Guillaume, Patrice (CGGVeritas Massy.) | Lambaré, Gilles (CGGVeritas Massy.) | Leblanc, Olivier (CGGVeritas Massy.) | Mitouard, Pierre (CGGVeritas Massy.) | Le Moigne, José (CGGVeritas Massy.) | Montel, Jean Philippe (CGGVeritas Massy.) | Prescott, Tony (CGGVeritas Massy.) | Siliqi, Risto (CGGVeritas Massy.) | Zhang, Xiaoming (CGGVeritas Massy.) | Zimine, Serge (CGGVeritas Massy.) | Vidal, Nicolas (CGGVeritas Massy.)
We present a fast turnaround strategy for building depth velocity models from kinematic invariants. Our approach is based on the concept of kinematic invariants describing locally coherent events by their position and slopes in the un-migrated pre-stack domain. 3D slope tomography can be based on kinematic invariants that fully characterize the events in terms of positioning and focusing. Kinematic invariants offer a versatile tool for velocity model building as they can be derived from dip and move-out picks made either in pre-stack depth migrated (preSDM) or pre-stack time migrated (preSTM) domains, or even in the unmigrated domain. Since the invariants are in the unmigrated domain, they only need to be picked once. The classical iterative velocity update made of several iterations of RMO picking, pre-stack migration and velocity update can thus be replaced by a more efficient sequential approach involving a single preSDM and a single residual move-out (RMO) picking followed by a non-linear tomographic inversion, should the quality of the initial PreSDM be appropriate for an automated volumetric picking.
A hydrocarbon reservoir in the subsurface is usually explored and monitored with geophysical techniques described and interpreted in a linear "approximation", i.e. the propagation, reflection and conversion etc. of these signals is treated in a linear way. This assumption has served the industry well for mapping subsurface structural information.
In a real setting we might find that despite the fact that physicists and mathematicians prefer the linear description because of its relative simplicity a lot of nonlinear elements (elastic, electric, etc.) are found which might alter the signal path for exploration and monitoring. In fact some of these nonlinear elements may actually lead to interesting effect allowing e.g. a more unique detection and delineation of fluids or other elements like faults. Examples are fractured systems, faults, two-fluid interfaces etc. which may lead to nonlinear or hysteretic or delayed behavior (e.g. if a fractured rock gets compressed it will behave nonlinear once the fracture surfaces touch, similar to a rubber foam, where elasticity initially depends on the air bubbles included, but at some point of compression the bubble walls touch and the bulk rubber will determine the properties; or the broken bell, which gives not a single sharp spectrum, but a wide variety of sidebands it literally "squeaks").
While nonlinear physics has been a fashion topic for quite some time, nonlinear effects in geophysics are rather a niche topic so far. To some extent they are discussed where large amplitudes (near surface effects or strong earthquakes) take place, but mostly geophysics operates in the "linear approximation mode".
Recently, several interesting bits and pieces were reported in geophysics: