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This paper presents three innovative technologies of PGS Company for marine geophysical studies: GeoStreamerGS™ is for marine seismic operations, EM for resistivity surveys in combination with seismic survey on the same vessel, and OptoSeis™ permanent reservoir monitoring during oil or gas production.
Seismics is the major marine geophysical technique. Unfortunately, in the conventional modification its effectiveness does not exactly comply with the requirements of our time. Improvements in both the marine seismic itself, its resolution capacity and informativity, and involvement of other geophysical techniques are on the agenda today.
PGS heavily invests in development of emerging technologies. The results are not late in coming. In this paper we present three innovative technologies, which our company started to offer at the geophysical services market in the last two or three years. The direct analogues that are comparable to them in terms of effectiveness and informativity are not yet present in the market.
GeostreamerGS™ technology. The technology has become the major one in PGS in the last tree years. The main difference with the conventional marine seismics is the design and types of receivers and sources. GeoStreamer uses dual-sensor (with two types of receivers) streamers with buoyant void filler instead of traditional seismic streamers with liquid fill and piezo pressure sensors (hydrophones). Low-density solid filler of special composition ensures guaranteed environmental security in case of abnormal situation of streamer failure. Two sensors types (hydrophones and geophones or geosensors) make possible registration of two wave types, namely: pressure waves like those in the traditional marine seismic streamer (hydrophones) and particle velocity (geosensors). Due to the fact that the pressure wave reflects from the free surface with the coefficient of (-1) while the particle velocity doesn't change phase (Fig. 1), in theory, ghost waves from the water-air boundary are completely removed when these waves are summed. This leads to the reduction of signal length at source and, as consequence, to spreading the signal spectrum, which results in noticeable buildup of seismic record resolution. The technology was named Geostreamer. However, the wide range of possibilities remains for further frequency extension, because the similar effect associated with the noise events from the free surface is present at the source, too.
Suppression of this noise is performed with the use of special time and depth distribution of air-operated wave transducers. They are towed at different depths and operate with delays distributed over time, which results in the reduction of wavelet length and frequency extension. This technology was named Geosource. Combination of the two technologies has the proprietary name of GeostreamerGS. Figure 2 shows an example of comparison of two time sections and amplitude spectra records obtained with the use of traditional streamer and conventional source (a) and with the use of GeostreamerGS (b). Along with the obvious visual advantages of the record, spectrum broadening into the low-frequency region allows to improve quality of seismic inversion and, consequently build better estimates of poroperm properties using seismic data. The GeostreamerGS technology can be used both in 2D and 3D seismic surveys.
An additional advantage of technology is the ability to tow the streamer at the depths of 15 to 25 meters without compromising data quality (the usual streamer is towed at the depth of 5 to 7 m). This removes the significant part of restrictions coming from the weather conditions, as operation can proceed at the wave height up to 5-6 meters, which results in noticeable decrease in performance time and, as a consequence, work cheapening compared to the conventional seismic operations.