In challenging economic times, efficiency and effectiveness are the top priorities for oil and gas operators. A critical step in protecting the integrity of an operation’s assets and the quality of the produced hydrocarbons is the treatment of injection fluids with the right biocide program. Left unchecked, microbial growth can lead to issues such as the formation of biofilm, souring of hydrocarbons and microbially influenced corrosion.

The use of biocides is not new. Over the years water- treatment microbicides have been used to help prevent the spread of waterborne diseases in drinking, recreational and industrial process waters. Yet the conditions in which a biocide needs to control the growth of microorganisms in an oil and gas operation is unique. There, a biocide program must address each phase of oil and gas exploration and completion (unconventional or conventional)—from preparing the water and treating topside to protecting the reservoir. Optimized biocide treatments include solutions that provide both a quick initial kill and long-term extended downhole protection.

During the shale gas revolution, technological innovation led to the adoption of more effective biocide programs and the expertise for optimizing them. Today, more importantly than ever, oil and gas operators rely on service providers to bring advanced biocide solutions designed to increase overall efficiency.

Combinations of biocides for extended protection bring economic value
Customization is key for a biocide program to successfully protect assets and sweet production from microorganisms. No single biocide can universally and efficiently address every phase of oil and gas exploration and completion. It is critical to consider the three main phases of the operation: prepare, decontaminate and protect (Figure 1).

Expert site-specific consultation gives operators the insight on how to select the right biocides at the right treatment ratio to offer effective microbial control. This is a highly scientific and tailored process that is approached on a case-by-case basis. Dow worked with its partners to test an operation’s water in its laboratories to define the best treatment program to address the local water conditions and microbial population.

One way to classify biocides is by their duration of effectiveness. Some biocides provide a quick-kill option and are effective for only several hours after application. Other biocides take longer for an effective kill but will provide increased protection when exposed to high temperatures and salinity.

Until recently, the main focus of the oil and gas industry was on quick-kill options, only measuring how much bacteria could be killed in 1 hr. As demands for increased efficiency become critical, there is a growing need to protect the reservoirs and the investments already made in them. Today we know that combining a fast-acting biocide with an extended protection biocide (“preservative”) provides the best microbial control program that addresses every phase.

Introducing an effective biocide program requires an upfront investment of less than 0.5% of the total cost of the fracturing fluid, which is a small investment that will pay off with increased efficiency. Optimized biocide treatments protect the integrity of the infrastructure and production quality, delivering excellent return on investment.

Evaluating a co-injection biocide treatment
Dow and Multi-Chem collaborated to test a two-part biocide treatment in the Niobrara Formation in 2012 and 2013. Seventy hydraulically fractured wells comprised of 25 well pads were evaluated. The reservoir contains both oil and natural gas, which lie at subsurface depths of 914 m to 4,267 m (3,000 ft to 14,000 ft).

Previously, wells were only treated with hypochlorite, a quick-kill biocide that is ineffective in the long term. Insufficient treatment led to issues that presented the opportunity to develop a better solution. Dow tested a dual-biocide treatment made up of glutaraldehyde, a fast-acting biocide, and dimethyl oxazolidine (DMO), which acts as a resilient preservative downhole once microbial reduction is achieved.

It was found biocides dosed in combination provided an antimicrobial effect greater than the sum of the two biocides alone. Laboratory studies defined the optimized ratio of glutaraldehyde and DMO for field tests.

Field trials showed that samples collected 90 days after the dual-biocide treatment contained relatively low levels of acid-producing and sulfate-reducing bacteria. Only 7% of samples contained 103 cells per milliliter, and no counts exceeded this level (Figure 2).

FIGURE 2. After 90 days of treatment, 100% of the samples met the key performance indicator of 103 bacteria per milliliter or less, with 93% of all samples surpassing the key performance indicator of 100 or less. This shows that the optimized treatment with quick-kill and extended-downhole protection was successful in controlling microbial growth. (Source: The Dow Chemical Co.)

This shows that the innovative co-injection treatment strategy can successfully protect against downhole bacterial activity for long periods of time. As a result, wells fractured using waters treated this way will have a reduced potential to experience a failure caused by souring and corrosion. Additionally, by reducing microbial contamination downhole, the integrity of the reservoir is protected from solids loading, which can obstruct pore spaces and ultimately reduce production.

An optimized use of biocides can not only positively influence the efficiency of oil and gas operations but also will help mitigate the contamination to effectively minimize economic, health and safety risks.

Myth Busters

Myth 1: An oxidizing biocide is sufficient for treatment.
Chlorine dioxide, an oxidizing biocide, only provides quick-kill topside. Today operators have advanced biocide alternatives for extended protection after the initial kill.

Myth 2: I’ll save more money by not using a biocide.
Untreated systems are open to uncontrolled microbial contamination. This could lead to costly souring, corrosion and plugging issues.

Myth 3: I don’t need a long-lasting biocide in extreme temperatures.
Certain types of bacteria, known as extremophiles, are able to grow in temperatures up to 120 C (248 F). In addition, there is a gradient of temperature downhole that is influenced as water is pumped below the surface. Even though microbial loading is typically lower in cold climates, there can be up to 10 million bacteria per gram of drilling fluid.

Myth 4: My water is fine. I don’t need a biocide.
It could take six months to realize corrosion or souring has occurred in an untreated system. Once the microbial influenced corrosion begins, it acts quickly. A pipe that should last 30 years might only last three months.