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Examples

In 1997, WesternGeco distributed a 2-D test dataset, acquired in the Mississippi Canyon region of the Gulf of Mexico, for the testing of multiple suppression algorithms. The data contain a variety of strong surface-related multiples, and enough geologic complexity to render one-dimensional methods ineffectual. Figure [*] shows the stack of the raw data.

Figures [*] and [*] illustrate the superior performance of the HEMNO operator versus 1-D NMO when used in LSJIMP. This figure is shown in better context in Brown (2003b). The strong top of salt seabed pegleg in Figure [*], dipping over this midpoint range, is clearly better removed when HEMNO is used. Figure [*] illustrates a more insidious problem: because the 1-D NMO operator did not focus a pegleg at the correct time, it caused a spurious event to be manufactured at a slightly smaller time.

Figure [*] compare the results of LSJIMP at a single midpoint (0 m), with and without HEMNO. The differences are fairly subtle, but illustrative. Although the dip in this region is mild, it is strong enough to cause the R1 pegleg multiple with $\tau=4$ sec to defocus at far offsets. The thinly layered reflection is particularly susceptible to destructive interference with dip. On the center row of the figure, notice that in the HEMNO result, the defocusing effect is modeled, while in the 1-D result it is not. The difference panel further shows that HEMNO better models this effect.

Figure [*] illustrates the HEMNO operator applied to a synthetic 3-D dataset. The dataset consists of a seabed reflection and multiples only, with constant velocity and inline and crossline dips of $4^{\circ}$ and $2^{\circ}$, respectively. Figure [*] shows a near-offset section after conventional NMO (left) and HEMNO for first-order multiples (right). The seabed multiple doesn't ``split'', but it is nontheless treated as a pegleg by HEMNO, so this example does test HEMNO's effectiveness in 3-D. Notice that over the entire survey area, the multiple and primary are mutually focused.

 
gulf.stackraw
gulf.stackraw
Figure 3
Stacked Mississippi Canyon 2-D dataset (750 midpoints), annotated with important horizons and multiples. Labeled events: R1 - strong reflection; TSR - top of salt; BSR - bottom of salt; WBM - first seabed multiple; R1PL - seabed pegleg of R1; R1PM - R1 pure surface multiple; TSPL - seabed pegleg of TSR; BSPL - seabed pegleg of BSR; TSPM - TSR pure surface multiple.


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stackcomp-dipcomp.1.gulf
stackcomp-dipcomp.1.gulf
Figure 4
LSJIMP stack comparison of HEMNO versus 1-D NMO operator. All panels windowed from 4.4 to 4.8 seconds in time; 14000 to 15000 meters in midpoint. From L to R: Raw data stack; Stack of estimated $\bold m_0$ using HEMNO; Stack of estimated $\bold m_0$ using 1-D NMO operator; HEMNO difference; 1-D NMO difference. Seabed pegleg from top of salt reflection is outlined in all panels.


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stackcomp-dipcomp.2.gulf
stackcomp-dipcomp.2.gulf
Figure 5
LSJIMP stack comparison of HEMNO versus 1-D NMO operator. All panels windowed from 4.8 to 5.2 seconds in time; 9200 to 10200 meters in midpoint. From L to R: Raw data stack; Stack of estimated $\bold m_0$ using HEMNO; Stack of estimated $\bold m_0$ using 1-D NMO operator; HEMNO difference; 1-D NMO difference. The ovals highlight a nonexistent event ``removed'' from data due to 1-D NMO's inferior performance over nonflat structure.


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comp1.lsrow.dip-nodip.gulf.0
comp1.lsrow.dip-nodip.gulf.0
Figure 6
Mississippi Canyon CMP 1 (y=0 m). All panels NMO'ed with stacking velocity and windowed in time from 3.5 to 5.5 seconds. Top row (L to R): Raw data; Estimated HEMNO primaries; Estimated 1-D primaries; HEMNO difference; 1-D difference. Center row (L to R): Raw data; Estimated HEMNO total first order seabed multiple ($\sum_{k=0}^1 \bold R_{1,1} \bold N_{1,k,1} 
 \bold S_{1,1} \bold G_{1,1} \bold m_{1,k,1}$); Estimated 1-D total first order seabed multiple; HEMNO difference; 1-D difference. Bottom row (L to R): Raw data; Estimated HEMNO total first order ``salt'' (R1 at this location) multiple ($\sum_{k=0}^1 \bold R_{1,2} \bold N_{1,k,2} \bold S_{1,2} 
 \bold G_{1,2} \bold m_{1,k,2}$); Estimated 1-D total first order salt multiple; HEMNO difference; 1-D difference.


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syn3d.comp
syn3d.comp
Figure 7
HEMNO demonstration on synthetic 3-D dataset. 8 swaths of 43 shots were acquired over a seabed reflector with 4 degrees of inline dip and 2 degrees of crossline dip. Acquisition was 3 streamers with 300 m crossline separation. Left panel shows the zero offset section after conventional NMO for primaries. Right panel shows zero offset section after HEMNO for multiples. Notice how, over all midpoints, the seabed reflections in each panel are coincident.


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Next: Conclusions Up: Brown: Imaging operator for Previous: Practical implementation of the
Stanford Exploration Project
7/8/2003