Paper No. 2748 - KPC publis… · Figure 1. Process Flow Diagram (PFD) of a Typical Crude Processing Facility (Gathering Centre). ©2013 by NACE International. Requests for permission

SOME EMPIRICAL OBSERVATIONS ABOUT BACTERIA PROLIFERATION AND CORROSION DAMAGE MORPHOLOGY IN KUWAIT OILFIELD WATERS

Abdul Razzaq Al-Shamari

TPL Specialist, Inspection & Corrosion Team Kuwait Oil Company, Ahmadi, Kuwait

Abdul Wahab Al-Mithin TL (S&E), Inspection & Corrosion Team,

Kuwait Oil Company, Ahmadi, Kuwait

Surya Prakash Sp Corr Eng, Inspection & Corrosion Team,

Kuwait Oil Company, Ahmadi, Kuwait

Moavin Islam Project Director, KOC ICMS Contract

Corrpro Companies, Inc., Ahmadi, Kuwait

Allen J. Biedermann Senior Engineer, KOC ICMS Contract


Ashok Mathew Corrosion Chemist, KOC ICMS Contract


ABSTRACT

It is well known that certain types of bacteria can cause microbiologically influenced corrosion (MIC) failures in pipelines and process equipment particularly in the oil and gas industry. A number of different types of bacteria strains have been implicated in the MIC process. Of these, the SRB (Sulfate Reducing Bacteria) strain is the best known and is perhaps the first to be implicated in the MIC process. The morphology of corrosion damage associated with SRB is often characterized by deep terraced pits. Strong evidence of planktonic and sessile bacterial proliferation, consisting of SRB, GAnB (General Anaerobic Bacteria) and GAB (General Aerobic Bacteria), in brackish water and effluent water systems in various Kuwait Oil Company (KOC) facilities, have been gathered during routine fluid sampling and corrosion monitoring services conducted over the last several years. Severe MIC attack on coupons has been observed and some equipment failures due to MIC have also been encountered. The corrosion morphology observed is typical of SRB attack. Effluent waters in some KOC facilities are very high in total dissolved solids (TDS) content, exceeding 200,000 mg/l and SRB counts in such waters have been found to be very low. However, the GAnB counts are high. Severe corrosion on coupon samples have been encountered in these high TDS waters and the corrosion morphology is very similar to SRB induced attack even though little or no SRB is detected. The present paper discusses these unique observations. Key words: Microbiologically Influenced Corrosion (MIC), Corrosion Morphology, SRB, GAnB

©2013 by NACE International.Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing toNACE International, Publications Division, 1440 South Creek Drive, Houston, Texas 77084.The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association.

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Paper No.

2748

INTRODUCTION It is well known that certain types of bacteria can cause microbiologically influenced corrosion (MIC) failures in pipelines and process equipment particularly in the oil and gas industry. In order for MIC problems to occur, the environmental conditions must be viable to allow growth of bacteria and the required nutrients have to be present. Bacteria require several different nutrients in order for microbial growth to occur. These materials may be naturally present or added in treating chemicals. In general, MIC will occur where the bulk solution pH ranges from 5 to 9 and total dissolved solids are less than 200,000 mg/l.1 Frequently, the elements for a corrosion cell are present before the bacteria become involved in the corrosion process. The presence and activity of micro-organisms greatly accelerates, and often concentrates, the corrosion phenomenon. Bacteria can be seen to intensify rather than act as the original cause of many corrosion incidents.2 A number of different types of bacteria strains have been implicated in the MIC process.1 These include among others, sulfate reducing bacteria (SRB), acid producing bacteria, iron fixing bacteria, sulfur bacteria, sulfide generating bacteria, and slime forming bacteria. Sometimes the bacteria species are referred to as SRB, GAB (General Aerobic Bacteria) and GAnB (General Anaerobic Bacteria). However, it may be noted that SRB are the best known agents of MIC and were the first to be implicated in the MIC process.3 Because SRB are so commonly found in corrosion situations, they are used as a marker organism to assess the risk of bacterial corrosion in a system. SRB have been extensively studied, and many mechanisms have been proposed to explain their effect on the corrosion process.4 The morphology of pits is often considered as an indicator of MIC. The presence of a terraced pit is usually attributed to SRB while pits within pits, or tunneling effects are considered to be signs of acid producing bacteria.1 It should be pointed out that these forms of corrosion can also be caused by other non-biological mechanisms. Identification of a corrosion failure as being MIC should include, besides morphology, detection of live bacteria in the corroded area and detection of metabolic products (e.g. sulfides, organic acids, etc.) showing that the bacteria were active in the area. Many techniques have been developed for detecting and quantifying bacterial proliferation in different process industries as well as in oil field environments. Comprehensive reviews of these methods are available in recent publications.5,6

Crude Oil Processing at KOC The Kuwait Oil Company (KOC), which is a major player among the Middle East crude oil production and processing concerns, operates a large number of facilities consisting of 22 Crude Processing Plants (or Gathering Centers), 4 Gas Processing Plants (or Booster Stations); 3 Effluent Water Disposal Plants, Seawater Treatment and Injection Plants, Early Production Facilities, and a vast network of pipelines carrying different products. At the Gathering Center (GC), the incoming crude oil from producing wells, consisting of a mix of emulsified oil, gases, dissolved salts and other solid impurities, is first put through Separators to separate the emulsified oil from the gases and solid impurities. The separated gas is sent to Booster Stations for further processing and the emulsified oil is sent to Wet Crude Storage Tanks where the oil and water separates. The separated water from the Wet Crude Tank, known as Produced Water (PDW) with a high salt content, is drained and sent to the Effluent Water (EFW) Storage Tank.


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The decanted crude oil from the Wet Crude Storage Tanks is sent to the Desalting Section comprising of a 1st Stage Desalter and a 2nd Stage Desalter. Brackish Water (BRW) from source wells (routed through BRW Storage Tanks) is utilized as wash water in the 2nd Stage Desalter which receives partially cleaned crude oil from the 1st Stage Desalter. The spent BRW from the 2nd Stage Desalter known as Recycle Water (RCW) is fed into the 1st Stage Desalter where it is utilized to wash the incoming crude oil received from the Wet Crude Storage Tanks. The spent RCW from the 1st Stage Desalter known as 1st Stage Effluent Water (EFW) is sent to the EFW Storage Tank. The Final Effluent Water (FEFW) consisting of PDW and 1st Stage EFW is sent to the Effluent Water Disposal Plant (EWDP) where it is either disposed through Disposal Wells or utilized for Water Injection after further treatment. The processed crude oil from the GC is either sent to one of the three Refineries in Kuwait or to the Export Terminal for export to other countries. Figure 1 shows the Process Flow Diagram (PFD) of a typical Gathering Center. Bacterial Proliferation at KOC Strong evidence of bacterial proliferation, consisting of SRB, GAnB and GAB, in brackish water and effluent water systems in various KOC facilities, have been gathered during routine fluid sampling and corrosion monitoring services conducted over the last several years. Severe MIC attack on coupons has been observed and some equipment failures due to MIC have also been documented.7 The corrosion morphology observed was typical of SRB attack. Effluent waters in some KOC facilities are very high in total dissolved solids (TDS) content, exceeding 200,000 mg/L and SRB counts in such waters have been found to be zero or very low. However, the GAnB counts are often high. Contrary to what is reported in the literature, severe MIC on coupon samples have been encountered in these high TDS waters and the corrosion morphology is very similar to SRB induced attack even though no SRB is present. Corrosion coupon, fluid analysis and bacteria data gathered from some of the KOC facilities are reported and discussed in the present paper with emphasis on the morphological aspects of the corrosion damage.

CHARACTERISTICS AND CORROSIVITY OF KUWAIT OIL FIELD WATERS

Water Chemistry

Chemical analysis of the different types of waters (BRW, PDW, RCW and EFW) associated with crude oil processing is carried out on a routine basis to determine various key parameters such as pH, conductivity, TDS, Total Hardness, Dissolved Oxygen, H2S and CO2 concentrations, Corrosion and Scale Inhibitor residuals, and iron content (total and dissolved). The different waters have significant variations in their chemistry depending on the production areas. Table 1 shows the typical composition of the different types of waters from the different oil producing areas in Kuwait designated as East, West, North and South. It can be seen that the BRW from the North area is much higher in TDS (Total Dissolved Solids), chloride, calcium and magnesium content compared to waters from the other areas. The PDW from the West and North regions also have very high TDS levels. The Final EFW from the West and North production areas tend to have very high TDS, with those from the West always showing TDS levels in excess of 200,000 mg/L.


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Figure 1. Process Flow Diagram (PFD) of a Typical Crude Processing Facility (Gathering Centre). ©2013 by NACE International.

Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing toNACE International, Publications Division, 1440 South Creek Drive, Houston, Texas 77084.The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association.

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Table 1 Typical Composition of Different Types of Waters from Different Oil Producing Areas of Kuwait

Parameter Unit

East South West North East South West North East South West North East South West North

Colour/Appearance Clear Clear Clear Clear ClearOily

WaterOily

WaterClear Clear Clear Clear Clear Clear

Slight Yellowish

Clear Yellowish

pH 7.0 6.9 7.1 7 7.1 6 7.1 7.3 5.8 6.3 5.6 5.8 6.1 6.1 5.8 5.8

Conductivity μs/cm 4880 4800 4620 18150 5360 7140 10610 19210 309000 281000 468000 407500 298750 262500 432000 338750

Total Dissolved Solids mg/L 2537 2300 2402 9485 2780 3705 5520 9990 160680 146600 243360 212875 155350 137000 224640 176000

Salt Cont. as NaCl mg/L 1319 1170 1608 8250 1650 2470 4120 9075 154550 142840 241710 206244 154550 130040 223112 165000

Hardness as CaCO3 mg/L 1500 2200 1500 3100 1520 2500 2400 3300 36000 32500 64000 52000 33500 33000 60500 39500

H2S Content mg/L 0.02 0.005 0.03 0.01 0..02 0.1 21 0.01 0.03 0.005 0.8 0.2 0.02 3.01 14 0.03

C.I Residual content mg/L 1.0 3.29 1.2 1.1 5.4 20.4 3.4 0.9 6.6 1.5 3.2 0.7 2.8 5.35 5.5 4.1

S.I Residual content mg/L 0.53 19.2 1.4 0.2 4.8 12.3 2.6 2.6 2.8 0 0.7 0 0.74 3.42 2.6 0.3

Fe Content (Total) mg/L 0.7 0.2 0.2 0.21 0.3 0.04 2 1.1 13 0.3 1.45 87.7

Fe Cont.(Dissolved) mg/L 0.6 0.04 0.1 0.13 0.2 0.01 1.3 0.3 3.0 0.8 13.9 2.3 10 0.12 1.35 80.2

Mn Content mg/L 0 0 0 0 0 0 0.04 0.1 1.0 0.03 0.9 1.4 1.8 0.02 0.5 2.35

Ca2+

Content mg/L 400 561 360 880 368 600 600 920 10200 9200 20800 16000 10000 10020 18800 12200

Mg 2+ Content mg/L 121 195 146 219 146 240 218 243 2552 2308 2916 2916 2065 1946 3214 2187

SO42- Content mg/L 1100 1013 1215 975 1250 1160 1350 1375 72 5 180 600 65 130 110 700

Cl - Content mg/L 800 709 1024 5000 1000 1500 2500 5500 93750 86560 147380 125000 93750 78810 136040 100000

M.Alkalinity as CaCO3 mg/L 20 170 200 120 90

HCO3- Content mg/L 24 207 244 130 110

Brackish Water (BRW) Final Effluent Water (FEFW)Produced Water (PDW)Recycled Water (RCW)


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Corrosion and Bacteria Data Internal Corrosion Monitoring activities are carried out on a routine basis in all KOC facilities with the help of Online Monitoring Equipment that include Corrosion Coupons, Corrosion Probes, Bio-probes, Hydrogen Patch probes etc. installed at key locations in the facilities. However, data from corrosion coupons are the ones most widely used for determining the corrosivity of the various process streams. Corrosion and pitting (localized corrosion) rates obtained from coupons are categorized as ‘Low, Moderate, High and Severe’ as per Guide Lines in NACE document RP07757 summarized in Table-1 below. Coupon processing is done as per ASTM procedure G-1.8

Table-2

Classification of Corrosion and Pitting Rates as per NACE Guidelines

General Corrosion Category

Corrosion Rate (mpy)*

Pitting Corrosion Category

Corrosion Rate (mpy)*

Low <1 Low <5 Moderate 1-4.9 Moderate 5-7.9

High 5-10 High 8-15 Severe >10 Severe >15

*mpy = mils per year (1 mil = 0.001 inch = 0.254 mm)

As per Company protocol, the corrosion monitoring service periods are at 45-day intervals for the first three services for new locations and then 45 days for locations with High to Severe category general and pitting rates, 90 days for locations with Moderate to High pitting rates, and 180 days for the locations with Low to Moderate corrosion rates.

Analyses for planktonic bacteria, consisting of Sulfate Reducing Bacteria (SRB) General Aerobic Bacteria (GAB) and General Anaerobic Bacteria (GAnB), are carried out on water samples while analyses for sessile bacteria for the same species are performed on the deposits from the coupons obtained during routine coupon retrievals as per approved Company protocols.9 Sessile sampling is done only from coupons with sufficient deposits. Bacteria analysis is performed by the Serial Dilution technique following standard NACE methodology.10 Guidelines for quantifying bacterial proliferation in terms of the afore mentioned bacteria strains are provided in Company Procedures11 and summarized in Table 3 below.

Table 3 Target Bacteria Population Density

(Maximum Allowable)

Bacteria Type

Sessile Bacteria Count

Planktonic Bacteria Count

SRB < 102/cm2 < 1/ml GAB < 102/cm2 < 104/ml

GAnB < 102/cm2 < 104/ml


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RESULTS AND DISCUSSION: Over the last few years a large amount of coupon corrosion data as well as data for both planktonic and sessile bacteria in different process streams have been collected from the various KOC facilities. Table 4 presents a snapshot of some of the corrosion data and corresponding sessile bacteria data obtained in different types of waters during 2011. It has been found that almost in all cases, coupons exposed to BRW suffer very severe localized corrosion. In a few cases, standard 3-inch coupons have been found to be almost totally consumed within 45 days of exposure. In all cases of severe localized corrosion damage, the presence of planktonic as well as sessile bacteria (all three species – SRB, GAB and GAnB) were positively identified and the bacteria counts were found to be significantly above the allowable limits given in Table 3. It may be noted that all three bacteria species had the same count in the BRW. Typical examples of the morphology of corrosion attack encountered in BRW streams are shown in Figure 2. The morphological features of the corrosion damage are similar to what is often cited in the open literature as due to MIC in presence of SRB. Severe localized corrosion on coupons have also been observed in RCW as well as in 1st Stage EFW and Final EFW streams as shown in Table 4. In all these cases, the common factor is the presence of bacteria. However, it is interesting to note that in these environments, the SRB count is seen to be very low or zero, and the GAnB is always high. The GAB count appears to vary. Typical examples of the corrosion morphology observed in these environments are shown in Figures 3 through 6. The morphological features are very similar to those observed in BRW environments which, as mentioned earlier is assumed to be due to SRB attack. From the above data and observations, it is quite clear that the severe localized corrosion encountered in all these types of waters is not due to normal corrosion processes alone but is bacteria related. The data also indicates that the severe localized corrosion can perhaps be attributed to the GAnB species rather than SRB since the former seems to be the common factor. Unfortunately, it is unresolved as to what specific bacteria strain or strains constitute the GAnB species and further study is warranted to identify these strains. Based on limited circumstantial evidence i.e. the presence on sulfides in the corrosion products, it would appear that the bacteria strains involved in GAnB influenced corrosion, are some sort of sulfate reducers similar to the commonly known SRB strain, but does not appear in the standard SRB test media. It should be noted that equipment and piping exposed to BRW, RCW, PDW and EFW in KOC facilities are usually coated. Currently, the piping for BRW circuits is mostly made of GRP. It is also important to point out that corrosion inhibitor treatment is carried out in all systems handling BRW, RCW and EFW. Biocide treatment is carried at the EWDPs and has recently been started at some of the GCs. In spite of these chemical treatments, severe corrosion continues to be observed on installed coupons and bacterial proliferation has persisted. It appears that the effectiveness of the corrosion inhibitor is hampered by the presence of bacteria (biofilms) on the metal surface. It is possible that these inhibitor products could indeed be effective in the absence of bacterial proliferation. It is likely that equipment and piping, which are not coated, may suffer corrosion damage and possibly unexpected failures if bacteria proliferation continues unabated.


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Table 4 Corrosion and Bacteria Data in Different Types of Oil Field Waters

Type of Water Coupon Retrieval

date

Exposure Days

Corrosion Rate (mpy)

Sessile Bacteria (Counts/cm2)

General Localized SRB GAB GAnB

BRW 24-Apr-11 46 10 504 27000 27000 27000 24-Jul-11 91 10 255 27000 27000 27000 18-Dec-11 49 30 473 27000 27000 27000

RCW 08-Sep-08 55 16 48 27 270 2700 19-Dec-11 102 18 227 2700 270 2700 06-Sep-11 89 17 260 2700 2700 27000

PDW 22-Jun-11 62 127 748 17 170 17000 25-Aug-11 64 164 724 17 170 17000 04-Dec-11 102 77 454 0 0 17000

1st Stage EFW 09-Mar-11 45 13 515 0 270 27000 24-Apr-11 46 41 504 0 0 27000 24-Jul-11 91 14 354 0 27 27000

Final EFW 17-Apr-11 18 55 178 17 1700 17000 01-Jun-11 45 40 490 0 1700 17000 05-Sep-11 29 83 352 17 170 17000

Note: BRW = Brackish Water; RCW = Recycle Water; PDW = Produced Water; EFW = Effluent Water

Figure 2. Typical Morphology of Localized Attack on Coupons in BRW


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Figure 3. Typical Morphology of Localized Attack on Coupons in RCW

Figure 4. Typical Morphology of Localized Attack on Coupons in PDW


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Figure 5. Typical Morphology of Localized Attack on Coupons in 1st Stage EFW

Figure 6. Typical Morphology of Localized Attack on Coupons in Final EFW


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SUMMARY AND CONCLUSIONS Strong evidence of planktonic and sessile bacterial proliferation, consisting of SRB (Sulfate Reducing Bacteria), GAnB (General Anaerobic Bacteria) and GAB (General Aerobic Bacteria), in BRW (Brackish Water), RCW (Recycle Water) and EFW (Effluent Water) systems in various KOC (Kuwait Oil Company) facilities have been gathered during routine fluid sampling and corrosion monitoring services conducted over the last several years. Severe MIC (Microbiologically Influenced Corrosion) attack on coupons has been observed and some equipment failures due to MIC have also been encountered. Coupons exposed to BRW suffer very severe localized corrosion. In a few cases, standard 3-inch coupons have been found to be almost totally consumed within 45 days of exposure. In all cases of severe localized corrosion damage, the presence of planktonic as well as sessile bacteria (all three species – SRB, GAB and GAnB) were positively identified and the bacteria counts were found to be significantly above the allowable limits. Severe localized corrosion on coupons has also been observed in RCW as well as in 1st Stage EFW and Final EFW streams. In all these cases, the common factor is the presence of bacteria. However, in some cases the SRB count is seen to be very low or zero, and the GAnB is always high. The GAB count appears to vary. The morphological features are very similar to those observed in BRW environments, which is assumed to be due to SRB attack. From the data and observations, it is quite clear that the severe corrosion encountered in all these types of waters is not due to normal corrosion processes but is bacteria related. The data also indicates that the severe localized corrosion can perhaps be attributed to the GAnB species rather than SRB. Unfortunately, it is unresolved as to what specific bacteria strain or strains constitute the GAnB species and further study is warranted to identify these strains. Based on circumstantial evidence i.e. the presence on sulfides in the corrosion products, it would appear that the bacteria strains involved in GAnB induced corrosion, are some sort of sulfate reducers similar to the commonly known SRB strain. The impact of bacteria proliferation on oil and gas production facilities can be multi-faceted which can seriously impact operating costs. Hence, the monitoring and control of bacterial proliferation in oil production and processing facilities should be a high priority. It has been observed that the effectiveness of corrosion inhibitors is often hampered by the presence of bacteria (biofilms) on the metal surface. Once the presence of bacteria and the occurrence of MIC is confirmed in a facility, appropriate biocide treatment should be immediately started. It is important to note that biocide treatment should not be carried out on an arbitrary basis. Prior to field application, a rigorous laboratory evaluation of candidate products should be carried out to identify the most effective biocide or biocides, determine appropriate treatment levels and mode of application as well as to determine compatibility issues with other commonly used oil-field chemicals. KOC is currently in the process of implementing biocide treatment in various facilities following such procedures.


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REFERENCES

1. “Strategy for Bacteria Analysis Associated with Process Fluids,” Final Report on Task 1-2 submitted to Kuwait Oil Company under Contract 10626 by CC Technologies (author J. Boivin), May 2002.

2. J. Boivin; "Oil Industry Biocides;” NACE Western Canadian Region Western Conference, Calgary, 1994; Reprinted in Materials Performance, V. 34 (2), pp. 65-68. Feb. 1995.

3. J. R. Postgate; in The Sulfate-reducing Bacteria (2nd Ed.), University Press, Cambridge. 1984 pp. 135-6, 1984.

4. J. Boivin and J.W. Costerton; "Corrosion in Bacterial Biofilms"; 11th International Conference on Offshore Mechanics and Arctic Engineering, ASME Paper #92-955, Calgary, June, 1992.

5. R. Sooknah, S. Papavinasam and R.W. Revie, “Monitoring Microbiologically Influenced Corrosion: A Review of Techniques,” Paper No. 07517, NACE CORROSION/2007, Nashville, TN, March 11-15, 2007.

6. S. Al-Sulaiman, A. Al-Mithin, G. Murray, A.J. Biedermann and M. Islam, “Advantages and Limitations of Using Field Test Kits for Determining Bacterial Proliferation in Oil Field Waters,” Paper No. 08695, NACE CORROSION/2008, New Orleans, LA, March 16-20, 2008.

7. NACE RP-0775, “Preparation, Installation, Analysis, and Interpretation of Corrosion Coupons in Oilfield Operations.” NACE International, Houston, Texas, 2009.

8. ASTM G1–03 (2011), “Standard Practice for Preparing, Cleaning, and Evaluating Corrosion Test Specimens,” American Society for Testing and Materials, PA, 2011.

9. Procedure for Microbial Collection and Analysis, CCI-004, Internal Corrosion Monitoring Services, Kuwait Oil Company, September 2011.

10. NACE Standard TM0194-2004 “Standard Test Method – Field Monitoring of Bacterial Growth in Oil and Gas Systems,” National Association of Corrosion Engineers International, Houston, Texas, 2004.

11. Document No. KOC-ICM-002 Rev#1, “Dosage Control Strategy for Internal Corrosion and Scale Control Chemicals,” Kuwait Oil Company, September 2005.


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Documents

Paper No. 2748 - KPC publis… · Figure 1. Process Flow Diagram (PFD) of a Typical Crude Processing Facility (Gathering Centre). ©2013 by NACE International. Requests for permission