treating flowback water with acid mine drainage (amd) for reuse in shale gas activities

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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

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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.

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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.

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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

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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• 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.

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• 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.

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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.

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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.

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Marcellus shale wells permitted

Acid mine drainage sites in PA

AMD and Marcellus Well Locations

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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.

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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.

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More Information

Project summary and updates at www.netl.doe.gov

[email protected]

412-386-4533

Radisav Vidic

[email protected]

412-624-9870