Chapter 5
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Total Water Cycle Management for Hydraulic Fracturing in Shale Gas Production Edwin Piñero* Senior Vice President for Sustainability and Public Affairs, Veolia North America, 200 East Randolph Street, Suite 7900, Chicago, Illinois 60601, United States *E-mail:
[email protected] As the number of shale gas fracturing operations increase, more water is being extracted from already strained water supplies. Disposal options for the higher TDS wastewater generated from both fracturing wells and producing wells are also becoming limited and less economical. Therefore, managing flowback and produced waters must recognize the unique situations in each region by maximizing the combination of technology, process, and management to get the best results that address those long term sustainability factors. Available treatment capacity will require a comprehensive water treatment strategy to address these challenges for future growth in the industry. The strategy must address any combination of: llimited alternatives to treat high TDS flowback and produced water; removal of free oil and grease; reducing overall waste volume; limited water re-use; and management of the entire water cycle. This paper discusses key steps in devising a treatment strategy.
Hydraulic fracturing is a topic that relatively recently has been in the forefront of the energy discussion. The significant growth of shale gas development as a source of energy, and advancement in approaches such as directional drilling, have prompted much discussion and action in terms of technology, operations, policy and regulation, and fundamental public debate. Interestingly however, this process of enhanced recovery of hydrocarbons from relatively tight formations is not new. Oil and gas production has used hydraulic fracturing and directional drilling for © 2015 American Chemical Society In Hydraulic Fracturing: Environmental Issues; Drogos, Donna L.; ACS Symposium Series; American Chemical Society: Washington, DC, 2015.
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decades. The resulting expansion of this recovery approach throughout the United States and elsewhere has raised public awareness and concern over the possible impact to water resources. There are many elements associated with shale gas production, including hydraulic fracturing, that have prompted discussion, and in many cases debate. This paper will focus on one element- the management of the water use cycle associated with hydraulic fracturing. As with many energy source development situations, dealing with water can be significant, and almost as important as the hydrocarbon resource itself. Even focusing on water, there are many aspects involved. It is important to distinguish water issues that are typical of any oil and gas operation, even if hydraulic fracturing is not involved, and even if shale gas itself is not involved. These include contaminant releases to surface water from well pad operations; sediment and erosion issues from site operations and related transportation (such as truck traffic). There are also water-related issues associated with the hydraulic fracturing process, but more a function of other activities. A good example of this is cross-contamination of aquifers during hydraulic fracturing, but not due to the hydraulic fracturing process itself, but due to poor well construction and/or poor understanding of the local geology. Herein we will focus on the water cycle focused on the water supply to serve as the hydraulic fracturing fluid medium, and management and treatment of the flowback water from the hydraulically fractured wells. Even within this relatively limited scope, we must deal with items such as: • • • • • • •
Availability of water to be used to prepare the fracturing fluids Transport logistics and costs of raw water and flowback water needing treatment Solid waste management of sludges resulting from treatment of flowback water Overall logistical issues such as remote and decentralized locations, storage restraints, limited in-place infrastructure (pipelines) Regulatory issues Ultimate disposal options for treated water Treatment options that are adaptable to variable conditions and settings
One must not look at this list as having single answers for each one. The truth about water cycle management is that all of these listed elements are very situationand location-specific. There is no single solution for the storage issue, for example. But on the positive side, these elements all lead to the need for cost-effective solutions that address the quantity and quality aspects of water related to hydraulic fracturing. It is important to realize the distinction between players in this process. Typically, the energy resource producer (the “oil company”) will manage the well site selection and drilling specifics, but contract others to actually do the hydraulic fracturing, and possibly yet another contractor to manage the water aspects. This paper is written from the perspective of the water management service provider. Water cycle management includes three basic phases: providing the water to be used for hydraulic fracturing; collection of resulting flowback water; and treatment and disposition of the flowback water. As a result, there are many 130 In Hydraulic Fracturing: Environmental Issues; Drogos, Donna L.; ACS Symposium Series; American Chemical Society: Washington, DC, 2015.
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opportunities to take innovative approaches to improve and enhance hydraulic fracturing-related water cycle management. Although these steps can be addressed as separate activities, we contend that the more preferred approach is to look at the entire water cycle holistically and look for synergies between the steps. At each of these steps, there are quantity as well as quality issues. For quantity, the issue could be ensuring there is enough water to prepare the fracturing fluids, and proper procedures in place to handle the produced water coming from the operation. For quality, it is not only the more commonly discussed quality of flowback water quality, but also the quality if the incoming raw water. The quality of the raw water is important to control to ensure that the chemical mix ensures an effective fracturing fluid. For both quality and quantity, sustainable solutions must include environmental and resource considerations; as well as economic and quality of life aspects. In other words, sustainable solutions should include consideration of environmental, economic, and social aspects. This paper mentions both hydraulic fracturing fluid and flowback water. It is appropriate to make the distinction at this point. The fracturing fluid is the mixture used by the producer or hydraulic fracturing contractor to inject into the well to fracture the formation. This mixture is typically over 90% water, 9% sand (as a propant) and approximately 1% of a mixture of chemicals needed to effectively fracture the formation and hold it open for gas to flow, without adversely reacting with the formation itself. For the fracturing fluid, the water must be of suitable quality to not adversely interact with the hydraulic fracturing chemicals and additives, and of course there must be enough water. The amount of water needed to hydraulically fracture a well is widely variable, and can range from less than a million gallons, to over five million gallons per well. Availability of such raw water is a crucial element of the water cycle management. For the water management however, the more important fluid is the flowback water. Once the fracturing fluid is injected into the well, its character changes and the resulting flowback water is of different character. Flowback water is the encompassing term for the water that comes back from the well after the fracturing injection pressure is released, and the well begins to flow. Because of immediate mixing with formation water, the character, volume, and chemistry of the fracturing fluid changes. In terms of treating the water, it is the volume and quality of the flowback water that is the more important issue. Flowback water chemistry typically includes some of the hydraulic fracturing additives, but also inputs from the formation itself. These compounds include salts, metals, organic compounds, and in some cases, naturally occurring radioactive materials. It is possible that the hydraulic fracturing additives react with the formation chemistry to produce yet other compounds that must be addressed. Flowback volumes are highly variable in that many oil and gas producing formations also produce copious amounts of water. It is possible to recover millions of gallons more water as flowback water than were originally injected into the well. Understanding these aspects and nuances of flowback water from hydraulic fracturing operations lead to opportunities for preferred solutions. In regard to quality, one approach is to apply the “fit for use” concept. This means that water treatment quality targets should be a function of intended disposition. Traditional 131 In Hydraulic Fracturing: Environmental Issues; Drogos, Donna L.; ACS Symposium Series; American Chemical Society: Washington, DC, 2015.
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approaches would treat to discharge permit quality levels, or to levels suitable for deep well injection. However, one way to reduce the cost and technical hurdles of treatment, and at the same time partially address the available quantity issue, is to treat the water to levels suitable for reuse. For operational purposes, Veolia defines three levels of treatment from which to choose in order to specify the optimal technology choice. Level I is minimal treatment, where the only treatment may involve physical treatment and total suspended solids removal. Depending on the reuse intent, such as for hydraulically fracturing another well, such treatment may be sufficient. However, if additional treatment is needed, one can go to Level II, which also includes specific ion removal. This level would be needed to ensure no adverse interaction between reused water chemistry and either fracturing fluid and/or formation water chemistry. The third and most involved and expensive level is Level III, which treats to discharge permit limits. Specific limits for Level III would be a function of the receiving water body, and would be reflected in any permits. Level III treatment typically may include thermal (evaporation and crystallization) for high total dissolved solids (TDS) levels; or membrane technology for lower TDS levels. The technology for such treatment levels exist. What leads to the best option takes into consideration the flowback volumes (total and rate) and site specific logistics. In other words, what are the local logistics. On the one extreme, examples exist in the Marcellus area of Pennsylvania where modular treatment units are necessary because of the isolated and decentralized nature of well locations. These treatment options are capable of rapid and simple mobilization/demobilization, but also able to handle high flow rates (over 10,000 barrels per day) and get levels suitable for water reuse. If cost effective transportation or storage of treated water for reuse is not practical or economical, these technologies can also treat water to Level III discharge limits. At the other extreme is an example from San Ardo, California where there is a high density of production, resulting in an opportunity to manage large volumes of water and for installation of more permanent infrastructure. The San Ardo case, although not directly involving fracturing water, does handle large amounts of formation water. San Ardo is also unique in that the treatment process not only effectively and sustainably treats the water, but also actually results in a net positive for the local water resource. First, some of the treated water from the formation is used to generate steam. The steam is used to inject into the formation to reduce the viscosity of the hydrocarbons to facilitate recovery. Rather than having to use freshwater from the local ecosystem, the steam demand is partially made up by reused formation water. Secondly, the excess treated water not used for steam is released into the local waterway. Because this is a relatively arid area with low flows, especially during drought, the treatment operation actually improves the local water balance. The San Ardo facility is able to provide 70,000 barrels of water per day for steam generation, and another 50,000 barrels per day as surface discharge. The water quality is so pure from the treatment process that it must be re-mineralized before surface discharge. One other attribute of this facility is that the recovered oily waste can be included with crude oil production of the local fields. 132 In Hydraulic Fracturing: Environmental Issues; Drogos, Donna L.; ACS Symposium Series; American Chemical Society: Washington, DC, 2015.
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As we see from these cases, a total water cycle management approach allows for integrating quality and quantity aspects to come up with more effective and efficient solutions. We see from the examples that treating water from hydraulic fracturing operations is already very possible; yet processes and technologies continue to improve. At the core is the ability to reuse the treated water. If this treatment can be coupled with innovative approaches to deal with the logistical challenges, hydraulic fracturing process water management will not be a hindrance to shale gas development. Mobile treatment units, high flow rate treatment technologies, and larger geographic scale water management can offer solutions to the physical challenges posed by current hydraulic fracturing operations in less mature areas in regard to oil and gas production infrastructure. Having the ability to address the whole life cycle, and coordinate among production sites is the preferred solution. The next big leap will not be incremental improvements in how we handle each individual step of the cycle, but how we integrate it all together to choose the best treatment option for the situation at hand. Leveraging innovative options that support reuse provide both quality and quantity answers.
133 In Hydraulic Fracturing: Environmental Issues; Drogos, Donna L.; ACS Symposium Series; American Chemical Society: Washington, DC, 2015.
