Chu-Ong Ting

Taking apart beam migration

The years 2000–2001 sparked a flurry of activity on various flavors of beam migration. GEOPHYSICS papers by Yonghe Sun et al. on slant-stack Kirchhoff migration and Ross Hill on Gaussian-beam migration showed the potential of migration methods that combine aspects of Kirchhoff migration with some novel preprocessing. As a result, a number of variant beam-migration methods have arisen in the last few years, some promising great efficiency and some promising great imaging fidelity. On the other hand, because of beam migrations extra preprocessing, a simple interpretation of beam migration, analogous to that of Kirchhoff migration, has been hard to pin down. In this article, we try to add some intuition to the discussion of beam-migration methods. Our task is challenging since, for the most part, we will describe Gaussian-beam migration, which is possibly the most complicated of the slant-stack migrations. Of course, a successful understanding—even a partial understanding—of this important method will make ...

Subsalt Steep Dip Imaging Study With 3D Acoustic Modeling

SUMMARY W e present a 3D acoustic wave equation modeling study with the objective of understanding imaging challenges for steep dips (faults and three-way closure) beneath allochthonous salt sheets. Narrowazimuth, wide-azimuth and full-azimuth surface acquisition configurations as well as a 3D vertical seismic profile (VSP), are simulated using a two-way acoustic finite-difference modeling algorithm and followed by reverse time migration (RTM). Modeling results show that even full-azimuth surface seismic is not able to image steeply dipping subsalt events associated with faults and three-way traps. Only a 3D VSP is able to image targeted subsalt steep dips by placing receivers below the salt. The imaging success of VSP in this study emphasizes its complementary role to surface seismic.

Controlled beam migration applications in Gulf of Mexico

In the deep water Gulf of Mexico, the salt tectonics creates complicated salt bodies, including various shapes of salt sheet, salt canopy, and salt dome. This high velocity medium poses a serious challenge to seismic acquisition and imaging that its high velocity contrast to surrounding sediment field creating a lens that distorts the wave field propagation. As a result only limited portion of the seismic energy is able to transmit down to the subsalt target, and even less is able to reflect back and to be received by seismic recorder at the surface, depending on the receiver coverage. In conventional narrow azimuth towed streamer (NAZ) acquisition, the receivers are layout in a 2D sense along the shooting direction so most reflected subsalt energy was not acquired in the data. The latest wide azimuth (WAZ) acquisition is designed to address this issue. Its receivers cover a much wider azimuth range, thus have a better chance to capture all the reflected subsalt energy in the acquired data.

A Simulated Wide Azimuth Simultaneous Shooting Experiment

The cost of conventional wide azimuth (WAZ) acquisition is generally several times that of narrow azimuth (NAZ) acquisition. Simultaneous source acquisition is a direct way to reduce this cost. The main drawback of this technique is interfering noises. We present a simulated simultaneous source experiment to evaluate the impact of noise on subsalt imaging and sediment model building. Although results show the noise is negligible to the subsalt image, it is severe on Kirchhoff migrated gathers. Controlled beam migration (CBM) is able to suppress the noise and yield usable gathers for tomographic update.

Application of 3D Interbed Multiple Attenuation in the Santos Basin, Brazil

Imaging of pre-salt reservoirs in the Santos Basin can be significantly affected by the presence of strong interbed multiples in the data. These multiples can be predicted using a data-driven, true azimuth convolution method similar to surface-related multiple elimination (SRME), and removed using a suitably constrained subtraction technique. We discuss the application of this method to Santos Basin data, and present results on 2D synthetic data and 3D real data.

Application of Interbed Multiple Attenuation In the Santos Basin, Brazil

Imaging of pre-salt reservoirs in the Santos Basin can be significantly affected by the presence of strong interbed multiples in the data. These multiples can be predicted using a data-driven, true azimuth convolution method similar to surface-related multiple elimination (SRME), and removed using a suitably constrained subtraction technique. We discuss the application of this method to Santos Basin data, and present initial results on both synthetic and real data from the Tupi oilfield.

Optimizing 3D SRME on Wide Azimuth Data

We discuss how to optimize our 3D SRME method to take advantage of wide azimuth (WAZ) data, while overcoming challenges posed by the data. Compared to narrow azimuth data, the main advantage of WAZ data is the wider distribution of azimuth angles. The challenge is how to handle the larger source separation and the lack of near offsets. We use a real WAZ dataset to show that the optimized 3D SRME algorithm is effective in removing multiples.