GUIDE TO Pro4D TABLE OF CONTENTS. Pro4D Guide

Transcription

1 TL-Pro4D v3.0 1 GUIDE TO Pro4D TABLE OF CONTENTS Pro4D Guide Introduction to TL-Pro4D... 2 Using GeoView... 3 Starting Pro4D... 6 Modeling Well Logs/Systematic Changes... 8 Calibration and Analysis of Time Lapse Seismic Data Importing Horizons Data Manager Modifying the Seismic Display Picking Horizons Calibration Inversion Volumetrics... 84

2 2 Hampson-Russell Software Services Introduction to TL-Pro4D TL-Pro4D is a program that integrates all the key elements required for time-lapse seismic monitoring. The program includes a well log toolkit, fluid replacement and rock physics modeling, synthetic seismic generation, and a library of functions for the display, comparison, calibration, interpretation and inversion of multiple 3D data volumes. The general objective of time lapse or 4D seismic monitoring is to track production related changes in the reservoir and determine areas of bypassed production, or inefficiencies in the production process. This is accomplished through the comparison of 3D seismic surveys that have been recorded at various points in time over the life of the field. The analysis of time-lapse seismic data generally includes the following steps: 1) Estimate the types of velocity and density changes that will occur in the reservoir during production. 2) Create synthetic seismic traces that represent the reservoir conditions for a range of production scenarios. 3) Analyze the synthetic traces to determine the types of changes that may occur in the seismic data. 4) Compare the seismic surveys that were recorded at various times in the field s production history. 5) Calibrate the 3D seismic volumes to remove spurious differences related to seismic acquisition and processing as well as changes in the near surface. 6) Subtract the calibrated seismic surveys and map the differences. 7) Interpret the calibrated 3D surveys and the difference surveys to determine the areas of the field that have been changed during production. 8) Create Time Lapse Inversion with low frequency updates and 4D Inversion 9) Compare the seismic differences to the synthetic traces to analyze the types of changes that have occurred in the reservoir (pressure, temperature, saturation, etc.). 10) Estimate the area and volume of these produced areas and compare to the known production of the field. This tutorial takes you through the entire time-lapse analysis process from modeling to the analysis and comparison of two 3D seismic data volumes. The locations of several wells and one actual set of well logs are included to help interpret and map the differences in the reservoir where production induced changes have occurred. January 2008

3 TL-Pro4D v3.0 3 Using GeoView GeoView is a program that has been provided to you along with Pro4D. GeoView serves two purposes. One purpose is to load and manage all well logs that are used by any Hampson- Russell program, including Pro4D. The second purpose is to launch other programs, such as Pro4D. To start this tutorial, first start the GeoView program. If you are on a Unix workstation, do this by going to a command window and typing in the command: geoview <RETURN> If you are on a PC, double click on the GeoView icon or select GeoView under the Start menu. The GeoView main window now appears: If you are running GeoView for the first time, it will appear blank. If you have run GeoView before, it will show the database you last worked on. In this tutorial, we will read in a database that has been previously constructed, containing 13 wells. If you are unfamiliar with the options in GeoView, or if you are uncertain about the process of entering logs into GeoView, it would be a good idea to go through look under the Help button under the GeoView banner. Open the existing GeoView database by clicking on Database / Open: Using the file selection menu, select the directory called Pro4D.wdb as shown below.

4 4 Hampson-Russell Software Services Note that databases within GeoView are identified by the extension, wdb. Click on OK on this menu. The GeoView main window now shows the 13 wells within this database: January 2008

5 TL-Pro4D v3.0 5 Unfortunately, the logs for 12 of these wells are not available for inclusion in this database. Only their coordinate data is included here to provide location information to the Pro4D program. However, Well 1 included here is from a nearby field and has logs loaded that can be used in modeling. If you click the Well 1 name on the GeoView view list and select Display Well under the Table View, you will see the logs for this well including the checkshot information: GeoView contains many versatile functions for loading, editing and displaying logs, including check shot correction and log correlation with seismic data. For a complete tutorial on these capabilities, see the tutorial section entitled: Using GeoView and elog.

6 6 Hampson-Russell Software Services Starting Pro4D On the main GeoView window, click the Pro4D button and then select Start a New Project: Under your current directory, type in the new Project name Models and select OK. January 2008

7 TL-Pro4D v3.0 7 The main Pro4D window appears with the current project and database indicated in red at the bottom. Before starting the Pro4D project, it is a good time to look at the on-line help features in Pro4D. If you click on the Help button at the top of the Pro4D main window, you will see a pull-down menu with several choices. Click on Hampson-Russell Assistant, and a new window will appear showing you the complete documentation for the Pro4D program. Let us now review our objective, at this point in the Pro4D process. We want to estimate the types of changes that may occur in the reservoir as a result of the production process. In this example exercise, the production process is gas injection. To do the estimation, we will load well log data from the area and modify the velocity and density logs in a manner that is consistent with gas injection at the top of the reservoir.

8 8 Hampson-Russell Software Services Modeling Well Logs/Systematic Changes Start the Modeling process by bringing the logs from the GeoView database into the modeling window. To do this, click on the Single Well option under the Modeling button on the left of the Pro4D window. The following menu will appear. Highlight Well 1 and press OK to continue. Well 1 will be read into the modeling window and it will appear as follows: January 2008

9 TL-Pro4D v3.0 9 Select the Display Current Wavelet option on the Wavelet pull -down menu on the sidebar of the Modeling window.

10 10 Hampson-Russell Software Services The default wavelet for processing is wave0. Several options to extract or create a new wavelet are available under Wavelet on the main Pro4D Modeling window. The processing history of the wavelet and its frequency content can be displayed by selecting the tabs on the right of the wavelet display: Close the wavelet display window by clicking the X in the upper right corner and return to the main Modeling window. The objective of our modeling study is to predict the changes in seismic response that will occur when gas is injected into the reservoir. The velocity and density structure of the model has been defined by the well log data. All of the necessary information is available to generate the synthetic seismograms. Select the Systematic Changes option under Synthetic. The zone identified in the following window will determine where the systematic changes will be applied. Set the depth for the zone of interest from meters. It is assumed that low porosity rocks will not have sufficient permeability to allow the transfer of fluids during production. These low porosity areas of the reservoir are effectively removed from the modeling process by using a density cut-off of 2800 kg/m3. If the log density values exceed this threshold the program will assume that fluid replacement did not occur and the input log samples will be copied to the output well log. Set these parameters as shown below: January 2008

11 TL-Pro4D v After filling in this menu, click Next >> to continue and activate the Systematic Changes menu. Fill in the parameter selections as shown:

12 12 Hampson-Russell Software Services This menu allows you to create a series of well logs, based on the initial well, that represent the types of production-induced changes that are expected in the reservoir. In this example, gas has been injected into the top of the reservoir over a 12 year time period. During this time, the thickness of the injected gas bank will increase and the gas saturation will increase as well. Fill in the menu as shown to create 44 pseudo wells, which represent the range of gas thickness and saturation values shown here. Synthetic seismic traces are automatically calculated for each of these modified wells and are organized into a systematic grid for display. Zone thickness will be changed from zero to 100 meters incrementing by 10. Saturation levels ranging from 0 to 60% will be calculated. The option to Output Base Survey is useful to include in order that comparison of the synthetics with and without the systematic changes may be facilitated. In essence, the base survey is a volume of identical synthetic traces created prior to any fluid replacement, in the same format or geometry as the output volume containing the modeled changes. Before the updated well logs can be created, we must define relationships between P and S velocities, density and gas saturation. We will use Gassmann s equation to calculate the changes in these seismic properties as a function of fluid saturation. Select Next >> to generate the menus which define key parameters for Gassmann s equation. The menu shown below specifies information relating to the initial state of the reservoir and the log data. January 2008

13 TL-Pro4D v The pulldown tabs beside each option reveal the alternatives available to describe the input logs. As was mentioned earlier, the most recent version of the logs will be defaulted as the input for further processing. It is always important to check the input name since several versions can be created in a project, especially in testing and the most recently created version may not always be best choice. Copy the S-wave option and Water Saturation Constant parameters as shown above and select Next >>. The Biot-Gassman Parameters menu gathers key parameters that are used to perform fluid substitutions using Gassman s relation. There is a wide range of menu paths that might be chosen from here to denote the petrophysical properties to be modeled. Toggle the Type for any of Gas, Oil or Brine to view the initial selections. For the current exercise, the rock matrix will be defined by calculation from minerals. We are modeling the response of gas injection into a dolomite reservoir. Select Calculated from Minerals as shown to obtain the following menu. Select Dolomite, press Apply and OK to register these changes.

14 14 Hampson-Russell Software Services When this warning menu appears, click Yes. Select the Use Fluid Calculator option and that menu will appear. Fill in the Fluid Properties Calculator as shown and then press the Calculate button: January 2008

15 TL-Pro4D v Press OK here and again on the Biot-Gassman menu to move to the Output Saturation Ratio menu. Adjust the Output Ratio percentages: All the necessary information is now available to create new well logs that will contain changes in velocity and density that are consistent with a gas flood in the reservoir. Press OK, then Next >> to continue with modeling. The next menu defines the output file specifications. Click Next>> to accept the default parameters.

16 16 Hampson-Russell Software Services The final menu in this set will appear. This menu, shown below, allows us to review the parameters we have provided to the program. This same information is available after processing as well and can be accessed by pressing the History tab at the top of the Pro4D window. Press OK to generate the synthetics. The synthetics will be created and displayed in a Pro4D window as shown below. Another window, the Well To Seismic Map Menu will also be created. This menu will be discussed in the seismic data matching section of the guide but since it is not relevant at this stage; press Cancel to remove it. January 2008

17 TL-Pro4D v Scroll the synthetic seismic display to see a variable thickness gas bank (from 0 to 100 m) with constant Gas Saturation (0%) within the gas bank. The synthetic can be examined in more detail by adjusting the display parameters under View (or by clicking on the eyeball icon). View/Parameters allows you to control all aspects of the Pro4D display. Choosing the well_1_syn_vp file next to Color Data Volume allows us to display the velocity logs, in color, underneath the synthetic trace response. Press Apply. Selecting the Color Key tab brings up the menu shown below, which allows us to modify the color scales of the data. Press Data Range to select a velocity range which will highlight the changes caused by variation in gas saturation.

18 18 Hampson-Russell Software Services Adjust the velocity scale to 4500 to 5500 as shown. Click OK here and Apply on the View Parameters menu, choose the Scale tab, change the Time Axis to 15 inches/sec and click OK. Finally, choose View/Wiggle Traces: Fill Off to remove the variable area fill of the peaks. (Fill on or off will variably help or hinder the optics of your displays, change this setting according to your preference.) January 2008

19 TL-Pro4D v The display will look as shown below on Line 2 where Gas Saturation is 10%: The velocity reductions in the reservoir zone are obvious in this display, along with the corresponding changes in seismic character.

20 20 Hampson-Russell Software Services Using the arrow key on the top of the display and notice the changes as you scroll from Gas Saturation of 0 % through until you reach Saturation line 7. The display on the right shows the response at 60% gas saturation. Click on the pulldown arrow beside Saturation, select Thickness and scroll through the synthetic data again along the Thickness axis. January 2008

21 TL-Pro4D v Each crossline Thickness display shows the effects of a constant gas thickness with variable saturation. These synthetic seismograms can easily be examined to reveal the differences caused by the modeled changes in gas saturation. To accomplish this, first click on Window/Copy Window option at the top of the display to make a replica of this existing window. Then press File/Close Seismic to remove the vp file from the new window. On the selection menu, select well_1_syn_vp, click on Close Selected Volume, confirm this choice when asked and then Cancel the Seismic Volume List menu. Click the eyeball icon on this window to access the display parameter menu. Click on the pulldown beside Color Data Volume and you will now be able to subtract the two volumes as shown below.

22 22 Hampson-Russell Software Services Select the parameters shown above including the View Mode, and press OK. Then change the view axis back to Gas Saturation line 7 to create the display shown below. This display shows the subtraction of the base (constant) and monitor (variable gas saturation and thickness) synthetics. Selecting the difference between base and monitor synthetic as the trace overlay as well as the color volume can enhance this display further. Do this by clicking on the eyeball icon and changing the Trace Data Volume. This display should be scrolled through to examine the types of differences that should be caused by gas injection in the reservoir. Note that we have put the trace fill back on in this display, but this is optional. January 2008

23 TL-Pro4D v We have now completed the first part of the Pro4D guide. Close down the Pro4D program by closing all of the modeling windows and clicking on File/Exit Project in the main Pro4D window.

24 24 Hampson-Russell Software Services Calibration and Analysis of Time Lapse Seismic Data This example will illustrate the use of Pro4D to compare, calibrate and analyze two 3D seismic volumes that were recorded before and after gas injection. Several steps will be repeated from the previous example so they will be covered briefly here. In this exercise we will use the same Database as was used in the first exercise. To start Pro4D again, click on the Pro4D button on the GeoView main window. You will see the following menu appear: We wish to create a new project and name it Pro4D_guide, as shown below: January 2008

25 TL-Pro4D v Click on OK and the Pro4D main window appears: The first task is to load the seismic data to this project from segy files. Find your SEGY data directory and use Add All >> to select the file base.sgy and mon.sgy as shown.

26 26 Hampson-Russell Software Services Click on Next >> on this menu and the General Information menu appears. Click on Grouped Volumes and name the group 4D as shown: Click Next>>. January 2008

27 TL-Pro4D v The information derived by the program is correct, so click Next >> to see the SEGY Format page:

28 28 Hampson-Russell Software Services Here, the Inline and Xline byte location values are not correct. Proper header locations for the Inline and Xline bytes, are found using the Header Dump option. Update the header information as shown. The correct header byte for Inline is byte 9 and for Xline is byte 13. Click the Apply Format to all files button. If you are reading this data set for the first time, the following message will appear, warning you that the data will now be scanned, and certain information stored: January 2008

29 TL-Pro4D v Click on Yes to begin the scanning process. This may take several minutes during which time you will see a progress dialog box indicating the progress. When the scanning has finished, the Geometry menu appears: This menu is used to specify the detailed geometry of the seismic grid, including the X-Y locations of the origin, and possible rotation. Click on OK. After building the geometry files, a new window showing the seismic data will appear. A second window shows how each of the wells is mapped into this seismic volume:

30 30 Hampson-Russell Software Services In this case, all the wells are mapped to the correct Inline / Xline locations because the pseudo X and Y locations have been properly set within the GeoView database. If this had not been done previously, you could type in new values for the Inline and Xline numbers. Click on OK to accept this menu. The Pro4D main window now shows Inline 110. We need to see the Base map so that we can orient our data. To do that, click on View / Base Map on the Pro4D main window: The base map appears, showing that the seismic volume is a rectangular grid. You can also see the 13 wells located within the volume. Close the basemap. January 2008

31 TL-Pro4D v Importing Horizons An important component for analysis between two time lapse surveys often lies in the comparison of seismic attributes following horizons in the zone of interest. The horizons can be used to window the data vertically and to guide it horizontally. Pro4D allows both picking of new horizons and import of horizons that have been previously picked elsewhere. Pro4D can read in picks in Landmark, Geoquest, or General ASCII formats. To start the Import process, click on Data Manager/ Horizon /From File: From the menu selection box in the guide directory, select the file called top.hrz in your Pro4D guide data file: Click on OK on this menu and the Pick File Format menu appears.:

32 32 Hampson-Russell Software Services We will be reading in a file with one horizon in Free Format. Select the items on the menu as shown above and click on Display the first selected file to see the file that we are reading: Stretch or scroll the window to see all columns and click on Next >> on the Pick File Format menu to open the Name & Column Number page, describing the format of this file: Fill in the menu as shown below. Note that we do not need to Append the Volume name to horizon name in this simple project example. Click on OK and close the display of the import horizon file. January 2008

33 TL-Pro4D v Verify the Pick Summary by clicking OK and the new horizon will be displayed at 1000 milliseconds in the Pro4D seismic window whether you display the base or monitor data.

34 34 Hampson-Russell Software Services Data Manager Often in Time Lapse interpretation, the data contains several vintages of seismic that need to be calibrated and compared to the original survey. This generates a very large and often confusing amount of data. The Data Manager feature of Pro4D facilitates organization, ensures consistency of processing and interpretation of all volumes at every stage throughout the calibration process. The guide example has only one monitor survey but the data management feature is designed to handle any number of surveys with the same ease as the single monitor application. Select the Data Explorer option under Data Manager. The Data Type pull down offers lists and detailed information for all of the data currently loaded or created within the project. Select Seismic Volume under Data Type. The volume names are listed in the Tree View on the left of the window. Click the Information View option at the top of the window if you wish to add the Geometry and volume History information as well. The Information View is updated to the volume highlighted on either Tree or List View. Finally, highlight the 4D_base(base) volume and then Set as Reference under the Actions tab. This will indicate to the program for all processes to follow, which volume will be used as the reference for data calibration. An asterisk will identify the selected reference volume. January 2008

35 TL-Pro4D v Double Click on 4D_base(base)*. The new 4D super-volume window will be opened:. The color display will show the difference of the selected sub-volume associated with the 4D super-volume minus the base data. Close the Data Explorer and the previous Pro4D window.

36 36 Hampson-Russell Software Services Modifying the Seismic Display Currently the display is showing the base seismic (4d_base) as a wiggle trace and the difference volume as a color background. In this case the difference volume has zero amplitude because the base data is subtracted from itself. There are several display modifications we might choose to make using the Seismic View Parameters menu. We can make the display menu appear under View/Parameters or by clicking on the eyeball icon as shown: The Seismic View Parameters Menu will appear. The 4D super volume is selected as the wiggle trace data as shown below. Press OK: At the bottom of the display window a new selection box will appear where the wiggle trace data can be toggled between the volumes that are contained in the supervolume. Select the monitor volume as shown below: When this is selected, the wiggle trace will change to show the monitor data and the difference volume will change to the difference between the monitor and base surveys. The resulting display is shown below. January 2008

37 TL-Pro4D v To look at a different inline, type the number 190 in the numerical field at the top of the display and press Enter. Inline 190 now appears. Stretch your window and scroll down the data so that you can see a sonic log displayed for Well 1: To see one of the cross lines, click on the field on the icon bar at the top of the display which currently says Inline. Select the option Xline on the pulldown menu. Then type in the number 228 and Enter to see Cross Line 228 (Cross lines can also be selected by double clicking on the corresponding seismic trace). Another way to change lines is to use the Base Map and simply click on the line you wish to display in the seismic windows. The grid cross-reference at the bottom of the map identifies the location.

38 38 Hampson-Russell Software Services Picking Horizons Pro4D provides the capability to pick additional horizons. In this example, we will pick a marker horizon below the reservoir for use as a calibration reference. Use the Supervolume selection box at the bottom of the window to display the base survey prior to picking. Then use the line selection box to display Inline 190. To pick a horizon, click on Interpretation / Pick Horizons on the side bar of the Base_data display: A menu appears, allowing you to specify the name of the new horizon: January 2008

39 TL-Pro4D v Change the name for the horizon we will pick to Horizon 2. In cases where the same horizon will be picked on various vintages of the survey, the Append volume name option would be needed but in this case, we will pick the horizon only on the base data so the unique Horizon name is sufficient. Click on OK. The bottom of the Pro4D main window changes as shown below, and a map option will be offered, which will display your picks. Select Yes to display the map. Scroll down to window the strong peak at 1200 ms..

40 40 Hampson-Russell Software Services Modify the parameters for picking so that the Mode is Left & Right Repeat and ensure that Snap is set to Peak. Picking is done by pointing the mouse at specific locations and clicking the left mouse button. This requires the program to find the nearest peak from your first pick and to automatically track that event to the left and right of the pick, all the way to the ends of the displayed line. To do that now, move the mouse cursor to the strong peak, just below 1200 ms as shown below: Click the left mouse button and the event will be picked across the entire visible cross line as shown: At the same time, the picked times will be displayed on the base map although they are not immediately visible under the seismic location line. Simply step one line away from the line: January 2008

41 TL-Pro4D v Now let s pick two more crosslines manually, and then ask the program to pick the rest of the volume automatically. Change the display to show crossline 228, by typing that number in the Xline number field and pressing Enter. The display now looks like this: Note that an orange cross appears at the intersection of inline 190. This will help guide us as we pick through, especially more complicated, datasets. Point and click at any location along the peak horizon. The event is now picked on cross line 228: Now change the display to another crossline by simply clicking a new location on the map. Use the Guide at the bottom of the map to help locate Xline 274 and double click. Then pick the event as shown below:

42 42 Hampson-Russell Software Services Now our horizon map shows the three colored lines that we have picked: With these three picked cross lines, we will ask the program to pick the rest of the horizon automatically. To do that, choose Automatic Picking from the list of horizon Options: The Automatic Picking menu contains various options, in particular, the Search Distance is set to +/- 25 ms from the interpolated pick value at every trace. Note that the option exists to Apply restricted zones and limit automatic picking in areas such as fault regions, as specified by the user. January 2008

43 TL-Pro4D v Click on OK to perform the automatic picking with the parameters shown. At the end of the process, the completed horizon map appears:

44 44 Hampson-Russell Software Services Sometimes it is helpful to smooth the picked horizon. To do that, go back to Options and click on Smooth Horizon: On the Smooth Horizon menu, set the smoother lengths to 5 inlines by 5 cross lines: Click OK, and the picked horizon is modified and the map updated: January 2008

45 TL-Pro4D v If another horizon were to be picked at this point, we would use Options or the Horizon pull down menu to choose the horizon or to name a new horizon to pick. The user can select any dataset loaded into the Super-volume for the display and then choose an existing, or create a new, horizon to pick. The program will automatically identify the corresponding data volume with its horizons in the Data Explorer. Finally, save Horizon 2 by clicking OK to the left of the Options button at the bottom of the seismic display window. Horizon 2 is now displayed in blue and you have exited the horizon picking operation. We are now ready to begin the unique features of Pro4D. Return the trace display to mon on Crossline 228 and close any extraneous windows at this time.

46 46 Hampson-Russell Software Services Calibration During the actual calibration processing, the efficiency of handling multiple volumes through a single set of commands will become evident. Under the Comparison pulldown menu, select Cross Correlation and update the first menu as shown: Throughout Pro4D processing, the Set Reference volume chosen earlier in the Explorer option of Data Manager will always be selected as the reference from which to compare other data January 2008

47 TL-Pro4D v volumes. The input volume will be automatically updated as the various processes are applied to the monitor data. The default selection of volumes available for processing will default to Process All Sub Volumes. This will ensure the consistency required when there are several monitor surveys that need to be calibrated. We have requested the output of data slices showing the correlation coefficient and the time shift required to align the traces. Press Next >> to continue. We will run the cross correlation in a single window from 1000 to 1300 milliseconds and set a maximum time shift of 35 ms. Click Next >> to continue and then OK. Two data slices or maps will appear as well as a trace display showing the correlation of each trace.

48 48 Hampson-Russell Software Services The correlation slice indicates that with no processing of these datasets, the average correlation coefficients are less than 75%. The band of red and brown indicating lower correlation, below 0.53 (53%) is in the area of wells in which we are expecting to see production-induced changes in this data. It is important to leave these areas out of the processing window during data matching so that these production-related effects will not be artificially reduced in the final differencing. The horizontal red line across these maps indicates the location of the current line in the seismic display window. These indicators can be removed by clicking on the Mark Seismic Lines option under the View button. The Correlation time shift slice shows that there is a rough average bulk shift of 22 milliseconds between these two datasets. January 2008

49 TL-Pro4D v The statistical distribution of the time delays can be observed by pressing control h on while focused on the dataslice window. Pressing shift s will bring up a menu showing a statistical summary. At this point, we will close the cross correlation windows. All maps can be closed by simply pressing the escape key. To reopen data slices at any time use Data Explorer in Data Manager, select and double click to display, any map within the project from the list given under the Data Type: Data Slice.

50 50 Hampson-Russell Software Services We will continue with calibration of the time and phase shifts needed to match these two datasets where production effects are not expected. This will be an iterative process. We will initially perform a first order global phase correction and bulk time shift. Other matching processes will follow. Visual comparison between corresponding seismic data before and after each calibration process is easiest when we use the split screen view loaded with the super-volumes. To have the program automatically place and update the current comparisons in split window mode, de select the option to Display Output in New Dialog under the View button. January 2008

51 TL-Pro4D v Begin Phase and Time Matching, by making that selection under Design and Apply in Calibration: The menu is filled in correctly as shown below. Select Next >>. On the following parameter menu, we will specify a Global Average for the phase and time shift correction. This option ensures that we will not remove trace by trace spatial variations in the data that may be the defining characteristics of the production process. Our zone of interest on this dataset is between 1000 and 1300 milliseconds so this is where we want to set our design window. The correlation threshold is set to trace pairs whose correlation is greater than 0.65 or 65%. Finally we will set the maximum correlation shift to 35 milliseconds since we saw shifts of nearly that magnitude on our earlier cross correlation. Traces that meet the required thresholds are assumed to be free of production effects and their average values will be used to define the phase and time matching parameters. The correction will be applied to every trace in the volume so the local variations will be preserved. Select Next >> and then OK.

52 52 Hampson-Russell Software Services After processing is complete the following information message will appear: January 2008

53 TL-Pro4D v Look at Crossline 228. Scroll down to a window within the zone of interest ( ms.). The phase shift we just applied is most visible looking at the strong events around 1200 milliseconds. We can clearly see here also that the 30 ms time shift has been applied: In the mon display, before any phase and time matching between the base and monitor surveys, we see significant difference energy all over the data. In the display on the right, after global phase and time matching we see relatively few bright amplitude areas. The region of the reservoir where we are expecting to see production effects is around 1080ms. We can see that we need to further minimize the difference amplitudes away from the reservoir. If this project had contained more than one monitor survey, we would simply use the Trace display controls at the bottom of the window to view the phase and time matching for each additional monitor processed. The next step is to apply a Shaping Filter, again found under Calibration/Design and Apply. We will now look for improvement in the base data compared to the phase and time shifted monitor data. Update the Input menu as shown and click Next >>:

54 54 Hampson-Russell Software Services The shaping filter processing parameters include a Maximum correlation shift and a Correlation threshold. The limit for shifts is set to 10 ms since bulk shifts have already been applied. The threshold is a key parameter that tells the program to exclude traces where the correlation is lower than 70% because these areas are where the production effects are dominant. We want to design the frequency and phase shaping where the data is unaffected by production and the correlation should be higher. Fill in the menu as shown and proceed with the operation. January 2008

55 TL-Pro4D v Referring to statistics in the Notepad window, we see that after the phase matching and prior to the first pass of the shaping filter, the maximum correlation found in the data was 86%. However, after the first pass of Full matching shaping filter was applied the maximum correlation increased up to almost 97%. The initial the correlation was not above 75%, so we have seen a significant improvement in the data during the matching process. The traces not contributing to the shaping filter had lower correlation and were likely to be in the area of production effects or on the outside edges of the dataset. Again, the significant improvement in correlation is obvious since the post shaping filter section, on the right, has fewer bright spots. One of the few areas of lower correlation, which we were hoping to see, is in the trough at 1080 ms and just above it. The Filter is relatively zero phase, but it attempts to make a full phase, frequency and amplitude match between the datasets.

56 56 Hampson-Russell Software Services At this point, the wavelets have been matched between the two datasets. However, trace by trace time delays have not been corrected. Proceed under Calibration/Design and Apply to XCorrelation Time Shift. Fill in the menus as shown below: January 2008

57 TL-Pro4D v In this cross-correlation, the window ends in the shallow data above the zone of interest. We have limited the time shift to10 ms again because the larger bulk shifts have already been removed. After we apply these optimized statics to the shallow data, where we expect no differences, we will apply time variant statics to the data. This will improve the correlation not only above but also within and beneath the gas-injected area, where time differences are expected to occur as well. Click OK to begin processing. When processing is complete there will be 3 new windows: the correlation slice, the time shift slice and the shifted monitor seismic data which we will want to compare to the monitor prior to the shallow window statics shift.

58 58 Hampson-Russell Software Services The correlation is generally smooth and not indicating the trend of the well locations. The shifts are very small: minus 5 to plus 6 ms. Close these slices once you have taken a look at them and return to the seismic display now containing 4D_phsh_shp_shifted. One way to assess the quality of the overall calibration is to repeat the same cross-correlation process that was done at the beginning of the process. Use Comparison / Cross Correlation. Output a correlation slice using a time window starting at 1000 ms and extending 300 ms below that. When the slices are created, compare them to the correlation_raw slices that were created at the beginning of the calibration process. January 2008

59 TL-Pro4D v The single static shift above the reservoir decreases the level of difference above the zone of interest. At the same time the areas of production (at 1080 ms and the trough above it) and corresponding areas below the producing zone are becoming brighter. This is because velocity changes in the reservoir affect the travel time of the events beneath. Time-variant time adjustments are designed to compensate for these changes in velocity so that differences are comparing only the differences in reflectivity between the two surveys and not mis-alignments in structure. Before we apply Time-variant statics, we will pick Horizon 2 on the Monitor dataset in preparation for Inversion. Inversion of the monitor survey is often compromised due to changes in velocity that are below the frequency content of the seismic wavelet. When this occurs, the impedance differences do not accurately represent the reservoir changes. By picking Horizon 2

60 60 Hampson-Russell Software Services on the monitor data we can provide time delay information that will enhance the inversion model below the seismic bandwidth. First remove Split View option under View. And then toggle the Color option to the off position on the seismic window displaying 4D_phsh_shp_shifted seismic data. Then reopen the Horizon Picker by selecting Interpretation/Pick horizons Then give the new Monitor Horizon a name and select a Presentation color. Pick the peak horizon on a couple of Inlines and Xines and then use the Automatic Picking Option to infill the new horizon. January 2008

61 TL-Pro4D v Again use the Horizon Picker Option to Smooth Horizon: Click OK on the bottom of the window to close the Horizon Picker and save the new Monitor Horizon. Click the Eye icon and then the Horizons tab. Select All Horizons in Project and then click OK to overlay the horizons on the seismic. Now we will toggle the color overlay back on by clicking the box at the bottom of the seismic display. Under View, toggle the Wiggle Traces Fill On again and also under View, return to the Split View seismic display. Return the seismic display to Xline 228:

62 62 Hampson-Russell Software Services Now we can continue to derive and apply time variant statics. These statics corrections can either be applied in a single step, or in a two step process that allows removal of bad correlation picks prior to application. In this case, we will apply the process in two steps. First, select Comparison/Cross Correlation. In the next menu, select the 3D Cube Output as shown below. In the Cross Correlation Parameter menu, set the start time to 750 ms, window length at 40, with a maximum time shift of 11. With these settings, the first cross correlation window will extend from the start of the live data to 790 ms. Next, set the 3D Cube Number of Samples to 135 and the 3D Cube Sampling Interval to 4 ms. With these settings, there will be a total of 135 cross correlation windows (each one 40 ms long) and each of these windows will be delayed by 4 ms, or one time sample (ie. The next cross correlation window will be from 754 to 794, the next will be delayed by another 4 ms and so on, the last will be from 1290 to 1330). This will provide two January 2008

63 TL-Pro4D v D cubes. One of time shift and the other of cross-correlation coefficient starting at 770 ms ( /2) to 1290 ms. The resulting cubes are shown below.

64 64 Hampson-Russell Software Services Press the eyeball icon on the xcor display. Then click on the Color Key tab. Set the display to Individual and remove the Normalized Scale option as shown. Click on the Data Range button and use Default Scan to set the individual range. Change the Color Scheme to Rainbow on the xcor display. Click OK. Typically, bad time shifts occur when correlation coefficients are poor. This is often due to poor reflectivity. These time shifts will be removed in the next step when the shifts are applied. January 2008

65 TL-Pro4D v Time Variant statics are applied under Calibration/Apply Only. Select DataSlice Time Shift. Check the Use Advanced Features box and give a new name to the output data: 4D_TVshifted. Press Next >>.

66 66 Hampson-Russell Software Services January 2008

67 TL-Pro4D v The final comparison of the seismic sections before and after Time Variant Statics is shown above. Now the differences have become more subtle and difficult to assess with the current display. There are a couple of simple ways to highlight the final improvement in calibration processing. First, select the View parameters for each side of the Split View Seismic window and display the difference traces in the Trace display.

68 68 Hampson-Russell Software Services A large number of coherent difference events, particularly in the deeper section before time variant statics are gone or very much attenuated after the last process. Yet, the areas of production effects, around the wells still show a lot of bright amplitude in the zone between the two marker horizons. Finally, the aerial extent of the production-affected zones can be defined through creating amplitude slices from the monitor base difference volume. First remove Split View option under View. This will allow the window to perform subtraction of the base reference from the final processed monitor survey without creating a difference volume. Select Attributes/Horizon Attributes: Choose the difference Input Volume 4D_TVshifted 4D_base and select the Normalized Difference RMS option: January 2008

69 TL-Pro4D v Extracting difference amplitudes from the reservoir zone (between Horizons 1 and 2) allows us to highlight the reflectivity changes caused by the production process. Fill in the parameter menu as shown:

70 70 Hampson-Russell Software Services The final normalized difference amplitude map shows the data matching has reduced the differences to about 30% of the original signal level in areas that were not affected by production. However, in the areas near the wells, the difference in amplitude is often greater than 50% of the original signal level. This large change in reflectivity is due to the changes caused by production during the time period between the two surveys. January 2008

71 TL-Pro4D v Inversion Inverting seismic time lapse volumes can provide detailed information regarding acoustic impedance changes between the base and monitor surveys. Unfortunately, time delays caused by velocity changes in the reservoir can adversely affect the inversion comparison. Inversion of the monitor survey is often compromised due to changes in velocity that are below the frequency content of the seismic wavelet. When this occurs, the impedance, or velocity, differences do not accurately represent the reservoir changes. Time delay information can be used to enhance the inversion process and provide information that is below the seismic bandwidth. Velocity decrease can be calculated from the cross-correlation and time shift cubes already used to determine time variant statistics. Scalers are multiplied with initial models to provide the low frequency information. This greatly improves the Inversion differences over past versions. Click the 4D Inversion button to open the time lapse inversion option located in the AutoCalibration portion of Pro4D. Click OK on the Autocal license agreement to initiate the process. After the Autocal window opened, click Inversion. Then click Model to create the initial low frequency model for inversion and select Build/Rebuild model to begin the modelling process.

72 72 Hampson-Russell Software Services Create a blank new model (default) and provide a name for the model. Click Next to continue. Choose Typical setup and click Next to continue. Since the geology is relatively consistent, we will select only Well 1 for building the initial model. Add Well 1 to the Selection window. Click Next to continue. Select the 4D_base volume from the Pull down list, to provide the geometry for the model. Then click Next. January 2008

73 TL-Pro4D v Units for the log data should default as shown, click Next: Using the Add and Remove buttons, select top (Horizon 1) and the original Horizon 2 to provide structure for the model. Click Next.

74 74 Hampson-Russell Software Services Choose Apply smoother to filter the interpolated well logs using the default frequency. Click Next. Choose Display in new window and press OK. January 2008

75 TL-Pro4D v The model will appear. Adjust the window to view Xline 228: Click the Apply LF Scaler button and select Horizon Based to update the low frequency model for the monitor survey. The Input Model will be shown first. Click Next and the Horizon Selections menu will appear: Fill in the Horizon selections as shown. This will create a series of scalers for each low frequency model. These scalers will be filtered to the same frequency as the low frequency

76 76 Hampson-Russell Software Services model. The updated low frequency model will be saved in a supervolume format for use in the time lapse inversion. Press Next. Create a Bandpass filter to filter the model scalers. Accept defaults on other menu pages and press OK on the final menu page to create the updated models. The updated model will appear in the seismic window: January 2008

77 TL-Pro4D v Click Inversion on the main Autocal window to continue the inversion process. Fill in the first menu to appear as shown: On the next Menu, select the Inversion target zone and then click Next:

78 78 Hampson-Russell Software Services Accept the defaults on the next menu and continue: Choose the Calculate and apply single global scaler option as shown and continue. This will insure the inversion process will not produce inconsistencies in amplitude: January 2008

79 TL-Pro4D v Set the scaling window as shown and press Next: Leave the default for Single trace inversion. Click Next and then OK on the next and the final menu. The inversion process should now start and the program will invert the subvolume(s) with the appropriate model. A window will pop up that allows Speed Optimization. The number of threads refers to the number of CPUs available on your computer. Update as appropriate and click OK.

80 80 Hampson-Russell Software Services When the inversions are complete, they will appear in the seismic window. The display will show the inverted traces with the impedance difference in the color background. Select the mon display from the options at the bottom of the window: The resulting inverted volumes are available in the main Pro4D window. Open a Data Explorer window and under Seismic Volume find the Inverted_result supervolume. Double click on the reference volume to display this volume in the main Pro4D window. January 2008

81 TL-Pro4D v Using the supervolume controls at the base of the window, display the inversion differences as background color: From the Pro4D window, click Attributes and select Horizon Attributes. For Input volumes, choose the difference between the inverted result and the base result. Select Normalized Diff RMS as the attribute. This will create a slice showing the fractional change in impedance estimated by the inversions.

82 82 Hampson-Russell Software Services Complete the next menu as shown to restrict the analysis to the reservoir zone. Click Next. The results can be automatically smoothed as shown in the menu below. Click OK to create the slices. January 2008

83 TL-Pro4D v This shows the areas affected by production and the maximum velocity decrease between the base and monitor at about 10%. This concludes the inversion exercise.

84 84 Hampson-Russell Software Services Volumetrics Interpretation of the 4D seismic response and its relation to production information can be very difficult. This is partly due to the non-uniqueness of the 4D response. When volumetric estimates are calculated for 4D anomaly maps, like those created in the previous exercise, this can help to estimate the reservoir volume affected by the production process. This reservoir volume estimate can be compared to the injection and production volumes recorded for the field to help reduce the non-uniqueness in the time lapse interpretation. In this example, gas was injected in the top of the reservoir for a 12 year period between the 2 surveys. The gas bank is assumed to be between 20 and 30 meters, based on contact logging and volumetric estimates, over most of the reservoir area. However, there is a large uncertainty in gas saturation in the gas flooded region. Volumetric analysis can help to reduce this uncertainly, as we will see in the following example. In order to perform volumetric analysis, further information regarding reservoir thickness, porosity, fluid saturation and formation volume factor (FVF or the ratio between fluid volume at surface and reservoir conditions) must be provided. Porosity, reservoir thickness, and saturation information can be provided in map form, and multiple realizations can be used to examine uncertainty. Zones may be identified on the maps, and thresholds set to isolate the cells that correspond to time-lapse changes. Average values or a range of parameters can be used to create several volume estimates. Actual injection and production data can be provided for each well to be compared to the estimated data. Begin by clicking the Volumetrics button on the seismic window sidebar. Click on the 4D Anomaly Map option under Area and select the final Normalized RMS amplitude map created over the zone of interest. When restricted zones and threshold are not set, the program simply uses the map to provide area information, assuming the reservoir covers the entire map region. January 2008

85 TL-Pro4D v Click the Thickness tab and set the range from 20 to 30 meters at a one meter increment. In this case, the range from 20 to 30 meters covers the uncertainty in average gas thickness in the reservoir area. Porosity is expected to be 15% on average. Fill in the Saturation Range also as shown:

86 86 Hampson-Russell Software Services Click the N/G & FVF tab. Allow the N/G (Net to Gross Ratio) to default to 1. Enter a FVF (Formation Volume Factor) value of to translate the volume of gas at surface to the volume of gas under conditions of reservoir pressure and temperature. Next, click the Actual tab and set the Actual Volume to 240,000,000 m^3, which corresponds to the volume of gas at standard conditions that was injected into the reservoir over the 12 year period. Finally, click Calculate and the Table will become active showing the range of volume values calculated using each variance of the input variables. January 2008

87 TL-Pro4D v Where the Calculated to Actual volume ratio (C/A Ratio) is near 1, the combination of variables provides a consistent interpretation. Double click on the Calculated Volume name to display the histogram of injected gas volumes that were estimated based upon the assumptions that were made in the previous panels. The resulting histogram, shown below, indicates that the average volume estimate is several times larger than the actual volume of injected gas. This indicates that at least one of the parameters is significantly in error.

88 88 Hampson-Russell Software Services In this case, we have assumed that the injected gas is distributed evenly over the entire field. This is not consistent with our time lapse anomaly map which indicated that the seismic response did not change significantly over most of the field area. In order to correct this problem, we will return to the Area tab and apply a threshold value of 0.5 to the time lapse anomaly map. This means that reservoir volumes will only be calculated from cells where the seismic signal has changed by more than 50% relative to the original signal levels. January 2008

89 TL-Pro4D v After you have set the Threshold values, as shown above, press Calculate to generate the new table of volume estimates. This table, which only calculates the pore volume from areas of the field that indicated time-lapse change, shows the estimated volumes are now closer to the actual injected volume. Double clicking on the Calculated Volume label will generate a histogram of the pore volume estimates. This new histogram, as shown below, now indicates that the actual injected gas volume is now in the middle of the range of estimated values. There is a large uncertainty in the calculated pore volumes, due to the uncertainty in the average gas thickness and the gas saturation within the gas bank. It is often impossible to obtain the detailed level of engineering data required to reduce this type of uncertainty, however, the Pro4D volumetric tools provide a means of reducing this uncertainty in several ways. The method we will examine involves making a cross plot between the calculated to actual volume ratio and the

90 90 Hampson-Russell Software Services thickness of the injected gas bank. This Cross Plot is created by clicking on the Graph item on the toolbar as shown below. In the next menu, choose C/A Ratio for the X Axis Variable and Thickness as the Y-Axis Variable. Select Hydrocarbon Saturation as the Color Variable. The resulting cross plot provides important insights into the relationship between the thickness of the gas bank and the gas saturation within the flooded region. Assuming that the time lapse anomaly map accurately defines the area of the injected gas bank in the reservoir, and the average porosity is correct, the correct combinations gas thickness and saturation must agree with the known injected gas volume. All of these possible combinations are shown along the vertical line associated with a Calculated to Actual volume Ratio of 1.0 on the cross plot. From this plot we can observe that if the gas saturation is 70%, then the gas bank must be less than 20 m thick (on average) and if the gas saturation is 40% or less, the gas bank must be greater than 30 m. If the gas thickness is 22 m, then the gas saturation within the bank must be 60%, and if the gas saturation is 50%, then the gas bank must be 27 m thick on average. As you can see, this plot can successfully reduce the range of possibilities that agree with the 4D seismic interpretation and the production engineering data. January 2008

91 TL-Pro4D v Before leaving Volumetrics, save the results under File/Save As so that the data can be reviewed or modified at a later time. Close all graphs and the Volumetrics window.

92 92 Hampson-Russell Software Services We are now almost at the end of the Pro4D tutorial. Before finishing, it is useful to look at a few utility functions. One important function is to display the history associated with a particular volume. To do that, click on History / Display History on the inversion in the seismic window: This causes a window to appear, containing the parameters used to create that volume. By scrolling up through the history of the processes you can track exactly which datasets were used and the parameters that created the volume. A second useful utility is the ability to create hardcopy through CGM files. To see how this is done, click on File / Hardcopy / CGM File on the final data volume seismic window: January 2008

93 TL-Pro4D v This will lead you through a series of menus which will result in the creation of a CGM file displaying the Inline or Cross line currently shown on the Pro4D window. Finally, we will exit the Pro4D project. To do that, click on File / Exit Project on any of the Pro4D windows: Your project will be saved for you; click on Yes: