Evoqua, a manufacturer of water treatment packages for the Oil and Gas sector have seen growing interest in the application of UV disinfection for the treatment of sea water used for well injection in enhanced oil recovery applications.
UV light is a chemical-free, physical disinfection technique that is widely used throughout the offshore sector for applications such as potable water disinfection, RO membrane protection and B.O.P. hydraulic operation fluids.
Microorganism and bacteria control is increasingly an important topic of discussion in the oil and gas industry, with a number of operators linking instances of poor water quality used in stimulation fluids to an increase in operational costs, and the failure of capital assets. Negative consequences of inadequate water treatment include:
- Microbiological induced corrosion
- Damage of capital equipment and components
- Loss of fluid stability during injection
- Souring the well with hydrogen sulphide gas H2S
- Solids formation and plugging of equipment & pipework
- Solids formation and plugging of the well
Evoqua have successfully used UV for the control of microorganisms such as SRB’s (Sulphate Reducing Bacteria), Acid Producing Bacteria and Slime Forming Bacteria in well injection applications for over 30 years. Using standard UV doses, a single pass through a UV treatment system (0.2 seconds exposure) will typically achieve a minimum 5.0 log (99.999%) reduction of Sulphate Reducing Bacteria (based on an seawater influent of 1.1 x 106 (1,100,000) of SRB’s).
Working with Conoco Phillips, Evoqua carried out the original research (1993) into the effectiveness of UV treatment for SRB reduction used in well injection applications, which lead to the supply of a number offshore UV treatment plants being installed in the Norwegian North Sea sector, with the largest plant – Eldfisk and Ekofisk treating 4,500 and 4,000 m3/hr daily.
SIGNIFICANTLY REDUCES OPEX COSTS
UV treatment significantly reduces the need for chemical biocides, which typically have a high associated operational cost and are hazardous to handle, transport and store in an offshore environment. As a chemical free, physical sterilisation technology, a correctly sized UV treatment package will typically reduce the volumes of required biocide by 90%, and maintain a minimum 5.0 log reduction (99.999%) of SRB’s and other microorganisms from the water.
In a recent study, a leading U.S. oil and gas operator compared the costs of using chemical biocides (Acrolein Injection, transportation, handling and storage) for a 2,000 m3/hr well injection project versus a chemical free, UV disinfection package. The results, based on a 5 year OPEX calculation showed a substantial business case for using UV disinfection:
UV treatment package: £129,000
Biocide (acrolein injection): £3,459,000
A typical ATG™ UV disinfection package for well injection treatment and SRB reduction is supplied within a standard 20ft DNV certified offshore container. The package is designed to be fully turn-key and is both simple to operate and easy to install into existing pipe work with minimal disruption. A small amount of biocide such as Hypochlorite is still required to maintain residual protection, and occasional shock dosing with chemicals may still be needed to flush pipework downstream of the UV package. However as the UV system is used as the primary disinfection solution, post treatment with chemicals does not require the complex monitoring equipment that would be necessary if biocides were used as a primary disinfectant for everyday operation.
Evoqua are currently trailing a number of ATG™ UV packages for well injection water, produced water reinjection, produced water discharge and recently have received government backed funding to complete a UV trial for the treatment of flowback water produced from Shale Gas wells during hydraulic fracturing operations.