Robust internal multiple prediction algorithm Zhiming James Wu, Sonika, Bill Dragoset*, WesternGeco

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1 Roust internl multiple preition lgorithm Zhiming Jmes Wu, Sonik, Bill Drgoset*, WesternGeo Summry Multiple ttenution is n importnt t proessing step for oth mrine n ln t. Tehniques for surfe- rpily in the relte multiple elimintion hve improve pst yers. Internl multiple ttenution n still e very hllenging ue to poor isrimintion etween primries n multiples. A t-riven internl multiple preition metho with minimum requirement of priori informtion is presente. The metho is n extension of surfe multiple preition n is suitle for ll quisition geometries. Introution Multiple ontmintions, oth surfe- n intere- of interest. A relte, n osure the refletions tht re strong refletor suh s wter ottom retes strong surfe multiple n iffrte multiple energy tht overwhelms the setion, n the priority in t proessing is to remove this energy. Over the lst few yers, 3D surfe-relte multiple elimintion (3D SRME) hs evolve rpily, oth lgorithmilly n omputtionlly (Moore et l., 2008), n is epte toy s prt of the si requirement for t proessing. Intere multiples, minly ontminting ln tsets, hve een more iffiult to ress. These multiples usully pper very similr to the primries ue to omprle veloities; they re hene iffiult to ifferentite espeilly in res with reltively flt geology s is ommonly seen in most Mile Estern sins. Tritionl methos, se on veloity isrimintion or perioiity, hve not een ompletely effetive in ttking these multiples. One-imensionl intere multiple preition (IMP) moelling on post-migrtion t hs een prtilly suessful (El-Emm et l., 2005), ut it n e onsiere too little n too lte in the seismi t proessing sequene. Reently, the reserh for internl multiple ttenution hs een fousse on lrey proven methos suh s moel-se, t riven surfe emultiple tehniques n lso some other new pprohes suh s point-sttering methos. This pper isusses the pplition of roust, t-riven tehnique for preiting intere multiple. omponents to three omponents. The onept is illustrte in figure 1; the internl multiples n e preite y onvolving two primries X s,x 1 n X r,x 2 n removing or orrelting with X 1,X 2. The ownwr refletion point (DRP) ours t p2, the multiple generting horizon. The position of X 1, X2 is not known, -priori. The solution to this is shown in figure 2 whih epits the sme se in pln view. For single tre, SA n RB re onvolve n then orrelte with tre AB for ll possile gri lotions, within the perture, to form multiple ontriuting gther (MCG). The MCG is then stke, n the onstrutive n estrutive interferene of the tres, gives the multiple moel for the tre, for prtiulr horizon. All of the multiple generting horizons must e ientifie n the multiple moel must e rete for eh of them. The extent n smpling of the MCGs etermine the qulity of the preite moel. The lgorithm se on this onept is suitle for ll quisition geometries whether 2D, 3D, or ln orthogonl geometries n hs een esigne to preit multiple moels for more thn one genertor simultneously; hene it is lle the Extene Intere Multiple Preition (XIMP) lgorithm. Figure 1: A shemti for intere multiple preition Tehnil Desription The extension of the surfe-relte multiple ttenution tehnique, s propose y Jkuowiz 1998, eomposes the internl multiple preition from two wvefiel Figure 2: Pln view of DRP for trget tre SR SEG Sn Antonio 2011 Annul Meeting 3541

2 Roust internl multiple preition lgorithm Extene intere multiple preition XIMP is true-zimuth intere preition lgorithm tht ssumes input t re free of surfe-relte multiples. The onept is reltively simple; ut the tul implementtion is quite omplite ue to the millions of tres tht re quire n nee to e proesse to generte the multiple moel. To ompute the internl multiple moel for soure X s n reeiver X r, (figure 3) - one soure-sie tre X s, X 1,i is onvolve with ll possile reeiver-sie tres X r,x 2,j ; X r X 2,j+1 n so on n orrelte with tres X 1,i, X 2,j ; X 1,i,X 2,j+1... respetively to form n inner MCG. The next soure-sie tre X s, X 1,i+1 is hosen n the proess of onvolving n orrelting is repete with this tre n susequent tres ( X s, X 1, i+2 ) to form the full MCG (figure 4). The unstke MCG n e visulize s sle shpe. Stking inner MCGs forms the outer MCG (figure 4). Stking the outer MCG genertes the multiple moel for the trget tre. n orrelte to proue the multiple moel for eh tre: the numer of triplets for eh trget tre inreses exponentilly with offset n perture. Figure 5 shows the theoretil numer of DRPs for generl surfe multiple preition (GSMP) n for intere multiple. For the surfe multiple preition, primry n seonry perture of 1000m ws use; for the internl multiple preition we show the results with primry perture of 300m (in lue) n of 1000m (in re) with zero seonry perture. XIMP (perture 1000m) XIMP( perture 300m) GSMP(perture 1000m) Figure 5: Theoretil numer of DRPs for surfe multiple preition n for intere multiple preition Figure 3: A shemti for MCG formtion Inner MCGs Figure 4: ) Unstke MCG ) Outer MCG The mount of omputtion require is epenent on the numer of DRPs for eh trget tre. In surfe multiple preitions the numer of DRPs require for eh trget tre inreses linerly with offset n perture. For the intere multiple preition, triplets of tres re onvolve As is ler from the preeing prgrph, huge omputtionl effort is require for eh tre n eh multiple-generting horizon. Ielly, intere emultiple requires top-own pproh, tht is, multiple preition n sutrtion for the top multiple genertor followe y the next n so on. Due to expete exessive runtimes, the top- y simultneous own methoology hs een reple preition for ll genertors. The omputtions for the first horizon re sve in memory n use for eh susequent horizon whih mkes the lgorithm fster n enles multiple preitions for mny horizons. The output from this proess is one multiple moel for eh generting horizon ut exept for the top horizon, the multiple moels re ontminte y rtifts or multiples of multiple ue to non-top-own methoology. Hving preite ll of the multiple moels, there is now the hllenge of sutrting these multiples from the t. Eh multiple moel, exept the first, goes through n ptive sutrtion proess to seprte the rtifts, followe y simultneous ptive sutrtion using ll seprte moels to get the finl output. Simultneous ptive sutrtion provies the ility to mth eh moel in winow n the results tke into ount the qulity of eh multiple moel. This multiple preition proess is very flexile t- ffete y poor riven tehnique ut n e versely signl-to-noise rtio n poor smpling espeilly for shllow multiple genertors. These prolems n e prtilly resse with proper preonitioning of the t n optimize quisition esigns. Also, the multiple SEG Sn Antonio 2011 Annul Meeting 3542

3 Roust internl multiple preition lgorithm genertors must e ientifie using well t, VSP n then interprete over the survey to generte the multiple moels. Horizon 1 multiple moel Syntheti Results Syntheti t ws rete using finite-ifferene moelling. The syntheti moel onsiste of three min horizons. One of the shots n the ompute multiple moels for the three horizons re shown in figure 6. A primry perture of 200 m n zero seonry perture were use to generte the multiple moels. Horizon 2 multiple moel Figure 6: ) Syntheti shot with three min horizons ),),) Multiple moel for eh horizon Stke results from syntheti 3D t re shown elow. Multiple moels from the first n seon horizon were preite n sutrte. First horizon generte mny intere multiples whih were preite n ptively sutrte to lerly show remining multiples. Seon horizon preits the remnnt multiple energy n hs een suessfully sutrte (figure 8). Horizon 1 Horizon 2 Horizon 3 Figure 8:, ) Preite moel stk from horizon 1 n horizon 2, ) Results fter ptive sutrtion Figure 7: Syntheti stk with multiple generting horizons SEG Sn Antonio 2011 Annul Meeting 3543

4 Roust internl multiple preition lgorithm The lgorithm is le to hnle ny quisition geometry n preits multiples t true zimuth. This eomes very importnt for rih-zimuth ln quisition. Syntheti t were rete for orthogonl ln quisition geometry (figure 9). Ner-offset shots n fr-offset shots were use to evlute the qulity of the multiple preitions. Multiple moels were preite for the ner-offset shots with mny vrying zimuth n offsets n lso for fr-offset shots where the zimuth n offset rnge re more limite. In oth ses the multiple moels were preite urtely proviing goo result (figure 10) Syntheti ner offset shots Fr offset shots Intere multiple moel Ner offset shots Figure 9: 3D Orthogonl ln geometry Syntheti fr offset shots Figure 10:, ) Ner-offset syntheti shot n multiple moel Conlusions Intere multiple moel Intere multiples hve long een known to e prolem ut now it is possile to ress the issue y implementing this theoretilly, reltively simple ut omputtionlly intensive t-riven lgorithm. Extene intere multiple preition provies true-zimuth, intere multiple moel, suitle for ll quisition geometries. It proues n urte estimte of the multiple energy in the t, whih n e remove from the originl seismi t using ptive sutrtion tehniques. When use in onjuntion with 3D surfe emultiple tehniques the result is muh etter representtion of the primry energy. Aknowlegements The uthors wish to thnk WesternGeo for permission to pulish this work. Figure 10:, ) Fr-offset syntheti shot n multiple moel SEG Sn Antonio 2011 Annul Meeting 3544

5 EDITED REFERENCES Note: This referene list is opy-eite version of the referene list sumitte y the uthor. Referene lists for the 2011 SEG Tehnil Progrm Expne Astrts hve een opy eite so tht referenes provie with the online mett for eh pper will hieve high egree of linking to ite soures tht pper on the We. REFERENCES El-Emm, A., I. Moore, n A. Shrwi, 2005, Intere multiple preition n ttenution: Cse history from Kuwit: 75th Annul Interntionl Meeting, SEG, Expne Astrts, Jkuowiz, H., 1998, Wve eqution preition n removl of intere multiples: 68th Annul Interntionl Meeting, SEG, Expne Astrts, Moore, I., n W. Drgoset, 2008, Generl surfe multiple preition (GSMP): A flexile 3D SRME lgorithm: 70th Annul Interntionl Conferene n Exhiition, EAGE, Extene Astrts, SEG Sn Antonio 2011 Annul Meeting 3545