4-D Petrophysical Seismic Inversion on the Troll West Field

Inversions of seismic surveys often give low-resolution results that are difficult to compare with well data and geological models. We are therefore developing a multi-vintage seismic inversion based on a Petro-Elastic Model, called PetroSI-4D. This involves input from the geological model and control on the petrophysical correlation between porosity and PEM-based velocities. All vintages and angle stacks are combined to jointly invert for layer thickness, rock properties and saturations. Perturbations of selected properties are introduced using a simulated annealing algorithm to optimise the match between the synthetic and the real angle stacks. The base inversion result is delivered in porosity cubes instead of ordinary acoustic impedances. The 4D inversion is planned to deliver saturation cubes instead of cubes of acoustic impedance changes. These parameters should be easier to compare and use in update of geological and reservoir models to validate the results. The Troll West Field shows that the Petrophysical seismic inversion with rock physics PEM connected to the inversion, gives good results and comparison with the porosity input model is shown. The purpose of 4D petrophysical inversion is to make use of all available seismic data simultaneously, multi-vintage and pre-stack, to constrain the evolution of the saturation field.