Summary

Reservoir management in offshore fields is a challenging task, particularly for mature fields because of a typical excessive production of water and/or gas. Because of several constraints on facilities capacity, an assisted reservoir management process can deliver solutions to optimally operate offshore fields, seeking to increase oil production with better assessment of water and gas production and injection. Optimal reservoir management (ORM) can be applied aiming at maximizing reservoir performance and to deliver well controls applicable to field operations. In this work, we implemented an assisted optimization procedure to maximize overall oil production for a field offshore Brazil in Campos Basin.

We applied our ORM technique in an important field offshore Brazil, where cumulative oil production is maximized by optimally controlling water rates through injection wells. Injection rates can vary with time, honoring operational requirements of smoothness. Geomechanical limits on injection pressures are considered to avoid loss of rock integrity, and platform constraints on overall production and injection are imposed at all times. Our approach deals with reservoir uncertainties described within a large set of calibrated simulation models to decide on optimal injection rates, taking into account possible risks.

The model-based ORM under uncertainty that we developed showed gains in total oil production over 20 years of operation up to 7.2% with respect to the base strategy currently applied. On average, results show an increase of near 4% in oil production, with concomitant reduction in total water production and in overall water injection.

To guarantee that the gains forecast by our study are feasible, a pilot test in the actual field has been implemented to verify the consistency between modeling and reality (data observation). We have chosen an area in the field to proceed with the optimal injection control pilot, aiming to check the quality of the uncertain models in comparison to the observed data in practice. The pilot area has been selected on the basis of aspects related to geological description, connectivity expected in the reservoir, and operational constraints. The results of 8 months of the pilot show clear coherence between models and reality that is well within the uncertainty range accepted at the reservoir of interest.

To the best of our knowledge, it is the first time that an offshore field is actually operated on the basis of a set of controls obtained through an assisted ORM procedure, although it was performed at a pilot scale. Results suggest robust benefits under reservoir-uncertainties consideration, and large-scale application will take place soon, but that is outside the scope of this work. The pilot provided more confidence in field applications, leading to a broader perspective for full-field implementations.

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