A comparison of shot‐encoding schemes for wave‐equation migration

Abstract

A B S T R A C TIn the last decade the seismic imaging industry has begun collecting data volumes with a substantial amount of data redundancy through new acquisition geometries including: wide-azimuth, rich-azimuth and full-azimuth geometries. The increased redundancy significantly improves image quality in areas with complex geology, but requires considerably greater computational power to construct an image because of the additional data and the need to use advanced imaging algorithms. One way to reduce the computational cost of processing such datasets is to blend shot-records, using shot-encoding, together prior to imaging which reduces the number of migrations necessary for imaging. The downside to doing so is that blending introduces strong, non-physical, cross-talk noise into the final image. By carefully choosing the shot-encoding scheme, we can reduce the additional noise inserted into the image and maximally reduce the number of migrations necessary. We describe a theory of blended imaging that explains all shot-encoding schemes, and use the theory to design a new class of encodings that use amplitude weights instead of phase-shifts or time-delays. We are able to use amplitude encoding to produce blended images of the same quality as previous encoding schemes at a similiar computational cost. Furthermore, we compare the results of amplitude encoding with the results from well-known shot-encoding schemes from previous work including: plane-wave migration, random-time delay, modulated-shot migration, and decimated shot-record migration. In our comparison, we find that plane-wave migration is in many ways an optimal shot-encoding scheme. However, we find that plane-wave migration produces results that are comparable to decimated shot-record migration when the total cost of imaging is taken into account, thereby calling into question the utility of shotencoding in general. Overall, this work questions the potential for shot-encoding in standard (shot-record) seismic imaging because blended imaging does not appear to sufficiently reduce the cost of imaging given the quality of the blended image compared to decimated shot-record migration..

Shot encoding with random projections

“…• Decimated shot encoding performs better than most other shot-encoding schemes reported in the literature (Godwin and Sava, 2011).…”

“…In order to complement the survey of Godwin and Sava (2011), we also analyze the distributions of the corresponding crosstalk matrices.…”

“…Examples for shot encoding schemes are phaseencoding (Romero et al, 2000) and modulated-shot migration (Soubaras, 2006). A recent survey contains an overview of many shot encoding schemes (Godwin and Sava, 2011).…”

Efficient amplitude encoding least‐squares reverse time migration using cosine basis

“…). For plane‐wave encoding, the length of the time padding for large ray parameter may exceed the length of the shot record (Godwin and Sava ; Hu et al . ).…”

Imaging blended vertical seismic profiling data using full-wavefield migration in the common-receiver domain

“…The deblended data, i.e., the separated shot records, can be fed into the conventional processing and imaging methods. On the other hand, there have been investigations in performing processing (e.g., van Groenestijn and Verschuur, 2011;Bagaini et al, 2012;Hou et al, 2012), imaging (e.g., Tang and Biondi, 2009;Berkhout, 2009, 2011;Jiang and Abma, 2010;Berkhout et al, 2012;Dai et al, 2012;Huang and Schuster, 2012;Godwin and Sava, 2013), and inversion (e.g., Ayeni et al, 2009;Ghazali et al, 2010;Routh et al, 2011;Choi and Alkhalifah, 2012;Guitton and Diaz, 2012;Plessix et al, 2012) of the blended seismic data directly, without actively separating the sources in advance.…”