Technologies for Oil and Gas Produced Water Treatment
Table 2: Applications of Advanced Membrane Filtration Technologies7 Membrane
Separation specifications filtration
Microfiltration >100,000 Da 10–0.1 µm
Ultrafiltration Nanofiltration
10,000–100,000 Da 0.05–5 e-3 µm
1,000–100,000 Da 5 e-3–5 e-4 µm
Bacteria, viruses, suspended solids, etc.
Proteins, starch, viruses,
colloid silica, organics, dyes, fats, paint solids, etc. Starch, sugar, pesticides,
herbicides, divalent ions, organics, BOD, COD, detergents, etc.
Reverse osmosis Salts and lower MWCO Metal ions, acids, sugars, 1 e-4–1 e-5 µm
aqueous salts, dyes, natural resins, monovalent salts, BOD, COD, ions, etc.
Key: BOD = biochemical oxygen demand; COD = chemical oxygen demand; DA = daltons; MWCO = molecular weight cut-off.
Figure 7: A Two-chambered Vertical Induced Gas Flotation System8
Different horizontal induced gas flotation vessels are used in industries with single or multiple chambers or cells (see Figure 6). Vertical induced gas flotation vessels are favourable for offshore platforms because they take up less space (see Figure 7).8
Membrane Filtration
Membranes are widely used in separation processes. The most applicable membrane filtration processes for oilfield produced water are microfiltration, ultrafiltration, nanofiltration and reverse osmosis (see Table 2). Microfiltration is the separation of suspended particles, ultrafiltration is the separation of
Figure 8: Comparison between Crossflow and Vibratory Shear Enhanced Process (VSEP®
) Separation13 Crossflow VSEP
A number of different aerobic and anaerobic biological processes have been used for treating oil- and gasfield produced water.
macromolecules and reverse osmosis is the separation of dissolved and ionic components. Nanofiltration membranes are generally designed to be selective for multivalent rather than univalent ions. Reverse osmosis membranes are designed to reject all species other than water. They are unable to offer a significant barrier to dissolved gases and certain low-molecular-weight organic molecules.4
oil in water that is 2 µm and larger in diameter (see Figure 5). The technology is a multistage adsorption and separation system. An adsorbent medium, the re-usable petroleum adsorbent (RPA®), removes large and small oil droplets. In the process of adsorption, the medium continuously adsorbs the oil emulsions, coalesces and then desorbs them into larger oil droplets. In the recovery chamber, oil droplets desorbed by the medium float to the top in accordance with Stoke’s law.11
Induced gas flotation
Induced gas flotation is a process in which gas flotation is carried out inside a horizontal or vertical vessel to help the separation of the oil.
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A key technical obstacle to the cost-effective application of membranes in produced water treatment is fouling: the adsorption or accumulation of certain components of produced water on the membrane surface or in the membrane pores eventually causes flux efficiency to decline.12
New Logic Research uses a vibratory shear enhanced process (VSEP®) separation system that employs torsional vibration of the membrane surface.13
The system creates very high shearing energy at the surface and the pores. The result is a reduction of colloidal fouling and polarisation of the membrane (see Figure 8).
EXPLORATION & PRODUCTION – VOLUME 9 ISSUE 2 Oil
Produced water
Oil/water separator
Water SMZ regeneration Air for
Key: MBR = membrane bioreactor; RO = reverse osmosis; SMZ = surface modified zeolite; VPB = vapour phase bioreactor.
feed Air VPB MBR RO system
Treated water
Treated gas
Applications (removal of) Figure 9: Schematic Treatment Plant (Los Alamos National Laboratory)14
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