Nasyrov, Denis (Saint-Petersburg State University) | Kiyashchenko, Denis (Shell International E&P) | Kiselev, Yurii (Saint-Petersburg State University) | Kashtan, Boris (Saint-Petersburg State University) | Troyan, Vladimir (Saint-Petersburg State University)
The quality of the subsurface images obtained using VSP data strongly depends on the velocity model used for migration. The velocity model derived from surface seismic is often not accurate enough for VSP imaging and there is a need for its improvement. We propose the method for updating of velocities using VSP data. The main idea is to use the images of the subsurface obtained using different types of waves: primary reflections and surface-related multiples. If the background velocity is correct, then these images will be similar, and they will not coincide, if the velocity model is erroneous. We develop the algorithm of velocity updating based on this criterion. The proposed method allows us to retrieve the velocity below the borehole receivers. This is complementary to first break VSP travel time tomography, which helps to retrieve velocity only above the receivers.
Introduction Full tensor gravity gradiometry is becoming more commonplace within exploration projects where the benefits of high resolution, multi-component data is proving invaluable for discerning both deep and shallow structures. This paper will demonstrate how the signals measured by gradiometers achieve this by presenting a series of simple examples. Exploiting multi-tensor measurements When a full survey is conducted over an area with adequate sampling then, within the limitations of signal to noise and a few constants of integration, it is possible to predict the gravitational potential and any of its associated derivatives using measurements of only a single field quantity. Common methods of achieving this include Fourier transformations (integration and differentiation in the spatial frequency domain) and equivalent source inversions. For these ideal surveys, measuring multiple components of gravity or gravity gradient serves only to increase the accuracy rather than the ...