Application of a grid-consistent inversion to a 4D reservoir model

Abstract

Extraction of the 4D signal from time-lapse seismic is an efficient way to evaluate the lateral evolution of changes in fluid pressure and saturation during hydrocarbon production. This 4D seismic signal can be used in two ways (Castro et al., 2009): qualitatively (from a static perspective), thus evaluating whether a compartment has been drained or not, or if a fault is permeable or not; or quantitatively (from a dynamic perspective) by trying to exactly match changes in dynamic properties predicted from fluid-flow simulation with 4D seismic signal itself. In both approaches, the main difficulty is to link the seismic information with a description of the reservoir grid, especially with regard to scaling problems. Relative to the simulation model, the 4D seismic signal is obtained with a higher lateral resolution (12.5 or 25 m) and a poorer vertical resolution (10–20 m). Indeed, the reservoir grid consists of a set of layers with a very high vertical resolution (1–5 m) and limited lateral resolution (50–100 m). Here, we present a novel approach which aims to solve these problems by estimating the 4D seismic signal at (almost) reservoir grid scale. We demonstrate this by application to an oil-producing field in West Africa to finally derive a complete workflow for history matching the reservoir model using the 4D seismic signal.