Two-dimensional SH-wave and acoustic P-wave full waveform inversion: A Midland Basin case study

Abstract

Building a reliable S-wave velocity model remains challenging from P-wave land seismic data as multi-parameter elastic full waveform inversion which updates P- and S-wave velocities simultaneously is not yet widely adopted due to its computational cost, highly nonlinear nature and noise contamination from land seismic data. To overcome this challenge, we propose implementing the SH-wave full waveform inversion to obtain the S-wave velocity model. The value of this approach has been examined by applying two-dimensional time-domain SH- and P-wave acoustic full waveform inversion to a nine-component three-dimensional seismic survey acquired in the Midland Basin. The nine-component seismic survey was acquired by using both vertical and horizontal component vibrators and receivers, which enables us to apply both SH- and P-wave full waveform inversion to the raw and preprocessed shot gathers along a two-dimensional line. The SH- and P-wave full waveform inversion applied to the raw shot gathers provide more detailed P- and S-wave velocities compared to the velocities from the stacking velocity analysis. Additionally, there are no problematic artefacts in the inverted S-wave velocity model, which shows the stability of the SH-wave inversion. Through the SH-wave full waveform inversion from the preprocessed shot gathers, we reveal the lateral velocity variations in the Grayburg–San Andres interval, which coincides with the depositional environment changes suggested by the previous regional study mainly based on well log and cores. These variations demonstrate that SH-wave full waveform inversion can identify additional geological features that are not observed in the inverted P-wave velocity model. The inverted P- and SH-wave velocities are validated by the flattening of the events observed in the common image gathers after Kirchhoff depth migration. The SH-wave migration image further reveals the irregular geometries of carbonates in the Spraberry formation. V_p/V_s ratios calculated from the independently inverted P- and S-wave velocity models show strong lateral variations in the Wolfcamp interval (key-producing interval), which could be caused by the organic content variations between the reservoir and non-reservoir rocks. The inversion results demonstrate that the SH-wave full waveform inversion can be used to provide an S-wave velocity model that is comparable to the P-wave velocity model derived from acoustic full waveform inversion, which is widely used for P-wave velocity model building from P-wave land seismic data.