4D Interpretation

Interpretation of 4D data is focused on the production & development stages of a field and is concerned with changes in the reservoir, usually the fluid content and movement within the structures. By tracking these, it is possible to monitor the flow of hydrocarbons within the reservoirs, gain greater understanding of the reservoir behavior and optimize its development.

In addition to providing world-class processing services, CGGVeritas, through its subsidiary Hampson-Russell, also provides a powerful 4D characterization package, PRO4D.

Global 4D Elastic Inversion

Changes in fluid saturation and reservoir pressure can be estimated by applying 4D inversion followed by rock physics inversion. CGGVeritas’ StratiSI 4D global inversion scheme inverts all data vintages simultaneously, constrained by simple rock physics rules restricting the range of variations between consecutive surveys.

Geomechanics

In addition to the movement of fluids, changes in pressure and stress are a natural consequence of production.

For high-pressure reservoirs, pressure depletion during production is associated with compaction within the reservoir, causing variation in velocities and formation thicknesses which can be observed as 4D time shifts. Geomechanical modelling can be used to explain and predict these 4D time shifts.

Compaction of the reservoir also generates significant changes in radial stress which creates a 4D anisotropy signature. CGGVeritas has extended geomechanical inversion to include the estimation of 4D anisotropy using offset-dependent 4D time shifts to provide a unique solution for the delineation of depleted and compacted zones in the reservoir.

Benefits:

• Improved understanding of 4D response of compacting reservoirs
• Production monitoring in fields with small 4D signatures
• Indication of potential well bore instability in HPHT fields
• Complements 4D elastic inversion techniques to improve discrimination of production effects within the reservoir.