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Interpretation of three-Dimension Seismic Data AAPG

CHAPTER 2: Color, Character & Zero-Phaseness

Assessment of phase and polarity:

Zero-phase:

The waelet is symmetrical with the ma!ority of the ener"y #ein"

concentrated in the central lo#e$

This waelet shape minimi%es am#i'ity in associatin" o#sered

waeforms with s'#s'rface interfaces$

A hori%on trac( drawn at the center of the waelet coincides in

time with the trael time to the s'#s'rface interface ca'sin" there)ection$

The ma*im'm amplit'de occ'rs at the center of the waeformand th's coincides with the time hori%on$

The resol'tion is #etter than for other waelets with the same

fre'ency content+

A )'id contact is always an increase in impedance+

Phase of :

The most common phase distortion

Common in:

o .ow-impedance interals$

o /as sands Red-oer-#l'e sandwhich character+ 0o'#lin" eents indicate a

phase shift

CHAPTER 1: tr'ct'ral 3nterpretation

alt:- 0epth mi"ratio and pre-stac( depth mi"ration in 10 hae

recently #ecome economically feasi#le and hae #een 'sede*tensiely for ima"in" 'nder salt+

- 3t is the lar"e elocity contrasts that ma(e this more ela#oratemi"ration necessary+

4(ipped chapters5

CHAPTER 6: Reseroir 3denti7cation

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3f the seismic data 'nder interpretation hae #een processed to %erophase, then the detailed character of the #ri"ht spots, )at spots andother 0H38s can #e ery dia"nostic+

0ecrease in A3 9 pea( which is #l'e and an increase is e*pressed as a

tro'"h which is red 4E'ropean polarity5

ri"ht spot:- ;ater sand has an aco'stic impedance lower than the

em#eddin" medi'm and the impedance of the "as sand isf'rther red'ced

- The si"nat're of the sand is pea(-oer-thro'"h and, for the "as-7lled portion, the amplit'de is "reater

- im'ltaneo's increase in top and #ase amplit'des < =nat'ralpairin"8

Tro'"h if increase in A3>

0im spot:- The water sand has a hi"her aco'stic impedance than the

em#eddin" medi'm- when "as replaces some of the water in the pores of the sand,

the aco'stic impedance is red'ced

Phase chan"e:- rec'tion of aco'stic impedance of the sand, #eca'se of "as

sat'ration, ca'ses the aco'stic impedance to chan"e from a

al'e hi"her than that of the em#eddin" medi'm to one lowerthan that of the em#eddin" shale+ Hence the polarities of there)ections for the top and the #ase of the sand switch

- 3n order to o#sere s'ch a phase chan"e or polarity reersal, thestr'ct'ral dip m'st #e clearly determined from non-reseroirre)ections !'st a#oe and?or !'st #elow the sand 'nder st'dy+

/as reseroirs atten'ate hi"h fre'encies more than do roc(s witho't"as sat'rations+ .ow instantaneo's fre'encies immediately #elow as'spected reseroir can #e a "ood indicator of "as+

The sta#ility of interal elocities "ets pro"ressiely worse for "reaterdepths and also for thinner #eds+ This "enerally means that interalelocities are not s'@ciently acc'rate to play a 'sef'l role in #ri"htspot alidation+

CHAPTER : Reseroir Eal'ation

ri"ht spot re"ime < hi"h amplit'de desira#le

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0im spot re"ime < low amplit'de is desira#le

.ow aco'stic impedance reseroir, hi"h amplit'de is "ood #eca'se itmay #e ca'sed #y hi"her net-to-"ross ratio, hi"her porosity, or hi"herhydrocar#on sat'ration+

Pore ol'me 9 amplit'de * isochron