Tomieka Searcy University of Oklahoma

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) Developmentof 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. Well Locations Fort Worth Basin Study Area (modified from Montgomery, et al 2005)

13. Stratigraphy (Montgomery, et al 2005)

14. 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 Lithology (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 Microearthquakes Three Component Geophones

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. Extracting frac events from raw data files FRAC_DETECT Frac Event Data Processing System Shot records Eventfiles 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. Stations Orientation of Horizontal Component of the First Shear Wave(Visual Method Results) Time Legend Preferential Orientation

23. Stations Orientation of Horizontal Component of the First Shear Wave(Automated Method Results) Time Legend Preferential Orientation

24. Overlay of Results

25. Stations Let’s Highlight Similarities Legend Preferential Orientation Automated Visual Time

27. RESULTS OVERLAY Stations Time Legend Preferential Orientations Automated Visual Level of Agreement Match Close Match Match With Less Angles Similar but More Angles Differ

28. Statistics

29. Totaling the ones that match, match closely, and match with less angles gives the level ofprecision 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 ofacceptance 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. Discussion

30. Scenarios for Microearthquake Locations According to Time and Space

31. Velocity, ft/s Velocity, ft/s 10000 10000 15000 15000 20000 20000 5000 5000 -6600 -6800 P - wave S1 - wave S2 - wave -7000 -7200 Depth, feet -7400 -7600 -7800 P–wave (Vertical, ) P–wave (Horizontal, ) S1–wave (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. Depth’ feet Perforation Shot Location o Source – to –well distance (feet) Depth’ feet Perforation Shot Location o Source – to –well distance (feet) (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 Automated Results for All Frac Events Visual Program Results

34. Side View Automated Results for All Events Visual Program Results

35. Energy Distribution for Visual Results Study Frac well 1 Study Monitor well 1 Total number of events located = 552

36. Marble Falls Limestone Upper Barnett Limestone Depth Upper Barnett Shale Forestburg Limestone Lower Barnett Shale Ellenberger Limestone 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. x3 x2 x1 x3 x1 x2 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. Dr. Evgeni Chesnokov Devon Energy, Inc. Mike Ammerman Dr. Sergey Abaseyev Dr. Roger Slatt Dr. Roger Young Jan Dodson School of Geology and Geophysics Acknowledgements • 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. Questions