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a Nalco and the logo are trademarks of Nalco Company

b Ecolab is a trademark of Ecolab USA Inc.

C All other trademarks are the property of their respective owners 

# Opportunities for Treatment and Reuse of Acid Mine Drainage and Produced Water in
Oil and Gas Shale

Timothy S. Keizer and Jason R. Burney Nalco a 

## , An Ecolab Company b 

## 1601 W. Diehl Rd. Naperville, IL 60563, USA

Jarod C. Limke, Joon H. Min, and Young J. Eum BKT Co., Ltd. c 

## 1225 N. Patt St. Anaheim, CA, 92801, USAIWC 12

‐ 69 Keywords: Hydraulic fracturing, membrane, produced water, flowback water, Acid mine drainage, Mine influe nced water, reuse

ABSTRACT

Hydraulic fracturing is a water intensive process that is used to release gas and oil from tight shale formations. The large demand for wate r on a well pad can significantly complicate sourcing and logistics for exploration companies. As such, locating an alternate source of water or reuse of produced water that could be acce ssed on site is very desirable. Acid Mine Drainage (AMD) and some surface waters coul d be accessed on site but can contain high amounts of sulfate, which will have an undesired reaction with Barium and Strontium present in the some shale formations. Likewise, sulfate me tabolized by bacteria could sour the gas. Explorations of non-traditional treat ment methods are being piloted.IWC 12

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INTRODUCTION

Natural gas plays a large role in meeting the energy demands of the United States, supplying around 23 percent of the nation’s energy. (Newell 2010) According to the U.S. Energy Information Administration, in 2009 shale gas represented approximately 14 percent of the U.S. natural gas supply, a number that is expected to grow to 46 percent by 2035. (N ewell 2010) To enable this large growth in shale gas supply, numerous new wells will need to be drilled and stimulated via hydraulic fracturing. Hydraulic fracturing involves pumping a water-sand-chemical mixture into a well at high pressure to fracture the shale formation and allow the natural gas to flow to the wellbore. The water quantities needed for a well stimulation using the slickwater methodology range from 3 to 5 million gallons per well. The extensive water demands present a significant cost to well completions activities. The total cost of procuri ng and transporting the millions of gallons of water to a well site can run well over $1 million per well. Tightening water restrictions in some areas of the U.S. and the exorbitant cost of buying and moving the fracturing water makes the search for easily accessible alternate water sources highly desirable.

A common side effect of sub-surface mining is Acid Mine Drainage (AMD). As the depth of the mine reaches below the water table, ground water seeps into the mine. This water must be removed from the mine-shaft in order for the mine to produce. In abandoned mines, the water is often left unchecked and the mine floods. AMD is highly concentrated with sulfates and metals which oxidize and pollute natural waterways. The Marcellus Shale region is uniquely situated in that a large natural gas bearing shale is located close to numerous abandoned mines, which could present a very attractive source of water. Ideally, a gas company could drill into an abandoned mine full of AMD, pump the water to the surface, treat the water, and use it for fracturing. One hurdle facing the feasibility of using AMD for fracturing in some shale is the high levels of sulfate present in the AMD. In particular the Marcellus Shale formation is rich in Barium and Strontium, which will react with sulfate in AMD and precipitate down hole and plug the well. Likewise, the sulfate may be metabolized and cause potential odor issues. The intent of implementing the anti-fouling system (Park 2010) developed by BKT with various nanofiltration (NF) membranes from commercial suppliers is to give value to this previously unusable water source. (Min 20113) The NF membranes should lower the sulfate levels in the AMD to a point where the treated AMD can be used in completions along with scale inhibitor chemistries. Treated Produced Water (PW) can be reused as fracturing water as long as the hardness, metals , and conductivity thresholds are within reuse limits after treatment. NF membranes are tested to evaluate rejection of the listed parameters in highly saline Marcellus PW.

The unique design of the anti-fouling system should limit the amount of pretreatment needed for the AMD/PW and lower costs.IWC 12

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ACID MINE WATER

The primary goal of the project is to use a NF membrane to remove sulfate (<100 ppm), conductivity, and suspended solids from AMD water.
The results of the membrane selection trials are presented in Table 1. All data were obtained using a constant pressure of 170 PSI (12 kg/cm 2 ) and an average temperature of 80 o F (27 o C).

Table 1. AMD membrane selection results summary

Membrane Sulfate Flux

NF grade Feed Permeate Rej. Average

ppm ppm % GFD (LMH)

A 833 12 98.6 48 (81)

B 562 3 99.5 45 (77)

C 600 300 50 75 (128)

D 613 3 99.5 70 (119)

The results are consistent with the NF manufacturers guidelines; membrane A and B both yielded the highest rejection of monovalent ions (average 45 μ S/cm conductivity), but the lowest flux of 47 Gallons/Ft. 2 /Day [GFD] (79 Liters/M 2 /Hr.[LMH]) average between each membrane.

Membrane C and D both yielded higher average flux (average 73 GFD (125 LMH)) but less rejection of conductivity. Sulfate rejection by membrane D was the highest among the tested membranes. Since membrane C did not reject sulfate below the threshold (100 ppm) it was not considered for further testing. The membrane selected for the feed concentration trial was membrane D due to the highest rejection of sulfate, 99.5%, and flux, 70 GFD (119 LMH).

FEED CONCENTRATION FINDINGS

― The average flux of the AMD using membrane D was 65 GFD (110 LMH) after 92% recovery. The temperature range of the AMD feed water was broad, initially at 72 o F (22 o C) and finishing at 92 o F (34 o C). The increasing flux data shown in Figure 1 (from 0% to 70% recovery) is attributed to the rise in temperature of the feed water. Temperature rise is attributable to energy transfer from the feed pump and high speed vortex generation inside the pilot unit.

Figure 1. Filtering AMD with membrane D: Flux and feed temperature as a function of recovery

After removing 70% of the feed water as permeate, membrane flux began to decline due to TDS (sulfate, suspended solids, salts) buildup in the feed water. Both the rise in temperature and decline in flux are natural occurrences in batch mode filtration processes.

Figure 2 shows the sulfate levels observed in both the feed water and permeate as the batch mode 40 50 60 70 80 90 100 110 120 130 140

0% 20% 40% 60% 80% 100%Flux (LMH) and Temperature(deg F)

Recovery (% water treated) Flux as LMH

Temp as FIWC 12

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concentration progressed. The upper sulfate concentration limit in the composite permeate is 100 ppm. Sulfate rejection was greater than 99% throughout the trial. Likewise, the conductivity in the permeate and feed display a similar trend and is shown in Figure 3.

Figure 2. Sulfate concentration as function of % recovery

The maximum measured sulfate concentration in the permeate was 32 ppm, while the maximum measured sulfate concentration in the concentrated feed water was 14,000
ppm.

Figure 3. Conductivity as a function of % recovery

Because the AMD permeate is to be reused as a product (fracturing water), a high recovery is important to the economics of the project. ACID MINE DRAINAGE WATER QUALITY

― Table 2 contains data obtained from an analytical laboratory. Membrane D shows hardness and sulfate removal rates of >98% and >99%, respectively. Iron and calcium rejection are >99% and >98%, respectively. A significant portion of the measured parameters, including hardness and heavy metals, were measured below 0.01 ppm in the permeate.

Table 2. Filtering AMD with membrane D: Water quality analysis

Metals Initial
AMD
Feed Final
AMD Permeate Final
AMD Concentrate Rejection

ppm ppm ppm %

Ca 230 3.7 1200 98.4

Fe 2.2 <0.02 21 99.1

Mg 60 0.97 570 98.4

Mn 0.3 <0.01 3.5 96.7

K 6.9 1.6 57 76.8

SiO 2 10 8.2 26 18.0

Na 410 100 3300 75.6

Sr 2.5 0.04 17 98.4

Hardness (CaCO 3 ) 820 13 5500 98.4

Figure 4. Feed and permeate samples for AMD pictured 0 4000 8000 12000 16000

0 5 10 15 20 25 30 35

0 20 40 60 80 100Feed (ppm)Permeate (ppm)

Recovery (% water treated) Permeate Sulfate

Feed Sulfate

0 2 4 6 8 10 12 14 16

0% 20% 40% 60% 80% 100%Electrical Conductivity (mS/cm)

Recovery(% water treated) Permeate EC, mS/cm

Feed EC, mS/cm

Feed PermeateIWC 12

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Each membrane tested successfully removed all solids and color (turbidity <<1 NTU), as shown in Figure 4 and 5.

Figure 5. Concentrate and permeate of AMD water in anti-fouling system feed and collection tanks

Concentrated AMD AMD permeate

PRODUCED WATER

The primary goal of the PW project is to use an NF membrane to remove sulfate, hardness, metals, conductivity, and solids from produced water. The sample received was exceptionally difficult to treat using NF membranes. The high conductivity (~50% higher than sea water) gave rise to charge balance phenomena which may explain the flux and rejection data in Table 3. The average flux of the batch was 22 GFD (37 LMH) after an 80% recovery using Membrane C. The turbidity in the composite PW permeate was 0.6 NTU, well below the target value. The temperature r ange was moderate, initially at 77 o F (25 o C) and finishing at 95 o F (35 o C). The conductivity in both the feed tank and permeate remained constant throughout the trial, indicating stable, but low rejection. As shown in Table 3, conductivity rejection averaged 14.4%, which may be attributed to the high concentration of salts in the water. The charge balance (i.e. high osmotic pressure) across the NF membrane is heavily polarized, and thus a viable explanation of the rela tively low flux and low rejection for PW when using an NF membrane. These results are preliminary and may be refined with prolonged testing.

Table 3. Filtering PW with membrane C: Water quality analysis

Ions Initial PW
Feed Final PW Permeate Final PW Concentrate Rejection

ppm ppm ppm %

Ba 2600 1400 4100 46.15

B 21 19 19 9.52

Ca 7700 5800 9400 24.68

Fe 180 61 440 66.11

Li 50 44 43 12.00 Mg 710 440 1200 38.03

Mn 4.2 3.1 6.4 26.19

K 360 310 320 13.89

SiO 2 14 <7.5 47 N/A

Na 24000 21000 23000 12.50

Sr 2000 1100 3200 45.00

Hardness (CaCO 3 ) 22000 16000 29000 27.27

TDS 97000 83000 110000 14.4

EXPERIMENTAL

ANTI-FOULING SYSTEM PILOT TRIAL PROCEDURE - A typical pilot trial procedure is divided into two major tasks: (1) membrane selection and (2) batch mode concentration. For each task, adequately mixed sample was transferred into the feed tank and the system was operated in recirculation mode (retain concentrate in closed loop) as depicted in Figure 6.

MEMBRANE SELECTION

― Determination of the optimal membrane is the most important aspect of the inhouse pilot trial.IWC 12

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Four NF grade membranes were tested using approximately 2.5 gallons of sample each; all permeate was returned to the feed tank to maintain the initial feed concentration. The filtration time for a membrane selection is typically 60-90 minutes which allows adequate time for membrane stabilization and reproducible flux and rejection data.

Figure 6. PFD for anti-fouling system nanofiltration pilot of acid mine drainage

BATCH MODE CONCENTRATION

― The most optimal membrane as determined by the membrane selection process is reused during the batch mode concentration. Approximately 60- 80 liters (16-21 gallons) of sample are transferred into the feed tank. Permeate is continuously removed allowing the concentration of rejected species to increase in the feed tank. Feed concentration time may vary greatly depending on initial feed volume and water quality. Under these conditions, flux typically decreases as the filtration resistance (solids concentration) increases. Feed water temperature will increase due to mechanical energy transfer. The testing parameters used in each trial are summarized in Table 4.

Table 4. Testing conditions for NF membranes with anti-fouling module Pilot Model Anti-fouling system

Membrane Surface
Area 0.94 ft 2 (0.087 m 2 )

Operating Pressure 142 - 170 PSI (10 - 12 kg/cm 2 )
Average Testing Temperature 84 o F (29 o C)

Vortex speed (1) 280 RPM

Note: (1) Vortex speeds differ according to scale-up factor, max industrial model speed is 270 RPM

SUMMARY

The membrane select ed for further study for AMD was membrane D. This membrane yielded the highest rejection and flux among the tested membranes. Membrane D offered an average flux of 65 GFD (110 LMH), 92% recovery, and sufficient sulfate rejection (>99%) during the 510 minute batch mode concentration. Each membrane successfully removed all solids and color (turbidity <<1 NTU) for each batch mode concentration. Preliminary results indicate that AMD permeate from membrane D can be reused as frac water due to 99.5% sulfate rejection (2 ppm in permeate). For the PW membrane C yielded the highest rejection and flux among the tested membranes. Membrane C offered an average flux of 22 GFD (37 LMH) throughout an 80% recovery and low TDS (approximately 14.4%) during the 1020 minute batch mode concentration based on the limited conditions tested. The anti-fouling system industrial unit has 1021 Ft 2 membrane surface thus the unit would have a permeate flux rate of 46 gpm for the AMD and 15.5 gpm for the PW. Future work may include long term pilot testing near production sites whereIWC 12

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treatment options and variables (i.e. different NF membranes, anti-scalant doses) can be evaluated with certainty.IWC 12

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Reference

Min, J. H. et al., “Anti-fouling membr ane system for industrial wastewater treatment and recovery”, International Water Conference, 2011.

Newell, R., “Annual Energy Outlook 2011”, EIA, 2010.

Park, G. T. and Kim, S. W ., “Rotor for generating vortex water flow, and filtering apparatus employing the same”, U. S. Pat ent 7,666,305 B2, 2010.