Dual-sensor Technology Research Articles

Applying wavelet transform to suppress ghost in ocean-bottom node dual-sensor technology

Applying wavelet transform to suppress ghost in ocean-bottom node dual-sensor technology

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Dual-sensor towed streamer: from concept to fleet-wide technology platform

The launch of the dual-sensor towed streamer technology in 2007 is seen by many in the industry as the most important milestone in marine seismic technology in the last decade. The introduction of the technology triggered a significant interest and demand for broader bandwidth seismic data and increased the industry-wide awareness of the geophysical benefits of such broadband data for both frontier exploration and production monitoring in mature basins. It also resulted in the rapid development of new acquisition and processing technology, both concerning the source and receiver side, as well as changes to seismic vessel design and equipment. The geophysical benefits of broadband data and the availability of up- and down-going wavefields as part of the dual-sensor deghosting methodology are now routinely exploited throughout the entire seismic value chain, including seismic imaging and reservoir characterization. After the first 2D dual-sensor survey in 2007, which was quickly followed by the first 3D acquisition commencing on New Year’s Eve 2008, PGS has steadily converted its seismic fleet from hydrophone-only to dual-sensor streamers. The pace of the technology roll-out has been largely driven by the life-cycle of existing streamer inventory and the equipment needs for newly launched seismic vessels as part of an ongoing fleet renewal process. The fleet-wide roll-out of dual-sensor technology will finally be completed in the 4th quarter of 2015 with the upgrade of the last Ramform vessel. Given the scale and complexity of replacing and industrializing a complete acquisition platform, there have naturally been significant lessons, some of which we will be sharing in this article. We will also discuss some of the acquisition and processing technologies that have been developed and/or adapted in order to fully utilise this new marine seismic technology platform.

A Mediterranean petroleum province on the North Africa Plate margin: The Sicily Channel

Increased exploration of the multiplay hydrocarbon providence between Sicily and Tunisia has resulted in large gas discoveries offshore Sicily (Italy), Tunisia's first deep-water well (ADX 2010), and several recently acquired 2D and 3D dual-sensor seismic surveys. While the area is well known to be tectonically complex, it is at the same time considered a highly attractive exploration basin offering large structural anticlines, medium-sized transtensional horst blocks, stratigraphic traps, and a range of hydrocarbon play types with already discovered accumulations. However, some geologic uncertainties that have stunted exploration in this area for the past 25 years, especially in northern Tunisian waters, still require risk reduction. This paper gives several examples of some risks and uncertainties in this area and explains how better seismic imaging can significantly reduce risk. A large dual-sensor 3D survey acquired by ADX in 2010 with PGS dual-sensor technology (Geostreamer) serves as an illustration.

Improved seismic inversion and reservoir description of the Ichthys gas-condensate field, Browse Basin, Western Australia

Seismic inversion has become a standard geophysical tool to enhance seismic resolution, predict the reservoir porosity distribution, and to discriminate between reservoir and non-reservoir pay zones. Conventional seismic data does not record the low frequencies necessary for inversion. To enable a complete bandwidth, low frequencies are modelled from well data and are typically interpolated throughout the volume using seismic velocities. This often causes the resultant porosity distribution calculated from the inverted P-impedance to be biased by the well data and the geometry of well locations. Dual-sensor GeoStreamer technology was used to acquire a regional multi-client 2D survey by PGS in 2008, including some lines over the Ichthys gas-condensate field in the Browse Basin. Dual-sensor streamer processing recovers a wider frequency bandwidth than conventional seismic. Receiver ghost removal combined with deep streamer towing simultaneously boosts both the low and high frequencies. The improved bandwidth enables a higher quality of velocity analysis, which further improves resolution throughout the section. Simultaneous inversion of the data validated the uplift of the low frequency data, and significantly reduced the bias towards well data for the low frequency model. The resultant P-impedance data demonstrated an excellent tie to well data. The dual-sensor technology promises to improve the description of the porosity distribution within our reservoir model.