Produced water is a complex mixture of organic and inorganic compounds and is the largest volume of byproduct generated during oil and gas exploration and production.
Natural (or formation) water is always found within petroleum reservoirs that are routinely accessed via a well. The water is slightly acidic and sits within and below the hydrocarbons in porous reservoir media.
A well is a boring in the Earth and is generally created for the purposes of exploration, appraisal, production or injection.
Exploration
For an exploration well the geological target is chosen to confirm the existence of a viable hydrocarbon reservoir or to verify its extent.
Production
For a production well, the target is picked to optimise production from the well and manage reservoir drainage.
Injection
A third objective is established for the injection well, typically used to locate the point of injection in a permeable zone, which in some cases may support disposing of water or gas and/or pushing hydrocarbons into nearby production wells.
Produced Water Treatment
As produced water is generally contaminated (which varies from well to well and even over the life of the same well) it is classified as an industrial wastewater. In some cases, it may be re-injected, but this is not always an option. Therefore, there is the ever more common requirement for appropriate, environmentally compliant and cost-effective treatment.
Due to remote locations both onshore and offshore and the relatively large and continuous volumes produced, it is incredibly expensive to ship and treat produced water at a facility located elsewhere. Moreover, transporting these volumes has an adverse environmental impact.
Consequently, it is more attractive (financially, operationally and environmentally) to treat and dispose of produced water at source.
Produced Water Handling Offshore
A perfect example of this approach to produced water treatment is found 150km off the coast of Lincolnshire, UK. Operated by Neptune Energy, the Cygnus complex (which consists of two installations, Cygnus Alpha and Cygnus Bravo) has been producing gas since December 2016 and is now the largest single producing gas field in the UK, contributing around 6% of the country’s domestic gas demand.
The Cygnus Alpha installation consists of three bridge-linked platforms: a wellhead drilling centre (for extracting gas), a processing/utilities or PU unit (for processing and exporting gas) and a living quarters/central control room.
Gas from the Cygnus Field is exported via a 50km, 24" pipeline connection to the Eagles Transportation System (ETS). To meet the ETS entry specification the gas is processed via the PU unit, a process that includes:
- Separation (2 Trains)
- Condensate handling (2 Trains)
- Produced water handling
- Gas compression (2 Trains)
- Gas dehydration
Treating Produced Water At Source
Over a number of years, Separo's SepSORB® wastewater treatment system has successfully reduced hydrocarbon content in produced water on the Cygnus Alpha installation. By treating the water at source, our clients are able to meet regulatory and contractual demands, lower their carbon footprint and reduce costs.
The SepSORB® system meets the needs of operators who were asking for a compact, unobtrusive and efficient method of produced water treatment in isolated and often unattended locations.
A modular, plug and play system with a small footprint is perfectly suited for use on rigs, platforms and installations where space is at a premium. Because it has no moving parts and removes contaminants with a single pass and on a continuous basis, it operates without personnel which further increases its appeal to rig and platform operators.
Efficiency is key in the oil and gas sector, and real-time monitoring of input/output water quality provides the analytical data required to enable the system to be adjusted, optimised and effectively tailored to the specifics of almost any wastewater stream.
The SepSORB® units are designed to remove contaminants such as:
- Emulsified oil
- Volatile Organic Compounds (VOC)
- Benzene Toluene Xylene (BTX)
- Chromates
- Organo tin
- Poly chlorinated benzene
- Poly acrylic hydrocarbons
