Building 4D Constraint for History Matching from Stratigraphic Pre-Stack inversion - Application to the Girassol Field

Adequate history matching is mandatory to understand properly the physical changes occurring in an hydrocarbon field that are related with production. However, this process has no unique solution. 4D seismic, which consists in repeating a 3D seismic survey at different calendar times is an additional source of data, which provides information about production effects. Its integration in the history matching process can therefore help in better identifying permeability barriers, by-passed oil zones, and therefore influence the field management. In this paper, we focus on the definition of this 4D seismic constraint on Girassol, a giant deep-offshore field located offshore Angola. The methodology we have used is based on a sequential stratigraphic inversion of pre-stack data from the different seismic vintages. The methodology to invert the monitor survey is divided into 4 parts: - time realignment of seismic events from monitor survey on the base survey; - verification of the invariability of wavelets with calendar time; - updating of a priori model; - pre-stack stratigraphic inversion of the monitor survey; Finally, we interpret the variations of inverted impedances between the different vintages in terms of production effects.