Introduction Shallow geological hazards possibly affecting drilling, platforms anchoring, and subsurface installations are a major threat lurking in the shallow zone below the seabed. These hazards could appear in different forms such as fault scarps, gas hydrates, gas-charged sediments, pockmarks, buried channels, abnormally pressured sands, and reefs. The detection and interpretation of these shallow located multiform hazards requires high-resolution, fit for purpose 3D seismic data. Since Kerry Campbell in a 1999 TLE article stated that, "Clearly, the most reliable technical approach to minimize geo hazards risk would be to use 3D exploration seismic data for a preliminary geo hazard assessment...." the use of exploration and reservoir oriented 3D seismic have been accepted among the shallow hazards specialists. Nowadays their use appears completely mandatory as Nader C. Dutta & al. stated in their TLE special section article in 2010, " We think that the use of 3D seismic data could be and should be a standard practice….?? The production of shallow hazard dedicated seismic volumes (later called SHAZ cubes) by enhancement of classical exploration or reservoir 3D seismic raw data through specialized processing flows is now well controlled and accepted by the industry. These specific flows could greatly improve the added value that could be extracted from exploration and high resolution reservoir 3D volumes acquired with classical acquisition designs. We present a decision pathway for the optimization of the processing sequence for SHAZ cube production. Three different processing flows are proposed, relying on the full exploration processing sequence. Pro's and con's of each flow are discussed in terms of result quality, turnaround and cost. This embedded SHAZ cube production approach yields first of all to a better quality output products but also allows a regional scale interpretation, reducing " rush-hush?? situations frequently associated to localized so-called short offset cubes and to cost saving. Discussion: Exploration and reservoir oriented 3D surveys allows the production of 3D cubes (SHAZ) through specific Short-offset processing. Such dedicated SHAZ cubes are instrumental to shallow geological hazard interpretation and evaluation and they lead to a better assessment of related risk for E&P activities. SHAZ cubes are deemed a mandatory tool for assessing the sea bottom and subsurface conditions at large scale. Early availability of these specialized datasets are always welcome by interpreters in order to have a broader view of the potential hazards at a local and regional scale. An efficient way to produce efficiently regional SHAZ cubes will be implemented by systematically including the production of such cube in any given new processing or reprocessing project. Derogations to this rule will be granted if such validated fit for purpose recent dataset is already available for the designated area.
U.S.A., This paper describes a post-stack methodology to compensate the amplitude loss prior to commencing further seismic reservoir characterization studies in Peciko field. The available 3D seismic data shows that the high frequency part (25-55 Hz) of the seismic signal contributes more significantly to the variability of extracted wavelet amplitude than the low frequency part (5-25 Hz) and within the high frequency part, the amplitudes of the extracted wavelets correlate positively with the RMS amplitude of seismic traces from which the wavelets have been extracted.This analysis led to the design and testing of a two-step amplitude correction scheme based on maps of RMS amplitude derived from the low and high frequency bands. The first step consists of locating the areas where the seismic signals require correction. The second step respects the defined correction area and uses specific gain maps for the low frequency and high frequency components. These corrections were optimized and controlled under the careful scrutiny of quantitative seismic-towell ties and attribute maps.Application of the methodology has brought significant improvements to the initial seismic dataset, e.g. better preserved amplitudes, less variability of wavelet amplitude and enhanced seismic detection. All of these advantages were successfully obtained while barely influencing the background information. However, it has been shown that the relative added-value resulting from this approach will depend on the quality of the initial dataset itself. Heavily damaged amplitudes under massive shallow gas or anomalously low velocity features will probably be insufficiently compensated. In this perspective, careful control at many well locations and the mapping of QC attributes are very important to assess the method.In our Peciko case, the compensated cube enables refinement of the previous interpretations and optimization of the development plan. Furthermore, these results motivated the application to the existing angle sub-stacks and opened the way to pre-stack seismic inversion for a more extensive reservoir characterization. This workflow has been applied to the other 3D datasets, such as Tunu and Bekapai 3D, which suffer from similar amplitude losses phenomena associated with carbonate or coal masking and shallow gas pockets.
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