Survey of Microbial Activity in Oil and Gas Produced WatersI. Introduction

A. Purpose of project1. Why chemical and biological monitoring is essential for water treatment systems2. What can be done to make filtration more efficient and less costly

II. Survey of methods used during microbial study A. Trial organization

1. Equipment failure2. Continuous Filtration using both low energy microfiltration and nanofiltration

i. What happens to bacterial levels during treatment ii. What happens to the water chemistry

III. Conclusions

I. IntroductionA. Purpose of project

The removal of hydrocarbons, total dissolved solids (TDS), and total suspended solids (TSS) using current pretreatment procedures is well documented in many studies1. Monitoring bacterial activity however, has not been identified as an important water component to monitor. The purpose of this study therefore, is to evaluate the efficiency of membrane treatment in removing or reducing biological activity in oil field waters. Chemical components related to microbial growth and biological activity will be monitored to determine if membrane treated water could still exhibit bacterial growth during storage or use. Results of the study will be used to plan future field trials of produced water treatment by A&M researchers. 1. Why chemical and biological monitoring is essential for water treatment systems

Current practice does not account for biological activity in operating procedures, and considers only water volume when administering biocides. Treatment of water with biocide and corrosion inhibitors for completion activities is estimated to cost approximately $25,600 per well depending on the quality2. Even after treatment, high levels of equipment failures are still encountered in the field. These failures are attributed to the ineffective dosage of biocides and anti-scaling chemicals3. With these efforts, it is hoped that industry will be made aware of the importance of bacterial concentrations in water and its relation to treatment efficiency.

2. What can be done to make filtration more efficient and less costly

Filtration technology has been tested in past studies as a treatment option to re-use raw produced water. Unfortunately, early filtration technologies were idesigned around municipal and pharmaceutical wastewaters. High levels of dissolved organics, salts, solids, and biological components make treating this type of water a challenge. Addressing this problem, technology developers are

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evaluating the application of a more aggressive pretreatment, which will make chemical biocide and anti-scaling treatments more efficient and cost effective. Pre-treatment procedures are generally focused on removing hydrocarbons, total dissolved solids, and total suspended solids1 Bag and cartridge filters connected in sequence with oil coalescing filters are generally used in most pre-treatment procedures to accomplish removal.

II. Survey of methods used during microbial study A. Trial organization

Trials were broken into three separate experimental filtration runs. Equipment failure trial was used to demonstrate the changes that may occur in water quality during an extended period of stagnancy. All information provided in the report for this run will be identified as “Failure Test”. Trials one and two were designed to demonstrate water quality during nonstop filtration treatment. All information provided in the report for these two runs will be identified as “Trial 1 and Trial 2”.

1. Equipment Failure

Water treatment was started during the morning hours around 9:00AM, and stopped for approximately 1 hour to simulate a minor failure. Treatment was continued after 1 hour downtime and again stopped at 5PM. Microfiltration permeate water was collected, sealed, and stored in a cold room (4ºC) for 4 days. Cold storage was used in an effort to slow bacterial growth to a level that would still allow accurate quantification after storage. The 4 day downtime was intended to simulate a major equipment failure. Microfiltration water permeate water was removed from the cold room and run through the nanofiltration system to determine if nanofiltration was worth pursuing.

2. Continuous Filtration using both low energy microfiltration and nanofiltration Water treatment was started during the morning hours around 9:00AM, and was run continuously until 4:30PM. Again, the purpose of trial 1 and trial 2 was to determine the efficiency of microbial substrate removal in microfiltration and nanofiltration processes.

i. What happens to bacterial levels during treatment

Bacterial levels were quantified using the Bactiquant Meter sold by Mycometer, Inc. Bacterial measurements are based on the metabolism of a substrate molecule linked to a fluorophore. Fluorescence levels measured as the Bactiquant number represent a linear correlation to the amount of metabolically active cells present in solution. Efforts are being made by the company to develop a cell forming unit (CFU) conversion to make reporting bacterial numbers easier for their customers. However, all data collected for this study will be analyzed and described on a biomass basis. Figure 1 below

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shows bacterial activity during the failure test, and both nonstop filtration trials.

MF_Raw_Feed Pretreated MF_Permeate NF_Permeate0.1

1

10

100

1000

10000

100000

1000000

Failure TestTrial 1Trial 2

Bacti

quan

t Val

ue (m

l^-1

)

Figure 1. Biomass levels after treatment with microfiltration and nanofiltration technologies.

Trials 1 and 2 demonstrate good removal of bacterial biomass however, the failure test does not appear have a large effect on the level of biomass. It was

determined that during the 4 days of storage, bacteria present in the permeate due to contamination from environmental factors during the treatment process were able to utilize the nutrients still present in the permeate water. Treatment of the stored permeate water was only able reduce the biomass to a level equivalent to the level present before storage. Overall, the failure test was concluded to be less efficient in removing biomass than trials 1 and 2.

ii. What happens to the water chemistry

Each successive step in the treatment scheme was observed to improve the water quality of the produced water. However, 100% substrate removal was never achieved due to the heavy biological and chemical loads each raw produced water started with. Environmental engineers use pH, dissolved oxygen, conductivity, alkalinity, total hardness, and carbon levels to determine a system’s ability to support life. Figures 2-4 provided below are the figures that displayed the most important findings from the study.

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MF_Raw_Feed

Pretreated

MF_Permeate

NF_Permeate

0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

120.00%

140.00%

Failure Test Total Organic CarbonTrial 1 Total Organic CarbonTrial 2 Total Organic Carbon

% T

otal

Org

anic

Carb

on

Figure 2. Percent removal of total organic carbon after treatment with microfiltration and nanofiltration technologies.

Figure 2 shows that carbon removal was achieved using both microfiltration and nanofiltration technologies. The increase in the carbon content observed from the failure test is evidence of microbial activity during storage. Filtration removes larger humic acid compounds leaving smaller fulvic acids for microbial metabolism. Filtration activity can also aid in carbon compound degradation due to the physical separation mechanism that is occurring.

MF_Raw_Feed Pretreated MF_Permeate NF_Permeate0

10

20

30

40

50

60

70

80

90

100

18.91

0.01

10.02251.925.70

10.051.37 0.04

Trial 1 Total Soluble IronTrial 2 Total Soluble IronTrial 1 Ammonium, Ammonia, Ni-triteTrial 2 Ammonium, Ammonia, Ni-triteSp

ecie

s (m

g/l)

Figure 3. Potential electron donor species present after treatment with microfiltration and nanofiltration technologies.

Figure 3 shows that even after treatment using micro and nanofiltration technologies, potential electron donor species important for microbial growth were still present in permeate waters. Figure 4 below shows that potential

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electron acceptor species important for microbial growth were also still present in treated permeate waters.

MF_Raw_Feed Pretreated MF_Permeate NF_Permeate0

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100

150

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300

0

1

2

3

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0.73 0.73 0.73750.55

0.31 0.33 0.32 0.200.04

3.37

2.332.61

0.040.04 0.04 0.04

2.07

2.72

5.46255.72

0.79

2.97

5.37

Trial 1 ManganeseTrial 2 ManganeseTrial 1 NitrateTrial 2 NitrateTrial 1 Dissolved Oxygen Trial 2 Dissolved Oxygen Trial 1 SulfateTrial 2 Sulfate

Spec

ies (

mg/

l)

Figure 4. Potential electron acceptor species present after treatment with microfiltration and nanofiltration technologies.

III. Conclusions

According to the above findings, it was determined that water intended for re-use in oil and gas operations should be physically and chemically treated in preparation for storage. Neglecting to do this could results in abnormally high souring and corrosion rates. Treatment using a low energy filtration system would reduce microbial biomass and increase the effectiveness of initial biocide treatments.

As mentioned before, microbial substrates were found to still be present at a level that could support opportunistic microbes that may contaminate treated waters during operational use. In order to deter microbial growth, a residual biocide level should be maintained in all stored oil and gas waters intended for re-use in hydraulic fracturing activities.

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i. David B. Burnett, F. M. P., and Carl J. Vavra, Achieving Water Quality Required for Fracturing Gas Shales: Cost Effective Analytic and Treatment Technologies. In SPE International Symposium on Oilfield Chemistry Society of Petroleum Engineers: The Woodlands, TX, USA, 2015; p 17.2. 2015 Well Cost Study Canada, 04/30/2015, 2015; p 70.3. S. Sherman, D. B., and S. Kakadjian, Microbial Influenced Corrosion of Coil Tubing Milling Strings in the Eagle Ford Shale. In International Petroleum Technology Conference Sponsor Society Committees of International Petroleum Technology Conference: Kuala Lumpur, Malaysia, 2014; pp 2-4.