Geology Seismic Data Analysis and Interpretation Matlab

Geology Seismic Data Analysis and Interpretation Matlab

 
provide short paragraph answers with description of the figures (what is shown) and explanation of your results / observations. 1) Utilze Matlab script seismic_filter.m to examine seismic traces and filter unwanted noise. Matlab reads seismic in file “data.mat” and calls the script “plotseismic.m” to plot the data. a) Take a look at the time-domain traces (figure 1). Do you know what is the dominant frequency of the data? b) What data frequencies can you see in the frequency spectrum (figure 2)? Comparing them to the dominant frequencies found in the time domain data, how do they compare? c) Decide on an appropriate cutoff frequency for removing high frequency noise. Use a cutoff frequency of 100 Hz to view the data, despite the fact that we know it is excessive. Then, re-run the test with the cutoff frequency you want. What was your pick of the cutoff and in what way do the filtered data compare to the original data (figure 3)? d) Giving an average seismic velocity of 2200 m/s, what is the dominant of the S data? Amplitude, frequency, phase, filtering: Provide short paragraph answers with description of the figures (what is shown) and explanation of your results / observations. 1) Use Matlab script seismic_qc_filt.m to examine seismic traces and filter unwanted noise. Matlab reads seismic in file “data.mat” and calls the script “plotseismic.m” to plot the data. a) Examine the traces in the time domain (figure 1). What is the dominant frequency of the data? b) What data frequencies are shown in the frequency spectrum (figure 2)? How do they compare to the dominant frequency identified in the time domain data? c) Based on your determination of useful frequencies in the data (from figures 1 & 2) select an appropriate cutoff frequency to remove high frequency noise. Use 100 Hz as cutoff frequency to view the data, although we know it is too high. Re-run with your choice of cutoff frequency. What cutoff filter value did you select and how do the filtered data compare to the original data (figure 3)? d) Assuming an average seismic velocity of 2,200 m/s, what is the dominant wavelength of the seismic data? Introduction to Rock Physics modeling Submit a word document with text and figures justifying your answers. For this assignment we will use the slides on rock physics provided by Hampson Russell (available on Blackboard) to illustrate some basic concepts in rock physics and fluid substitution. You can refer to Chapters 1 & 2 of Chopra and Castagna AVO book for more detailed presentation. Use Matlab or Excel for your modeling work: 1) Density vs. Water Saturation and varying pore fluid: Illustrate the effect of: a) varying water saturation to density (water saturation from 0% to 100%) and b) varying fluid type to density (i.e. substituting gas for oil) in the water saturated sandstone. a) Sandstone porosity=33%, densities (g/cc) matrix=2.65, water=1, oil=0.8, gas=0.001. Code the bulk density equation shown in slide 50 to create the graph shown in slide 51. b) Repeat for a different “reservoir” rock of your choice (e.g. carbonate, shale ...). Select appropriate modeling parameters from the literature and class notes. Reference the source of your selected modeling parameters in your report. 2) Velocity vs. Water Saturation and varying pore fluid: Illustrate the effect of: a) varying water saturation to velocity (water saturation from 0% to 100%) and b) varying fluid type to velocity (i.e. substituting gas for oil) in the water saturated sandstone. a) Use the Whyllie equation for sandstone with porosity=33%, velocities (m/s) matrix=5700, water=1600, oil=1300, gas=300 to model saturated sandstone P-wave velocities. Code the Whyllie equation shown in slide 60 and create the corresponding graph. b) Use the Biot-Gassmann approach for gas (slide 70) and oil (slide 72) saturated sandstone for reservoir porosity=33%, Kmatrix=40 Gpa, Kdry=3.25 Gpa, Kw=2.38 Gpa, Koil=1.0 Gpa, Kgas=0.021 Gpa, Shear Modulus=3.3 Gpa. Compute the fluid bulk modulus as a function of water saturation (0% – 100%) for gas-water and oil-water saturated rock (slide 67). Use equation 1 (slide 64) to compute Ksat and equations in slide 61 to obtain Vp and Vs. Take into account density vs. water saturation and fluid computed in question 1. Generate the graphs shown in slides 70 and 72. 3) Discuss the differences in the Vp models obtained using Whyllie vs. Bio-Gassman methods.