Digital Quality Seismic Streamer System

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ABSTRACT The marine seismic streamer is an integral part of the complex signal detection system used in offshore oil exploration. The "Century" DSS-V digital seismic streamer system was designed to meet today's expanded requirements in seismic techniques. It incorporates up to 120 data channels, a maximum active length of 4800 meters, Multidyne? acceleration cancelling hydrophones for low noise towing, and an electronic shipboard interface which eliminates signal distortion due to salt water leakage in the streamer and provides various array configurations to meet both high resolution and high penetration geophysical needs. INTRODUCTION Developments in marine seismic techniques have come rapidly and with increasing complexity during the past few years. While many, perhaps the majority, of these have been in data processing, it is also true that a significant impetus for processing improvements has been the tremendous volume of marine geophysical data acquired at modest cost per mile. Hardware developments coupled with associated operational techniques have, over this time frame, contributed greatly in this effort to reduce the cost of marine seismic data without sacrificing data quality. Significant hardware developments include fast cycling non-dynamite acoustic sources, and towed detector arrays (seismic streamers) with extremely low self noise and with detector configurations specifically designed to minimize both mechanical and radiated noise signals. It is to the latter of these developments, towed arrays, that this paper is addressed. W. A. Schneider in a paper on developments in seismic data processing, published in the December, 1971 issue of Geophysics5, said the following, "Of equal significance, and in support of these processing and analysis trends, are data acquisition developments which, deserve special mention. In particular, the continuing trend toward the use of longer spread and higher stacking multiplicity has resulted in more accurate velocity and statics estimates, improved record-section SiN ratios, and generally better deep data." He continued, lithe bulk of marine data currently collected is 24-fold and is collected with 8,000 foot streamers 48-fold will likely become the future standard with streamers approaching 10,000 feet. Some argue that both operational and physical constraints limit present streamer design philosophy beyond 10,000 feet. Stacking fold, however, can and will increase beyond present levels until the incremental gains in product improvement no longer offset the added expense." Also pointed out by Schneider, the expected benefits associated with longer spreads and higher fold coverage and processing may be further enhanced by synergism in the several steps involved in processing and interpretation. Figure 1 indicates how parameters in the processing cycle are affected by increased fold and spread length. How important these may be individually is obviously a function of physical and geologic conditions, as well as the exploration objectives of the geophysicist working the area.