No one is talking crisis, but water is very much on the mind of every company developing US shale plays. This is both a practical issue and one permeated with infrastructure and ecological sensitivities that must be managed with care.

The oil and gas industry is being proactive because it is clear that current water management practices are likely to be unsustainable over time. Arguably, the industry is at a crossroads where the continuing success of developing shale oil and gas plays may depend on companies revising their water strategies through the accelerated adoption of emerging water treatment technologies. Systemic changes to daily operating protocols will be required to alleviate logistical and environmental stresses while providing sustainable sourcing options, thereby securing the long-term future of this vital resource.

Water sourcing

The costs and logistics of operating a viable shale project, especially in remote areas, are significant. Developing a 65-sq-km (25-sq-mile) project can necessitate sourcing billions of gallons of water. Options may include surface water, groundwater, and municipal water (both fresh and waste streams) along with increasing the use of flowback and produced water. Horizontal wells can require up to 2 MMgal of water during the drilling stage and more than 10 MMgal of water during the completion phase. This water must be transported to the wellhead, most likely involving a combination of services and logistical gymnastics.

Water sourcing is becoming increasingly problematic, with a minority of voices raising questions over the impact of fracturing activities on the supply and safety of potable water supplies. Shale operators can offer plenty of irrefutable evidence that fracing, on average, uses less than 1% of water in any given region. But the relative percentage in certain geographic areas can be substantially higher, and the visibility of operations makes for a different perception.

This is magnified in areas such as the Permian basin where persistent drought conditions have led to water use restrictions. Industry water demands are bound to be highlighted, even if these are minimal as compared, for example, to 60% to 70% agricultural usage. In Texas water rights involve a further complication: Groundwater is owned by landowners free to sell their water, whereas elsewhere in the US this is a public resource, which makes for easier area water supply planning that takes into account all industrial and domestic consumers.

Water recycling as an option

The obvious strategy for operators is to source and use water as efficiently as possible within the parameters of their particular shale projects. This strategy has placed the focus firmly on recycling options. The benefits include less pressure on water supplies, less produced water disposal, and reduced logistical stress for supply and disposal, all of which can add up to a reduction in overall costs.

Recycling possibilities available to an operator depend on a number of factors, but the geologic composition of the formation will define characteristics of the produced water. The salinity or total dissolved solids (TDS) can vary significantly by basin and from well to well within the same geostructure. Other water quality characteristics that may influence water management options necessary for consistent control of gel frac chemistry include concentrations of hydrocarbons, suspended solids, soluble organics, boron, iron, calcium, magnesium, and constituents such as benzene and silicates. In certain circumstances naturally occurring radioactive materials (NORMs) also may be present.

Options for recycling will vary. Often, the first choice is to transport flow-back/produced water to a central facility for minimal treatment. Suspended solids are removed, and the water is returned for blending and reuse. Obvious issues include no removal of TDS concentrations, potential interference with completion performance through reuse, and the environmental concerns associated with maintenance and security of frac water storage ponds with high concentrations of dissolved solids.

A second option that reduces the transport cost element is onsite primary treatment of flowback water for the removal of suspended solids, oils and greases, microbes (through disinfection), and friction-reducer polymer prior to reuse in another frac job.

A third option is the more intense primary treatment mentioned above plus the possible removal of scale-forming constituents such as calcium, magnesium, and barium. This is then followed by blending and reuse. At the point where brine concentration in flowback water becomes too concentrated for reuse, it must be transported to an approved injection well facility. Some service providers believe that focusing on the composition of flowback water using chemical additives and other processing can enable continued recycling of water, effectively tolerating TDS and salinity issues.

For every frac job there has to be a calculation about the suitability of flow-back/produced water for reuse depending on its salinity, TDS content, etc. In practice, early flowback water often can be used a number of times in certain geological conditions with a minimum of basic filtering, blending with freshwater, and adding frac chemicals to improve hydrocarbon flow. But sooner or later the buildup of brine and other constituents must be dealt with, and this is the point where production cost and environmental imperatives have to be resolved.

Thermal distillation provides different option

None of the options listed above address the removal of salts and other constituents, known to interfere with polymer crosslinking and associated breakers. Thermal distillation effectively removes all constituents (to less than 50 ppm) from these recyclable water streams. 212 Resources provides mechanical vapor recompression processes for both onsite and centralized service. The process is based on a system providing a consistent, high-quality effluent regardless of the widely varying constituents in the feed stream. The by-product – highly concentrated 9.6-lb brine – can be filtered and reused as a drilling fluid, kill fluid, and feedstock for conversion to other oilfield chemicals such as hydrochloric acid and sodium hypochlorite. The process also removes contaminants such as NORMs and endocrine-disrupting compounds as well as various aldehyde compounds commonly found in produced/flowback water.

In regions where disposal costs can threaten future field development, thermal water treatment processes can process produced/flowback water to national pollutant discharge elimination system standards. 212 Resources operated such a facility, treating 5,000 b/d for discharge into a Class 1 cold-water aquatic life stream feeding into the Upper Colorado River drainage system. The end result was a significant reduction in daily disposal costs, enabling cost-effective development of the field.

The mechanical evaporation approach is still evolving but is arguably one of the most promising in its focus on well productivity, smart water management, reduced costs, and the environmental hazards of shale oil and gas development.