SHALE TECHNOLOGY REVIEW
Water management tools and techniques continue to expand
To use water resources more efficiently during hydraulic fracturing associated with shale development, the E&P industry continues to add new devices and innovative techniques, including this collection of eight recent items.
By now, the sourcing, logistics, reuse and disposal challenges of water for shale frac operations are well known to everyone with even a peripheral interest in the subject. Outside the technical challenges, perceptions (or misperceptions) among some, of environmental hazards associated with hydraulic fracturing also loom. Water management is not specifically a shale-frac issue. In fact, the World Economic Forum community identifies water crises as one of the top 10 global risks, which serves to raise the visibility of frac-water use.
As the industry works at a feverish pace to meet the demands of high-tempo shale development, its successes promise not only more efficient production of much-needed energy resources, but also a change in public perception of shale operations.
API Guidance Document HF2, “Water Management Associated with Hydraulic Fracturing” (June 2010), describes fluid requirements for successful fracturing. These requirements are the result of the geology, the operating environment, the frac design, the scale of the development process, and the results required for total project success.
The document boils it down to this: “What does the reservoir rock need, and what will the rock give back after fracturing?”
It also points out that understanding the in-situ reservoir conditions is critical to successful stimulations, and in the design of the fracture treatment and fluid used. While the concepts and general practices are similar, the details of a specific fracture operation can vary substantially from resource to resource, from area to area, from operator to operator, and even from well to well.
The ideal properties of a fracturing fluid relate to its compatibility with the formation rock; its compatibility with the formation fluids; its ability to transfer enough pressure throughout the entire fracture to create a wide fracture, and be able to transport the proppant into the fracture, while breaking back down to a low-viscosity fluid for cleanup after the treatment.
In 2011, the U.S. Environmental Protection Agency (EPA) began research under its Plan to Study the Potential Impacts of Hydraulic Fracturing on Drinking Water Resources.1 The purpose of the study is to assess the potential impacts of hydraulic fracturing on drinking water resources, if any, and to identify the driving factors that may affect the severity and frequency of such impacts. Scientists are focusing primarily on hydraulic fracturing of shale formations to extract natural gas, with some study of other oil- and gas-producing formations, including tight sands, and coalbeds. The EPA has designed the scope of the research around five stages of the hydraulic fracturing water cycle, Fig. 1. Each stage of the cycle is associated with a primary research question:
|Fig. 1. The five stages of the hydraulic fracturing water cycle, from the EPA report, “Potential impacts of hydraulic fracturing on drinking water resources: Progress report,” December 2012.
- Water acquisition: What are the possible impacts of large-volume water withdrawals from ground and surface waters on drinking water resources?
- Chemical mixing: What are the possible impacts of hydraulic fracturing fluid surface spills on, or near, well pads on drinking water resources?
- Well injection: What are the possible impacts of the injection and fracturing process on drinking water resources?
- Flowback and produced water: What are the possible impacts of flowback and produced water (collectively referred to as “hydraulic fracturing wastewater”) surface spills on or near well pads on drinking water resources?
- Wastewater treatment and waste disposal: What are the possible impacts of inadequate treatment of hydraulic fracturing wastewater on drinking water resources?
As API and EPA suggest, frac-water technologies are certainly not one-size-fits-all. Numerous, recent approaches aim to solve the technical problems associated with water reuse, which often have a knock-on benefit of shrinking logistical difficulties.
A THREE-STAGE PROCESS
A three-stage process claims to cost-effectively create fresh water from a variety of contaminated wastewater sources, while yielding beneficial salt products and distilled water, Fig. 2. Water distillate from Integrated Water Technologies’ FracPure process2 is said to be safe to return to the environment and exceeds all EPA and state environmental regulatory agency drinking water standards. Wastewater sources that can be treated for frac operations include wastewater treatment plants, sewage plants, mine water effluent and other industrial wastewater.
|Fig. 2. Interior of the FracPure crystallization plant (image courtesy of Integrated Water Technologies).
In Pennsylvania’s Marcellus shale, one of the company’s main operating areas, the process is creating pure water from abandoned mine effluents and acid mine drainage sources in close proximity to natural gas sites. To date, the company has established brine treatment plants in several strategic locations regionally throughout the Marcellus shale, to reduce trucking costs from drilling sites and allow for handling large volumes of brine locally.
At these plants, water sources undergo solids removal, chemical treatment, and evaporation and crystallization processes that result in complete re-use and disposal of all frac and produced water. According to the company, the process hedges risk against disposal wells, produces distilled water and 99.7% pure salt products, and treats all produced water to drinking water standards.
In forward (or direct) osmosis (FO), water from one solution selectively passes through a membrane to a second solution, based solely on the difference in the chemical potential (concentration) of the two solutions. The process is spontaneous and can be accomplished with very little energy expenditure. Thus, FO can be used, in effect, to exchange one solute for a different solute, specifically chosen for its chemical or physical properties. For desalination applications, the salts in the feed stream could be exchanged for an osmotic agent, chosen specifically for its ease of removal, e.g. by precipitation, Fig. 3.3
|Fig. 3. Block diagram illustrating strategy for applying FO and thermal precipitation of an osmotic agent to accomplish desalination.
Oasys Water uses forward osmosis to produce clean water from produced water, which can have salt concentrations up to five times higher than seawater and is often laced with radioactive materials. The company’s Membrane Brine Concentrator (MBC) is a movable system that can treat up to 4,000 bpd or 116 gpm of produced water, industrial brines, or RO concentrate, Fig 4. It says the system has successfully treated challenging, produced water streams and has demonstrated the ability to reduce disposal volumes by more than 80%, reducing the total cost of water treatment by up to 30%.
|Fig. 4. The Oasys process is a patented membrane-based desalination platform that can turn up to 15% salt water (approximately five times the salinity of seawater) into fresh water (image courtesy of Oasys Water).
Feed water stays in liquid form, requiring significantly less energy. The non-metallic process uses readily available components, so there is no use of high-pressure components or exotic metals. Low pressure on the membrane reduces fouling and scaling.
In early 2012, the company completed a four-month test of the system using 1,430 bbl (60,000 gal) of produced water from the Marcellus shale. Typical of oilfield waste, the raw water had greatly variable salinities and other constituents. The average salinity of the raw water was 73,000 parts per million of total dissolved solids (ppm, TDS), roughly 10% higher than RO brine. Boron was measured at concentrations that exceeded safe limits for drinking water and agriculture applications.
The system test consistently produced water that meets EPA drinking water standards (below 500 ppm, TDS) and achieved a brine concentration over 200,000 ppm, TDS. The company calculates the total cost to treat the water, including pretreatment and energy costs, at more than 35% lower than mechanical vapor recompression.4
MOBILE, HIGH-VOLUME TREATMENT
Omni Water Solutions’ platforms are intended for applications where contaminated water has complex, variable and/or unpredictable levels of heavy metals, organic compounds and dissolved solids.5 One such mobile, high-volume treatment platform is the H.I.P.P.O. unit, which enables treatment and re-use of water at the point of use for frac operations. The company' s automation technology allows operators to treat water to the appropriate level regardless of changes in the raw water chemistry. Transport, purchase and disposal costs for fresh and wastewater are reduced significantly.
The portable, self-contained unit treats water at a rate of up to 350 gal/min., without advance consideration of source water contaminants. No pretesting or pre-treatment is required. The control system enables water treatment without an operator on-site.
Since June 2013, Omni’s mobile water treatment unit has been used in a Marathon Oil water recycling pilot project to convert produced water into fresh water, clean brine and hydrocarbon streams. The objective in this pilot was to reduce boron levels from 90 ppm to less than 5 ppm in the freshwater stream. The system has successfully treated over 140,000 bbl to date, with results verified by analysis from three different independent labs.
MIXED OXIDANT BIOCIDE-FREE FRAC PROCESS
For high-level bacteria issues, a process from Neohydro uses mixed oxidant generators to create ozone, HOCL, free-radical and hydrogen peroxide onsite for on-the-go oxidizing of high-level bacteria influents.6
Preceding the hydraulic fracture, the Neo-Frac process uses a freshwater-based fluid that continually removes bacteria throughout the entire frac operation. The fluid eliminates corrosive buildup and improves overall well efficiency. Water returned from the frac is treated to remove heavy metals, organics and cations, entirely on-site.
Using the company’s proprietary electro-oxidation technology, HOCL brine solution is created on-site and added on the fly to eliminate iron related bacteria (IRB), sulfate-reducing bacteria (SRB) and slime-forming bacteria (SLYME). The HOCL works on contact and has residual capabilities equivalent to biocide capabilities. There is no need to store or transport toxic biocides, and harmful effects of biocides on the environment are eliminated.
Wastewater is pumped into units exposed to an electric field. In a process called high-voltage electrolysis, the chemical bonds of salt (NaCl) and water (H2O) inside the solution are released; producing ozone from water, monotonic chlorine, free radicals, and hydrogen peroxide. All are powerful sterilizing elements that destroy all biological oxygen demand (BOD) or chemical oxygen demand (COD) organic/inorganic pollutants and biofilm present in the water.
The water is subjected to electro-oxidation long enough to destroy all biological and chemical contaminants. Trace elements re-bond when the process ends, safely and efficiently converting 99.9% of the supplied water into acceptably regulated levels of chlorine and mixed oxidants.
BENEFICIAL USE OF OZONE
Although about 20% to 60% of the water used for fracturing shale flows back, its reuse is prohibited because of the contaminants. The common spoilers of the flowback water are hydrocarbons, oil and grease, diesel-related organics, BTEX, polyacrilamides, transition metals, barium and strontium.
KTI’s Nanozox process has, as its basis, peroxide-coated micro- to nanobubbles, which persist as a negatively-charged bubble emulsion to effectively treat the contaminants of concern.7 Organics oxidize to carbon and oxygen. Metals are precipitated and filtered out in a form that can be immobilized for disposal. The water can be treated further to concentrate salinity for granular salt production, road de-icing, or deep-well disposal. Evaporated water, free from volatile organics, can be returned to river systems.
Recycling water is produced by a combination of treatment of the first stage of flowback water, treatment and dilution of the second stage of flowback water, and treatment and desalination of third-stage flowback water.
TREATING HIGH DISSOLVED SOLIDS
A system from ThermoEnergy processes flowback and produced water from wells, lagoons or other similar sources with TDS (total dissolved solids) content of more than 30,000 to 250,000 mg/l.8 Typical throughput is 4,000 bbl or over 165,000 gal of water per day, with an estimated recovery of 65% to 90%, at less than 500 ppm, TDS in the distillate.
The system is based on the company’s patented technology and consists of four vessels in series. The evaporative process uses flash vacuum distillation to separate out TDS from water. The technology was originally developed for difficult-to-treat high TDS industrial wastewater. By using flash vacuum distillation, the company says the TurboFrac system is able to treat both very high TDS waters—in the range of 100,000 to 250,000 mg/l—that other evaporative processes cannot handle. By staging the vessels, the system has energy consumption equal to MVR/crystallizers at significantly lower capital costs.
The skid-mounted system can be combined with other pre-treatment technologies, such as degasifiers, to remove H2S gas from the incoming feed water, coagulation and flocculation to remove fracing chemicals, and a multimedia filter to remove suspended solids. The final product or distillate from the system can be reused as fracing source water, or it can be discharged.
REDUCING TRANSPORTATION COSTS
Unlike the science of water treatment, which offers numerous avenues of investigation, the logistics of water tend to have predictable and unchanging components—trucks, trains and pipelines. But within the physical constraints of transportation, new ideas do emerge.
In an effort to reduce the costs of transporting water, LTR has developed a way to transfer water long distances that eliminates most trucking, at less cost than traditional poly pipe lines.9 A high-rate, high-pressure, lay-flat discharge hose decreases costs by decreasing set-up time and equipment.
Available in 8-in. and 10-in. sizes, the long sections and fewer joints reduce the chance for leaks and enable fast set-ups by the company’s field technicians. This method can reduce labor costs, as well as truck traffic. The polyurethane hose operates in a wide range of temperatures.
USING PRODUCED AND BRACKISH WATER
According to Apache Corporation, the company is expanding its use of alternative water sources in an effort to minimize freshwater used in hydraulic fracturing operations.10 The company says that it has increased its use of produced water and brackish water for drilling in the Anadarko and Permian basins, and has recycled more than 500,000 bbl of produced water for hydraulic fracturing in the Anadarko basin.
The produced water is recycled at the company’s Stiles Ranch water recycling plant in Wheeler County. It is treated to remove components that would interfere with hydraulic fracturing, such as particulate matter and iron sulfides. It is also treated to control bacteria and algae growth before it is delivered by pipeline to hydraulic fracturing locations, where it is used instead of fresh water.
The company also uses groundwater from the brackish Santa Rosa aquifer for hydraulic fracturing operations at some of its Permian basin wells. The company uses nearly all the produced water available in some areas, and, if necessary, it mixes treated produced water with brackish water, eliminating the need for fresh water.