Gas-lift Optimization by Controlling Marginal Gas-Oil Ratio using Transient Measurements

Abstract

This paper presents the application of a steady-state gradient control using transient measurements to a gas-lift optimization problem. Optimal operation of a gas-lifted field involves controlling the marginal gas-oil ratio (mGOR), which is the steady-state gradient of the oil rate with respect to the gas lift rate. In this paper, we apply a novel method to estimate the marginal GOR online using a dynamic model and transient measurements, without the need for additional perturbation. The proposed method is based on linearizing the dynamic model around the current operating point to estimate the marginal GOR, which is then controlled using simple feedback controllers to achieve optimal operation. In case of disturbances, the proposed method is able to adjust fast to the new optimal point, without the need to solve computationally expensive optimization problems. By using transient measurements, it does not need to wait for the process to reach steady-state to update the model. The proposed method was tested in simulations and was shown to provide similar performance as an economic MPC.