The benefits of elastic full-waveform inversion for subsurface imaging in North Sea shallow-water environments

Abstract Until recently, industrial applications of full-waveform inversion (FWI) have, in practice, been limited by the use of the acoustic wave equation, which considers longitudinal (P) wave velocities but ignores shear (S) wave velocities. This simplifies the differential equations involved by reducing both the parameter space and the computational burden of solving these equations. Moreover, it has resulted in acoustic FWI being adopted as the workhorse tool for velocity model building worldwide, supported by many excellent field data examples. However, in areas of complex geology, strong impedance contrasts can generate highly elastic behavior leading to the breakdown of the acoustic assumption. In these cases, accurate earth models cannot be obtained without considering S-wave velocities via the elastic wave equation. With modern computational power and capacity, elastic FWI is now practical on a large scale, albeit still considerably more computationally demanding than its acoustic counterpart. Many previous studies of elastic FWI typically focused on deepwater areas where large salt structures generate strong elastic effects in the observed seismic data. We offer an alternative perspective on elastic FWI, highlighting its value over acoustic FWI in accurately describing elastic effects observed in shallow-water environments, particularly around the chalk packages prevalent throughout much of the North Sea and adjacent regions.