Cooperative, Structural and Grid-based Simultaneous Joint Inversion for Salt Base and Presalt Imaging

The Nordkapp Basin is an intra-continental basin with complex salt structures such as diapirs and possible traps/sealing mechanisms for oil reservoirs at Carnian level.

The study presents 3D Simultaneous Joint Inversion (SJI) in three possible workflow configurations, used for cascade modelling and imaging of the deep salt base in Nordkapp basin. The salt, almost absent in the initial seismic image, is characterized by particular issues: limited acoustic impedance contrast at its base, poor seismic reflectivity. The salt itself presents overhangs in some regions that haven’t been properly modelled in the prior structural model.

After SJI, in almost half of the block the base of the salt is now imaged.

The explicit computation of Cross-Gradient of velocity and density properties, namely the cross-product squared modulus of the velocity and density property gradient, allows speculations about the residual uncertainty of the earth model result.

The SJI solution reaches a lower multi property Cross-Gradient than that of two independent inversions, ensuring that both datasets are simultaneously honoured as well as the similarity between the two properties. SJI also provides a spatial measure of the uncertainty of the result.

The seismic result has increased its image interpretability thanks to the SJI workflow.