What is FAZ?
Full-azimuth (FAZ) seismic data is data acquired over 360 degrees of azimuth over the full offset range. The subsurface geology is sampled in all directions and at all required offsets to give the optimum dataset. There are no compromises.
Why does the industry need FAZ?
FAZ data improves imaging in areas of complex structures, providing more detailed illumination for fracture and fault mapping, and it will improve our understanding of anisotropy and anisotropic velocity models. FAZ data is now readily achievable on land and at sea using efficient techniques and technology developed by WesternGeco.
How do we acquire FAZ?
On land the introduction of the WesternGeco UniQ integrated acquisition system, which is capable of recording up to 150,000 live channels of point-receiver seismic data, enables very large spreads to be deployed and therefore allows FAZ data to be acquired using any of today’s efficient source techniques.
At sea the WesternGeco Coil Shooting single-vessel full azimuth acquisition technique uses Q-Marine technology to acquire FAZ data by shooting in a series of overlapping circles.
On both land and sea, careful survey design and modeling allows FAZ data to be acquired over the full 360 degrees of azimuth, and at all offsets, to achieve the necessary illumination of complex structures such as diapiric salt. This approach also helps illuminate faults and fracture trends that may be poorly imaged using conventional narrow-azimuth or even wide-azimuth techniques.
How do we process FAZ data?
For FAZ data the processing effort starts before acquisition. While this may sound contradictory it acknowledges the fact that elements of the processing flow need to be recognized and understood to aid the survey design. No imaging challenge is simple, and no imaging challenge is the same as another; solutions all need to be tailored. So the key first step is to ensure that the survey is modeled and designed accurately. This takes time and is a collaborative effort between our customers and our survey evaluation and design (SED) modeling teams.
The next key issue is to ensure that, in processing, every trace of the FAZ dataset is handled according to its true azimuth. The azimuth of a trace is important information that must be maintained throughout the imaging workflow. For example, multiples can often be very difficult to attenuate because of their complex 3D raypaths. True 3D surface related multiple elimination (SRME) techniques, such as the WesternGeco 3D GSMP generalized surface multiple prediction method, fully honor true azimuth. FAZ datasets provide ideal input for GSMP processing because of their high shot-density and the full range of azimuths.
Velocity models too can be constructed with greater accuracy and confidence when they are based on data from a full range of azimuths at all offsets rather than from clusters of azimuths; the high-fold and full azimuth range aids the tomographic velocity analysis process, providing stable solutions. Well-sampled high-fold datasets can be split into sets of azimuthal common-image-point gathers and used to constrain high-resolution tomography studies. The results are detailed velocity models with a high degree of accuracy. Well, VSP, and magnetotelluric data as well as geomechanical studies can provide further constraints on the solutions derived and lead to more accurate and geologically consistent models.
Onshore, with the launch of the WesternGeco UniQ land seismic system, we are able to routinely acquire FAZ data. When we record onshore FAZ data using point-receiver recording techniques, we have a uniquely sampled dataset. This allows us to deploy new and novel noise-attenuation techniques, and to build near-surface models with greater accuracy than ever before.
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