The seismic industry has tended to use the term “broad- band” to refer to temporal bandwidth and vertical res- olution. A narrower wavelet gives sharper resolution, while a reduction in side-lobe energy leads to a more direct view of the geology. This improves interpreters’ ability to see complex detail in the subsurface and assess risk; however, interpreters also must take care that the frequency content observed in the data is real.
Frequency spectra contain both signal and noise, and it is often difficult for geophysicists to measure a reliable signal- to-noise ratio on the final migrated section. Methods used to measure noise can become the basis of methods to sup- press the noise, and, as a result, the residual noise becomes closer to resembling signal. Interpreters also are learning that much of the noise comes from issues related to the spatial sampling limitations of acquisition geometries. For example, shallow overburden noise may alias to appear at different spatial frequencies.Adequate spatial sampling is re- quired to avoid such aliasing, so survey design is influenced as much by noise characterization as by signal requirements.
The Earth presents complex 3-D geology, so interpret- ers must consider what happens to the signal in such envi- ronments. Complexity in the seismic wavefield results from large-scale macrostructures as well as distortions caused by smaller geologic features located closer to the sources and receivers. Assumptions, based on simplistic 1-D geologic models predicting emergent waves propagating vertically, no longer apply.
Interpreters must, therefore, expand the definition of broadband to encompass resolution in all directions, includ- ing spatial as well as temporal.This places new demands on the methods required to sample and reconstruct the seismic wavefield and a greater emphasis on controlling both amplitude and phase across the full bandwidth.
The term broadband should include spatial band- width, increasing the range of wave numbers in all directions—X, Y and Z—over which useful information content contributes to the image volume. Achieving adequate sampling to avoid spatial aliasing of the recorded seismic wavefield means that the data can provide high-resolution images of geological features irrespective of their orientation in the earth.
The IsoMetrix marine isometric seismic technol- ogy not only broadens the temporal bandwidth of towed-streamer seismic data though 3-D deghost- ing but also allows generation of datasets on a fine, evenly sampled grid. This provides a spatially de- alised broadband product in all three dimensions:
in-line, cross-line and depth. This fine-scale resolution of the wavefield in all directions can translate directly to fine-scale resolution of the geology in all directions, enabling a more accurate representation of the subsurface.
Barents Sea Schlumberger multiclient program, provides many examples of the benefits of acquiring a high-quality broadband IsoMetrix dataset. The Western Barents Sea is well known as a structurally complex region where sev- eral tectonic events have resulted in the development of a number of fault complexes.This new dataset is providing fresh insights into the geology of the area and its associated hydrocarbon prospectivity.
The survey area contains two main fault systems associ- ated with the Asterias fault complex and a remote part of the Hoop fault complex, a strike-slip fault system angled at about 45 degrees to each other.The high spatial resolution of the seismic image has made it possible to auto-track the entire fault system independent of fault orientation. Some of the faults seem to control shallow hydrocarbon reservoirs in the Upper Triassic stratigraphic interval, and their map- ping is crucial for shallow target exploration.
A complex Upper Triassic channel system is another important geological feature of the Loppa High area. High-quality seismic data demonstrate the Snadd For- mation channel system associated with floodplain devel- opment in the Upper Triassic. Seismic attributes such as variance can highlight the fluvial depositional system.The data reveal a variety of small-scale fluvial geomorphologi- cal features, including point-bar systems, clustered channel fill complexes and ribbon channel sandstone bodies. For more information about 3-D broadband data acquisition and multiclient data from the Barents Sea, visit Schlumberger at booth 940.
Only IsoMetrix marine isometric seismic technology provides single-sensor true 3D broadband measurements for full-bandwidth imaging of fine-scale structures in the subsurface in all directions—vertically,along the streamer, and crossline between the streamers—for the most detailed imaging from seabed to reservoir.
Fine-scale isometric subsurface characterization enables generation of 3D interpretation attributes independent of the orientation of viewing. This translates into more detailed
representations of the subsurface structure and stratigraphic variations, enabling a new level of insight into the geology of an asset.
Improve acquisition efficiency using a single-vessel wide-tow source
Conventional marine 3D surveys are typically acquired using a single vessel with 50-m source separation and streamers towed 50 to 100 m apart, leading to sparse sampling of the wavefield in the crossline direction. Using this type of acquisition, the only way to improve efficiency is to compromise data quality.
IsoMetrix technology enables you to acquire more data and increase coverage using a single vessel with 250-m wide-tow source separation, improving efficiency by 15% without degrading the subsurface image.
Improve acquisition efficiency using a single-vessel wide-tow source
Conventional marine 3D surveys are typically acquired using a single vessel with 50-m source separation and streamers towed 50 to 100 m apart, leading to sparse sampling of the wavefield in the crossline direction. Using this type of acquisition, the only way to improve efficiency is to compromise data quality.
IsoMetrix technology enables you to acquire more data and increase coverage using a single vessel with 250-m wide-tow source separation, improving efficiency by 15% without degrading the subsurface image.
Tow wider and deeper with advanced deghosting capabilities
The three measurements provided by the IsoMetrix technology multimeasurement streamer make it possible to reconstruct spatially dealiased wavefields between the cables where there are no sensors—offering the ability to tow streamers farther apart—resulting in a continuous, reliable representation of the deghosted wavefield in all directions.
Advanced deghosting capabilities make it possible to tow the entire length of the streamer spread at greater depths, extending the weather window and providing powerful attenuation of noise from rigs or other seismic surveys.
Achieve a new level of detail from seabed to reservoir
IsoMetrix technology makes it possible to accurately reconstruct the full 3D wavefield between the streamers, isometrically sampled at a 6.25-m by 6.25-m surface grid of data for every shot record.
This fine sampling makes the data suitable for use in a wide range of interpretation and modeling applications, including high-resolution near-surface imaging, deep reservoir characterization, field development planning, and 4D (time-lapse) production monitoring.
IsoMetrix technology enables the industry’s most efficient and cost-effective acquisition of seismic surveys—improving data quality and reducing operational and environmental exposure.
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