Abstract

Enhanced Oil Recovery (EOR) is a way to increase petroleum reserves in the short term. However, the conventional EOR methods need to be reassessed and/or modified to face the new concepts of sustainability, clean production and energy efficiency, but above all, the stricter environmental laws that now guide economic decisions. One of the most important problems in the oil industry is the large volume of produced water that must be separated from the production stream and disposed. Polymer flooding is a method that changes the swept efficiency, or, in other words, improves drainage area of the injected phase and thus can reduce the use of water. Other methods are more focused in the oil phase. Thereby, the polymer flooding is indispensable in EOR projects, alone or in combination with other methods. Motivated by this scenario, the present paper restudies polymer applications in Brazil to reevaluate the lessons learned.

The first Brazilian experience with polymers was in 1969-72, in the Carmópolis Field during primary recovery (before water injection). Decades later new projects were carried out in the fields of Carmópolis (1997), Buracica (1999) and Canto do Amaro (2001), all in the Northeast of Brazil. Those three new projects were implemented in mature fields to evaluate the real potential of polymer in the context of reducing the problems related to large volumes of water production.

The evaluation of EOR pilot projects has several difficulties, such as the long time collecting and processing information and the inherent difficulty to maintain continuity with a multi-disciplinary team. Another point that is critical in the evaluation of polymer flooding pilot projects is the choice of the pilot area itself. Ideally, the area must be almost confined (in terms of mass balance), because unconfined areas strongly influenced by external wells affect negatively the evaluation. In this work, to minimize the error in each of the pilot projects, an assessment was made considering the total wells and the inner wells less subject to interference from wells outside the grid of the pilot project. This consideration was made because the objective of this work is not restricted to verify whether the pilot was or not a success but to gain information about the polymer injection process in mature fields focusing on future applications. These pilots represent the extension of laboratory research on a field scale. The evaluation of the polymer application was made by comparing the total recovery with that of the injected water, not focusing only in the oil gain, but also in the use of water of each pilot. The results in terms of oil gain and reduction of water is not directly proportional to the amount of polymer injected. On the contrary, the pilot who consumed the least amount of polymer had the best performance. The challenge now is to understand the physical mechanisms governing this amazing behavior.

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