Advanced 3-D Land Internal Multiple Modeling and Subtraction, a Wide Azimuth Oman Case Study
Benjamin, Nigel 1; Plasterie, Pierre *2; Bendjaballah, Malik 1; Pica, Antonio 2; Leroy, Sylvain 2; Delmas, Laurie 2; Zwartjes, Paul 3; Smith, Richard 3; Van Dijk, Tom 3
(1) CGGVeritas, Muscat, Oman. (2) CGGVeritas, Massy, France. (3) Petroleum development Oman, Muscat, Oman.
Internal multiple attenuation presents a major problem to both the geologist and the geophysicist. First, the amount of noise can often be such that accurate interpretation of the primary seismic wavefield is impossible making the seismic data unusable. Second, internal multiples are hard to distinguish in the total wavefield, and the problem is more difficult to deal with than with surface related multiple. Internal multiples have a dispersed character that creates a curtain of noise often stronger than primaries where move out discrimination or deconvolution techniques fail.
If strong reflectors generating multiples are present and identified in the subsurface, re-datuming the wavefield of all shot points and receivers to the generators is possible, thus making each reflector a new buried surface from which the SRME process can be engaged. However in the Middle East it is not always possible to identify clearly the multiple generators given the large number of possible candidates.
Here we propose a new approach using a wave equation based internal multiple modeling technique, which consists of modeling the multiple wavefields for all possible multiple generators within a region of the sub-surface, without the need for accurate identification of the specific generators. This is achieved by modeling internal multiples, of all orders, using a number of different windows such that all suspected multiple generators are included. These multiple models are then adaptively subtracted from the input wavefield.
This is illustrated with a case study from Oman using a high-density wide-azimuth survey. The high-density acquisition has good near-offset coverage, allowing an accurate shallow reflectivity model of the multiple generators in near surface to be derived. The multiple wavefields are subtracted in the common offset vector (COV) domain. For wide azimuth surveys, subtraction in COV domain allows flexibility for testing, production and quality control, as well as optimum efficiency.
The results are extremely encouraging. The method is fully 3D, accurate, and efficient yet primary wavefield preserving and integrates well in the seismic processing workflow of both modern and vintage (narrow azimuth) seismic surveys.
AAPG Search and Discovery Article #90141©2012, GEO-2012, 10th Middle East Geosciences Conference and Exhibition, 4-7 March 2012, Manama, Bahrain