The benefits of employing hydraulic fracturing (HF) to stimulate the flow of natural gas, arguably the ‘cleanest’ fossil fuel, from both new and existing wells are obvious. However, one of the downsides is that the technique consumes huge quantities (along the lines of millions of litres per well) of often regionally scarce water, and – according to opponents – can contaminate drinking water supplies. This has been a controversial, politically charged issue in the United States; and the US Environmental Protection Agency recently initiated a new, science-based study to determine if the practice does indeed pose a risk to human health or the environment. Now, with Shell and several other energy companies exploring the potential for initiating HF operations in the Karoo, the controversy over HF has spilled over into South Africa.
To help address some of the water-related issues, several leading water technologies companies have introduced mobile water treatment solutions. These are designed to make it possible to treat and recycle both HF flowback and the brine water produced during drilling, HF, and other industrial operations and, in this manner, reduce the strain on freshwater supplies. On-site water treatment also reduces the need to transport HF flowback and produced water offsite for safe disposal. Water technology companies are also building permanent treatment facilities designed to reduce the percentage of total dissolved solids from the HF flowback produced water prior to processing at municipal wastewater treatment facilities, which often are not equipped to handle this type of effluent.
In addition, several universities in the US, including Texas A&M, Carnegie Mellon University, and West Virginia University have initiated research projects (often involving substantial funding from the US Department of Energy) intended to develop new, more effective technologies for treating the effluent from oil and gas drilling and HF operations.
HF operations consume huge quantities of water
With hydraulic fracturing, water under high pressure forms fractures in the rock, which are propped open by sand or other materials to provide pathways for gas to move to the well. Petroleum engineers refer to this fracturing process as ‘stimulation’. A variety of different chemicals, typically representing less than 0,5% of the total volume, are also used to facilitate the process. The tremendous volumes of water required (typically eight to 20 million litres per well), of which 25 to 100% may be returned to the surface as flowback water, must be recovered and disposed of responsibly (or recycled for further industrial use) before gas production can commence.
In western US states in particular, where freshwater supplies are already extremely scarce, hydraulic fracturing can further strain existing water resources. The water used for drilling and fracking active wells in the Barnett Shale area can equal the typical water usage for 185 000 households (or more). In water-stressed South Africa, as well, this is a huge issue that cannot be ignored.
In the US, Texas state and county agencies now closely monitor volumes of water used during drilling and a consortium of Barnett Shale drilling companies have developed best management practices for water conservation, with the goal of keeping the pace of drilling and production activities within the bounds of sustainable water use. Producers in Marcellus Shale gas production areas have had similar discussions.
Water treatment solutions enable water re-use to reduce fresh water and transportation requirements
Produced water from HF operations is typically disposed of in three ways:
1. Transported off-site for disposal in permitted underground wells.
2. Transported off-site for treatment prior to disposal to surface waters.
3. Treated on-site for re-use in HF or drilling operations.
The unique nature of the flowback water produced from HF operations located in different geographic regions (and the different chemicals used) requires different water treatment solutions. For example, water treatment operations in the Marcellus Shale region in the eastern US must be able to deal with the extremely high brine content of the HF flowback water.
Several companies, including both Siemens Water Technologies and GE Power & Water, have introduced mobile treatment units that can treat produced water on-site for re-use using a variety of different technologies. The on-site approach both reduces the strain on local water resources and minimises the cost, wear and tear on roads and greenhouse gas emissions associated with hauling the large quantities of flowback and produced water to often-distant disposal wells or off-site treatment facilities in tank trucks. The Siemens solution utilises flotation/filtration technology, while the GE solution utilises evaporation technology. As with most technology approaches, each has its pros and cons.
Clearly, the limited availability of water appropriate for use in HF operations constrains the oil and gas industry’s ability to produce shale gas and other unconventional energy sources. Furthermore, the current high cost of treating and/or transporting and disposing of both produced water and HF flowback water represents a considerable cost to the oil and gas industry. The current concerted effort by leading water industry suppliers, government and academia, to develop, commercialise, and deploy new mobile and fixed technologies for treating produced water and HF flowback water cost-effectively will provide significant benefit to the oil and gas industry and the general public alike. However, water consumption and ground and surface-water pollution are just two of the environmental issues that must be resolved to help eliminate (or at least minimise) the controversy surrounding hydraulic fracturing, particularly in sensitive regions such as the Karoo.
ARC Advisory Group is preparing a series of reports on industrial water management for its Advisory Service clients. These reports will include approaches and success stories across a variety of different industrial sectors, including both upstream oil and gas production, downstream refining and petrochemicals manufacturing, mining, and metals processing.
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