The offshore oil and gas industry is experiencing increasing water cuts as the reservoirs mature. The increase in produced water stresses the currently deployed deoiling technologies, resulting in more oil in the discharged water. Deploying membrane filtration to reduce the hydrocarbon concentration inherits additional complications related to fouling of the membranes: A process where the accumulation of material within and on the membrane surface adds additional flow resistance. This paper reviews and analyses the fouling detection, removal, prevention, dynamical and static modeling, with emphasis on how the membrane process can be manipulated from a process control perspective. The majority of the models rely on static descriptions or are limited to a narrow range of operating conditions which limits the usability of the models. This paper concludes that although the membrane filtration has been successfully applied and matured in many other industrial areas, challenges regarding cost-effective mitigation of fouling in the offshore deoiling applications, still exist. Fouling-based modeling combined with online parameter identification could potentially expand the operating range of the models and facilitate advanced control design to address transient performance and scheduling of fouling removal methods, resulting in cost-effective operation of membrane filtration systems. With the benefits of membrane filtration, it is predicted that membrane technology will be incorporated in produced water treatment, if the zero-discharge policies are enforced globally.

In the offshore oil and gas sector, produced water is discharged into the sea, but increasing environmental concerns and stricter governmental regulations require new technologies to be considered. Membrane filtration is a promising technology to improve separation, but fouling of the membranes causes a significant reduction in flow capacity. To reduce fouling, optimization of the backwashing parameters is given much attention. Comprehensive and time-consuming experiments are used to model the effect of backwashing, but most methods neglect time varying features present in the offshore produced water treatment train. In this paper, a backwashing scheduling algorithm is proposed, which dynamically selects the filtration and backwashing durations to maximize the average net permeate production. The proposed algorithm is tested on a lab-scaled pilot plant, where it was able to adapt as irreversible fouling accumulated and the OiW concentration changed. The paper concludes that the removal rate of oil fouling was observed to be dependent on the rate at which the backwashing pressure could be established. As the proposed method online adapts to the current conditions, it can improve the filtration capacity compared to cases with constant backwashing and filtration durations throughout the lifetime of the facilities.

In offshore oil and gas productions increased attention is directed at the oil-water separation process, as environmental laws demand lower hydrocarbon concentrations in the discharged produced water. Membrane filtration is one possible candidate for significantly improving separation efficiency. However, fouling is one major challenge, where contaminants accumulate within the membrane and thereby adds additional flow resistance. This paper investigates the possibility of improving reference tracking and reducing fouling by improving control pairings and actuator placement. This is achieved by investigating the interaction between commonly deployed decentralized control loops on a membrane process model. The relative input-output interactions are evaluated across varying feed flow rates and membrane flow conductances to ensure that decoupling is maintained beyond the defined operating point. This work concludes that the location of the actuators affects the degree of decoupling significantly and to achieve the maximum degree of decoupling, different actuators must be selected across a variety of operating condition.