What Is Produced Water and Flowback in Oil and Gas?
Like every other manufacturing process, the industrial-scale recovery of oil and gas generates different by-products, including water. The water in these cases is not a result of any chemical reactions occurring at the time of exploration but is due to the escape of water trapped in geologic formations while the oil is being pumped to the surface.
This water, which is referred to as produced water or formation water, has a significant impact on the production process in terms of cost of handling, treatment, and disposal. The inability to properly manage formation water could have dire consequences on both process efficiency and the surrounding biological environment (water bodies and aquatic life).
What Is Flowback?
Following oil and gas fracking, various fluids rise to the surface as “flowback.” These fluids are a complex mix of water, volatile hydrocarbons, and hydraulic fracking fluids introduced by operators.
Other components of flowback fluid include mud, artificial chemicals, and metallic ions. The composition of flowback necessitates its careful handling and processing as it poses a potential health risk to flowback operators.
How Long Is Flowback Generated?
Flowback generated by oil recovery efforts typically flow for 30 to 120 days. During this period, the operator’s priority is keeping the well open by managing the particulates within the flowback fluid. Flowback sand separators are effective in this regard, as the centrifugal forces generated when they are in operation rapidly remove sand from the recovered fluid.
What Is Produced Water in Fracking?
In addition to housing collections of oil and gas, natural rock formations typically also contain water. When the water trapped within these underground geological formations is brought to the surface during exploration, it is referred to as produced water.
Due to close contact with pockets of hydrocarbon-bearing rocks over long centuries, the produced water reaching the surface includes many different components.
Produced Water Salinity
The concentration of salt within the produced water from an underground oil reservoir can be defined as its salinity. Depending on the rock formation involved, produced water salinity can vary from negligible (comparable to freshwater) to significant (in some cases as much as 10 times greater than seawater).
Other Constituents of Produced Water
Apart from dissolved salts, produced water contains variable amounts of other organic and inorganic substances. Other common components in produced water are outlined below.
Produced Water Oil and Grease
This is a term loosely used to refer to the various organic compounds present in produced water that give it oily characteristics.
Produced Water Chemicals
Formation water reaching the surface usually contains varying amounts of both organic and inorganic substances. These substances become associated with the water as a result of long-term contact with formation rocks containing hydrocarbon compounds.
Radioactive Produced Water Material
Some oil and gas formations have naturally occurring radioactive material in low concentrations. These materials can be transferred into the produced water and generally pose little risk to operators although there is a risk of accumulation in sludge within tanks and transport pipes.
Differences between Flowback and Produced Water
The fundamental difference between flowback and produced water is their origin. While flowback is mainly a mixture of fluids artificially introduced by operators during exploratory efforts, produced water is naturally occurring fluid that already existed in the underground reservoir. This fluid is brought to the surface alongside oil and gas removed from explored geological formations.
Significance of Flowback and Produced Water to O&G Industry
Both flowback and produced water can be associated with high levels of particulate matter (mud and sand) which can hinder efficient oil and gas production. Both flowback and produced water require significant production budget allocation for treatment and disposal.
It is important that operators adhere to industrial treatment standards to boost process efficiency while adhering to local/municipal regulations on handling and disposal of both produced water and flowback.
Flowback and Produced Water Management
The treatment and safe disposal of flowback and produced water is an important aspect of oil and gas recovery procedures. Properly handling these fluids will ensure the preservation of the natural environment while promoting personnel safety.
Frac Water Treatment
The treatment of produced water (frac water) includes various physical, chemical and biological processes. Most treatment plants employ the techniques outlined below
- Elimination of dissolved organic compounds
- Removal of metallic ions
- Elimination of suspended particles by flocculation, coagulation, sedimentation, and filtration
Produced Water Re-injection
Produced water can be safely re-injected into ongoing oil and gas recovery processes or disposed into nearby water bodies only after its proper treatment. Produced water must meet minimum environmental safety requirements before its reuse.
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