DW Tomo 8.1 User Guide

Transcription

1 DW Tomo 8.1 User Guide Copyright 2016, All rights reserved.

2 Table of Contents Preface...1 Conventions Used in This Guide...1 Where to Find Information...1 Technical Support...2 Feedback...2 Chapter 1 Introducing DW Tomo Interface...3 Title Bar...4 Menu Bar...4 File Menu...5 Trace Menu...6 Pick Menu...6 Tomography Menu...7 Display Menu...7 Window Menu...8 Help Menu...8 Toolbar...8 Display Window...9 Status Bar...9 Chapter 2 Processing Seismic Data...10 Importing Seismic Data...11 Loading Seismic Data...15 Checking Geometry...17 Displaying Seismic Data...18 Display Settings...18 Trace View...19 Editing Seismic Data...20 Frequency Filter...20 Gain Control...22 Single Trace Scaling...23 Reverse Polarity...24 Trigger Delay Correction...25 Inputting Elevation Data...27 Chapter 3 Picking First Breaks...28 Creating a TT Curve File...29 Opening a TT Curve File...29 Making First Breaks Easier to Be Identified...30 Zooming In Seismic Data...30 Adjusting the Display Gain...31 Picking First Breaks...32 Adjusting First Break Picks...34 Saving First Break Picks...35 DW Tomo 8.1 User Guide i

3 Supporting 3rd Party Picks Formats...37 Merging TT Curves...38 Chapter 4 Running Refraction Tomography...39 Building Initial Model...40 Gradient Model...41 Geogiga Refractor...42 Manually Defined Model...43 Setting Tomography Parameters...45 Modeling...45 Inversion...45 Running Tomography...47 Analyzing Fitting Errors...48 Reviewing Tomography Results...49 Chapter 5 Customizing Tomography View...50 Setting View Visibility...51 Updating Tomography View...52 Plotting TT Curves...53 Setting Curve Display...53 Choosing Curve Options...54 Showing Ray Paths...55 Displaying Tomography Image...56 Defining Velocity Grades...56 Changing Display Parameters...59 Trimming Image...60 Plotting Well Data...61 Chapter 6 Outputting Results...63 Exporting results as XZV Format...64 Calculating Tomo Statics...65 DW Tomo 8.1 User Guide ii

4 Preface Thank you for choosing DW Tomo the Refraction Tomography Software in Geogiga Seismic Pro. Using DW Tomo, you can: Import seismic data while assigning geometry and integrating files. Edit seismic data with frequency filter and gain control. Correct trigger delay according to the time or surface velocity. Pick first breaks with a trace magnifier. Build an initial model with three options. Estimate complex velocity structures directly from first arrivals with the robust grid ray tracing and regularized inversion approach. Interactively control and review the tomography procedure. Print, save, and export the velocity model as XZV format. Conventions Used in This Guide The conventions used in this guide are given below: Bold Represents keystrokes, menu items, window names, or fields. Italic Uses for file names, directory names, and emphasis as well. Courier Denotes the text to enter. Where to Find Information The following list explains what you can find in this guide: Chapter 1 introduces the DW Tomo interface. Chapter 2 describes how to input, display, and process seismic data. Chapter 3 provides the details on picking first breaks. Chapter 4 talks about the refraction tomography.

5 Chapter 5 shows how to customize the tomography view. Chapter 6 explains how to output results. If you are a first-time user, first read the Getting Started with Geogiga Seismic Pro which can be opened by clicking the Getting Started command under the Help menu in the Geogiga Seismic Pro Launchpad. Technical Support If you have questions, need additional assistance, or encounter a problem, please contact Technical Support using the information given below: Telephone: support@geogiga.com Web: Feedback To help us improve the future documentation, we want to know any corrections, clarification or further information you would find useful. When you contact us, please include the following information: The title of the documentation you are referring to The version of the application you are using Your name, company name, phone number, and address Please send us your comments at sales@geogiga.com. Preface 2

6 Chapter 1 Introducing DW Tomo Interface The DW Tomo interface has five parts as shown in figure 1-1: Title Bar Menu Bar Toolbar Display Window Status Bar The following will explain these parts in detail. Title Bar Menu Bar Toolbar Display Window Status Bar Figure 1-1: The DW Tomo interface Chapter 1 Introducing DW Tomo Interface 3

7 Title Bar The Title Bar shows the filename of traveltime (TT) curve. When the first break picks are changed, a * symbol will appear at the end of the filename to remind you to save the TT curve file. Menu Bar The Menu Bar has following menus: File Menu Trace Menu Pick Menu Tomography Menu Display Menu Window Menu Help Menu When you click one of the menu names, a drop-down submenu appears and displays a list of related commands. Chapter 1 Introducing DW Tomo Interface 4

8 File Menu The submenu under the File menu, as shown in figure 1-2, contains following commands: New Load seismic data and create a TT curve file. Open Open a TT curve file with the option of loading seismic data. Import Seismic Assign geometry in multiple files (one file per shot) and integrate these files. Save Save TT curve file. Save As Save TT curve file with a new name. Save Seismic Save seismic data file. Save Seismic As Save seismic data file with a new name. Edit Elevation Input elevation data. Merge TT Curves Merge multiple TT curves saved in different files. Print Print an image plotted in the Display Window. Save Image Save an image plotted in the Display Window. Close Close TT curve and seismic data files. Exit Exit DW Tomo. Chapter 1 Introducing DW Tomo Interface Figure 1-2: The File submenu 5

9 Trace Menu The submenu under the Trace menu as shown in figure 1-3 contains following commands: Show Change the visibility of trace view. All Records Switch the trace view between a single record and all records. Geometry Check geometry. Filter Filter seismic data. Gain Control Scale seismic data with gain control. Scale Up Increase the data amplitude of a selected trace by 2 times. Scale Down Reduce the data amplitude of a selected trace by 2 times. Reverse Polarity Reverse the data polarity of a selected trace. Trigger Delay Correction Correct trigger delay according to the time or surface velocity. Undo Erase changes done to seismic data. Redo Reverse the Undo. Figure 1-3: The Trace submenu Pick Menu The submenu under the Pick menu as shown in figure 1-4 contains following commands: Settings Change the pick settings, such as the option of manual or automatic picking. Trace Magnifier Magnify a selected trace to make the first break easier to be identified. Previous Shot Display previous shot record. Next Shot Display next shot record. Chapter 1 Introducing DW Tomo Interface Figure 1-4: The Pick submenu 6

10 Tomography Menu The submenu under the Tomography menu, as shown in figure 1-5, contains the following commands: Initial Model build an initial model. Settings Set tomography parameters. Start Start the tomography. Pause Pause or resume the tomography. Stop Stop the tomography. Fitting Error QC Check the fitting errors. Review Review the tomography. Views Choose the visibility of tomography views and the way to update views. Calculate Statics Calculate tomo statics. Export as XZV Output results to a text file as XZV format. Figure 1-5: The Tomography submenu Display Menu The submenu under the Display menu, as shown in figure 1-6, contains the commands given below: Trace Display Change the display of seismic data. TT Curve Visual Choose the visibility of curves. TT Curve Display Set the display of TT curves including axis, gridlines, background, and fonts. Ray Visual Change the visibility of ray paths overlaid on velocity section. Trim Image Trim the image with ray coverage. Image Grade Define color grades. Image Display Customize the display of image such as scale, label, and colorbar. Display Wells Plot well data on velocity section. Chapter 1 Introducing DW Tomo Interface Figure 1-6: The Display submenu 7

11 Window Menu The submenu under the Window menu, as shown in figure 1-7, contains the following commands: Toolbars Change the visibility of the Toolbar. Statusbar Toggle the visibility of the Status Bar. Figure 1-7: The Window submenu Help Menu The submenu under the Help menu, as shown in figure 1-8, contains the commands listed as follows: Manual Open the User Guide. About View the information related to DW Tomo and the computer system memory. Figure 1-8: The Help submenu Toolbar As shown in figure 1-9, the button icons on the Toolbar correspond to the commonly used commands under the menus. To run a command, click its related button icon. Figure 1-9: Icons on the Toolbar Chapter 1 Introducing DW Tomo Interface 8

12 Display Window In the Display Window, the left is the Trace View, the right top is the Travel Time Curves View, and the right bottom is the Tomography Image View. To adjust the view sizes, just drag the separator bar as shown in figure The Trace View is a dockable window. You can undock or dock it by double-clicking the Trace View label as shown in figure After the Trace View is undocked, you can drag it to change the location of the window. To toggle the visibility of the Trace View, click the Show command under the Trace menu. To switch the Trace View between a single record and all records, click the All Records command under the Trace menu. To change the visibility of the Travel Time Curves View and the Tomography Image View, click the Views command under the Tomography menu. Travel Time Curves View Double click the Trace View to dock or undock the trace view window Separator Bar Trace View Separator Bar Tomography Image View Figure 1-10: The Display Window Status Bar On the Status Bar, you will see the information related to commands, seismic data, or curves when moving the mouse cursor over the DW Tomo interface. Chapter 1 Introducing DW Tomo Interface 9

13 Chapter 2 Processing Seismic Data This chapter covers most of the operations related to seismic data including: Importing seismic data Loading seismic data Checking geometry Displaying seismic data Editing seismic data Inputting elevation data Chapter 2 Processing Seismic Data 10

14 Importing Seismic Data If the data are saved as per shot per file, you need to import seismic data first. The purpose of importing seismic data is to: Assign geometry in multiple files (one file per shot). Integrate multiple files after geometry assignment. To import seismic data, open the Geometry Assignment and Files Integration dialog box by clicking the Import Seismic command under the File menu. On the dialog box as shown in figure 2-1: (1) Select the Group 1 name from the Geometry Definition Group list box. The group concept is designed to make the geometry assignment quicker and easier. Normally, a group should have similar features in order to use the filling rule described in the step (4). (2) Enter numbers in the Auxiliary Traces field, such as 1, 2, 6-9. Leave the field blank if there are no auxiliary or dummy traces in each shot record. (3) Add multiple files to the Files table by clicking the Add button under the Files table. (4) Input the relevant geometry information for each shot under the following columns in the Files table. Shot No. the shot number which can be any unique number. Shot(x) the shot X coordinate. Shot Depth the shot depth. 1st Rcvr(x) the 1st receiver X coordinate. Rcvr(dx) the receiver interval in the X direction. To quickly assign the geometry, utilize the filling rule in the Assign drop-down list box which can be accessed by clicking the arrow button next to the Assign button. The filling rule, applied to a selected column, includes: Extrapolation Based on the values in the first two cells, the values in the other cells are linearly extrapolated. Chapter 2 Processing Seismic Data 11

15 Repetition The other cells are filled out with the same value as that in the first cell. Filename The other cells are filled out according to the file naming rule and the value in the first cell. Current Column The values in all cells under the current column are loaded from a text file. Assign All with the First The other rows are filled out with the same values as those in the first row. For example, if the receiver interval is uniform, enter the value in the first cell under the Rcvr(dx) column, then click the arrow button next to the Assign button and select the Repetition name from the drop-down list box to automatically fill out the other cells under that column. (5) Click the View button to open the Geometry dialog box as shown in figure 2-2. On the dialog box, you can review the layout chart, check the receiver coordinates, and input or load irregular receiver coordinates from a text file. To input irregular receiver coordinates, enter the coordinates in the relevant cells in the Receiver Locations table. If some receivers have constant intervals, enter the first two receivers' X coordinates in the relevant cells, and then click the Auto Fill button to automatically fill out the other cells below these two cells. For instance, a shot array, as shown in figure 2-2, has 12 geophones with 960m at 1st receiver, 10m spacing of 1~6 receivers, 5m spacing of 7~12 receivers, and 20m spacing between 6th and 7th receivers. You can: First, enter 960 and 970 in the 1st and 2nd cells, and then click the Auto Fill button. Secondly, enter 1030 and 1035 in the 7th and 8th cells, then select the 7th and 8th rows by holding down the Shift or Ctrl key while clicking the 7th and 8th row headers, and finally click the Auto Fill button. After inputting the coordinates, you can save them in a text file by clicking the Save button. To set all coordinates to 0, click the Clear button. To load receiver coordinates from a text file, click the Load button. The coordinates are saved as per row per receiver in the text file, such as, Chapter 2 Processing Seismic Data 12

16 To change the display of layout chart on the the Geometry dialog box, click the arrow button next to the Display label below the layout chart, then a drop-down list box will appear. From the drop-down list box, you can: Choose whether to display all spreads and use the fixed display range. Set the display of layout chart including background, gridlines, and annotations. Change the plotting colors for shots and receivers. (6) Add a new geometry definition group by clicking the Add button next to the Geometry Definition Group list box. Then, repeat step (2)~(5). To remove a geometry definition group, select the group name and click the Remove button next to the Geometry Definition Group list box. (7) Enter the output filename in the Output field. (8) Click the Integrate and Load button to assign geometry and integrate files, then load seismic data and create a TT curve file. Or click the Integrate button to only assign geometry and integrate files. Later, click the New or Open command under the File menu to load seismic data. To save the geometry definition in raw seismic data files, click the Save button. The above steps are illustrated in figure 2-1. Chapter 2 Processing Seismic Data 13

17 Figure 2-1: The Geometry Assignment and Files Integration dialog box Figure 2-2: Checking or Inputting irregular receiver coordinates in step (5) Chapter 2 Processing Seismic Data 14

18 Loading Seismic Data After importing seismic data, you can load the data by clicking the New or Open command under the File menu. When you click the New command, the Open Seismic File dialog box appears. On the dialog box as shown in figure 2-3: (1) Select the seismic data file. (2) Specify the TT curve filename in the Output file field. To change the filename, type in the field or click the Browse button next to the field. (3) Click the Open button to load seismic data and create a TT curve file. Figure 2-3: The Open Seismic File dialog box Chapter 2 Processing Seismic Data 15

19 When you click the Open command under the File menu, the Open TT Curve File dialog box appears. On the dialog box as shown in figure 2-4: (1) Choose the TT curve file. (2) Select the Seismic option, and then click the Browse button to locate the seismic data file if needed. (3) Click the Open button to open the TT curve file while loading seismic data. After loading seismic data, check the geometry and set the display of seismic data to make first breaks easier to be identified. Figure 2-4: The Open TT Curve File dialog box Chapter 2 Processing Seismic Data 16

20 Checking Geometry To check the geometry after loading seismic data, click the Geometry command under the Trace menu to open the Geometry dialog box as shown in figure 2-5, where you can review and modify the geometry. To review the geometry, choose a record by clicking the Previous Shot or Next Shot button icon on the Toolbar or clicking the left mouse button on the top horizontal annotations in the Trace View, then you will see the layout chart and the coordinates are accordingly updated. There are two ways to modify the geometry: Input or load from a text file. For details on how to input or load coordinates, refer to Step (5) in Importing Seismic Data described earlier. After changing the geometry, click the Apply button to overwrite the coordinates in the file header for the chosen shot record. To set the current geometry for all shot records, click the Apply All button. To save the change of geometry in seismic data file, click the Save Seismic or Save Seismic As command under the File menu. Figure 2-5: The Geometry dialog box Chapter 2 Processing Seismic Data 17

21 Displaying Seismic Data After loading data, you may change the display settings and set the visibility of trace view. Display Settings To change the display of seismic data, open the Trace Display dialog box by clicking the Display command under the Trace menu. On the dialog box as shown in figure 2-6, you can: Choose the plot type and adjust the display gain. Specify the display range of seismic data and view the sample rate. Define the scale factors. Change the annotation settings. Select to plot the trace graph. To learn about this dialog box, read Chapter 4 in Getting Started with Geogiga Seismic Pro. Figure 2-6: The Trace Display dialog box Chapter 2 Processing Seismic Data 18

22 Trace View To toggle the visibility of the Trace View, click the Show command under the Trace menu. To switch the Trace View between a single record and all records as shown in figure 2-7, click the All Records command under the Trace menu. Single Record All Records Figure 2-7: Switching the Trace View between a single record and all records Chapter 2 Processing Seismic Data 19

23 Editing Seismic Data The following lists the ways to edit seismic data in DW Tomo: Filter data with frequency filter. Apply different types of gain control. Scale up or down a single trace. Reverse the polarity of a single trace. Correct trigger delay. Frequency Filter The seismic data can be filtered with low-pass, high-pass, band-pass, band-reject, or notch filters. Two types of filters are available: Butterworth filter and Ormsby filter. To apply frequency filtering on data, open the Frequency Filter dialog box by clicking the Filter command under the Trace menu. On the dialog box as shown in figure 2-8: (1) Set the display of amplitude spectrum by: Dragging the Max Frequency slide bar to adjust the display range of frequency. Clicking the arrow button next to the Display button to choose whether to display the Power or Amplitude spectrum in db, or clicking the Display button to change the spectrum view settings including colors, gridlines, etc. (2) Update the amplitude spectrum. By default, the spectrum of the 1st record is plotted. To plot the spectrum of a different record, choose a record by clicking the Previous Shot or Next Shot button icon on the Toolbar or clicking the left mouse button on the top horizontal annotations in the Trace View, and then click the Refresh button. To plot the spectrum of a trace, click the Selected Trace radio button, then choose a trace by clicking the left mouse button on the top horizontal annotations in the Trace View, and finally click the Refresh button. To normalize the display of spectrum, click the Normalize button. (3) Select the Butterworth filter or Ormsby filter by clicking the drop-down list box next to the Filter label. Chapter 2 Processing Seismic Data 20

24 (4) Choose the Low Pass, High Pass, Band Pass or Band Reject by clicking the dropdown list box next to the Type label. When the Band Reject type is chosen, you can select whether to use notch filter by clicking the Notch check box. (5) Decide whether to apply a window function by clicking the Window check box. Here, the Hanning window is used. (6) Set the parameters of Pass and Slope (or Cut for the Ormsby filter) by: Horizontally dragging the relevant control nodes marked as green dots on the gate curve in the spectrum window. Or entering values in the relevant fields and then clicking the Set button. (7) Choose the data Traces to be Filtered among the All Records, Current Record, and Selected Traces options. The All Records option will be invisible when a single record is displayed in the Trace View. (8) Click the Apply button to filter seismic data. To check the effect of filtering or tune the filter parameters, click the Undo and Redo button icon on the Toolbar. Figure 2-8: The Frequency Filter dialog box Chapter 2 Processing Seismic Data 21

25 Gain Control To apply gain control on seismic data, open the Gain Control dialog box by clicking the Gain Control command under the Trace menu. On the dialog box as shown in figure 2-9: (1) Select the types of gain among the following options and set the relevant parameters: AGC(Automatic gain control). Trace Balance including RMS, Quantile, and Mean Subtraction. Scale including Time, Exp, Power, and Constant. (2) Choose the data Traces between the All Records and Current Record options. (3) Click the Apply button to scale seismic data. To check the effect of gain or determine the types of gain, click the Undo and Redo button icon on the Toolbar. Figure 2-9: The Gain Control dialog box Chapter 2 Processing Seismic Data 22

26 Single Trace Scaling To make first breaks easier to be identified, the Trace RMS is chosen as the default display Scale Type on the Trace Display dialog box as shown in figure Before scaling a trace, make sure the Scale Type is set to any of the following options: Global Maximum Global RMS Global Average Histogram Figure 2-10: Choosing the display Scale Type Next, click the Settings command under the Pick menu to open the Pick Settings dialog box as shown in figure 2-11 and deselect the Pick option. Chapter 2 Processing Seismic Data 23

27 Figure 2-11: Deselecting the Pick option Finally, select a trace by clicking the left mouse button on the top horizontal annotations in the Trace View, then scale up or down the trace by: Clicking the Scale Up or Scale Down button icon on the Toolbar. Or holding down the Shift key while pressing the right arrow key( ) or the left arrow key( ) on the keyboard. To cancel the scaling done to the trace, click the Undo button icon on the Toolbar. Reverse Polarity To reverse the polarity of a single trace, select a trace by clicking the left mouse button on the top horizontal annotations in the Trace View, and then: Hold down the Shift key while pressing the P key. Or click the Reverse Polarity command under the Trace menu. To cancel the change, click the Undo button icon on the Toolbar. Chapter 2 Processing Seismic Data 24

28 Trigger Delay Correction To correct trigger delay, open the Trigger Delay Correction dialog box as shown in figure 2-12 by clicking the Trigger Delay Correction command under the Trace menu. Figure 2-12: The Trigger Delay Correction dialog box On the Trigger Delay Correction dialog box: (1) If the correction is applied after the picking of first breaks, turn on the With First Breaks option to shift both seismic data and picks. (2) Select the rule of correction by clicking the Time or the First Break radio button. If the Time option is selected, enter the delay time in milliseconds in the text field next to the Time radio button. You can also click the left mouse button in the Trace View to set the time value in the text field if the Pick option on the Pick Settings dialog box is turned on. If the First Break option is selected, enter the surface velocity in the Surface Velocity field. You may choose this option when the trigger delay is different for each record and the surface velocity is constant, for example, in marine survey. Make sure that first breaks are picked before choosing this option. (3) Choose the Trace Range between the All Records and Current Record options. (4) Click the Apply button to correct the trigger delay. To cancel the correction, click the Undo button icon on the Toolbar. To reverse the Undo, click the Redo button icon on the Toolbar. Chapter 2 Processing Seismic Data 25

29 After editing seismic data, click the Save Seismic or Save Seismic As command under the File menu to save the change in seismic data file. In DW Tomo, you can edit seismic data with: Frequency filter Gain control Single trace scaling Reverse polarity Correct trigger delay For more editing functionalities, such as: Scale up or down multiple traces Reverse polarity of multiple traces Swap traces Shift a single trace vertically Mute seismic data Resample seismic data Refer to the Front End User Guide. Chapter 2 Processing Seismic Data 26

30 Inputting Elevation Data DW Tomo allows variable surface. You can input the elevation data anytime before running tomography. To input elevation data, open the Elevation Input dialog box by clicking the Edit Elevation command under the File menu. On the dialog box as shown in figure 2-13, (1) Input elevation data from a text file by clicking the Load button. The text file has two columns as shown below with 1 st column for X coordinates and 2nd column for elevations: -5, 5 0, 5 6, 4 33, 0 70, 12 If elevation data is not saved in a text file, go to step (2). (2) Enter the X coordinates and elevations in the text area below the X, Z Coordinates label. The input values are normally separated by a comma or space. You can also use the Ctrl-C and Ctrl-V keys to copy and paste the elevation data from other text editors or Windows Excel. To save the elevation data in a text file, click the Save button. (3) Click the OK button to apply and save elevation data in the TT curve file. Figure 2-13: The Elevation Input dialog box Chapter 2 Processing Seismic Data 27

31 Chapter 3 Picking First Breaks This chapter covers the following topics: Creating a TT curve file Opening a TT curve file Making first breaks easier to be identified Picking first breaks Adjusting first break picks Saving first break picks Supporting 3rd party picks formats Merging TT curves Chapter 3 Picking First Breaks 28

32 Creating a TT Curve File A TT curve file is used to save first break picks. There are two ways to create a TT curve file: When importing seismic data, click the Integrate and Load button on the Geometry Assignment and Files Integration dialog box as shown in figure 2-1. The TT curve filename is same as that in the Output field but with an extension of ttx. Click the New command under the File menu to open the Open Seismic File dialog box as shown in figure 2-3, where the TT curve filename can be specified. Opening a TT Curve File To open a TT curve file, click the Open command under the File menu. Seismic data can also be loaded along with a TT curve file as shown in figure 3-1. Figure 3-1: Opening a TT curve file with seismic data Chapter 3 Picking First Breaks 29

33 Making First Breaks Easier to Be Identified To make first breaks easier to be identified, you can: Zoom in seismic data Adjust the display gain Expand the Trace View window Change the display scale type Apply gain control Scale up a single trace The first two methods are commonly used. Zooming In Seismic Data To zoom in the display of seismic data, click the Zoom In button on the scrollbar in the Trace View window as shown in figure 3-2. Figure 3-2: Zooming in the display of seismic data Chapter 3 Picking First Breaks 30

34 Adjusting the Display Gain To adjust the display gain, drag the Display Gain slide bar on the Trace Display dialog box as shown in figure 3-3. Figure 3-3: Adjusting the display gain Chapter 3 Picking First Breaks 31

35 Picking First Breaks Before picking first breaks, click the Settings command under the Pick menu to open the Pick Settings dialog box and turn on the Pick option as shown in figure 3-4. Figure 3-4: The Pick Settings dialog box There are two ways to pick first breaks in the Trace View window: Manually Automatically The Manually option is the default choice. To pick first breaks manually: (1) Select the Manually option on the Pick Settings dialog box. (2) Click the left mouse button on a seismic trace or drag the left mouse button over multiple traces. To pick first breaks automatically: (1) On the Pick Settings dialog box, select the Automatically option, and then Enter the maximum jump in milliseconds in the Max Jump field or click the arrow button next to the field. Chapter 3 Picking First Breaks 32

36 Choose whether to use the velocity as a guide in the automatic picking procedure by clicking the Velocity check box. If the Velocity check box is selected, enter the average apparent velocity in the text field next to the check box. To check the apparent velocity, click the Test Velocity radio button, then drag the left mouse button along the first break events on seismic data in the Trace View window as shown in figure 3-5. The velocity value displayed on the Status Bar is updated accordingly. Choose whether to use the phase of an event as a guide in the automatic picking procedure by clicking the Phase check box. If the Phase check box is turned on, enter the phase width in milliseconds in the Wavelet Width field or click the arrow button next to the field. (2) In the Trace View window, click the left mouse button on a seismic trace where the first break is clearly identified. After that, first breaks are automatically picked based on this pick. Figure 3-5: Testing apparent velocity in the Trace View window After picking first breaks, you can adjust or delete picks. Chapter 3 Picking First Breaks 33

37 Adjusting First Break Picks The picks can be adjusted simultaneously or individually. There are two ways to adjust all picks on a shot record simultaneously: If the Manually option is selected, turn on the Shift All Picks option, then move the mouse cursor over the picking line on a trace and drag the picking line vertically. This will constantly shift all picks. If the Automatically option is selected, move the mouse cursor over the picking line on a trace and drag the picking line vertically. This will automatically adjust all picks. To adjust an individual pick: (1) Select the Manually option and turn off the Shift All Picks option. (2) Select a trace by clicking the left mouse button on the trace or pressing the right arrow key ( ) or the left arrow key ( ) on the keyboard. (3) Move the mouse cursor over the picking line on the selected trace and then drag the picking line vertically. To adjust a pick precisely, open the Trace Magnifier window by clicking the Trace Magnifier button icon on the Toolbar. In the window as shown in figure 3-6, drag the red picking line vertically to adjust the pick, while the pick's time and amplitude are changed accordingly. The buttons at the bottom of the Trace Magnifier window are used to magnify the plotting, toggle the transparent background, and change the visibility of the zero line. Figure 3-6: The Trace Magnifier window Chapter 3 Picking First Breaks 34

38 To delete picks, hold down the Ctrl key while clicking the left mouse button on a selected trace or hold down the Ctrl key while dragging the left mouse button over multiple traces. To pick or adjust first breaks at a different shot record, click the Previous Shot or Next Shot button icon on the Toolbar, and then repeat the picking or adjusting operations. During the picking, saving the TT curve file frequently is recommended. Saving First Break Picks To save first break picks, click the Save or Save As command under the File menu. The picks file, called as the TT curve file, has the following format as shown in figure 3-7: 1st line the application name 2nd line the version number of TT curve file format 3rd line ~8th line comments 9th line total number of elevation data (for example, 6) 10th line ~ 15th line elevation data 16th line total number of shots 17th line 1st shot number 18th line 1st shot location 19th line total number of receivers for 1st shot 20th line column names # - receiver number x receiver x coordinate z receiver z coordinate T_OBS picked first breaks T_CAL calculated first breaks 21th line and continued lines column values. Here, The at the 3th receiver row and the T_OBS column is an invalid value, which indicates that the first break is not picked at the 3 th receiver. Chapter 3 Picking First Breaks 35

39 After saving the TT curve file, you can open it later by clicking the Open command under the File menu. Figure 3-7: TT curve file format Chapter 3 Picking First Breaks 36

40 Supporting 3rd Party Picks Formats Most of the 3rd party picks formats are supported. To open a 3rd party picks file: (1) Click the Open command under the File menu, then the Open TT Curve File dialog box appears. (2) On the dialog box as shown in figure 3-8, choose the 3rd Party picks option from the Files of type drop-down list box, then select a filename and click the Open button. DW Tomo automatically recognizes the picks format, loads the picks and saves them in a file which has the same filename but with an extension of ttx. Figure 3-8: Opening a 3rd party picks file Chapter 3 Picking First Breaks 37

41 Merging TT Curves The normal steps are to import seismic data and then pick first breaks. However, you can also load each shot file individually, pick first breaks, and then merge the picks files. To merge TT curves saved in the individual files: (1) Open the TT Curve Files Integration dialog box by clicking the Merge TT Curves command under the File menu. (2) On the dialog box as shown in figure 3-9, enter a filename in the Output File Name field, then click the Add button to add TT curve files in the TT Curves file list box, and finally click the OK button. To remove a file from the list, select the filename and then click the Remove button. To show the file path, turn on the Show Path option. To change the list order, select a filename and then click the Up or Down button, or click the Sort Ascending or Sort Descending button. The list can have any orders, since the integration depends on the shot location not the list order. Figure 3-9: The TT Curve Files Integration dialog box Chapter 3 Picking First Breaks 38

42 Chapter 4 Running Refraction Tomography This chapter covers the following topics: Building an initial model Setting tomography parameters Running tomography Analyzing fitting errors Reviewing tomography results Chapter 4 Running Refraction Tomography 39

43 Building Initial Model An initial model is required in the refraction tomography. To build an initial model, open the Initial Model Build dialog box as shown in figure 4-1 by clicking the Initial Model command under the Tomography menu. Figure 4-1: The Initial Model Build dialog box On the Initial Model Build dialog box as shown in figure 4-1: (1) Enter the maximum inverted depth in the Maximum Depth field. For reference, the maximum offset of the array is shown in the Maximum Offset field. The inverted depth is normally equal to 1/3 ~1/6 of maximum offset. (2) Choose the method to build an initial model from following options and set the relevant parameters. Gradient model Geogiga Refractor Manually defined model (3) Click the Apply button. The following discusses the options to build an initial model. Chapter 4 Running Refraction Tomography 40

44 Gradient Model To define a layered gradient velocity model, select the Gradient Model option, and then: Click the Load button to load a layered velocity model from a text file and display it in the Depth~Velocity list. The text file has two columns: 1st column is the depth of a layer, 2nd column is the velocity of a layer. Or enter the depth and velocity of a layered model in the Depth~Velocity list. The depth and velocity of a layer are separated by a comma or space. Or click the Calculate button to define a layered velocity model based on the picks of all records in the Calculate Velocity dialog box as shown in figure 4-2. In the figure of the dialog box: The vertical axis represents the travel time, and the horizontal axis represents the offset, i.e., the distance between shots and receivers. The green lines are the timeoffset curves of all records. The yellow line is the averaged time-offset curve of all records. The red line is the time-offset curve of the initial model, which is assumed to be a layered velocity model. As the initial model is assumed to be a layered model, the nodes are the turning points corresponding to each layer. To insert or delete a node, click the left mouse button on the red line while holding down the Ctrl key. To adjust a turning point, drag the node using the left mouse button. After defining the nodes, click the Apply button to generate an initial model. After entering or calculating a layered velocity model, click the Save button to save the model in a text file, which can be loaded next time with the Load button. Figure 4-2: Calculating a layered velocity model Chapter 4 Running Refraction Tomography 41

45 Geogiga Refractor To load a model from the results generated in Geogiga Refractor or from a XZV file, turn on the From Geogiga Refractor option, and then: (1) Click the Load button to open the Load Initial Model dialog box and then load the model from a text file as shown in figure 4-3. (2) If required, select the Smoothing option and enter the smoothing radius in the X and Z fields to smooth the initial model in X and Z directions. Here, the smoothing radius is represented by the number of grids. (3) Click the Apply button. Then, the initial model is plotted in the Display Window. Figure 4-3: Loading an initial model from a text file Chapter 4 Running Refraction Tomography 42

46 Manually Defined Model To manually define an initial model, select the Manually Defined option as shown in figure 4-4, and then click the Define button to open the Build Model dialog box. On the Build Model dialog box as shown in figure 4-5, build a velocity model with following instructions: Specify the Step of X and Z in the Geometry fields, and then click the Update button to update the model plotting. The Step defines the grid for the freehand drawing. The Start and End of X are determined by the geometry in TT curves, while, the End of Z depends on the maximum inverted depth. Enter the velocity values and choose the corresponding colors in the table next to the Geometry fields. To change a value, double-click the relevant cell under the Value column, then enter the value in this cell, and finally click the Refresh button. To change a color, double-click the cell filled with a color under the Color column. To append another row, delete a row, or sort the table, click the Add, Remove, or Sort button next to the table. Draw the initial model. To draw the model, first select the brush by clicking the brush image button, then click the velocity row in the table, and finally click or drag the left mouse button on the color grid. To adjust the brush size, drag the Width slide bar next to the brush image button. To set the model with a uniform velocity value, click the Paint button below the brush image button. To zoom in the model plotting, drag the Zoom slide bar. To cancel or repeat the previous drawing, click the undo or redo image button next to the Paint button. After drawing the model,save the definition in a file by clicking the Save button. And the Load button is used to load the model definition from a file. Click the Close button to complete the model definition. Chapter 4 Running Refraction Tomography 43

47 Figure 4-4: Selecting the Manually Defined option Figure 4-5: The Build Model dialog box Chapter 4 Running Refraction Tomography 44

48 Setting Tomography Parameters To set the tomography parameters, open the Tomography Settings dialog box by clicking the Settings command under the Tomography menu. On the dialog box as shown in figure 4-6, the parameters are grouped by: Modeling Inversion Modeling The grid ray tracing method is used to calculate the forward modeling. The precision and speed of modeling are mainly determined by: Horizontal and Vertical Spacing. The default horizontal spacing is equal to half of the receiver interval in the X direction (dx), while, the default vertical spacing is equal to 1/4 of dx. Horizontal and Vertical Order. The default orders are 5. In theory, the smaller Spacing and the higher Order, the higher precision in modeling but longer calculation time. Inversion The regularized inversion approach is used in the refraction tomography. Following are the major parameters in the inversion: Max Iteration the maximum number of iterations. Constraint including Disturbance the maximum change of average velocity allowed per iteration. Min Velocity the minimum limit of velocity in the inversion. Max Velocity the maximum limit of velocity in the inversion. Picking Error the estimated error of picking in milliseconds (ms). This is a key parameter since the picking precision determines the accuracy of results. Smoothing including Horizontal the horizontal smoothing length. Chapter 4 Running Refraction Tomography 45

49 Vertical the vertical smoothing length. Weighting the smoothing weighting factor in percentage(%). Scalar the smoothing scalar per iteration. Normally, the larger Horizontal or Vertical smoothing length, the more smoother the model in the horizontal or vertical direction. After changing the parameters, you can save the settings in a file by clicking the Save button. Next time, load the settings from a file by clicking the Load button. Finally, click the OK button to apply the settings. Following are some general tips when running the refraction tomography: Start the tomography with the default settings, then change one parameter at a time. Pick first breaks as accurately as possible, and estimate the picking error reasonably. Figure 4-6: The Tomography Settings dialog box Chapter 4 Running Refraction Tomography 46

50 Running Tomography To start the tomography: (1) Click the Start command under the Tomography menu. Then, you will see the Tomography Settings dialog box on which the OK button is replaced by the Start button as shown in figure 4-7. Because the tomography is time consuming, the Tomography Settings dialog box reappears to let you double-check the settings. (2) Check the parameter settings, and then click the Start button. The tomography is started and the results in each iteration are saved in a subdirectory under the directory of the TT curve file. This subdirectory is named as the prefix of TT curve filename + _pxw. After starting the tomography, you may click the Pause or Stop button icon on the Toolbar to pause/resume or stop the inversion at any time. Figure 4-7: Starting the tomography on the Tomography Settings dialog box During the tomography, you can analyze the RMS fitting errors between your picks and the calculated picks. You can also check the errors when reviewing the results after iterations. Chapter 4 Running Refraction Tomography 47

51 Analyzing Fitting Errors To analyze the fitting error, click the Fitting Error QC command under the Tomography menu to open the Fitting Error QC dialog box, where the fitting error of each shot is plotted as a bar graph as shown in figure 4-8. Figure 4-8: The Fitting Error QC dialog box On the dialog box as shown in figure 4-8, you can highlight the current shot by turning on the Highlight the Current check box and change the display of bar graph by clicking the Display button. If there are large fitting errors between your picks and the calculated picks at some shots, check your picks on seismic data by clicking the corresponding bar on the dialog box. Chapter 4 Running Refraction Tomography 48

52 Reviewing Tomography Results To review the results after the tomography is finished: (1) Open the Tomo Review dialog box by clicking the Review command under the Tomography menu. (2) On the dialog box as shown in figure 4-9, click the name in the Tomo Iteration list box to review the tomography results. Here, the name shows the iteration number followed by the average fitting error in ms. If the Tomo Iteration list box is empty (normally after you exit the DW Tomo), click the Load Project button to update the list. To review the iterative results with fixed color grades, turn on the Fixed Mapping Range option. To set color grades, see Displaying Tomography Image in Chapter 5. Figure 4-9: The Tomo Review dialog box After analyzing the fitting errors and reviewing the results, you may: Check your picks or change tomography settings, and then restart tomography. Customize the tomography view and output results. The next chapter will talk about how to customize the tomography view. Chapter 4 Running Refraction Tomography 49

53 Chapter 5 Customizing Tomography View This chapter covers the following topics: Setting view visibility Updating tomography view Plotting TT curves Showing ray paths Displaying tomography image Plotting well data on the velocity section Chapter 5 Customizing Tomography View 50

54 Setting View Visibility As described in Chapter 1, the Display Window has three views: the Trace View, the Travel Time Curves View, and the Tomography Image View. To toggle the visibility of the Trace View, click the Show command under the Trace menu. To set the visibility of the Travel Time Curves View and the Tomography Image View, open the Tomography View dialog box by clicking the Views command under the Tomography menu. On the dialog box as shown in figure 5-1, Click the Tomography Image check box, or the Travel Time Curves check box to toggle the relevant view. Figure 5-1: The Tomography View dialog box Chapter 5 Customizing Tomography View 51

55 Updating Tomography View During the tomography, the calculated first arrivals and ray paths are updated in the Display Window. To change the option of view update, open the Tomography View dialog box by clicking the Views command under the Tomography menu. On the dialog box as shown in figure 5-2, Choose the A Receiver Per Update, A Shot Per Update, or After Iteration option to plot the calculated first arrivals and ray paths when running the tomography. Figure 5-2: Selecting the option of view update Chapter 5 Customizing Tomography View 52

56 Plotting TT Curves The following talks about how to set the display of TT curves and choose the curve options. Setting Curve Display To change the curve display, open the Curve Display dialog box by clicking the TT Curve Display command under the Display menu. On the dialog box as shown in figure 5-3, you can: Define the curve display range and change the visibility of gridlines. Change the annotation settings and choose the background color. To learn about this dialog box, view Chapter 5 in Getting Started with Geogiga Seismic Pro. Figure 5-3: The Curve Display dialog box Chapter 5 Customizing Tomography View 53

57 Choosing Curve Options To select the curve options, open the TT Curve Visual dialog box by clicking the TT Curve Visual command under the Display menu. Figure 5-4: The TT Curve Visual dialog box On the TT Curve Visual dialog box as shown in figure 5-4: Toggle the curve visibility by clicking the relevant check boxes. Change the curve color by clicking the relevant button filled with a color. Highlight adjacent curves by turning on the Highlight Previous/Next Shot option. When there are too many TT curves displayed, choose to show only some of the TT curves by entering the start and skip numbers in the Start and Skip text fields. Toggle the view points of receivers on TT curves by clicking the Show Receivers check box, and specify the point size by entering a value in the Size field. Choose whether to synchronize the display of Trace View and TT Curve View by clicking the Auto Set Time Range with Trace View check box. If this option is selected, the time range of TT curves will be automatically updated when you click the zoom button in the Trace View. Chapter 5 Customizing Tomography View 54

58 Showing Ray Paths The grid ray tracing method is used in the forward modeling. To display the ray paths on the tomography image, open the Ray Visual dialog box by clicking the Ray Visual command under the Display menu. On the dialog box as shown in figure 5-5: Set the visibility of ray paths by clicking the Show All Rays, Show Rays of the Current Shot, or Hide All Rays option. Figure 5-5: The Ray Visual dialog box Chapter 5 Customizing Tomography View 55

59 Displaying Tomography Image The following explains how to define the velocity grades, set the display parameters, and trim the image. Defining Velocity Grades To define the velocity grades, open the Section Grade Definition dialog box by clicking the Image Grade command under the Display menu. On the dialog box as shown in figure 5-6: (1) Select the Mapping Mode by clicking the Linear or Logarithm radio button. (2) Change the number of grades by clicking the Insert, Append, or Remove button. (3) Enter the grade values in the cells under the Value column. For reference, the original and the mapping data ranges are shown above the table. When the grade values are changed, the mapping range will be updated accordingly. To interpolate the grade values based on two cells, select a block of cells by dragging the left mouse button over the relevant cells or clicking the left mouse button on the first and last cells of the block while holding down the Shift key (clicking the Value header will select all cells), then click the Value button under the Interpolate label. (4) To plot sections with colors, turn on the Color option and then change a grade color by double clicking the cell filled with the color under the Color column. To interpolate the grade colors based on two cells, select a block of cells by dragging the left mouse button over the relevant cells or clicking the left mouse button on the first and last cells of the block while holding down the Shift key (clicking the Color header will select all cells), then click the Color button under the Interpolate label. To reverse the color map, click the Reverse button next to the Color check box. (5) To plot sections with symbols, turn on the Symbol option and then set a grade symbol by double clicking a cell under the Symbol column then selecting a symbol from the drop-down list box in that cell. The >> button next to the Symbol check box is to edit predefined symbols. (6) To plot sections with contours, turn on the Contour option, and then select whether to label the contours by clicking the Label check box, finally choose the contours to be plotted by clicking the check boxes under the Contour column. Chapter 5 Customizing Tomography View 56

60 To plot all contours, click the On button next to the All label. To cancel all contours, click the Off button next to the On button. (7) Click the Apply button to update the display with the defined settings. After defining the values, colors, and symbols, you can save the settings in a file by clicking the Save button. The file can be loaded anytime with the Load button. Figure 5-6: The Section Grade Definition dialog box To edit predefined symbols, click the >> button to open the Symbol Editor dialog box as shown in figure 5-7, and then: Edit a symbol by selecting a symbol name from the Symbol List box, then clicking or dragging the left mouse button to draw or the right mouse button to erase on the grids in the Edit panel, and finally clicking the Update button. Chapter 5 Customizing Tomography View 57

61 Design the filling pattern of a symbol, as shown in the Sample panel, by selecting a symbol name from the Symbol List box, then selecting the Shift or Skip option, and finally clicking the Update button. Rename a symbol by selecting a symbol name from the Symbol List box, and then changing the name in the Name field, finally clicking the Update button. Add a symbol by clicking the Add button and then editing the symbol. Delete a symbol by selecting a symbol name from the Symbol List box and then clicking the Remove button. Click the Save button to save the symbols in the g3symbols.sym file under the C:\Users\<username>\.geogiga directory. These symbols are shared by all applications in Geogiga Seismic Pro. Figure 5-7: Editing symbols on the Symbol Editor dialog box Chapter 5 Customizing Tomography View 58

62 Changing Display Parameters To set the display parameters, open the Section Display Settings dialog box by clicking the Image Display command under the Display menu. Figure 5-8: The Section Display Settings dialog box On the Section Display Settings dialog box as shown in figure 5-8: Set the display scale under the Scale label by turning off the Auto option and then entering values in the X and Y fields. The image size, shown in the relevant non-editable fields, is updated accordingly. When the image size is larger than the Display Window size, a scrollbar will appear. Change the annotations of axes under the X Axis or Y Axis label by turning off the Auto option and then entering values in the relevant Major and Minor fields. Chapter 5 Customizing Tomography View 59

63 To modify the start coordinate of annotations, enter a value in the relevant Start field. To define the decimal places of annotations, enter a value in the relevant Decimal Places field or click the arrow button next to the field. To reverse the color section, turn on the Reverse option. Specify the type of tick mark by clicking the Tick Mark combo box and then selecting an option among the None, Inside, Outside, and Cross options from the drop-down list. Toggle the visibility of colorbar by clicking the Colorbar check box. If the Colorbar option is selected, click the Vertical check box to display the colorbar vertically or horizontally. If the velocity section is filled with colors and symbols, click the Value check box to annotate the colorbar with velocity values or symbol names. To specify the decimal places of annotations for colorbar, enter a value in the Decimal Places field under the Colorbar check box or click the arrow button next to the field. Display the title by turning on the Title option and then entering the name in the field next to the option. To update the display with the defined settings, click the Apply button. Trimming Image An image can be trimmed based on the ray coverage as shown in figure 5-9. To toggle the option of trimming, click the Trim Image command under the Display menu. Figure 5-9: Trimming velocity image Chapter 5 Customizing Tomography View 60

64 Plotting Well Data Well data can be plotted on a velocity section as shown in figure Figure 5-10: Plotting well data on a velocity section To display well data, click the Display Wells command under the Display menu to open the Input Well Data dialog box. On the dialog box as shown in figure 5-11: (1) Click the Add button, and then input the well name under the Name column in the Well List. (2) Enter the well location and the starting depth of the well in the Location and Starting Depth fields. (3) Input the depths of well data under the Depth column and select the lithologic symbol from the Lithologic Symbols list to describe the layers. (4) Repeat steps (1)~ (3) to add more wells. To remove a well from the well list, click the Remove button. To save the input of well data in a text file, click the Save button. The well data can be loaded from the text file by clicking the Load button. Chapter 5 Customizing Tomography View 61

65 (5) Click the Apply button to plot well data in color section. To cancel the display of well data, deselect the Show option. To specify the width for the display of wells, enter a value in the Width field or click the arrow button next to the field. Figure 5-11: Inputting Well Data Chapter 5 Customizing Tomography View 62

66 Chapter 6 Outputting Results After running the refraction tomography and customizing the tomography view, you can: Print results. Save results as an image. Export results as the XZV text format. Calculate tomo statics for static correction used in seismic reflection. The following talks about exporting results as XZV text format and calculating tomo statics. To learn how to print results or save results as an image, view Chapter 6 in Getting Started with Geogiga Seismic Pro. Chapter 6 Outputting Results 63

67 Exporting results as XZV Format To export results as the XZV text format: (1) Click the Export as XZV command under the Tomography menu to open the Export Model dialog box. (2) On the dialog box as shown in figure 6-1, enter a name in the File name field and then click the Save button. The XZV text format is recognized by Seismapper. If the output will be plotted in a 3rd party program, turn on the option of Output the full range of data with blanking file if needed. Figure 6-1: The Export Model dialog box Chapter 6 Outputting Results 64

68 Calculating Tomo Statics To calculate tomo statics, open the Calculate Statics dialog box by clicking the Calculate Statics command under the Tomography menu. On the dialog box as shown in figure 6-2: (1) Input the datum and replacement velocity in the Datum and Replacement Velocity fields. (2) Select the Base option between Elevation and Depth, and enter the corresponding parameters. If the Elevation option is selected, the bottom of velocity section will be flat. If the Depth option is chosen, the bottom of velocity section will vary with the topography. (3) Specify the output files for source statics and receiver statics in the Source and Receiver fields. (4) Click the Apply button to calculate tomo statics. Figure 6-2: The Calculate Statics dialog box Chapter 6 Outputting Results 65