Effect of Enhanced-Oil-Recovery Chemicals on Oil/Water-Separation Processes, from Laboratory Scale to Flow-Loop Scale
Authors: Cassar Cyril , Mouret Aurélie , Salaün Mathieu , Klopffer Marie-Hélène 
Published: October 2020

With the use of chemically based enhanced-recovery methods, water management, which has always been a major point in the production-operation processes, needs to be considered and adapted because the whole water cycle will be affected by the backproduced additives. Enhanced-oil-recovery (EOR) chemicals such as alkali molecules, high-molecular-weight polymers, or surfactant formulation will dramatically modify pH, viscosity, and phase behaviors of produced fluids. The main issues encountered in oil/water-separation processes are directly related to the risk of tight emulsion formation, which might considerably complicate the surface-water-treatment processes.

The objective of this paper is to underline the effect of one of these chemicals, a surfactant formulation, on the produced-water cycle when they are backproduced first at a laboratory scale and second on a large-scale separation unit using an industrial-size flow loop and a well-instrumented separator.

Our goal is first to investigate the impact of surfactant on the water/oil mixture separation efficiency, and second, to find an efficient demulsifier specific for this case. At the laboratory scale, the impact of surfactant within produced fluids on oil/water separation (regarding separation kinetics but also oil/water phase qualities) will be evaluated by performing bottle tests.

Those laboratory bottle tests enabled us to screen different parameters, such as the surfactant concentration, the water cut that can strongly affect the type of formed emulsion [oil in water (O/W) or water in oil (W/O)], and its stability. The oil/water phase qualities were quantified and correlations with parameters related to the large-scale experiment were drawn, helping us in defining the key parameters for this campaign.

Indeed, to get closer to a field case, a semi-industrial-scale test platform was used. The flow loop reproduces separation process conditions encountered in a field treatment facility, including the production separator, the controlled temperature, and the oilfield chemical injection rate. The main operating conditions are liquid flow rates and temperature. The influence of different parameters can be studied, such as the surfactant concentration, mixing conditions, residence time, water cut, and the presence of chemicals that will help the separation process. Different types of emulsions were formed depending on the conditions, and their stability was evaluated through the measurement of separation profiles using a single electrode capacitance probe (SECAP) within the separator.

The results obtained show how the surfactant, as well as the demulsifier concentration, have led to different types of emulsions and have affected the oil/water separation processes. These tests have confirmed that separation is more difficult in the presence of surfactant and that water quality was degraded. It has also been shown that separation processes can be greatly improved by adding some EOR-compliant demulsifier to recover a better water quality compared with the surfactant case.

Laboratory workflows, as well as experiments performed at large scale using an industrial size separator, could help to minimize risks of operations to mitigate these challenges in terms of separation issues.

This work illustrates that water management is a major challenge for produced fluids containing EOR chemicals that need an integrated approach and should be studied beforehand.