3DSymSam - Geophysical Advice provides advice on 3D seismic survey design based on 3D symmetric sampling theory and offers courses on 3D seismic wavefield sampling and various acquisition techniques.

This website also contains some contributions to current and past geophysical discussions.

In October 2002 the SEG published “3-D seismic survey design” by Gijs J.O. Vermeer. This book is a slightly modified version of Vermeer's PhD thesis, which was published early 2001. The Leading Edge of May 2003 published a rave review of the book. A Chinese translation appeared in 2008 (see picture below).

A web version of 3DSymSam's Acquisition Design Wizard has been installed on this website. Just click “Design Wizard” on the menu on the left to gain access to the Wizard.

Wide-azimuth towed streamer data acquisition is becoming quite popular, albeit very expensive. To increase efficiency it has been proposed to use simultaneous sources. This website now includes a paper that argues that WATS configurations with parallel source and receiver tracks cannot benefit much from simultaneous sources. Instead a zigzag WATS is proposed.

Here follows some text from the introduction

“This paper starts with the description of some characteristics of a typical WATS configuration. Next it is argued that this configuration can be viewed not only as parallel geometry but also as areal geometry, because a major objective of WATS is to acquire 3D shot gathers. If viewed as areal geometry, the inline source sampling is often quite dense, whereas the crossline source sampling is often quite coarse. Other aspects, such as binsize, edge effects and feathering, are discussed as well in the light of what would be an ideal areal geometry. Next, I argue that simultaneous sources will only help to reduce acquisition cost and time of areal WATS configurations in case more than about 8 sources are used.

Geometries that would benefit from simultaneous sources are those that require dense sampling of sources along the source lines. Narrow-azimuth geometry and zigzag WATS are discussed as examples of such geometries. This paper is rounded off with a discussion of pros and cons of zigzag WATS configurations.”

Summary and Full paper

From time to time it is argued that cable-free systems would bring freedom in the choice of receiver station locations. To learn how this is viewed in the light of 3D symmetric sampling requirements, read the note "Noise suppression, prestack imaging and freedom of choice".

NMO stretch has an effect on the resolution of final stacked and migrated data that depends on the mix of offsets contributing to the final product. For the same range of absolute offsets, 2D data are less affected by resolution loss than 3D data. This is discussed in the note "NMO stretch for P- and C-waves and its link to resolution, AVO and mute offset".
The note also discusses the link between AVO-requirements and NMO stretch, the link between mute offset as a function of depth and NMO stretch, and the note describes NMO stretch for C-waves.

Wide-azimuth towed streamer (WATS) acquisition is a new technique with potential for better subsalt imaging. It is a highly expensive technique, because it involves traversing the survey area multiple times with varying crossline offsets between streamer vessel and source vessels. The expense of the technique has led to undesirable corner cutting such as acquiring data in only two of the four source-receiver azimuth quadrants. In some papers this cost-saving method has been justified on basis of reciprocity: reciprocity would make data acquired in opposite quadrants redundant.
The paper "Reciprocal offset-vector tiles in various acquisition geometries" presented at the 2007 SEG Conference held in San Antonio, Texas, argues that in sparse geometries data acquired in opposite quadrants are complementary rather than redundant.
The Power Point file of the paper as presented at the Conference can be viewed here as well (including presentation text in Notes pages).

The News Archive is located here.

Peiming Li (left) of BGP just handed a copy of the Chinese translation of “3-D seismic survey design” to Gijs Vermeer. Venue: SEG Pavillion at SEG Conference, Las Vegas, November 2008.