Data Enhancement From A 486 - Channel Streamer
Authors: Dragoset William H. , Larner Kenneth L. 
Published: October 2008

Seismic reflection data obtained with a 486-channel streamer cable can be processed by array-forming techniques that include optimal weighting of individual channels and/or beam steering. Such processing can improve the resolution of horizons at early and intermediate times as well as enhance the continuity and clarity of later reflections. The originally recorded data may also be processed to simulate results obtainable with a wide variety of conventional streamers.

To demonstrate data enhancement obtained by these techniques, a selected line was surveyed in the Gulf of Mexico, first with the 486-channel system and then with a conventional 48-channel streamer. Comparison of stacked sections shows that:long, steered arrays can enhance deeper events while retaining the high frequency content of shallow data, andshort arrays at small group intervals allow finer resolution of shallow events.

When the 486-channel data were processed to duplicate the 48-channel data, the larger system yielded somewhat better results; this improvement may be attributed in part to reduced cable noise.

INTRODUCTION

Since the beginning of seismic reflection exploration, there has been a growing trend toward more complex and specialized geophone spreads in the field. Examples of this trend include long arrays designed to suppress multiple reflections and diffraction noise, optimally weighted and non-uniformly spaced arrays designed to attenuate coherent noise such as ground roll, and ministreamers designed to obtain high-resolution shallow data. Although these techniques have provided improved sections in selected areas, the trend of specialization puts an undesirable constraint on the planning, processing, and interpretation of seismic surveys. Also "optimum" geophone arrays are often determined from past experience or by analyzing field tests. These practices can lead to resurveys when serious problems are discovered in the course of processing initial survey data or when interpretation targets change at later dates. Furthermore, no particular array design can provide optimized data at all depths over an entire survey. This constraint is especially limiting for marine surveys because a standard streamer cannot easily be reconfigured in the field.

Innovations in electronics make possible a seismic streamer cable of 500 or more independent data channels. With such a large number of short receiver groups distributed within a standard length cable (say 3 km), the spatial density of observation points is comparable to that for individual hydrophones within the arrays of standard streamers. The individual groups in the SOO-channel streamer are, however, short enough to be considered as points. As a result, the recorded data are not constrained by restrictions imposed by a fixed choice of array design.

Since routine processing of such a large number of channels could be prohibitively expensive, reduction of the data by array-forming is desirable at present. Now, however, because the array design occurs at the data processing stage, a new realm of options becomes available. In this paper implications of several of these processing options are investigated for a seismic line recorded with a 486-channel streamer in the Gulf of Mexico.