Geologic model building in SEAM Phase II — Land seismic challenges

Abstract

Three digital earth models were designed and constructed during SEAM Phase II to study exploration challenges at the scale of modern land seismic surveys. Although built as generic models, each was based on one or more related geologic type areas. The Barrett model represents the seismic anisotropy of complex laminated and fractured shale reservoirs, based on the Woodford and Eagle Ford formations and set below a stratigraphic overburden and near surface of a North American midcontinent basin. The Arid model features the extreme property contrasts of desert terrains in a 500 m thick near surface that juxtaposes hard carbonate bedrock and soft sediments filling karsts, typical of the Saudi Arabian Peninsula. The Foothills model contains sharp surface topography and alluvial fan-like sediments above complex fold-and-thrust structures based on the compressive tectonics of the Llanos Foothills of South America. All three models were built in workflows that combined automated steps with a large measure of manual model building, which represents the current state of the art in geologic modeling for large-scale geophysical simulations. The Barrett and Arid models each contain about 1.5 billion grid cells representing regions 10 × 10 × 3.75 km in physical size. The Foothills model has about 2 billion cells representing a region about 14.5 × 12.5 × 11 km. Full elastic-wave simulations with these models were run for a combined total of about 170,000 shots, usually with millions of recorded channels per shot, generating several petabytes of seismic data in standard and novel shot-receiver geometries. Selected shots from these simulations show that large, detailed earth models can reproduce features of land seismic surveys that continue to challenge the best modern seismic data processing and imaging techniques.

A discontinuous Galerkin fast-sweeping eikonal solver for fast and accurate traveltime computation in 3D tilted anisotropic media

“…We define a physical domain with a complex topography using a part of the SEAM II model (Regone et al, 2017). We consider a domain of size 3 km along the x-axis, 7 km along the y-axis, and 2 km along the z-axis.…”

“…In this example, our FSM-DG scheme is applied onto the same part of the isotropic SEAM II model (Regone et al, 2017). Here, we consider the original topography as provided with the model (no amplification factor).…”

A numerical study of multi-parameter full waveform inversion with iterative regularization using multi-frequency vibroseis data

“…We note that the classical Tikhonov weights can also be space-dependent and can help to adjust the local velocities. The meshing technique extends the generality and can help to model known discontinuities, such as topography, arid terrains and karst fields [48].…”

Data-oriented strategy and Vp/Vs model-constraint for simultaneous Vp and Vs reconstruction in 3D viscoelastic FWI: Application to the SEAM II Foothill dataset

“…The structure is characterized by gentle dip in the x-direction with folding structures and an unconformity at 2-3 km depth. The near-surface has alluvial deposits resulting from rapid erosion (Regone et al, 2017). These channels have low shear velocity, about 550 m/s at the surface, which are main obstacles for FWI.…”

“…The SEAM Phase II Foothill model and dataset are created by the SEAM consortium to reproduce the imaging challenges in mountain regions (Regone et al, 2017). Starting from relatively crude initial models, we focus on the simultaneous reconstruction of compressional and shear waves velocities from the pseudo-2D dip-line visco-elastic survey.…”