Software and Data Preprocessing

GEOP 320 Spring 2006 Lab Assignment # 1 Software and Data Preprocessing (Due date: 26/3/2006)

Objective The objective of this lab assignment is to get acquainted with our processing software (Seismic Unix) and preprocess our dataset.

Introduction Preprocessing involves the following steps: (1) Demultiplexing. (2) Reformatting. (3) Editing. (4) Gain application. (5) Setup of field geometry. (6) Application of field statics.

Exercises (1) The data has been demultiplexed already. (2) The data is in a SEG-Y format file called l052.sgy and we want to reformat it into an SU format file called l052.su. (a) Reformat the SEG-Y file to SU format using the Visual-SUNT button “Start conversion module” and choose “SEG-Y to Seismic Unix”, which brings a dialog box for entering the parameters of SEG-Y to SU reformatting. (b) Use the following information to fill in the needed parameters: a. Number of samples = 1001. b. Sample rate = 4000 s. c. Leave everything else! d. Provide a table showing your selected values for these parameters and justify your answer. (c) Using this process should have produced three files: l042.su that contains the seismic traces (size = 19,811 KB), binary that contains binary information about the dataset (size = 1 KB), and header that contains text information about the line (size = 4 KB). (d) Load l042.su using the button “Load a seismic SU section” to look at your data. This brings a dialog box asking for some file parameters. Note: a. Number of channels per record = 239. b. Number of records = 20. c. Number of traces = 4780. d. Leave everything else! e. Provide a table showing your selected values for these parameters and justify your answer. f. Click “Display” button. g. Now you should be able to see your data. 2

h. Display your shot records one at a time. Take a look at all of them. i. Provide printouts of shot records # 1, 5, 10, 15, and 20. (3) *Use the button “starts or ends Kill trace module” to kill ONLY the bad traces. Please be careful NOT to kill any trace unless it is extremely bad because you do not want to loose too many traces unnecessarily. If you decide to kill traces, save the edited dataset as l042_edit.su. Provide printouts of the edited shot records before and after editing. (4) (a) AGC: Choose the button “Launch common SUNT modules”. Choose “Gain” button. This brings the AGC dialog box. Note: a. The following fields should be 1: b. “Do automatic gain” c. “AGC with Gaussian taper” (for smoothing edges of AGC window) d. “balance trace by div. by rms value” e. You should try different lengths for the “AGC Window (s)” and choose the one that gives you the best display. f. You should try AGC with “gain whole data set” (relative trace balancing) with values of 1 and 0 to see the difference. g. Provide a table showing your selected values for the AGC window length and relative balancing parameters and justify your answer. h. Save the gained dataset as l042_agc.su. Provide printouts of shot records # 1, 5, 10, 15, and 20 after AGC. (b) Spherical Divergence Correction: You should also gain the data using one of the spherical divergence correction processes we talked about in the lecture. Since we do not have the velocities yet, we will use the tm method as follows: a. Load your un-gained file l042.su. b. Choose “Start Batch editor” button. c. Under “Batch editor” in the “Select here a processing module” field, scroll down and select “SUGAIN”. d. To learn more about this process, you should read the help file under the red “Start SUNT help file”. e. Try different combinations of the parameters: tpow, epow, qclip, jon, and qbal until you are satisfied with the result. f. Provide a table showing your selected values for these parameters and justify your answer. g. Save the gained dataset as l042_tm.su. Provide printouts of shot records # 1, 5, 10, 15, and 20 after t m gain. (5) The geometry is already setup. (6) We will apply the field statics at a later stage.

Note on Printing Records:

For best printing results, use snapshots and edit them using appropriate programs (e.g., MS-Paint, PhotoShop, MS-Word, … etc). Here is an example.