Future work

This section will present proposals and recommendations for future work in order to increase the quality and achieve more realistic results. This work has been es-tablished on assumptions and simplifications in order to narrow the scope of the task.

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60 CHAPTER 6. CONCLUSION

6.1.1 Echo State Network

The ESN used in this work managed to identify the ESP satisfactorily, but it is necessary to reduce the size of the network to acquire a faster controller. It should also be developed a better method to access future states in the ESN, a task which was performed in a manual manner for this project.

6.1.2 Nonlinear Model Predictive Control

There are multiple areas that can be improved in the NMPC. Firstly,multiple shoot-ingshould be implemented for more speed and the opportunity to look further into future behavior.

A more suitable objective function is necessary in order to achieve more realistic results. Controlling the ESP intake pressure to a setpoint would be a better control target since the intake pressure directly affects the flow-rate from the reservoir.

This target would allow the operator to control the production flow-rate. It is also natural to minimize the ESP frequency to minimize the power usage in the ESP.

The change of ESP frequency is usually constrained in order to avoid fast changes in suction, while the change of the production choke valve opening is constrained by limits from the choke characteristics. These changes should be implemented as hard constraints established by the operators.

Lastly, there is no feedback implemented in the ESN. This will not cause any huge problems for a noiseless simulation, but once noise is introduced in the plant, a correction filter must be implemented. A correction filter is a low-pass filter that corrects the error between the predicted output and the current measured output.

The filter will also play a part in correcting modeling errors.

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NTNU Norwegian University of Science and Technology Faculty of Information Technology and Electrical Engineering Department of Engineering Cybernetics

Master ’s thesis