Surface-based Internal Multiple Elimination in the CMP Domain — Theory and Application Strategies on Land Seismic Data
Surface-based Internal Multiple Elimination in the CMP Domain Theory and Application Strategies on Land Seismic Data
Shiguang DENG 0
Wenjin ZHAO 0
Zhiwei LIU 0
0 Chinese Academy of Geological Sciences , Beijing, People's Repulic of China
A b s t r a c t The data-driven internal multiple elimination (IME) method based on feedback model, which includes CFP-based, surface-based and inversion-based methods, are successfully applied to marine datasets. However, these methods are computationally expensive and not always straightforward on land datasets. In this paper, we first proved that the surface-based IME method, which is the most computationally efficient method among the three methods, can be derived from the CFP theory. Then we extend it to CMP domain under the assumption of locally lateral invariance of the earth, which makes it more computationally efficient. In addition, we proposed applying a time-variant taper based on the first Fresnel zone to predict the multiples more percisely. Besides, the improved S/N ratio and dense offset distribution can be obtained by using the CMP supergather, which makes the CMP-oriented method more suitable for land data. Some practical processing strategies are proposed via case study. The effectiveness of the proposed method is demonstrated with the application to synthetic and field data.
internal multiple; feedback model; surface-based; CMPoriented; land seismic data
1. INTRODUCTION
Multiple reflections affect seismic imaging quality, especially when strong
subsurface reflectors exist. The interference of multiple energy with primary
events could result in interpretation uncertainties. It is necessary to remove
multiples before subsequent processing. In general, multiples consist of
freesurface multiples and internal multiples. Free-surface multiples are multiples
that have experienced at least one downward reflection at the air-water
“freesurface”; internal multiples are multiples that have all of their downward
reflections below the free surface. Land seismic data is mainly affected by
internal multiples. Internal multiples have experienced reflectors that are in
general more remote and harder to precisely define (in comparison with
freesurface multiples); hence, internal multiples are more difficult to predict and
attenuate (Weglein 1999).
Two major internal multiple elimination (IME) methods, based on wave
theory, are the inverse-scattering series (ISS) and feedback methods. The
inverse scattering series (ISS) method for internal multiple elimination is
discussed specifically by Araujo et al. (1994), Coates and Weglein (1996),
Weglein et al. (1997). The ISS method is fully data-driven and does not
require any subsurface information. However, the cost of the ISS approach is
considerably greater than the feedback method (Verschuur and Prein 1999).
In practice, the feedback method would be a more effective choice. Berkhout
and Verschuur firstly proposed the feedback method for the surface-related
multiple elimination (SRME) (Berkhout 1982, Verschuur 1991, Verschuur et
al. 1992, Berkhout and Verschuur 1997, Verschuur and Berkhout 1997).
Berkhout and Verschuur (1997) extended the algorithm from surface to
internal multiples by replacing shot records with common-focus-point (CFP)
gathers (Berkhout 1997, Thorbecke 1997). Berkhout and Verschuur (2005)
illustrated the internal-multiple-removal algorithm with numerical examples.
This algorithm can be formulated in terms of boundary-related and
layerrelated versions. Verschuur and Berkhout (2005) demonstrated the strategy
for applying the two versions of internal-multiple-removal algorithm on
physical-model and field data. The boundary-related approach requires the
construction of CFP gathers, using focusing operators with correct
traveltimes, while the layer-related approach allows traveltime errors. From
a cost perspective, the layer-related method costs twice as much computation
time as the boundary-related method, even though the boundary-related
method involves more user interactions. Despite the extra calculation cost,
the ease of use and the robustness of the layer-related approach make it
preferable to the boundary-related approach in most situations. Jakubowicz
(1998) proposed the surface-based IME method, in which the need for CFP
gathers in the boundary-related method is avoided, and internal multiples can
be estimated directly from the data measured on the surface. In van Borselen
(2002), an extension of this procedure is illustrated to remove internal
multiples that have crossed a pseudo-boundary that is chosen to lie between two
internal reflectors. Thus, the data-driven internal multiple elimination based
on surface data can be applied either in boundary-related version or
layerrelated version. Recently, Ypma and Verschuur (2013) redefined internal
multiple elimination as a full waveform inversion process, following the
principles of estimating primaries by sparse inversion (EPSI) (van
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