# Prepared Discussion of : 

# Evaluation of Brackish Groundwater Treatment for Use in Hydraulic Fracturing of the Bakken Play, North Dakota IWC 11

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Discusser: JOHN SCHUBERT, P.E, Senior Process Engineer

HDR Sarasota, Florida

It is often difficult to find real information on unconventional oil and gas water and wastewater issues, as producers have generally been reluctant to publish on this subject in the last few years. Papers like this give interesting insight into the issues surrounding water supply and wastewater treatment in the Bakken play. Part icularly, information on water characteristics and possible treatment methods available is very valuable to those looking for insight or reassurance related to their work in this area. The authors are to be congratulated for presenting valuable information on this timely topic.

The paper presented some background information on the Bakken formation and hydrofracturng practices there. Hydrofracturing water requirements were identified as 840,000 to 5,000,000 gallons per well. The upper values correspond to those seen in the Marcellus play among others, and seem reasonable. As a point of comparison, in the Marcellus play, it would be very rare to have water consumption at the low end of this scale. The authors indicate that initially they considered flowback treatment for recycle, but the high costs of thermal treatment and limited recovery eliminated that option. It woul d be interesting to see more information to support this conclusion.

In comparison, in a number of plays, treatment for recycle in hydrofracturing is a common practice, and involves removal of troublesome ions and compounds for the hydrofracturing process. The typical focus of producers from my experience are concerns related to (1) eliminating damage to the formation/yield from wastewater scaling components, and (2) interference with the chemical packages used in hydrofracturing, particularly friction reducers. However, 10% sodium chloride with lesser amounts of other ions is commonly acceptable for reuse by many producers, diluted with fresh makeup water to achieve a lower, but still significant TDS level. Some friction reducers can even tolerate NaCl levels as high as 10%, although there is a cost penalty on the chemical si de for this. Was any consideration given to this approach in the Bakken play ? This approach could supplement fresh water supplies and reduce overall water supply costs, as well as reducing or eliminating disposal costs.It appears that the normal method of disposal for frac flowback water in the Bakken play is deep well disposal. Is that common to many producers, and how would the costs of that approach compare with the cost of limited treatm ent and recycle of frac flowback water ?

Related to the pilot system operation, the description of the pretreatment processes in the paper was limited. Can the authors provide a description of the specific unit operations conducted in pretreatment ? It appears that while high in soluble salts, the water source is relatively low in scaling compounds and should not require excessive pretreatment. The implication in the paper is that filtration and scale inhibiters were the only pretreatment provided. It would be of interest to understand the type of filtration provided and particle size removal goals for it, and the objectives for scale inhibition in terms of the anticipated scaling products.

Can the authors supply any information on the configuration of the RO used ? In order to compare the performance of this system to other RO systems used on brackish water applications, it would be useful to identify the number of membranes, types of membranes and number of stages in the pilot system.

Since the pilot system was operated for a substantial period of time, is there data available that documents the performance of the system over time. Was there information collected daily for conductivity or some other gross measure of RO performance that allowed the pilot operator to understand that the RO membranes were intact and functioning ? Was there additional routine sampling conducted on a weekly or monthly basis to verify the level of performance. It would be unusual for anyone to make a decision to install a full scale facility based on one set of samples.

What is the planned disposition of the RO reject ?

One final point for discussion. The water supplie to and treated by the pilot RO had a TDS level of under 1%, neutral pH, and no appreciable amounts of scaling constituents. While this might not be attractive as drinking water, it would seem to be ideal as a source of water for hydrofracturing with little or no pretreatment and without an RO system. What is the perceived benefit to producers of RO product water from this source versus using this water straight out of the well ? At the very least, there would be a cost advantage to not having to install and operate a treatment system, and the cost of disp osal of the RO concentrate would also be

eliminated.

For those that have worked with frac flowback and produced water in one or more plays other than the Bakken, it is always interesting to observe the differences in the nature of the problems associated with water supply and wastewater disposition. While a number of questions can be (or have been) raised from this paper, the basic information presented provides some insight into the water supply and disposal issues in the Bakken play. Again, the authors’ efforts in this area are appreciated.