Next-generation seismic experiments – II: wide-angle, multi-azimuth, 3-D, full-waveform inversion of sparse field data

Abstract

S U M M A R Y3-D full-waveform inversion (FWI) is an advanced seismic imaging technique that has been widely adopted by the oil and gas industry to obtain high-fidelity models of P-wave velocity that lead to improvements in migrated images of the reservoir. Most industrial applications of 3-D FWI model the acoustic wavefield, often account for the kinematic effect of anisotropy, and focus on matching the low-frequency component of the early arriving refractions that are most sensitive to P-wave velocity structure. Here, we have adopted the same approach in an application of 3-D acoustic, anisotropic FWI to an ocean-bottom-seismometer (OBS) field data set acquired across the Endeavour oceanic spreading centre in the northeastern Pacific. Starting models for P-wave velocity and anisotropy were obtained from traveltime tomography; during FWI, velocity is updated whereas anisotropy is kept fixed. We demonstrate that, for the Endeavour field data set, 3-D FWI is able to recover fine-scale velocity structure with a resolution that is 2-4 times better than conventional traveltime tomography. Quality assurance procedures have been employed to monitor each step of the workflow; these are time consuming but critical to the development of a successful inversion strategy. Finally, a suite of checkerboard tests has been performed which shows that the full potential resolution of FWI can be obtained if we acquire a 3-D survey with a slightly denser shot and receiver spacing than is usual for an academic experiment. We anticipate that this exciting development will encourage future seismic investigations of earth science targets that would benefit from the superior resolution offered by 3-D FWI.

Toward a robust workflow for deep crustal imaging by FWI of OBS data: The eastern Nankai Trough revisited

“…It is likely that our 2‐D imaging has been hampered by 3‐D effects due to the complex geology of the eastern Nankai Trough. This raises the issue of how to design the next generation of 3‐D dense sea bottom acquisitions for deep crustal investigations [ Morgan et al , , ]. Although various advances have been achieved in seismic instrumentation and the ability of the academic community to perform OBS acquisitions is increasing, the gathering of large OBS pools remains challenging.…”

Near‐axis crustal structure and thickness of the Endeavour Segment, Juan de Fuca Ridge

“…The models are characterized by low velocities at the segment ends relative to the segment center that were interpreted in terms of increased fracturing in the upper crust created near the OSCs and possibly less hydrothermal infilling of porosity. More recently Morgan et al [] have used full‐waveform inversions to improve the resolution of shallow upper crustal structure in the central portion of the experiment footprint.…”

Resolving the fine-scale velocity structure of continental hyperextension at the Deep Galicia Margin using full-waveform inversion

“…Kamei et al (2012) applied frequency-domain FWI to a separate deployment of 54 OBS at the Nankai trough, resolving the fine scale velocity structure of megasplay faulting. Recently, Morgan et al (2016) demonstrated the application of three-dimensional (3D) time-domain FWI on an array of 21 OBS situated across the Endeavour oceanic spreading centre of the Juan de Fuca Ridge, revealing lowvelocity zones interpreted to represent a magmatic-hydrothermal reaction zone (Arnoux et al 2017). These studies have made use of relatively dense OBS deployments (~ 1 km spacing), or a 3D seismic shooting configuration, both of which are not always possible in academic experiments.…”