Sandra McSurdy, U.S. Department of Energy (DOE), ”Treating Flowback Water with Acid Mine Drainage (AMD) for Reuse in Shale Gas Activities” Researchers at the University of Pittsburgh and the U. S. DOE are developing a treatment for flowback water utilizing AMD. Treating and reusing flowback water on-site will reduce the amount of freshwater needed and the amount of wastewater that needs to be hauled by truck. Sulfate removal tests were performed on flowback and AMD water mixtures with a goal to achieve a final sulfate concentration of less than 100 mg/L for reuse.

1. ‹#›
Treating Flowback Water with AMD
for Reuse in
Shale Gas Activities
Sandra McSurdy
Physical Scientist, U.S. Department of Energy
National Energy Technology Laboratory, Pittsburgh, PA
Research performed under DOE funded project DE-FE0000975 by
Dr. Radisav Vidic, University of Pittsburgh, Pittsburgh, PA

2. ‹#›
Marcellus Shale Activities in Pennsylvania
• Hydraulic fracturing is utilized to
recover natural gas from the
Marcellus shale.
• A single well can require one to five
million gallons of water.
• Water needed for frac jobs - 40%
from public water supplies, 60%
comes from surface waters (rivers).
• 15% to 40% of injected water
recovered during flowback.

3. ‹#›
Marcellus Shale Activities in Pennsylvania
• Marcellus flowback water typically contains high levels of total
dissolved solids (TDS) ranging from 70,000 to 250,000 mg/L.
• Flowback water must be treated before being reused or
discharged to streams.
• Flowback can be reinjected into the well but high levels of
metals (Ba, Sr, Ca) can result in precipitation.
• Most flowback and produced water is hauled by truck to OH.
• Increased truck traffic is a large problem for congestion, road
safety and road wear.

4. ‹#›
Using AMD as Makeup Water
• Consider AMD for use as make-up
water at well sites in order to
reduce the amount of freshwater
needed and lower the associated
transportation costs.
• Remove barium, strontium and
calcium from flowback water with
sulfate and carbonate ions that are
often found in AMD in order to
prevent precipitation in the wells.
• Develop a treatment in which
flowback water is economically
treated on site and reused to frac
adjacent wells

5. ‹#›
Flowback Treatability Studies
• Barium, strontium and calcium can be removed from flowback water
when it is mixed with sulfate and carbonate ions that are often
found in AMD.
• Sulfate was shown to be an excellent removal reagent for barium
but very high concentrations of sulfate are needed in order to
remove strontium
• The presence of calcium ions was found to limit the removal of
strontium.
• Barium removal is mainly affected by the sulfate addition, while
calcium, strontium, and magnesium were more sensitive to
carbonate.

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Mixing AMD and Flowback
Removal of constituents after mixing flowback water and AMD
at different ratios.

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Treatment Experiments
Sulfate removal tests were performed on Marcellus flowback
and local AMD water mixtures with a goal to achieve a final
sulfate concentration of less than 100 mg/L for reuse by E&P
companies.

8. ‹#›
Membrane System Testing
• Membrane filtration was evaluated for the separation of
precipitates in AMD and flowback water mixtures.
• The presence of sub-micron particles in flowback water
resulted in severe membrane. These particles may have sizes
similar to the membrane pore size.
• Even under low trans-membrane pressure and medium to high
cross flow velocity, the membrane performance in terms of
permeate flux is very poor.

9. ‹#›
Membrane System Testing
• Neither barite nor calcite crystals that formed during the mixing
of the AMD and flowback water are responsible for the fouling.
• Organic matter present in the flowback appears to be the main
fouling agent.
• It was difficult to remove the foulant from the membrane
readily.
• Pretreatment of mixture by coagulation and chemical oxidation
can improve the performance of membrane.

10. ‹#›
Conventional Treatment Test Results
• The optimized conventional coagulation process for the
removal of barite formed after mixing of flowback water and
AMD includes both rapid mixing and slow mixing followed by
settling time.
• The optimal pH for this process is between 6 and 6.5 for the
waters tested.
• A clarifier will be used to remove solids.
• Based on lab experiments and modeling, it was found that the
final sulfate concentration levels in treated water are dependent
on the barium content in the flowback water as well as the
mixing ratio of flowback water to AMD.

11. ‹#›
Ballasted-sand Flocculation Test Results
• The footprint for a ballasted-sand flocculation is smaller than
conventional treatment systems.
• Anionic flocculant aids performed better than cationic aids.
• Contact time between the flowback water and AMD is only 10
minutes for ballasted flocculation versus 60 minutes for
conventional treatment.
• No need for pre-mixing in the ballasted flocculation treatment
process as barite precipitation was more than 90% complete in
the first 10 minutes of water mixing.
• The effluent quality from the conventional and ballasted
flocculation processes were of comparable quality.

12. ‹#›

13. ‹#›
Treatment Test Results
• The co-treatment of Marcellus Shale produced water and AMD
starts by characterizing the quality of both water sources.
• The blend ratio of flowback water and AMD is dependent upon
[Ba]/[SO4] mass ratio in the mixture and the desired final
sulfate concentration the finished water.
• Conventional coagulation/flocculation process is optimized
based on the coagulant dosage, pH and mixing conditions.
Microsand and flocculant aid can also be added.
• A clarifier will be used to separate solids with a fraction of the
solids recycling back to the reactor to provide barite crystal
seed and accelerate barium sulfate precipitation.
• The remaining precipitate will be dewatered for disposal.
Clarified effluent will be stored in surface impoundments or
storage tanks for subsequent hydrofracturing operations.

14. ‹#›
Barium Sulfate Affinity Tests
•Initial experiments revealed that small BaSO4 particles are
captured by the sand which causes an increase in pressure and
a decrease in permeability.
• When barite moves through sand proppant, its fate and
transport are determined by the flow velocity, barite particle size
and fluid viscosity.
•Minimum flow velocity can be determined in order to prevent
attachment of barite particles to the steel pipe surface.

15. ‹#›
Barium Sulfate Affinity Tests
•Bench-scale
experiments in a
recirculating system
were conducted to
validate theoretical
calculations.
•Results show that the
increase in flow
velocity leads to less
scaling.
•Higher temperature
would result in more
scaling.

16. ‹#›
Barium Sulfate Affinity Tests

17. ‹#›
Barium Sulfate Affinity Tests
•Many more questions need to be answered about how much
barium sulfate forms when the waters are mixed and how the
solid may precipitate either on the sides of the pipes or as plugs.
• The big question is if it affects gas recovery rates but that is
not known at this time.

18. ‹#›
Field Test Plans
• Dr. Vidic has several industry partners with availability to
flowback/produced water supplies, acid mine drainage sources
and water treatment systems.
• Possible sites include AMD treatment facility where flowback
can be hauled to the site.
• Need to locate sources of AMD bases on geography and water
quality.

19. ‹#›
PA AMD Database
• An AMD database has been created and includes flow rates and
chemical analyses for 242 sites over time.
• For the reclaimed sites, water analyses before and after
treatment are included in the database
• Users can search for AMD sites based on desired flow rates,
chemical analyses and location with search results being
displayed on a map.
• Database not yet public – researchers willing to make public.

20. ‹#›
Marcellus shale wells permitted
Acid mine drainage sites in PA
AMD and Marcellus Well Locations

21. ‹#›
Current Status
• Field treatment system was delayed in 2012 due to Federal
budget cuts across government.
• Researchers have identified several locations and treatment
systems available for field test in 2013.
• Field system is scheduled to operate for 3-4 weeks.

22. ‹#›
Research Implications
• Help outline water reuse guidelines for Marcellus frac jobs in
PA.
• Increase the use of AMD and define the successful parameters
of flowback treatment with AMD.
• Devise approaches to reduce the amount of freshwater needed
for Marcellus Shale development and minimize the disposal
liability and costs associated with new well drilling.
• Continue partnerships with oil and gas industry and AMD
treatment partners so symbiotic use can continue to develop.

23. ‹#›
More Information
Project summary and updates at www.netl.doe.gov
sandra.mcsurdy@netl.doe.gov
412-386-4533
Radisav Vidic
vidic@pitt.edu
412-624-9870