Deoiling of Produced Water Containing Polymer with Media Filtration
Authors: Cognet M. , Bruneau T. , Bonnier J. , Gathier F. 
Published: March 2024

Backed by decades of successful field applications, polymer flooding represents a sustainable and proven recovery technique to increase production efficiency and extends the economic producing life of conventional oil resources. Providing improved mobility control and in-situ conformance effect, the increased swept oil volume results in decreased water production and related energy / CO2 requirements, and a sustained period of higher oil rate.

A minimal satisfying quality of water is key to make the preparation and injection of a polymer solution efficient. It reduces the amount of maintenance required and issues on surface facilities, to preserve polymer integrity and injectivity over time. Those water quality requirements are the same as what should apply for a good water flooding injection program.

On the production side, produced polymer viscosity and anionicity effects need to be taken into consideration.

For further re-use, recirculation of produced water for injection or before water disposal, it is recommended to specially adapt the effluent treatment to prevent common process difficulties, like loss of separation efficiency, clogging or accumulation of unexpected material in tanks, pipes, etc.

Standard treatment processes, potentially challenged with presence of polymer, are always divided into several steps (primary, secondary and tertiary/polishing) and include equipment solutions as well as oilfield chemicals.

Among polishing technologies, multi-media filtration systems are very commonly used worldwide for deoiling and solid removal. In operation, Oil In Water (OIW) or solid particles become trapped in the media and the differential pressure across the bed increases. Periodically, a backwash is initiated to remove the solids and oil trapped in the bed.

The works describes the evaluation of 7 different filtering medias at pilot scale for deoiling of produced water with different polymer and OIW concentrations. The medias are commercially available materials from several vendors with different granulometry, composition, shape, hardness or density.

The main objective is to determine best operating conditions for the treatment of produced water, in systems with and without produced polymer, while maximizing the deoiling efficiency.

The first objective is to evaluate the capacity of the medias to reach lowest OIW concentrations and to compare the performances to identify best medias for specific inlet conditions. The second objective is to better understand media behaviors during filtration and backwash sequences. The overall aim is to achieve the longest possible filtration sequences and to compare pressure drop evolutions to identify the best medias for specific inlet conditions. A third objective is to optimize the backwash sequences and to compare media fluidizations to maximize media recovery by minimizing media loss, water volume and pumping requirements.

The study shows that there are optimal parameters in operation and specificities to take into consideration because of the produced polymer; eac media, with its own characteristics, having different behavior and being more or less sensitive to inlet OIW and polymer concentrations. The main impacts observed are on the pressure drop increase with time, on media fluidization during backwash and on the residual OIW concentration after treatment.

The comparison of the data allows to find an optimized balance between performance (deoiling efficiency) and operation (filtration duration and backwash frequency). A good understanding of the fluid properties allows to anticipate the efficiency of a media filter and to maintain performances over time by adjusting operations: first with the selection of the optimal media to usethen, for a specific media, with: optimization of the filtration duration before backwashoptimization of the backwash regulation according to pressure drop behavioroptimization of the backwash flowrate for media fluidization