(125e) Optimal Flow Control for Oil Production Under Gas Coning Conditions in Oil-Rim Reservoirs

Authors: 
Siddhamshetty, P., Texas A&M Energy Institute, Texas A&M University
In oil-rim reservoirs, a thin oil layer is trapped between an aquifer and a gas cap. Oil can be produced from the thin oil layer by drilling horizontal wells just above the aquifer. During the oil production, the Gas-Oil Contact (GOC) near the wellbore lowers and this phenomenon is called gas coning [1]. The gas coning may lead to gas breakthrough, which will significantly decrease the oil flow rate and in turn increase the gas production rate. Since the gas price is much cheaper than the oil price, we typically operate the oil extraction process only until the gas breakthrough to prevent the gas production. However, in practice, we can extract the oil even after the gas breakthrough at the expense of a reduced oil production rate. In this case, we have to impose a constraint on the gas-oil ratio (GOR) to restrict the amount of gas extracted from the well. Recently, there have been some efforts to design feedback control systems for the oil extraction from the oil-rim reservoirs, but they did not consider the oil extraction after the gas breakthrough, which is called the super-critical phase [2, 3, 4].

Motivated by these considerations, we propose a model-based control framework to maximize the oil production from the oil-rim reservoir during the super-critical phase. For this purpose, we first develop a first principles model to describe the gas-coning behavior, particularly the spatiotemporal evolution of GOR and GOC, which is determined by the oil extraction rate. Second, the data generated from the high-fidelity model is used to construct a reduced-order model (ROM). The ROM is used to design a Kalman filter that will utilize the real-time measurements at the wellbore to estimate GOR and GOC at the locations where the measurements are not available. Third, model predictive control (MPC) theory is applied in the receding horizon fashion for the design of a feedback control system that manipulates the oil extraction rate at the wellbore to maximize the net present value (NPV) of the produced oil in the super-critical phase. In the controller, we will explicitly consider practical constraints such as the actuator limitation and a limit on GOR for economically-feasible operations. Lastly, the developed feedback control system will be compared with the traditional back-stepping methods during the super-critical phase.

References:

[1] Mjaavatten, A., Aasheim, R., Saelid, S., & Gronning, O. (2006, January). A Model for Gas Coning and Rate-Dependent Gas/Oil Ratio in an Oil-Rim Reservoir (Russian). In SPE Russian Oil and Gas Technical Conference and Exhibition. Society of Petroleum Engineers

[2] Hasan, Agus Ismail, et al. "Modeling, simulation, and optimal control of oil production under gas coning conditions." SPE EUROPEC/EAGE Annual Conference and Exhibition. Society of Petroleum Engineers, 2011.

[3] Hasan, A., Foss, B., & Sagatun, S. (2012). Flow control of fluids through porous media. Applied Mathematics and Computation, 219(7), 3323-3335.

[4] Maree, J. P., & Imsland, L. (2014, October). Optimal control strategies for oil production under gas coning conditions. In Control Applications (CCA), 2014 IEEE Conference on (pp. 572-578). IEEE.