Abstract:

The investments to develop a reservoir are very large, so any improvement in the development plan could represent millions of dollars in additional profit. However, the decisions about the development plan are made in the presence of many sources of uncertainty. Geological uncertainty about the reservoir geometry and petrophysical properties, due to sparse sampling of the reservoir, is one of the uncertainties that could influence the reservoir management decisions significantly.

This research introduces a so called Full approach to incorporate the geological uncertainty in the selection of the best production scenario among a set of predefined scenarios. This approach makes use of multiple geostatistical realizations and presents the advantage of including the profit seeking and risk aversion profile of the company.

Different reservoir management problems were considered, with that related to location of a moderate number of wells being retained as the problem for which the geological uncertainty is most critical. The benefits of accounting for geological uncertainty in the well location decision are evaluated by comparing the results of the decisions made with the Full approach to those made with the conventional approach of using a single deterministic model.
The influence of the level of uncertainty is investigated, showing that the larger the number of available data, the smaller the uncertainty, the better the decisions and the smaller the benefits of modeling uncertainty. Nonetheless, the potential gains of including uncertainty are always on the order of millions of dollars, which is much higher than the computational costs required to incorporate multiple realizations into the decision-making.

This work introduces the concept of a quality map to locate wells. An L-optimal quality map, obtained by averaging the individual realization quality maps through a loss function, allows locating the wells accounting for the geological uncertainty as well as for the profit seeking and risk aversion profile of the company. This quality map is used within the Full approach to decide on the best number of wells with the corresponding optimized spatial configuration.
Because it is built from ow simulations, the quality map integrates all the three-dimensional geological variables and the uid variables into a single two-dimensional characterization of the reservoir. Besides well locations, this two-dimensional characterization of the flow responses can be used to visualize productivity areas, to rank realizations, to identify a most representative realization and to compare different reservoirs.

50 synthetic yet realistic reservoirs and more than 450,000 flow simulations were generated in the course of this research to develop and evaluate the potentials of the Full approach and quality map.

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Copyright 2000, Paulo Sergio da Cruz: Please note that the reports and theses are copyright to their original authors. Authors have given written permission for their work to be made available here. Readers who download reports from this site should honor the copyright of the original authors and may not copy or distribute the work further without the permission of the author, Paulo Sergio da Cruz.