Evaluation of Abandoned Mine Drainage as a water supply for hydraulic fracturing

Transcription

1 Evaluation of Abandoned Mine Drainage as a water supply for hydraulic fracturing E. Barbot, M. Li, K. Gregory, R. Vidic University of Pittsburgh Carnegie Mellon University Project funded by the US Department of Energy, National Energy Technology Laboratory civil and environmental engineering 1

2 Water Supply Issues Hydrofracturing one well = 2 to 6 Million gallons of water Surface Water Withdrawals Concerns about depletion of water resources, especially in drought years Impacts to aquatic life Ability to get withdrawals approved Transportation of water 1 MG = 200 trucks Cost can be significant ($0.1/bbl to $2/bbl) Water storage on site civil and environmental engineering 2

3 Fracturing fluid composition Proppant 8.96% Water 90.6% Other 0.44% Flowback water Chemicals added Friction reducer: reduce the pumping cost (polymer) Acid: clean the wellbore Antiscalant: limit precipitation and scaling Biocides: limit bacteriological growth (glutaraldehyde) civil and environmental engineering

4 Flowback Water Quantity vs. Time Five wells connected Volume injected = 18 million gallons (average 3.6 million per well) Flowrate (bbl/day) 16,000 14,000 12,000 10,000 8,000 6,000 4,000 2, Date and time Recovery (%) Very low recovery 8 15% after 20 days civil and environmental engineering

5 Flowback Water characteristics Constituent Concentration (mg/l) TDS 17, ,000 TSS Alkalinity ph High variability in quantity and quality due to location and time Constituent Concentration (mg/l) Cl 10, ,100 Na 2,789 46,260 Ca ,612 Mg Ba Sr Fe (total) SO civil and environmental engineering 5

6 Flowback Water Quality vs. Time 200, , ,000 Partly flowback water reuse 140,000 TDS (mg/l) 120, ,000 80,000 60,000 40,000 20,000 Close location Drinking water Site A Site B2 Site B Days after hydraulic fracturing Regular TDS increase civil and environmental engineering 6

7 Flowback Water Quality vs. Time Concentration (mg/l) 100,000 80,000 60,000 40,000 20,000 0 Cl Na Concentration (mg/l) 6,000 4,000 2,000 0 Ca Ba Sr Mg Days after hydrofracturing Days after hydrofracturing Alkalinity (mg/l as CaCO3) Days after hydraulic fracturing ph civil and environmental engineering 7

8 Flowback Water Management Waste disposal - Evaporation in pits/ponds - Injection/disposal wells - Discharge to POTWs Direct reuse for fracing Dilution / Treatment for surface discharge (TDS limit = 500 mg/l) civil and environmental engineering 8

9 Treatment Options for disposal Technology Maximum Feed TDS (mg/l) Energy Use (kwh/100 bbl) Capacitive Deionization 5, Electrodialysis 40,000 - Reverse osmosis 35, Evaporation 100, Membrane distillation 250, Crystallizer 300, Only sustainable solution: treat the flowback water and reuse it to fracture subsequent wells civil and environmental engineering 9

10 One approach to a dual problem 1. How to supply the well sites with water? 2. What are the management options for the flowback water? Flowback water Abandonned mine drainage (AMD) Hydraulic fracturing civil and environmental engineering

11 civil and environmental engineering 11 Drilling sites and AMD locations in PA Marcellus permitted well sites (07/26/10) AMD sites

12 civil and environmental engineering 12 Fracturing fluid requirements Constituent Effect ph Biocides work best below ph 7 Chloride Calcium, Magnesium, Barium, Strontium, Carbonate and Sulfate Iron Suspended solids Bacteria (APB, SRB) Increase demand for friction reducers and scale inhibitors Scaling Risk of well plugging (iron hydroxide) Still controversial Well souring Major constituents to remove: Barium, sulfate, iron, calcium (?)

13 AMD water chemistry Site A Site B Site C Site D Site E ph Alkalinity (mg/l as CaCO 3 ) SO Fe TDS Criteria - Location - Large flowrate - ph circumneutral - Varying concentrations of sulfate and iron civil and environmental engineering

14 civil and environmental engineering 14 Mixing AMD and Flowback water Aim: Assess the compatibility between flowback water and AMD Mixing with AMD will induce metal precipitation - Determination of the mix composition - Reaction kinetics - Precipitate characteristics Water softening by mixing with carbonate (Ca precipitation) Impacts of iron concentration Solids removal processes (settling, microfiltration) Comparison with theoretical calculations

15 civil and environmental engineering 15 Mixing step Flowback water composite: mix of samples from different days (composition dictated by the flowrate profile) Concentration (mg/l) Flowback water AMD Chloride 92, Sulfate Sodium 31, Calcium 15, Magnesium 1, Barium 236 ND Strontium 1,799 3 Alkalinity ph

16 Quality of Mixed AMD and Flowback water: theoretical results civil and environmental engineering 16 Expected outcomes of the blending: - Precipitation of insoluble barium sulfate - Precipitation of strontium sulfate - Precipitation of calcium and strontium carbonate if AMD contains alkalinity Barium Concentration (mg/l) Dilution only Dilution and reaction Mixing ratio to account for the 85% water loss 1:1 1:3 1:5 1:7 Flowback:AMD volume ratio

17 Quality of Mixed AMD and Flowback water SO4 concentration (mg/l) Dilution only Dilution and reaction 0 1:1 1:3 1:5 1:7 Flowback:AMD volume ratio Sr concentration (mg/l) 1:1 1:3 1:5 1:7 civil and environmental Flowback:AMD volume engineering ratio Dilution only Dilution and reaction

18 Crystal growth and composition Crystal composition after 30 min: Ba 0.75 Sr 0.25 SO 4 civil and environmental engineering

19 Crystal growth and composition 3 hr 5 hr Presence of calcite CaCO 3 Size increases with time 24 hr civil and environmental engineering

20 Conclusions AMD is a possible source of water for hydraulic fracturing Possibility of total barium removal by mixing AMD and flowback water without ph adjustment or chemical addition Strontium co-precipitates with barium to form Ba 0.75 Sr 0.25 SO 4 Particle size > 1µm, easily removable by microfiltration As is, process only viable if mixing performed directly in an impoundment (long retention time needed) Need for further chemical addition (bicarbonate) to remove calcium Potential need for further treatment to remove sulfate civil and environmental engineering

21 Acknowledgements Department of Energy and National Energy and Technology Laboratory Mary Kate Henrikson, Emma Wolff Gas developers companies Site completion managers and operators Hedin Environmental civil and environmental engineering