Summary

We present a technique in which 2 or more shots are acquired during the time it normally takes to acquire 1 shot. The 2 or more shots are fired in a near simultaneous manner with small random time delays between the component sources. A variety of processing techniques are applied to produce the same seismic images which would have resulted from firing the simultaneous shots separately. These processing techniques rely on coherency of the wavefield in the common-shot domain and unpredictability in common-receiver, -offset and -midpoint domains. We present results of its application in 2D in the Green Canyon area and in 3D on the Petronius field, both located in the Gulf of Mexico. These results demonstrate that in deep water with modest water-bottom reflectivity no special processing is required, whereas in shallower water with stronger water-bottom reflectivity the use of shot separation techniques is necessary. We conclude that this technique can be used robustly to improve source sampling and, for example, to acquire data from a range of azimuths simultaneously. This could potentially change the fundamental economics of wide azimuth acquisition.

Introduction

There are a number of potential advantages in being able to acquire 2 or more shots in the time that it normally takes to acquire 1 conventional shot. An obvious benefit is an increase in time and/or cost efficiency. If there is freedom to locate the additional source(s) at different locations relative to the main seismic vessel, then data may be simultaneously acquired which supplements the typical seismic configuration. Thus such a technique can be used generally to increase data sampling via increased fold, increased range of azimuths, or extended offsets, or it can be used to increase the time value of data by reducing the need for infill or allowing an acquisition program to complete in less time. Although a number of authors have discussed simultaneous shooting using vibratory sources (e.g., Ward et al., 1990), only a few (e.g. Beasley et al. (1998), de Kok and Gillespie (2002), Stefani et al. (2007), Hampson et al. (2008)) have discussed its application to impulsive sources, such as airguns. If a secondary source has asynchronous timing then it behaves like nearby seismic interference which Lynn et al. (1987) observe may be effectively attenuated by stacking or even more so by diversity stacking. Krey (1987) described the ability of migration and stacking to attenuate noise very effectively, particularly in 3D. Since it is current practice to use 3D migration algorithms we might expect asynchronous secondary source energy to be effectively attenuated simply by our conventional migration and stacking procedures. As a result we consider the possibility of using one or more secondary sources located at positions of our design with random timing delays all fired within the same conventional shotpoint timing cycle. We will briefly describe the technique and present results of its application in 2D on the Sigsbee synthetic model and in the Green Canyon area and in 3D on the Petronius field, both fields located in the Gulf of Mexico.

This content is only available via PDF.
You can access this article if you purchase or spend a download.