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117   Determining interval  velocities  from  seismic  reflection  surveys.   toa  CMP  to  estimate  stacking   two  to  each  of  the   the  stacking   velocities  mean  square   the  velocity  between   from   (c).   :   rock   velocity   A  profiles.   event.  An   the   from   Short-path   peel   Ye   can   may   The   representing   multiple   primary   overprint   travel

         Processing   5.16   Tyo  corrections  applied   used   down  reflectors  (b).  Assuming   root   interval  reflectors  (Viy7)is  computed   Equation   infer   to   lateral   primary   downward   5.17a).   stacking   multiple   A   5.18a).   (Fig.   the   of   two   will   the  twice


            FIGURE   gather  (a)  :are   velocities   velocities  are   (Vans),  the   two   Dix   the   [t,(1)]   [to(2)].   used   be   no   with   reflection   the   (Fig.   dae Lenin   then   5.18).   interface   hyperbola   hyperbola   the   up   they   have

                                                                    interface   interface   may  velocities   layers   seismic   on   after   time   reflects   that   interface   corrections   (Fig.  variety   deeper   reflection   line   will   5.18c).   (Fig.   processing,   will  multiple



                                            ~D
            Tumo   a                       &                        upper   to   lower   to   stacking   flat   of   noise   of   event,  some   interface   same   the   oie rae   moveout   long-path   a   from   a   along   lower-velocity   velocities   of  phase   in   with   surface

            After   Correction             8                        time   travel   time   travel   conditions   type   an   from   from   P   normal   the   reflection   lie   steeper,   stacking   out   be   dealt   sections.  A
                                            o
                                           a
                                           Y
            b)                            =                               from   ideal   common   distinct   a   again   5176)   of   will   the   of   will   adequately
                                           Ce                       two-way   two-way   as   reflection   (Fi   es   particularly   primary   selection   multiple   stacked
                                            &                             determined   under   a   upward   however,   than   not
                                           Le                                        are   arrives   the   ee .  ae   i   of  a   are   on
                                           Be                       vertical,   u   vertical,   b   velocities   only   but   5.8)   (Fig.   multiple   be   would   reflects   then   on   processing   multiples,   time   the   reflection,   RMS-velocity   Careful   the   while   multiples   reflections
                                           Q
                                            o
            Before  True   r   Correction                   >             Internal   velocities,   changes.   Multiples   Multiples   long-path   example   surface,   male   rellecis   ioen   The   attenuate   near  arrive   primary   higher   5.18b).   (Fig.   reflections,   If   primary
                                           8
                                            &
                                           &
            a)                             >





        a                                                       5
    es    ae          ae a      FQvat:  FOR   di   Me   ES:           3      gil






                      as   are   rays   mean   then         an   a   is   as   5.15b),   there-   the   and   DY
        Analysis      bending   Rays   3.22).   layers,  compared   Consequently,   root   disproportionate   term,   corrects   velocity   bending   (Fig.   is   reflecting   the   of  velocity   of  stacking   Sheriff   inlertaces,   [Vays(1)]   [Vays(2)]


        Waveform      describes   (Fig.   The  layers.   the   V,t,   the   in   best   that   stacking   to   Due   paths   velocity   above   average   form   the   of   130   (p.   Jetleeing   5.46);



        And       layer.   Law   velocities   high-velocity   5.15b).   for   velocities   layer.   i"   velocity   A  5.10).   interface.   “U-shaped”   stacking   A   material   the   interfaces   interfaces.   in   is   Equation   een   (Fig:   interface   interface   interface
        Processing,   i"   the   Snell’s   different   along   (Fig.  layers   higher-velocity   accounts   it   the   the  within   the   is   (Fig.   reflecting   follow   5.15a).   the   for   is  velocity   interfaces   two   two   surveys   Dix   Oe   velocities   lower   and   upper   from   lower  from



        Acquisition,   i'*   the   time  travel   Velocity   separating   low-velocity   time   by   averaged   velocity   i   the   travel   stacking   above   paths   RMS   interval   (Fig.  5.15c):   Vint   between   between   between   seismic   processing.   interval   between   for   for
     +          layer   within   (Vays)   horizontally   in   average;   squaring   sum:   layer   time   velocity   moveout   the   raypaths   (Fig.   velocity   Az/At   =   two   the   the   reflection   The   velocity   are:MS   upper   reflection   reflection


        Reflection:   velocity   of   two-way   (RMS)   interface   more  travel   through   travel   more   weighted   a   is   layers   the   of   square   mean   of  velocity   two-way   The   normal   for   material   interfaces,   straight,  “V-shaped”   the   of   The   (V;,,)   interfaces   velocity   of  layer   time  travel   from   during   ine   ee   velocities   velocity   velocity   velocity



                                                                                                                interval
        Seismic   seismic   vertical,   Square   Mean   an  across   they   that   travel  vertical   proportionally   velocity   high-velocity   in   root  square   root   =   seismic   V; =   vertical,   =   Velocity   gather   CMP   the   for  average   change   across   to   approximation   Velocity   two  between   average   =   thickness   =   one-way   =   information   determined   een   a)   lhestacking   that   ou  stacking   stacking   =
                                                                                                                =
                                                                                                                ‘at
        Chapter5   where:   V;, =   =   t;   Root   refract   rays   so  refracted   more   to   spend   (RMS)  square   time  travel   the  taking   where:   Vams   t;   Stacking   a   on  event   of   type   velocities   opposed   as   an   fore   interface.   Interval   material   where:   Vin   Az   At   Velocity   velocities   Sones   assuming   >>   V,



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