Methodology for Water Injection Strategies Planning Optimization Using Reservoir Simulation
Authors: Mezzomo C.C. , Schiozer D.J. 
Published: July 2010

Abstract
The decision-making process related to field development planning is very complex. It involves significant investment and it is necessary to account for a large number of geologic, economic, and technical parameters. Most of these parameters are uncertain and these uncertainties must be considered when evaluating the risks associated with the projects.
An appropriate choice of production strategy will ensure proper reservoir performance, leading to a satisfactory recovery. Therefore, it is very important to develop methodologies:to improve the quality of the results; and,to accelerate the process.
This paper introduces a new optimization procedure which is applied to the production strategy planning process. The procedure was developed for several types of reservoirs and includes producer and injector vertical wells. Furthermore, it uses reservoir simulations to provide reliable production/injection forecasts for the evaluation of an objective-function. The procedure was developed in a flexible way and can be adapted to different situations. The results obtained for some cases are presented.

Introduction
Field development planning is one of the most important activities in reservoir engineering. It is necessary to consider a previously defined objective and the physical, operational, and economic restrictions of the project.
During the initial field development phase, the amount of available information for the reservoir is very restricted and it is very difficult to obtain a correct reservoir model. Therefore, the use of simplified simulation models provides more reliable production/injection forecasts leading to better results.
This work proposes a methodology including a robust optimization procedure that uses the forecasts generated by reservoir simulations for the evaluation of an objective-function (NPV). This methodology helps in the decision-making process, looking to maximize the profits and minimize the risks associated with the investment. An example, based on an Atlantic offshore field in Campos Basin, Brazil, is presented. It shows the importance of reservoir simulation in field development planning for petroleum reservoirs, including water injection.

Methodology
This work proposes a methodology to support managers in the decision-making process for the initial field development stage. It presents a set of alternatives that are analyzed to select the water injection pattern that leads to the best reservoir performance, utilizing the objectives previously defined for the project. This methodology is comprised of six steps that can be simplified or discarded depending on the characteristics of the problem. These steps are presented in the flowchart in Figure 1 and the optimization algorithm is presented in Figure 2.

Case Study
The example used for the validation of the methodology developed in this work is water injection planning for an Atlantic offshore field in Campos Basin, Brazil. The reservoir is comprised of confined Albian-Cenomanian (Late Cretaceous) turbidite sandstone, with a gas solution production mechanism.
Because the field is in the initial development phase, the proposed reservoir model was simple and it provided adequate processing time for the required simulation runs. The model has six layers, with a total number of 8,568 blocks. These blocks were divided into three regions considering the faults.