Peracetic acid gains traction as a multifaceted water management tool

Peracetic acid (PAA) – a versatile oxidizing biocide approved for decades by the US Food and Drug Administration for use as a no-rinse antimicrobial agent for red meat and poultry – is proving its value as a multifaceted water-management tool at hundreds of unconventional well sites in the US.

Producers operating wells in several states, including most of the major US shale plays and the revitalized Permian basin of West Texas and southeastern New Mexico, are incorporating PAA into integrated chemical treatment programs as a biocide to control planktonic and sessile bacteria.

The chemistry is prepared onsite for deployment using procedures and handling methods perfected through decades of development in other industries to treat surface water in ponds and pits and to treat frac water on the fly during hydraulic fracturing operations. PAA also can cut through organic and inorganic contaminants to eradicate living species in the complex microbiomes of flowback and other produced wastewater to condition it for recycling or disposal.

Multiple reactive effects

PAA, an equilibrium product of hydrogen peroxide and acetic acid, has moderate oxidizing properties. PAA reacts with the more easily oxidized sulfides and more reactive amine sites in proteins and inorganic materials. PAA is an oxidizing biocide that breaks down to water and acetic acid (vinegar).

As an oxidizing biocide, PAA reacts with microbial cell proteins to provide its biocidal effect. Unlike stronger oxidizers, PAA does not interact with hydrocarbons, which permits it to provide effective biocidal activity in a system with a high organic load.

For oilfield fluids, PAA oxidizes hydrogen sulfide (H₂S) to control odor, provide a safer work environment, and enhance oil and gas products with sulfur contaminant issues. PAA also can clean up and prevent iron sulfide (FeS) emulsions and FeS oilfield equipment scale.

For water treatment, PAA has been deployed by many oil and gas producers using unconventional processes to permit the recycling of up to 100% of produced and flowback water for new hydraulic fracturing operations. The produced and flowback water is coming back with lower microbial, iron, and HS levels than observed prior to starting the PAA program, demonstrating a positive effect on the entire formation.

Importance of water management

The importance of effective water management at the well site has been magnified by the oil and gas renaissance in the US, triggered by the still-evolving technological capability to exploit previously unproductive low-permeability reservoirs. Concerns arise because of the large volume of water required to hydraulically fracture a typical well – especially in areas with limited surface water resources – and the quality of frac water and reservoir fluids that flow back out of a new well in the weeks, months, and years following well completion.

Many US operators have responded by trying to recycle as much water as possible for use in multiple fracturing treatments, which requires treatment with a broad chemical program tailored to resolve contamination issues at each specific well site.

A technical paper, “Peracetic Acid Use in Water Treatment for Oil and Gas Production” (in publication, to be presented during the International Water Conference as IWC 13-21), focuses on the synergistic effects of PAA applications for microbiological kill and control of HS and FeS in applications at unconventional oil and gas well sites. The paper highlights several varieties of PAA applications.

Produced water for hydraulic fracturing

PAA has been applied as part of a successful produced water recycling program to support hydraulic fracturing operations in a field in which wells experienced H₂S souring and iron buildup.

In an example field application, produced water enters a frac water tank battery from many sites, so water quality can vary considerably; tanks are connected in series to permit sedimentation before treatment with PAA in subsequent tanks to control microbes, oxidize FeS (which precipitated in the tanks), and break down crosslinked gels. A subsequent PAA treatment is then applied as a final biocidal treatment to the recycled frac water.

After more than a year of treatment, levels of microbiological contamination, iron concentrations, and H₂S souring in new produced waters are noticeably lower, ensuring a higher quality final product and easier water recycling.

Water ponds and pits

The performance of PAA was compared with that of sodium hypochlorite – another oxidative biocide – in treatments of two adjacent freshwater pits used for fracturing operations. Initial chemical treatments were applied to knock down microbiological contamination already present in the pits, followed by regular periodic doses of each treatment.

The tests showed that PAA had biocidal effects within established biological mats (sessile bacteria) on pond bottoms that were not touched by hypochlorite. The better light and temperature stability of PAA over hypochlorite also enhanced its relative biocidal effect.

Emulsion breaking and scale prevention

The effects of PAA on emulsion- and scale-forming sulfides prior to separation have been studied in applications involving both two- and three-phase production systems.

One study was conducted at a site where the operator was experiencing significant oil quality and water disposal issues due to FeS emulsion, high microbial contamination in post-separation water storage, and H₂S contamination. The free-water knockout (FWKO) oil/water separation unit in the production system, which was 3 m (10 ft) in height, contained an oil-wet FeS emulsion about 1 m (3 ft) in height. The focus of the testing was to determine whether PAA could remove both the FeS emulsion and planktonic and sessile microbiological contamination.

A two-day cleanout treatment with PAA was tested to demonstrate that both planktonic and sessile bacteria had been efficiently removed from both the FWKO and the large water-holding tanks fed by the FWKO. In addition, the FeS emulsion in the FWKO unit was virtually eliminated, which solved the operator’s oil post-treatment problem for the site. A side benefit to the operator was that the PAA treatment also reduced the concentration of H₂S in the FWKO water to zero from 30 ppm prior to the test. The site then implemented a low-level continuous PAA treatment focused on system maintenance.

In the applications cited in the IWC technical paper, PAA is shown to effectively remove microbial contamination; to significantly reduce or eliminate H₂S in water, oil, or gas, often using a nonstoichiometric concentration; and to remove oil-wet FeS emulsions and scale from production equipment and well structures.

Decades of safe and effective usage in other industries are proof-positive that when handled properly, PAA can be a valuable new water management tool in the oil and gas industry.