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.
Increasing seismic resolution is often the ultimate objective assigned to new surveys or to the reprocessing of existing data. This is especially true for HR2D surveys or 3D data (re)processing dedicated to the assessment of shallow hazards prior to the drilling operations. Over pressured and/or gas saturated thin sedimentary bodies to be drilled through represent one kind of such geo-hazard. Thus, it is paramount to improve the detection of thin beds and be able to identify their thickness and extension as accurately as possible in order to ensure safe operations.Increasing seismic resolution through the maximization of the high frequency content may not always be the best strategy. An alternate attitude can be the improvement of the signal-to-noise ratio as this proves to be a limiting factor for achieving good detection.Under careful control of the seismic wavelet characteristics (amplitude, frequency content and phase) and provided the noise level of the seismic data is sufficiently low, useful information can be extracted from instantaneous phase. It can serve the purpose of detecting beds much thinner than the conventionally accepted detection limit of a tenth of a wavelength.
Geohazards are a major threat which can affect drilling, platform anchoring, and the integrity of subsurface installations. Therefore the assessment of geohazards using geophysical data require the best achievable resolution. Geohazards need to be precisely detected, delineated and understood in order to validate geohazard free areas and safe environments for drilling and production operations. Major subsurface geohazards are gas-charged sediments, gas hydrates and over pressured sands which are generally associated to amplitude anomalies. Dutta et al. (2010) illustrated that shallow hazards detection from 3D dedicated seismic volumes (SHAZ) is perfectly valid. Saint-Andre et al. (2011) highlighted the importance during conventional seismic workflow definition, of a dedicated shallow hazards 3D processing (SHAZ cube) which can systematically be performed using adapted wokflows and would enhance spatial and temporal resolution, hence detectivity in the shallow parts. The recent developpement of broadband acquisition techniques brings out new perspectives concerning shallow hazards detection. The broader frequency spectrum of the data obtained with these new acquisition techniques may become a turning point in terms of geohazards characterization. As a result, this raises the question: Do new Broadband acquisition techniques allow to improve or replace the dedicated 3D seismic volumes for geohazards detection?
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