Near-surface P-velocity modelling by integrated seismic, EM, and gravity data: examples from the Middle East

Abstract

Onshore seismic data from the Middle East and around the world are adversely affected by near-surface velocity anomalies. Shallow-section velocity characterization represents a key issue for land data processing in both time and depth domains. In the Middle East, near-surface complexity can be attributed to sand dunes, wadies, sabkha environment, shallow high-velocity layers (carbonate outcrops), karsting, and fractured layers. The correct estimate of the near-surface velocity field is fundamental to obtain reliable seismic images. Conventional workflows for near-surface model building often involve interpreting and inverting refracted arrival information. These methods may fail to appropriately reconstruct the shallow velocity complexities in the presence of large velocity inversions, rapid lateral velocity changes, and noisy refracted arrival data. The combination of additional geophysical measurements (i.e., non-seismic), not influenced by the problems affecting seismic propagation, are needed to address the shallow velocity modelling problem. This paper describes three different approaches recently applied in distinctly different environments around the Middle East to solve near-surface modelling problems. The first example from the United Arab Emirates (UAE) demonstrates the integration of seismic and time-domain electromagnetics (TDEM) for sand dune statics application. The second example from Saudi Arabia also addresses sand dune statics, but this time by simultaneous joint inversion (JI) of seismic and gravity measurements. The final example applies the simultaneous JI technique for the near-surface velocity component of a depth migration model.