Abstract

For reservoir development study, there are a lot of uncertainties in different research aspects. But if these uncertainties are ignored, reservoir performance could be much worse than expected because of wrong development options possibly selected and applied. Therefore, uncertainty analysis should be addressed during reservoir development study, and uncertainty parameters should be analyzed and their impact should be evaluated in order to reduce the corresponding risks. The paper proposes that uncertainty analysis should run through the whole study process of reservoir development plan.

Based on the reservoir development stage and reservoir geological features, all related uncertainty factors are identified. And the uncertainty range of each factor are determined with upside, expected and downside values or models. Then all factors are embedded into the static and dynamic models, and the uncertainty impact on reservoir performance are quantitatively evaluated based on the upside, expected and downside dynamic models respectively. After that, uncertainty parameters are ranked into differernt groups.

Take one large multi-layered sandstone oilfield in Middle East for example, uncertainty analysis methods are illustrated. The large sandstone reservoir in Middle East is at its primary depletion development stage with only 5% recovery factor currently, and waterflooding is urgert. Firstly, key uncertainty parameters are determined, which can be mainly classified into two categoriesgeological model and dynamic model. Then according to the characteristic of this reservoir and uncertainties understanding of geological study, 3 static models with same probability are built. After that, uncertainties understanding of dynamic analysis are included into static models, and 3 dynamic models representing Upside, Expected and Downside models are generated in order to fully characterize all the uncertainties. So development options and development schemes optimization can be studied based on the 3 models in order to determine the uncertainties of water flooding performance. Finally the induced risks of each main uncertainty parameter are quantitatively evaluated, and corresponding treatments are proposed.

This paper offers the methodology and a case study on uncertainty analysis and management within the waterflooding development for a large multi-layered sandstone reservoir, and the results are valuable for the following development options decision making. It also provides a reference for uncertainty management of similar reservoir.

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