A B S T R A C TIn land surveys, the weathering layer can often distort the seismic signal due to it passing through rapid velocity and density changes, dispersion, scattering and inelastic absorption. In a simple spring-dashpot model for the earth response, an equivalent medium groups these complex phenomena into two parameters only; these are called ground viscosity and ground stiffness. The most recent controllers for vibrators can estimate both parameters. To validate these measurements, Saudi Aramco conducted an experiment measuring ground viscosity and stiffness from two different vibrator control systems over an area of varying terrain conditions, including unconsolidated sand and limestone outcrop. The two systems measured different values, but detected similar trends that correlated well with weathering conditions and surface geology, e.g. lower viscosity values on the outcrop than on the sand.The ratio of ground viscosity to ground stiffness can approximate the shallow S-wave velocity, which we converted into P-wave velocity through calibration with sparse uphole data. Static corrections incorporating this velocity information somewhat improved the focusing of seismic time sections. This new approach does not require additional acquisition efforts, and can model shallow complex formations in arid areas where classical static methods often fail.
A B S T R A C TWe present a seismic Test Line, provided by Saudi Aramco for various research teams, to highlight a few major challenges in land data processing due to near-surface anomalies. We discuss state-of-the-art methods used to compensate for shallow distortions, including single-layer, multilayer, plus/minus, refraction and tomostatics methods. They are a starting point for the new technologies presented in other papers, all dealing with the same challenging data described here.The difficulties on the Test Line are mostly due to the assumption of vertical raypaths, inherent in classical applications of near-surface correction statics. Even the most detailed velocity/depth model presents difficulties, due to the compleXraypath. There is a need for methods which are based on more complex models and theories.
A B S T R A C TAccurate statics calculation and near-surface related noise removal require a detailed knowledge of the near-surface velocity field. Conventional seismic surveys currently are not designed to provide this information, and 3D high-resolution reflection/refraction acquisition is not feasible for large survey areas. Satellite images and vibrator plate attributes are dense low-cost data, which can be used in spatially extrapolating velocities from sparse uphole data by geostatistics. We tested this approach in two different areas of Saudi Arabia and found that the optimal recipe depends on the local geology.
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