Technologies for Oil and Gas Produced Water Treatment Figure 2: Corrugated Plate Interceptor for Oil and Solids Removal9
Figure 5: Process Flow Diagram of the Total Oil Recovery and Remediation Technology11
The oily water flow is evenly distributed throughout the RPA® media for adsorption and coalescence
Oily water Clarified water Settling solids Figure 3: A Typical Hydrocyclone10
Accelerating helical flow path
Oil reject
Lighter phase migrates to central core
Water underflow
Reducing section
Tangential entrance
Produced water inlet Figure 4: A Sabian™ Black Walnut Shell Filter8 Rising oil
The oily water flow is coming from the bottom of the equipment through the middle of the cartridge
Drain
From upstream primary separator
Main pump Solids
filtration unit
Clean water
Back pressure device
Effluent Limitation Legislation for Produced Water Discharge In most parts of the world, national and regional limitations have been established for discharging produced water into the environment. In the US, the current limits for oil and grease in treated produced water for ocean disposal are 42 mg/l daily maximum and 29 mg/l monthly on average. Discharge of produced water in coastal and marine water is no longer permitted. In Australia, the permitted limits for treated produced water from offshore activities are 30 mg/l daily on average and 50 mg/l instantaneous maximum. Based on the Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR Convention), no individual offshore installation should exceed a performance standard for dispersed oil of 30 mg/l for produced water discharged into the sea. As regards the significant matter of protecting the environment, many countries have implemented more stringent regulatory standards for discharging produced water. The monthly average limits of oil and grease discharge and chemical oxygen demand (COD) prescribed by the People’s Republic of China are 10 mg/l and 100 mg/l, respectively.4
Conventional Technologies for Treatment
Treating produced water is an effective handling option. Treated produced water has the potential to be a harmless and valuable product rather than waste. The general objectives of operators for treating produced water are as follows.7
• •
water streams suitable for beneficial re-use: surface discharge and/or groundwater recharge points. This requires good treatment that meets certain water quality criteria.7
Increasingly, the lack of clean and fresh water is a serious problem worldwide due to population growth and the expansion of industrial activities. This problem is of major concern, especially in water- stressed areas and arid oil-producing regions.
Re-use and recycling of produced water includes underground injection to increase oil production and use for irrigation, livestock, wildlife watering and habitats. It also includes various industrial uses, e.g. dust control, vehicle washing, power plant make-up water and fire control.1
106 De-oiling – removing dispersed oil and grease.
Soluble organics removal – removal of dissolved organic compounds.
• Disinfection – killing micro-organisms. •
Suspended solids removal – removal of suspended particles and sand.
• Dissolved gas removal – removal of light hydrocarbon gases, carbon dioxide and hydrogen sulphide.
• • •
Desalination – removal of dissolved salts. Softening – removal of excess water hardness.
Miscellaneous, including removal of NORMs. Gravity Separation
Oil in water forms an emulsion. Oily emulsions are suspensions of immiscible oil droplets >0.1 µm diameter. Specific differences in gravity between oil and water enable the skimming of oil from the water surface. Gravity separation technologies can be divided into two main
EXPLORATION & PRODUCTION – VOLUME 9 ISSUE 2
Clean water is sent to the bottom of the equipment
In the recovery chamber, coalesced oil droplets and gas float to the top according to Stoke’s law
Note:
- Drawing not to scale - Instrumentation not all shown - Number of stages may vary
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