At the heart of the ‘Shale Boom’ in the US is the increased use of water for hydraulic fracturing of oil and gas wells – but how do we safely reuse or dispose of the waste water?
Figure 1: Oil production in the US (2000-2015) in MMbopd). Current estimates from EIA indicate more than half the crude oil produced today is from hydraulically fractured wells. EIA, US Energy Information Administration (March 15, 2016); EIA, completion and production data from Drilling Info and IHS.
The race to increase production in some of the most prolific oil and gas basins in the United States, such as the Permian Basin in West Texas, the Barnett in West Central Texas, the Marcellus in West Virginia and Pennsylvania, and the Haynesville in Louisiana, have contributed to escalating water use for hydraulic fracturing.
In the early 2000s, the combination of multi-stage fracking in horizontal wells, beginning with the Barnett shale gas followed by the tight oil in the Bakken and Eagle Ford, around 2008 and 2009 respectively, helped ramp up the production of oil and gas in the United States. Oil production profiles show that 23,000 completed and fracked wells produced approximately 102,000 bopd in 2000, in comparison to 4.3 MMbopd from 300,000 completed wells by 2015, when 51% of oil produced in the US was primarily derived from hydraulically fractured wells (Figure 1).
Oil and dry shale gas production grew rapidly from mid-2005, increasing significantly in 2011, as shown in Figure 2, and with improved performance from hydraulically fractured wells in shale basins across the country, the ‘Shale Boom’ has made the US an exporter rather than an importer of oil and gas.
Figure 2: US tight oil production on selected onshore plays (MMbopd). Sources: EIA derived from state administrative data collected by Drilling Info Inc. Data are through March 2019 and represent EIA’s official tight oil estimate, but are not survey data. State abbreviations indicate primary state(s).
Hydraulic Fracking Fluids
Figure 3: Barrels of water used by state per well (Median, 10% and 90%).
While the efficiency and performance of fracked shale wells continues to improve, the high volumes of water usage have also increased; in 2019, for example, an estimated 7,000 drilled but not completed wells will undergo hydraulic fracturing by Q3. The median volume of water used (barrel) per well for hydraulic fracturing was approximately 35,000 barrels (1.5 million gallons) between 2011 and 2013 as reported in FracFocus 1.0 by states (Figure 3). There was a great variation between the 10th and 90th percentile water used; 1,762 barrels/well (74K gallons/well) and 143,857 barrels/well (6 million gallons/well), respectively. Variations were attributed to several factors such as fracking design, different shale and well types, and fluid types. As a result, water management through disposal, reuse and recycling have become a priority for operators in the US.
Although the composition of hydraulic fracking fluids (Figure 4) varies depending on the type of shale, hydraulic fluids are primarily water and sand or proppant, with water making up 90–99% of the total volume injected into the well – hence the increasing need for water. Various chemicals or additives for slick water and energised fluid may contain biocides, corrosion inhibitors, foam, friction reducer, iron control, clay control, surfactants and gels, at different concentrations depending on the shale rock type in a specific basin in a particular play type.
Figure 4: A generalised composition of hydraulic fracking fluid.
Chemical mixing of additives is normally performed at the well site in storage trucks and tankers for the base fluids, with slick water or energised fluids making up the majority of the hydraulic fracturing mixture. The proppant or sand comprises the second highest component of the fracking fluids. An important aspect of chemical usage in the fracking fluid is characterising the type of chemicals and their migration and transformation throughout the whole cycle and process.
Sourcing Water for Hydraulic Fracturing
Figure 5: A generalised cycle of hydraulic fracking operations.
The full cycle of hydraulic fracturing operations requires a high degree of planning from the logistical point of view, from sourcing materials through to the development and production stages of a well. As part of this process, different operators have adapted several ways of sourcing water as well as dealing with produced and flowback water. A generalised cycle for hydraulic fracking operations is shown in Figure 5.
Figure 6: Comparison of sourcing water used for hydraulic fracking between (a) Marcellus shale (Pennsylvania, 2008–2013) and (b) Barnett Shale, Central Texas (2011 and 2013).
Water is obtained mainly from surface and groundwater sources but water sourcing differs between different states based on availability, climate and government regulations. In eastern states where it is more humid, surface water is used more extensively, while more groundwater is used in arid to semi-arid regions. Figure 6 demonstrates the difference between sources of water in the Marcellus Shale (Pennsylvania) – primarily surface water – and in the Barnett Shale (west central Texas), where an equal amount of surface and ground waters are used.
It is interesting to note that when water usage for primary hydraulic fracturing in unconventional oil production is compared to water consumption for injection in conventional oil wells, the unconventional wells use much less water than used in all the conventional stages (Figure 7).
Figure 7: A comparison of water consumption for conventional (COP) vs. unconventional oil production (UOP).
Waste Water from Hydraulic Fracturing: Reuse, Recycle or Dispose?
Produced water is a byproduct of hydrocarbon production. It originates in the formation and flows through the producing well to the surface, where it is separated from the oil and typically is stored and/or treated by the operator. Initially, water produced by hydraulic fracturing contains some of the returned hydraulic fluids but with time the produced water is coming from the production in the formation. The composition of produced water varies between different shales but typically includes salts, metals, dissolved organic compounds, and the returned hydraulic fluids.
Injection of produced water to a disposal well is a common practice with operators but it is costly and often not available due to limited capacity. Other management best practices are employed, such as water treatment in facilities for reuse for the next operation or recycled using different processes. Handling of produced water is very sensitive and care for handling is very important.
The escalating amount of water used for hydraulic fracturing to produce oil and gas is projected to increase even higher in the next few years. With the increased consumption of fresh water, the need for reusing and recycling produced and flowback water is even more important in the oil fields; some service companies have even transformed their strategies to focus on water. The challenge of sourcing, ensuring availability, moving, treating, and measuring water has become big business in drilling shale plays and from the standpoint of an environmentally conscious company, recycling and reusing treated water makes a lot of sense. The 7,000 wells already drilled that will be completed in late 2019 using hydraulic fracturing will create a bottleneck of large volumes of produced and flowback water that will need to be processed for treatment or reinjection.
Cleaning Water in Fracking Operations: Portable Closed System Solution
Pumping water from a lake for hydraulic fracturing in the Fayetteville Shale of Arkansas. Source: Bill Cunningham, USGS.
Houston-based Cabral Technology has been developing ways to clean water used in fracking operations by combining geo- and bioengineering technologies. Produced and flowback water can be cleaned and recycled for reuse after salts, residues and chemicals are removed. Cabral uses a portable closed system for water recycling and, unlike other water processing units, storage tanks, pipelines, facilities and water well injections are not needed. The system allows for readily available water for the next fracking operation as well as easy transportation away from the site. This recycling process prevents the spillage which happens when large amounts of produced water are temporarily stored in surface pits, and avoids water evaporation from open pits, which can affect local air quality. It also means that water is not reinjected into disposal wells, which can have potentially detrimental effects on groundwater quality and which may pressurise sufficiently to cause local earthquakes. Reinjection into disposal wells has been common practice, but migration of the produced water into permeable layers is unproven, and there is not enough data to determine the long-term effects on groundwater.
The oil and gas industry faces an increasing problem with regard to sourcing, moving, and handling large volumes of water. Hydraulic fracturing has created yet another logistical problem on the roads, with trucks carrying sand, chemicals and water moving in and out of drilling sites. Cabral Technology combines an innovative water technology with solving the logistics problem by utilising machine learning and AI technologies to mitigate the risks of accidents on the roads while decreasing the costs to operators. Cabral technology monitors the roads and current operations in real-time using satellite, lidar, real-time road construction and flow stream data to execute and deliver equipment on site in portable systems that can handle and manage the fluids which need to be recycled and reused.
Cabral Technology is a service company in the O&G industry.
