the automated
  • procedure of the Frac_Detect program.

40
Conclusions
  • In map view, the induced fractures trend of
    northeast to southwest.
  • - For both visual and automated procedures, most
    of the imaged fractures occur in the Lower
    Barnett Shale. This formation has high gas
    accumulations.
  • As a result, we can account economical production
    rates to the success of the hydraulic fracturing
    of this well.

41
Future Research Recommendations
  • Continue using the automated program
  • Determine the model for subvertical and
    subhorizontal rays
  • Similar to a Tilted Transversely Isotropic
    Medium

- Or a Medium with a weak orthorhombic type of
symmetry
42
Acknowledgements
  • Dr. Evgeni Chesnokov
  • Devon Energy, Inc.
  • Mike Ammerman
  • Dr. Sergey Abaseyev
  • Dr. Roger Slatt
  • Dr. Roger Young
  • Jan Dodson
  • School of Geology and Geophysics
  • Institute for Theoretical Geophysics
  • at the University of Oklahoma

I truly appreciate all who helped to complete my
thesis work.
43
References
  • Abaseyev, Sergey. Personal Interview. June 8,
    2005.
  • Abaseyev, Sergey, Seminar Presentation. March
    23, 2005.
  • Cheney, M. G. Stratigraphic and Structural
    Studies in North Central Texas. University of
    Texas Bulletin. No. 2913. April 1, 1929.
  • Meckel, Lawrence D. Jr., David G. Smith, and Leon
    A. Wells. Ouachita Foredeep Basins Regional
    Paleogeography and Habitat of Hydrocarbons. AAPG
    Memoir 55 Foreland Basins and Fold Belts.
    1992. Chapter 15. pp. 427 444.
  • Montgomery, Scott L., Daniel M. Jarvie, Kent A.
    Bowker, and Richard M. Pollastro. Mississippian
    Barnett Shale, Fort Worth basin, north-central
    Texas Gas-shale play with multi-trillion cubic
    foot potential. AAPG Bulletin, vol. 89, no. 2
    (February 2005), pp. 155-175.
  • Peppard-Souders. Structure and Stratigraphy of
    Fort Worth Basin. Peppard-Souders Consultant
    Study. 1975.
  • Williams, Peggy. The Barnett Shale. Oil and Gas
    Investor. Vol. 22, No. 3. p.34 45. 2002.

44
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