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![]() | Sigsbee2 Models | ![]() |
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For the purposes of this example a shot will be fired at 10 km along the horizontal coordinate and at a depth of 10 meters. Receivers are spread at a depth of 0 meters every 7.62 m (25 ft) along the entire scope of the model. This long receiver cable is impractical but useful for these purposes. Data is recorded on every receiver at time increments of 1 ms 3000 times resulting in 3 seconds of data.
An SConstruct file located within sigsbee/fdmod2A/ properly formats the model and inputs necessary parameters to perform a shot on the Sigsbee model. This file is reproduced below in Table 9.
from rsf.proj import * import fdmod ## # Sigsbee 2A ## data='sigsbee2a_stratigraphy.sgy' Fetch(data,'sigsbee') Flow(['vstr2A','vstr2Ahead'],data, ''' segyread tape=$SOURCE tfile=${TARGETS[1]} | put o1=0 d1=25 label1=z unit1=ft o2=10000 d2=25 label2=x unit2=ft ''',stdin=0) # ------------------------------ par = { 'nt':7000, 'dt':0.001,'ot':0, 'lt':'t','ut':'s', 'kt':100, # wavelet delay 'nx':3201, 'ox':0, 'dx':0.00762, 'lx':'x','ux':'km', 'nz':1201, 'oz':0, 'dz':0.00762, 'lz':'z','uz':'km', } # add F-D modeling parameters fdmod.param(par) # ------------------------------ # wavelet Flow('wav',None, ''' spike nsp=1 mag=1 n1=%(nt)d d1=%(dt)g o1=%(ot)g k1=%(kt)d | ricker1 frequency=15 | scale axis=123 | put label1=t label2=x label3=y | transp ''' % par) Result('wav', 'transp | window n1=200 | graph title="" label1="t" label2= unit2=') # ------------------------------ # experiment setup Flow('r_',None,'math n1=%(nx)d d1=%(dx)g o1=%(ox)g output=0' % par) Flow('s_',None,'math n1=1 d1=0 o1=0 output=0' % par) # receiver positions Flow('zr','r_','math output="0" ') Flow('xr','r_','math output="x1"') Flow('rr',['xr','zr'], ''' cat axis=2 space=n ${SOURCES[0]} ${SOURCES[1]} | transp ''', stdin=0) Plot('rr',fdmod.rrplot('',par)) # source positions Flow('zs','s_','math output=.01') Flow('xs','s_','math output=10.0') Flow('rs','s_','math output=1') Flow('ss',['xs','zs','rs'], ''' cat axis=2 space=n ${SOURCES[0]} ${SOURCES[1]} ${SOURCES[2]} | transp ''', stdin=0) Plot('ss',fdmod.ssplot('',par)) # ------------------------------ # Velocity Flow('vel','vstr2A', ''' scale rscale=.0003048 | put o1=%(oz)g d1=%(dz)g o2=%(oz)g d2=%(dz)g ''' % par) Plot('vel',fdmod.cgrey(''' allpos=y bias=1.5 pclip=100 color=j title=Survey Design labelsz=4 titlesz=6 wheretitle=t ''',par)) Result('vel',['vel','rr','ss'],'Overlay') # ------------------------------ # density Flow('den','vel','math output=1') # ------------------------------ # finite-differences modeling fdmod.awefd('dat','wfl','wav','vel','den','ss','rr','free=y dens=y',par) Plot('wfl',fdmod.wgrey('pclip=99 title=Wavefield Movie labelsz=4 titlesz=6 wheretitle=t',par),view=1) times=['1','2','3','4'] cntr=0 for item in ['9','19','29','39']: Result('time'+item,'wfl', ''' window f3=%s n3=1 min1=0 min2=0 | grey gainpanel=a pclip=99 wantframenum=y title=Wavefield at %s s labelsz=4 titlesz=6 screenratio=.375 screenht=2 wheretitle=t label1=z label2=x unit1=kft unit2=kft ''' % (item,times[cntr])) cntr = cntr + 1 Result('dat','window j2=4 j1=2 | transp |' + fdmod.dgrey('pclip=99',par)) End() |
Typing Command 4 within the sigsbee/fdmod2A/ directory runs the FD modeling script.
This script first constructs the survey acquisition geometry as was previously mentioned. An image of the survey is created and presented in Figure 9.
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vel
Figure 9. FD model geometry as performed on the Sigsbee 2A velocity model. The X represents the shot while the smaller * symbols represent receivers. The receivers extent along the right hand side although it is not clear in this image. |
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Firing the shot results the propagation of a wavefield which can be seen in the movie wfl.vpl that is generated. Typing Command 5 within the sigsbee/fdmod2A directory displays the wavefield movie.
Four frames from this movie are presented in Figure 10 illustrating the propagation of the wavefield in the model.
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time9,time19,time29,time39
Figure 10. Images of the propagating wavefield in the Sigsbee model generated by a finite difference model. |
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The resulting data is then presented in the file dat.vpl. This plot is reproduced here in Figure 11.
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dat
Figure 11. Data gathered by the receivers in the FD model survey. |
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FD models can be performed on the Sigsbee2B model in a similar fashion. The primary change would be in appending line six, the model input file, in the SConstruct file shown in Table 9.
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![]() | Sigsbee2 Models | ![]() |
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