Abstract Three-dimensional (3-D) seismic surveys have become a major tool in the exploration and exploitation of hydrocarbons. The first few 3-D seismic surveys were acquired in the late 1970s, but it took until the early 1990s before they gained general acceptance throughout the industry. Until then, the subsurface was being mapped using two-dimensional (2-D) seismic surveys. Theories on the best way of sampling 2-D seismic lines were not published until the late 1980s, notably by Anstey, Ongkiehong and Askin, and Vermeer. These theories were all based on the insight that offset forms a third dimension, for which sampling rules must be given. The design of the first 3-D surveys was severely limited by what technology could offer. Gradually, the number of channels that could be used increased, leading to discussions on what constitutes a good 3-D acquisition geometry. The general philosophy was to expand lessons learned from 2-D acquisition to 3-D. This approach led to much emphasis on the properties of the CMP gather (or bin), because good sampling of offsets in a CMP gather was the main criterion in 2-D design. Three-D design programs were developed that concentrated mainly on analysis of bin attributes and, in particular, on offset sampling (regularity, effective fold, azimuth distribution, etc.). This conventional approach to 3-D survey design is limited by an incomplete understanding of the differing properties of the many geometries that can be used in 3-D seismic surveys. In particular, the sampling requirements for optimal prestack imaging were not properly taken into account. This book addresses these problems and provides a new methodology for the design of 3-D seismic surveys.

Abstract Traditionally, a microspread or noise spread has been the tool for detailed investigation of the properties of the wavefield to be recorded in 2-D seismic data acquisition. Ideally, the noisespread consists of a single shot recorded by a receiver spread with receiver station intervals that are small enough for alias-free recording of the total wavefield, including ground roll. Such a data set allows analysis of the noise in relation to the signal and serves as a tool for the design of field arrays. Examples of noise spreads are shown in Figure 4.16 of Vermeer (1990) . In 1979, a noise spread with extremely fine receiver station sampling was acquired in the Paris basin by the field crew of Shell's E&P Lab. With its 0.25-m sampling interval, it was appropriately called the nanospread. Berni and Roever (1989) used this data set to illustrate the effect of statics variation across field arrays (intra-array statics). This paper showed an important application of noise spreads: the investigation of recording effects which cannot be analyzed after acquisition with usual spatial sampling intervals and arrays. A disadvantage of the 2-D noisespread is that it does not allow the investigation of 3-D effects. Instead, one would need a 3-D microspread. Therefore, in the context of Shell's research project, “Fundamentals of 3D seismic data acquisition,” it was decided to acquire such a data set. Originally, the idea was to acquire a 3-D shot with a dense coverage of geophone stations around it. This would involve months of acquisition time.

Abstract In this chapter the symmetric sampling criteria are expanded into guidelines for parameter selection for the survey geometry. Often, geophysicists dealing with the design of 3-D seismic surveys concentrate on the properties of the bin: offset distribution, azimuth mix, midpoint scatter. In my approach, even more emphasis is put on the spatial properties of a geometry across the bins. These spatial aspects are so important because most seismic processing programs operate in some spatial domain, i.e., combine neighboring traces into new output traces, and because it is the spatial behavior of the 3-D seismic volume which the interpreter has to translate into maps. These guidelines start with a brief description of the knowledge base, which has to be built to allow a satisfactory choice of all parameters. The first choice to be made is the type of geometry. In general, orthogonal geometry is the geometry of choice for land data acquisition and for marine data acquisition in combination with ocean-bottom cables. Yet, other geometries may also be selected, and a short review outlines pros and cons of various geometries that may be chosen. This chapter focuses on orthogonal geometry. If 3-D symmetric sampling is taken as a starting point, the choice of parameters for this geometry is simplified considerably. Instead of having to decide on the shot interval and on the receiver interval, a decision need only be made as to the sampling interval. Similarly, the maximum inline and maximum crossline offsets can be made equal. It is also recommended to see what the consequences are of making the shot-line interval and the receiverline interval the same.