Optimal control strategies with nonlinear optimization for an Electric Submersible Pump lifted oil field

Abstract

In an Electric Submersible Pump (ESP) lifted oil field, the ESP of each oil well should be operated inside its operating window. The total power consumed by the ESPs in the oil field should be minimized. The speed of the ESPs and the production choke valve opening should be optimally chosen for maximizing the total oil produced from the oil field. At the same time, the capacity of the separator should not be exceeded. In this paper, nonlinear steady state optimization based on Sequential Quadratic Programming (SQP) is developed. Two optimal control structures are proposed in this paper. In the first case, the optimal pump speed is controlled by a PI controller by varying the electrical excitation signal to the motors. The optimal fluid flow rate through each oil well is controlled by another PI controller by varying the production choke valve opening. The paper shows that the production choke valve for each oil well has to be always 100% open to maintain the optimal fluid flow rate. In the second case, the production choke valves are considered to be always 100% open as hard constraints. The optimal fluid flow rate through each oil well is controlled by a PI controller by varying the pump speed. It is shown that when the optimal fluid flow rate is tracked by the controller, the speed of each of the pumps is equal to the optimal pump speed calculated by the optimizer. This basically means that we can achieve the optimization objective with the same optimal results as in the first case by using only a single PI controller. The limitations of these two optimal control structures for very low values and for very high values of the separator capacity are discussed. For the feasible range of separator capacities, the optimal locus of the fluid flow rate and the pump speed are shown in this paper.

Mixed Integer Nonlinear Optimization for ESP Lifted Oil Field and Improved Operation through Production Valve Choking

“…Detailed modeling and simulation of the oil field can be found at [9]. In this paper, only the final equations of the model of the oil field have been rewritten similar to the paper by [10], [11] however with few improvements and details. The number of oil wells is taken to be four and the number of transportation lines is taken to be two.…”

“…It is economically better to reduce the speed of the pump (if it is possible and is inside its operating window) while fully opening the valve. Moreover, in several research works as in [10], [11] and [13], it has been shown that when all the oil wells in the field are used it is more profitable to keep the production choke valve fully opened. The speed of the pumps in each oil well is used to control the flow rate from the oil well.…”

Uncertainty and Sensitivity Analysis for a Model of an Electric Submersible Pump Lifted Oil Field

“…4, it can be stated that the estimation of the reservoir pressure should be performed with highest importance. The speed of the pumps should also be measured with higher accuracy if it is to be used for the purpose of control and optimization as has been done in [6]- [8]. …”

“…So the production choke valves and the productivity index values do not have larger interacting and nonlinear effect on the output from the oil field. In [6]- [8], it has been shown that for production maximization, the choke valves should be always fully opened. During the operation, for most of the time, the production choke valves are fully opened.…”

“…Detailed modeling and simulation of the oil field can be found in another article written by the authors at [2]. In this paper, only the final equations of the model of the oil field have been rewritten as also explained in the papers by the author at [6] and [17]. The superscript i and j denote the i th oil well and the j th transportation pipeline.…”