Application of Anisotropic Wave Form Inversion on Data from the Niger Delta

In transition regions or river deltas, surveys often combine onshore and offshore types of acquisition. We discuss our approach for inverting a Niger river delta survey in which dynamite and geophones are used on land, with airguns and hydrophones in the rivers and creeks. This context presents certain challenges, such as differences in the source characteristics between dynamite and airguns. The airgun data lacks the low 4-6.5Hz frequencies that the dynamite data possesses. We therefore split the survey into two separate dynamite and airgun surveys, processing them independently. This allows for conventional marine and land workflows but introduces acquisition gaps in the separated surveys. We perform a multi-stage multiparameter inversion, first using only dynamite data to improve the starting model so it’s suitable for higher frequencies. Acquisition gaps in the dynamite only inversion are overcome using spatially adaptive smoothing which increases in areas of low illumination. This prevents formation of spurious oscillations. We then run a combined airgun-dynamite inversion. The results of our inversions lead to better stack and gather quality across the field compared to the initial model.