Friday, 13 September 2013

Produced water disposal - a comparison with the conventional industry

A typical fracture stimulation stage requires approximately 1 million gallons of water. Depending on the specific site, you would expect between 25 - 75% of this fluid to return to the surface in the days following the frack. The fluid that comes back is called "flowback".

The injected fluid may contain about 1% chemical additive. The two principal additives tend to be friction reducers (which reduce the energy needed to pump the water) like polyacrimide (found in many cosmetic products) and thickeners (to help the fluid carry proppant) like guar gum (found in many food products). Cuadrilla have listed their ingredients here.

In addition, during its brief sojourn underground, the injected fluid can pick up additional material from the shale rock, including naturally occurring radioactive material (so-called NORM) and other minerals. Therefore, these fluids need to be treated before they can be safely returned to the water system.

The need to dispose of produced water is not a new problem for the oil industry. In most conventional hydrocarbon reservoirs, there is a certain amount of water trapped along with the oil. As the oil is produced, so is the water. As the field gets older, and most of the oil is gone, more and more water is produced alongside the remaining oil, and the "water cut" (the percentage of water produced alongside the oil) can be as high as 90% (i.e. 90% of the fluid produced from the reservoir is water, not oil).

As is the case with water injected for fracking, this water will have been in contact with the hydrocarbon reservoir, in this case for millions of years, rather than a few days. Therefore it may be highly saline, and it may contain NORM. This water, when produced, has to be dealt with.

A recurring theme in many of my posts is that what is proposed for UK shale extraction does not differ hugely from conventional operations, and also that we have a successful onshore industry with an excellent track record of minimising its environmental impact.

To make this point again, this time with respect to dealing with water produced from oil and gas wells, the table below lists the volumes of water (in barrels) produced from onshore UK oil and gas fields in 2012.
In total, over 73 million barrels of water are produced from onshore UK wells every year. The majority of this comes from the Wytch Farm oil field. Some of this water is re-injected into the reservoir to help force out more oil (approx 5 million barrels at Wytch Farm) but typically it is treated, and then, once clean it's discharged into the sea.

The larger UK offshore industry has to deal with an eye-watering (excuse the pun) 1.5 billion barrels of produced water every year!

A typical hydraulic fracture stimulation will use approximately 1 - 5,000 cubic meters (200,000 - 1,000,000 gallons) of water, or 6,000 - 30,000 barrels. Assuming that 50% returns to surface, that's 3,000 - 15,000 barrels of water to be processed for each frack stage.

This, again, is where comparisons with the conventional industry become pertinent - the current UK onshore industry has to deal with 73,000,000 barrels of produced water every year. It would take thousands of frack stages every year just to to match that rate. As an unnamed onshore operator commented to me recently (my emphases): "most people don't realise that all oil and gas wells produce water, more water than oil, and we have been dealing with it since way before shale gas. It is a lot of water. Can't blame the UK water on fracs!".

I'm not a chemist, so I'm not really up to speed with the details of how produced water is processed. I had an anonymous commenter on this post who seemed to really know his stuff. However, the best place to find out would be from the guys who are doing it, such as Lee Petts from Remsol, who has blogged about the issue here.  


  1. The eco-greenies like to use large numbers because it scares their simple minded followers. But put the amount of water into context and it's not so scary. 2.5mL is the amount of water in a swimming pool. So a typical well might use the equivalent of only a few leisure centre pools worth of water.

    The other way of fighting their massive scary figures is with scary figures too. For instance, the amount of water wasted in leaks every day is more than used in all the wells in a year.

  2. It was interesting to note how the issue was covered by Water UK (water industry body). The actual speech was pretty reasonable yet even Water UK's own press release was all "warned" and "risks".

    1. Hi Anonymous,
      I had the pleasure of being in the audience for this speech at UK Shale 2013. Several people sat near to me thought the speech was poor and error strewn. A case in point being the incorrect assumption that a site would need 20ML/day, and therefore that every site would need a 30cm gauge pipe to supply this.

      20ML/day may be the peak pump rate during a stimulation, but this is only for a short period of time. The company can fill up its tanks with water over a much longer time, at a slower rate, prior to using it all in one go during the frack. This is what Cuadrilla have done on the Fylde - as far as I'm aware they are supplied with a typical mains supply. Overall, the speech came of as very poorly researched.

      In contrast, United Utilities, the water company in the NW, are very happy to be working with Cuadrilla - potentially even allowing shale gas drilling on its land. Hardly the picture of a water company worried by shale:

      Some cynics on my table at the UK Shale meeting suggested that Water UK's 'concern' owes more to political positioning prior to next year's Ofwat negotiations that will set water prices for the next 5 years:

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  4. Water utilization worldwide is generally split,with 70% agricultural utilize,22% industrial use, and 8% domestic use (UNESCO 2003).A fifth of the population lives in areas of water shortage, and one in eight needs access to clean water.As of now,appropriately treated produced water can be recycled and utilized for water-flooding [produced water re-injection (PWRI)] and different applications,for example,crop irrigation,wildlife and domesticated animals utilization,aquaculture and hydroponic vegetable society,industrial procedures,dust control,vehicle and hardware washing,power generation, and fire control (Veil et al. 2004).

    Jessica Glenn.