The effect of acquisition direction on preSDM imaging

A production 3D preSDM project from the southern North Sea using several vintages of input data was run using a velocity-depth model common to the whole area, with good final results. The expected progressive improvement from postSTM to postSDM to pre SDM was demonstrated for the target horizons. As a seperate study to the production project, we undertook to investigate the effect of acquisition direction on final image quality. To achieve this, we selected two vintages of data which were shot orthogonally to one another, but which otherwise had the same acquisition parameters. These data had sufficient overlap to permit full imaging in the area under investigation. Ray trace studies were performed to assess the effects of target illumination from the dip-shot and the strike-shot surveys. Using the actual recorded navigation positions from the two surveys, 3D two-point finite offset ray tracing was performed using a common model.