3D wavefield tomography: Problems, opportunities and future directions

Wavefield tomography, otherwise known as full-waveform inversion, of two-dimensional<br>seismic data, has become a well-established technique over the past decade, with impressive<br>recovery of realistically complex synthetic models being reported by several groups.<br>However, despite its proven potential, its uptake to tackle real-world exploration and<br>production problems has been rather limited. In our view, this has been principally because<br>the increased spatial resolution, accuracy, and other benefits that the method brings are only<br>genuinely realised for field data when the method is extended to deal with three-dimensional<br>velocity structure, three-dimensional reflection geometry, and a three-dimensional array of<br>sources and receivers. Since the real world is always three-dimensional, very-accurate twodimensional<br>solutions to three-dimensional problems are nearly always illusory – the higher is<br>the spatial resolution of the method, and the more accurate is the physics of wave propagation<br>that is employed, then the more significant will be the errors that are introduced by neglect of<br>the third dimension. In essence, there is little utility to be gained from a model that is highly<br>resolved in two dimensions, but that is not at all resolved in the third, and where structure<br>from the missing third dimension is mapped incorrectly onto the 2D plane.