Some background on Attribute Analysis Environmental and Exploration Geophysics II Some background on Attribute Analysis tom.h.wilson tom.wilson@mail.wvu.edu Department of Geology and Geography West Virginia University Morgantown, WV Tom Wilson, Department of Geology and Geography

Seismic Attributes From Marfurt, 2006, SEG Short Course Tom Wilson, Department of Geology and Geography

Liner Classes: general, geometric, physical or geological basis Travel time > structural model > hydrocarbons are in structural highs: that’s an attribute Amplitude > negative amplitude bright spots and gas > tertiary basins throughout the world. Have to have the physics and the geology behind it. To avoid the false correlations you have to know the physics and the geology. From Marfurt, 2006, SEG Short Course Tom Wilson, Department of Geology and Geography

Interpreter would map these sequences 1979s through 80s and into 90s From Marfurt, 2006, SEG Short Course Tom Wilson, Department of Geology and Geography

In 1993 -94 companies got into 3D data and the A-B/C method for mapping stratigraphic plays fell out of favor. The interpretation and classification also depends very much on how you slice your data Around 1993 and 1994 3D. But had mechanical problems and there was no way to do the traditional seismic stratigraphy mapping. Computers don’t do well with alpha numeric data so that was out. Also you could start generating time slices. Fell into disfavor. We haven’t had the opportunity to discuss seismic stratigraphy in this class. I present a few lectures on this in Geol 510 – Computer Aided Subsurface Interpretation. From Marfurt, 2006, SEG Short Course Tom Wilson, Department of Geology and Geography

Has been replaced by seismic geomorphology Has been replaced by seismic geomorphology. Take inline dip and cross line dip square sum and take square root. At right is a volume attribute observed in the seismic data 200 ms below the sea floor. Extensional faults, mud diapirs, mud volcanoes, Volumetric measures measure the same kind of texture. From Marfurt, 2006, SEG Short Course Tom Wilson, Department of Geology and Geography

Volumetric attributesphantom horizon From Marfurt, 2006, SEG Short Course Tom Wilson, Department of Geology and Geography

From Marfurt, 2006, SEG Short Course Tom Wilson, Department of Geology and Geography

Volumetric attributes are tools one can use to look for geologic features From Marfurt, 2006, SEG Short Course Tom Wilson, Department of Geology and Geography

Yellows and reds are diverging to the right and the blues and cyans are converging to the right From Marfurt, 2006, SEG Short Course Tom Wilson, Department of Geology and Geography

What combination of attributes will produce a certain class of features observed in the seismic. High amplitude continuous (blues) So basically, take coefficients times attributes and it will come up with "This is High amplitude coherent." Channel axis with high net to gross From Marfurt, 2006, SEG Short Course Tom Wilson, Department of Geology and Geography

If it hleps capture some feature we’re going to use it. From Marfurt, 2006, SEG Short Course Tom Wilson, Department of Geology and Geography

Sparse well control and a seismic grid of data Sparse well control and a seismic grid of data. Measure porosity thickness and extrapolate onto the seismic. What is sensitive to porosity thickness: impedance, rms amplitude sensitive to porosity. Thickness – peak to trough time. Cohenrence doesn’t have anything to do with porosity so the trick is to use only those attributes that have something to do with porosity to come up with a correlation. From Marfurt, 2006, SEG Short Course Tom Wilson, Department of Geology and Geography

Tectonic history, geologic models. Carbonate terrain, fractured Tectonic history, geologic models. Carbonate terrain, fractured. Different attribute, different features. It’s hard to mess up the processing to create channels. Discuss grain size and morphology – meandering = slow=fine grained, distributary=fast= probably courser. They don’t need no stinking attributes, but they need to sell it to the banker. Don’t worry about that that’s an interference anomaly … From Marfurt, 2006, SEG Short Course Tom Wilson, Department of Geology and Geography

The third point is we ant to sell this to some New York banker The third point is we ant to sell this to some New York banker. Attributes allow you to communicate to other people that don’t have the training or the time. How do you express complicated ideas in a short time. Plays are subtle Music and math majors are pretty good at … geoscientists are going to the big companies: math major is good at finding faults, evaluating filters but find channels or reefs pretty hard to do: takes a lot of geological experience. Processing not quite so rigerous: generate a bank of filters and ask yourself which is best like telling whether you have a good pair of glasses. Here we have better statics and better velocities From Marfurt, 2006, SEG Short Course Tom Wilson, Department of Geology and Geography

Engineering quadrature Mathematicians analytical or real and imaginary Those of you older than 50 years old remember the Hilbert transform as convolution operator. So what do we do? Here is my analysis point right here at reference time zero. And my Hilbert Transform says let me take the sample one above, multiplied by plus one, one behind, multiplied by minus one, three in front multiplied by one third 3 behind multiplied by minus one third, one fifth, minus one fifth, one seventh, minus one seventh, and so on. So that's the Hilbert . It’s amix of things in the neighborhood. if you are younger than 50 you know about the Fast Fourier Transform. So what we would do is take our data d(t), cross correlate with sines and cosines, come up with correlation coefficients. Take everything that was a sine coefficient and name it a cosine coefficient, everything that's a cosine coefficient and name it a sine coefficient. We'll use the square root of -1 to do that and then cross correlate again taking the inverse Fourier Transform. Now, you'll notice I used the word 'original data' or 'the real component', here I call it the Hilbert transform or quadrature and the imaginary component. I have three names for the same thing. So I'll pick on Roger. Roger, why do we have three names for the same thing? Roger's not answering me. So research people get paid three times for Engineering quadrature Mathematicians analytical or real and imaginary Geophysicists name after dead people. From Marfurt, 2006, SEG Short Course Tom Wilson, Department of Geology and Geography