Use of Proxy Models in the Selection of Production Strategy and Economic Evaluation of Petroleum Fields
Authors: Avansi Guilherme D. 
Published: December 2009

Abstract
The traditional process of production strategy demands a high number of simulations due to the high number of variables and possibilities, causing sub-optimal results; while an automatic process can mitigate this problem but the computational effort increases as a result of the number of simulations generated in the process.
Thus, the objective of this work is an attempt of application of proxy models in the production strategy and in the economic evaluation in petroleum fields, allowing to define the production strategy in a high number of alternatives and increasing the chances to better evaluate the production strategy of petroleum fields, and at the same time using the experience from important applications of proxy models in others areas such as risk analysis, history matching etc.. The applied proxy models combine the following components: statistics methods, experimental planning, the response surface methodology and consistency checking.
The proxy models used in this work showed that can be used in a definition of production strategy, bringing an additional option in the process. Besides finding solutions that are not investigated by the traditional methods, proxy models create new possibilities to change a decision used in an economic evaluation process in a wider solution space.

Introduction
The main activity in reservoir engineering is the planning of strategies and economic evaluation for the development and management of petroleum fields. The numerical simulation is useful in a definition of a production strategy during the appraisal and development phases, especially in offshore heavy oil fields due to the low economic return, limited flexibility and importance of reservoir modeling. The flexibility is limited because of the requirements to design the production facilities based on the low amount of information. The use of reservoir simulation has several constraints, such as: high number of blocks, variables and attributes which are time-consuming for the simulation and processes analysis, mainly in complex fields. Besides the high number of possibilities in a production strategy definition and the computational time linked with the numerical simulation, the process can be slow, forcing simplifications in the optimization process and consequently, decreasing the probability of finding better solution for the problem.
Proxy models can be used as an auxiliary tool to deal with some of these constraints. This technique can simplify models with lower confidence levels in some outputs and an alternative for the numerical simulator in several procedures that do not require a higher precision in the results and a reduced number of simulations. Proxy models have been used in reservoir engineering applications, including uncertainty modeling, sensitivity analysis, history matching (Peng and Gupta, 2003 and Risso, 2007), risk assessment (Risso et al. 2007), performance prediction, upscaling (Schiozer et al., 2008) and development optimization (Venkataraman, 2000).
In this study, proxy models have been used in the selection of production strategy and economic evaluation of petroleum fields. Figure 1 presents the general idea of proxy model application used in this study.