High resolution imaging of the Earth with adaptive full-waveform inversion
Abstract:Three-dimensional full-waveform inversion (FWI) is a high-resolution, high-fidelity, quantitative, seismic imaging technique that has advanced rapidly within the oil and gas industry. The method involves the iterative improvement of a starting model using a series of local linearized updates to solve the full non-linear inversion problem. During the inversion, forward modeling employs the full two-way three-dimensional heterogeneous anisotropic acoustic or elastic wave equation to predict the observed raw field data, wiggle-for-wiggle, trace-by-trace. The method is computationally demanding; it is highly parallelized, and runs on large multi-core multi-node clusters. A recently developed adaptive version of FWI is able to overcome the requirement for a good starting model and low frequencies in the data, and this opens up the range of datasets and problems to which FWI can be applied.
Here, we demonstrate what can be achieved by applying this newly practical technique to high-density 3D seismic datasets acquired to image petroleum targets. We show that the resulting anisotropic p-wave velocity models match in situ measurements in boreholes, reproduce detailed structure observed independently on high-resolution seismic reflection sections, accurately predict the raw seismic data, and simplify and sharpen reverse-time-migrated reflection images of deeper horizons. The velocity models image individual faults, gas clouds, channels, and other geological features with previously unobtainable resolution and clarity. These same benefits can be obtained when this technique is applied to scientific targets provided that the data coverage is adequate in three-dimensions, and that an appropriate range of offsets and azimuths are available. Possible targets range from the water column, ice sheets, and Holocene deposits, through active faults, spreading centres, collision zones, rifted margins, magma plumbing, lower-continental crust, and deep crustal hot zones, to whole subduction zones, local and regional mantle heterogeneity, and the deep Earth.