Geology 554 Environmental and Exploration Geophysics II Final Exam

Transcription

1 Geology 554 Environmental and Exploration Geophysics II Final Exam In this exam, you are asked to apply some of the seismic interpretation skills you ve learned during the semester to the analysis of another 3D data set. We will spend some time in class introduction the data and getting our started on the analysis. This 3D data set is located near the near the training data set in east Texas that some of you are working on for your term report. This exercise includes a set of specific activities to undertake and complete. The extent that your efforts go beyond specified tasks will help reveal the depth of your understanding of 3D seismic interpretation issues. This study requests that you demonstrate capability to undertake basic horizon interpretation, perform depth conversion, spectral analysis, evaluate resolution limits and undertake attribute analysis an independent evaluation of an additional 3D data set. An important objective of the exam is to help reinforce basic interpretation concepts and procedures. This final interpretation effort will also help raise additional ideas and efforts that might be incorporated in your term report analysis. I will be helping you gain some familiarity with the data today and on Wednesday. For those working the Gulf Coast data set, consider that your team has completed the analysis of the initial data set and made their recommendations for potential drilling locations. In addition, you see the opportunity to expand exploration in the area and recommended acquisition of this additional 3D data set. For those working the Barents Sea this provides an opportunity to consolidate some of the in-class work we ve been doing in the east Texas area and may also point the way to additional work on your Barents Sea project. This work is to be done independently and without consultation with team mates. You will present your additional work as an appendix to your term report. The term report, including this appendix, is due the day of the final (1pm, May 8). To Begin> 1. Copy the 3D data set from the Common Drive (BEG folder) to your G Drive. 2. Bring up Kingdom and navigate to the BEG folder. 3. Bring up the project. Your project tree and base map should look similar to that shown below. 1

2 4. Your startup view may look different, so let s take a few minutes to explore the data. 5. Drop down the faults, formation tops, horizons and wells > All Wells lists in the project tree. 6. Note that there are several wells on the base map. 7. Bring up a cross line (EW line) through some of the wells in the center of the area. The line below (Figure 1) is EW line 53. Figure 1: Seismic from a different part of the Stratton field showing roll-over in the Vicksburg. 8. Note that logs are displayed next to each well. The red log responses are gamma ray logs. Also note that all your formation tops should be labeled. 9. If you want to turn off or turn on the log displays go to Logs > Settings and under the Scale and Style Setup move selected curves out of the displayed curves list (see display next page). 10. To move the logs back in for display you have to select them one at a time from the available logs list at left > click track1 or 2 and then click the right arrow (greater than sign). That will throw the log into the displayed curves list and in the specified track. 2

3 Evaluate the amplitude spectrum in the vicinity of your zone of interest. 1. Some of the wells in this survey appear to have sonic, however the range of values are altered and not usable for generating a synthetic. Thus a synthetic will not be constructed. However, you can calculate the amplitude spectrum and estimate the resolution limit. (Return to the Golden 3D and generate the necessary wavelet and calibration curves). A review of Horizon Interpretation Procedures 1. To review horizon interpretation and get you going, we will interpret one of the deeper horizons - From the Horizons dialog create a new horizon F Right click on the vertical seismic display line (Line 53) and select picking parameters. Make sure you are picking a peak. 3. Press the short cut key H to auto hunt this peak along the line. 4. You ll be picking the strong positive (see figure below) 5. Set your line skip interval at Pick all your crosslines (EW) 7. Don t worry about faults. 8. You should be able to pick this event using only autohunt, but you might have to click at more than one place along the line where the reflector is slightly discontinuous. 3

4 Polygon Hunt 1. Bring up your map view and drag your F11 times over to the map. You should get something like the following. 2. Now go to polygon hunt and select the entire area. 3. The area should fill from left to right 4

5 4. Notice the time-structural high running through the center of the prospect area. Velocity Map 1. Tools > Depth Conversion > Compute Average Velocity map (call it F11Depth). Make sure all wells are selected. 2. In the grid parameters window specify a projection distance of 2000 feet, low smoothing and extrapolate to the XY bounds > Apply 3. Your velocity map will appear. Do you need to adjust the projection distance? 4. Does the velocity trend is fairly uniform. 5. OK to exit and recreate the grid. Conversion to Depth 1. Tools > Depth Conversion > Depth May by Average Velocity Map 2. OK to create grid 3. View the structure map and ask yourself is there is closure on this horizon Flatten on the F11 and look at amplitudes on the F11 surface 1. Horizon > Flatten 2. Right click display and select Display Flattened Time Slice 3. Turn off the F11 4. Create a time slice view 5. Move your time-slice view up and down through time relative to the F11 and look for patterns in anomaly shapes that might be indicative of traps for hydrocarbon accumulation along a high, within channels (channels might contain accumulations of coarser sediment, higher porosity and permeability and thus represent a potential trap in which hydrocarbons could accumulate). Although significant faulting of the shallow section is not apparent, does you anomaly map reveal narrow roughly linear to 5

6 curvilinear zones that could be indicative of subtle faults and thus additional trapping mechanisms. Create Attribute Volumes 1. You are already familiar with the creation of standard attribute volumes. 2. Here we look at some additional capability provided in Tools> TracePak >Trace Calculator. 3. In the following Trace Calculator Window, I ve computed a volume of the peak-totrough ratio through the survey 4. Note that the procedures consist of: selecting the data volume (BEG in this case); clicking the > button to specify it as variable A; selecting a function from the function dropdown list (in this case PTRatio); Double click to insert this operator in the Fromula Line; Click A to insert the BEG 3D volume); Close off the right parenthesis (see below). 5. Select the survey/subset in the drop down list 6. specify the new data type PTRatio (i.e. click new data type and type it in) 7. Compute > 6

7 8. Yes to the message box and take the default storage location. 9. Close 10. Open up a line and select the new data type 11. Flatten on horizon 12. Display flattened time slice 13. Turn off horizon 14. Select a suitable color bar (This is a matter of personal preference. A color bar may help some see features that could be associated with traps, subtle faults, etc.) 15. The following shows the setup for computing the absolute value for the finite difference) 7

8 16. This derivative provides a sharper higher frequency view of some of the faults in the deeper section. 17. The vertical display such as that shown above or the map display (below) may provide you with some additional insights into the nature of the play and the potential existence of stratigraphic or structural traps (closure and subtle faults. 18. Since the normally scheduled exam time for MWF classes meeting at 3 or 3:30 is 11:00am to 1pm on Friday, May 8. Please turn your term report with exam supplement in to me by 1pm. 8

9 Final Exam (& Term Project Interpretation Supplement) Conduct an interpretation of the new data set. Present the interpretation supplement as an Appendix The Appendix should include the following efforts and illustrations with accompanying discussion. 1. Pick and interpret a horizon (other than the C38 and F11). Be sure to select the correct picking parameters (peak or trough) for the auto-picking process. 2. Continue your analysis by computing the amplitude spectrum of the data in the vicinity of your horizon of interest. 3. Specify the peak frequency and bandwidth. 4. Generate the calibration curves and discuss the vertical resolution limits. You can return to your Golden 3D and create an appropriate wavelet to use for generating the calibration curves. 5. Compare bandwidth and resolution limits associated with the spectral content in this data set to that from the Golden 3D used in the resolution exercise. 6. Illustrate the horizon you picked in vertical and map display. 7. Refer to both displays (vertical and map views) and discuss possible traps. 8. Convert your picked horizon to depth. 9. Re-evaluate your thoughts on possible traps within the context of the depth converted view of this horizon. Make sure you adjust the color bar to examine the depth converted map for possible closures. The quickest way to do this is just to grab and slide the color bar up and down. 10. Illustrate and discuss attributes you decided to use. Show vertical and map views of the attribute(s) and highlight or label features you think are of interest. 11. Did you see something in the attribute display that you didn t see or recognize as well in the amplitude display? Explain. 12. Prepare a summary and conclusions section for your analysis. The approach is up to you. Remember this kind of analysis results in an interpretation. It has to be plausible and consistent with the data and local geology. Putting interpretations to the test only happens when investors or division managers decide the risk is worth taking. I appreciate that the geological concepts and analytical approach is new to a lot of you, but don t let being unsure prevent you from suggesting possibilities. As long as interpretations are stated as such don t hesitate to make them. 13. Have fun with this! 14. As noted in the introduction to the problem This work is to be done independently without consultation with team mates. You will present your additional work as an appendix to your term report. The term report, including this appendix, is due the day of the final (1pm, May 8). 9