Conference PaperPDF Available

Developing a Metric for Microbilogically Influenced Corrosion (MIC) in Oilfield Water Handling Systems

Authors:
  • Infra-Tech Consulting LLC

Abstract and Figures

Bacteria population density may provide a viable corrosion control metric for microbiologically influenced corrosion (MIC) in oilfield water handling systems so that the population of the different strains of bacteria such as sulfate reducing bacteria (SRB), acid producing bacteria (APB) [also classified as general aerobic bacteria (GAB)] and general anaerobic bacteria (GAnB) in the operating environment can be kept below a target envelop. Consider, for example, a system that has been experiencing increased corrosion over a period of time. If the trend of increasing corrosion rate versus time parallels the corresponding plot of all bacteria population density over that same period of time, the general assumption is to ascribe the source of increased corrosion to increased bacteria population density. It is because of this empirical correlation that oil companies normally develop in-house guidelines for quantifying bacteria proliferation. There is, however, no generally accepted method for determining such guideline unambiguously. This paper provides a guidance to correlate the effects of bacteria population density on general and pitting corrosion rates with the goal of developing a self-consistent MIC performance indicator. It is based on microbiological and corrosion data obtained from various water handling systems at the Kuwait Oil Company. Key words: Microbiologically Influenced Corrosion, MIC, SRB, APB, GAB, GAnB
Content may be subject to copyright.
DEVELOPING A METRIC FOR MICROBILOGICALLY INFLUENCED
CORROSION (MIC) IN OILFIELD WATER HANDLING SYSTEMS
Abdul Razzaq Al-Shamari
TPL-SP1 Inspection & Corrosion Team
Kuwait Oil Company, Ahmadi, Kuwait
ASHAMARI@kockw.com
Dr. Olagoke Olabisi
Director, Internal Corrosion Engineering
Corrpro Companies, Inc., Houston, Texas
oolabisi@corrpro.com
Abdul Wahab Al-Mithin
TL (S&E) Inspection & Corrosion Team
Kuwait Oil Company, Ahmadi, Kuwait
AMITHIN@kockw.com
Ashok Mathew
Corrosion Chemist, KOC ICMS Contract
Corrpro Companies, Inc., Ahmadi Kuwait
ASMathew@kockw.com
ABSTRACT
Bacteria population density may provide a viable corrosion control metric for microbiologically
influenced corrosion (MIC) in oilfield water handling systems such that the population of sulfate
reducing bacteria (SRB), acid producing bacteria (APB), general aerobic bacteria (GAB), and
general anaerobic bacteria (GAnB) in the operating environment can be kept below a target
envelop to preserve asset integrity. Consider, for example, a system that has been
experiencing increased corrosion over a period of time. If the trend of increasing corrosion
rate versus time parallels the corresponding plot of all bacteria population density over that
same period of time, the general assumption is to ascribe the source of increased corrosion to
increased bacteria population density. It is because of this pragmatic correlation that oil
companies normally develop in-house guidelines for quantifying bacteria proliferation.
However, there is still no generally accepted method for determining such guideline
unambiguously. This paper utilizes the effects of bacteria population density on general/pitting
corrosion to establish an asset integrity risk ranking for the following oilfield water handling
systems: brackish water, seawater, recycle water, and effluent water.
Key words: Bacteria Population Density, Sulfate Reducing Bacteria, Acid Producing Bacteria,
General Aerobic Bacteria, General Anaerobic Bacteria, SRB, APB, GAB, GAnB, MIC
©2013 by NACE International.
Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to
NACE 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.
1
Paper No.
2299
INTRODUCTION
Kuwait Oil Company(1) is the sole exploration and producing Operator in Kuwait. Kuwait oil
reserve ranks 9th in the world and the Operator is projected to be producing about 4.0 million
barrels of oil per day by the year 2020. In the last 60 years of operation, the pipeline network
has grown to about 4,800 km. Corrpro(1) has been the Contractor for Internal Corrosion
Monitoring Services (ICMS) since 2006. The ICMS contract is focused on conducting internal
corrosion monitoring of all existing facilities under the guidance of the Inspection and Corrosion
Team. For the Operator pipeline network, the Contractor conducts corrosion monitoring,
bacteria detection and quantification by using:
1. Corrosion coupons for general/pitting corrosion, deposits, and sessile bacteria
2. Corrosion probes for general corrosion, deposits and sessile bacteria
3. Limited number of bio-probes for sessile bacteria and deposits
4. Planktonic bacteria analyses of liquid samples from all facilities
5. Fluid sampling for chemical analysis and treatment chemical residual analysis
6. XRD analysis of solid corrosion products from shut-down vessels and suspended solids
from pig runs
This paper relates to the activities of the ICMS contract pertaining to microbiologically
influenced corrosion (MIC) in oilfield water handling systems. All facilities are equipped with
on-line corrosion and bacteria monitoring devices as indicated above. Online monitoring
locations normally include: (a) each water source; (b) all points downstream of storage units
such as tanks; (c) downstream of all biocide injection points, (d) plant outlets; (e) the farthest
points in a system (e.g. injection wellhead); and (f) selected worst-case locations (e.g. dead
legs, etc.). Depending on risk assessment, fluid sampling for chemical analysis and planktonic
bacteria is conducted routinely at 30-day, 45-day, or 60-day intervals. Bacteria growth
analyses and interpretation for Sulfate Reducing Bacteria (SRB), Acid Producing Bacteria
(APB), General Aerobic Bacteria (GAB), and General Anaerobic Bacteria (GAnB) are based on
the Serial Dilution Test Method outlined in NACE International Standard TM0194-20041.
Coupon corrosion monitoring is done typically at 45-day intervals for locations exhibiting high
(5 mpy equal to 0.127 mm/y) to severe (>10 mpy equal to >0.254 mm/y) corrosion
characteristics; while 90-180 day intervals are used for locations with low (1 mpy equal to
0.0254 mm/y) to moderate (<5 mpy equal to <0.127 mm/y) corrosion characteristics. Part of
the corrosion monitoring activity involves testing for sessile bacteria using deposits on
corrosion coupons. Samples of sessile bacteria are normally recovered from the surface of
corrosion coupons. Coupon corrosion rates are determined using standard NACE RP0775-
20052 while coupon processing methodology is per ASTM procedure G1–033. The data are
grouped according to the fluid type so that the corrosion trends can be easily discerned in a
particular fluid.
In an earlier paper4, a methodology was outlined for the use of a single key performance
indicator in tracking monitoring strategy, mitigation strategy, and pipeline integrity for
aboveground pipelines in the North Slope. This paper utilizes the effects of bacteria population
density on general/pitting corrosion to establish an asset integrity risk ranking for the following
oilfield water handling systems: brackish water, seawater, recycle water, and effluent water.
(1) Trade name
©2013 by NACE International.
Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to
NACE 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.
2
APPROACH
Microbiologically Influenced Corrosion (MIC) is the degradation of a material under the
influence of environmental factors complicated by the metabolic activities of microorganisms.
As its name implies, MIC involves bacteria influencing corrosion. Frequently, the elements for a
corrosion cell are present before the bacteria become involved in the corrosion process.
Conditions, which lead to microbial corrosion, will often lead to corrosion, even if bacteria were
not involved. The presence and activity of microorganisms greatly accelerates, and often
concentrates, the corrosion. The bacteria involved in the corrosion process are held in place by
the matrix of gelatinous extra-cellular polymeric substances (EPS) generally referred to as
biofilms. They rely on the related activities of micro-organisms within the biofilm, and the build up
of metabolic products in the biofilm has a significant influence on the nature and type of metal
loss (corrosion) taking place. That is, MIC is a biofilm process. The microbiological attack of
process equipment used in the petroleum industry results in increased operating expenses and
reduced income. A partial list of these effects includes:
1. Cost of repair or replacement, and clean up if/when a system fails
2. Energy costs arising from line friction due to bacteria-induced build-up within
flowlines and pipelines
3. Energy costs arising from reduced heat transfer due to bacteria-induced fouling
4. Energy costs arising from injection well plugging induced by bacteria.
5. Cleanup costs associated with fouled and plugged injection wells, exchangers,
filters, and other assets
6. Reduced income associated with product quality loss due to contamination
(produced products, products in storage, and refined products)
7. Cost of removing metabolic products such as sulphides, slime, etc.
8. Reduced income from downtime associated with all of the above
9. Cost of biocide treatment chemicals, monitoring, and inspection programs
Microbial corrosion activity occurs principally in the following water systems: seawater,
brackish water, effluent water, recycle water, and firewater. To achieve effective bacteria
monitoring for these water systems, monitoring devices are located in the areas where the
buildup of biofilms and hence, sessile bacteria growth are expected to occur. This monitoring
strategy facilitates, not only the identification of the prevailing bacteria, but also the
implementation of the required corrosion mitigating measures.
FIELD DATA
Sessile bacteria samples are recovered by the monitoring crew from bioprobes and surfaces of
corrosion coupons after retrieval. Planktonic bacteria surveys are carried out by collecting
liquid samples from tanks, vessels, wellheads, and lines through sample valves. Aside from
identifying the type of bacteria present, planktonic bacteria surveys expose the primary
bacteria sources in an operation. Bacteria growth analyses and interpretation for SRB,
GAB/APB, and GAnB are performed based on the Serial Dilution Test Method outlined in
NACE International Standard TM0194-20041. DNA sequence analysis is not performed; the
bacteria were not identified either to the genus level or the species level by means of rDNA
sequencing.
©2013 by NACE International.
Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to
NACE 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.
3
Following removal, coupons are cleaned using chemicals or glass-bead “blasting”. Weight
loss is measured for corrosion rates and pit depth is measured with a microscope for pitting
rates. The results are placed in a database and used for trending corrosion. Coupons are
photographed for later review and, as digital photographs, archived on database. The used
coupons are placed in treated envelopes and saved.
General corrosion rates (in mils per year) are calculated from the measured weight loss as
follows:
CR = [(weight loss in grams)(22,300)/(area in square inch)(metal density in grams/cm3)
(365)/days of exposure] (1)
Pitting rates (in mils per year) are calculated from the maximum pit depth as follows:
Pitting rate = [(maximum pit depth in mils)(365)/days of exposure] (2)
Routine corrosion and sessile bacteria monitoring is conducted using strip corrosion coupons
for unpiggable pipelines containing seawater, brackish water, effluent water, and recycle water.
The specific locations investigated for the present study are presented in Table 1.
Table 1
Corrosion and Sessile Bacteria Monitoring Locations
Fluid Type Monitoring Locations
Sea Water Sea Water Injection Headers and
Well Heads
Brackish Water 2n
d
Stage Desalter Inlet
Recycle Water 1s
t
Stage Desalter Inlet
Effluent Water 1s
t
Stage Desalter Outlet
The field data on bacteria, general and pitting corrosion at the locations in Table 1 are
presented in what follows.
Seawater System.
Seawater, with a TDS of 40,000 - 45,000 mg/L, is sourced from the Arabian Gulf Sea using
intake lift pumps, treated with hypochlorite on its way to the Seawater Treatment Plant
(SWTP). At SWTP, the water goes into a clarifier tank, where it is treated with coagulant,
cationic electrolytes, and anionic electrolytes resulting in the suspended matter settling in the
tank. Clear water from the top is filtered and de-aerated so that the oxygen content is reduced
to a value as low as 100 ppb. The de-aerated water is further treated with oxygen scavenger to
reduce the dissolved oxygen levels below 10 ppb. Treatment chemicals – corrosion inhibitor,
scale inhibitor, and biocide shock treatment – are applied as the water passes to the Central
Injection Plant Facility (CIPF). At CIPF, the water is again shock-treated with biocides, and
additional oxygen scavenger is added if the dissolved oxygen exceeds 40 parts per billion. The
water is then pressure boosted and sent to the Sea Water Headers & Wells. For monitoring
planktonic bacteria and chemicals, routine water sampling is conducted at 30-day interval at
the following locations: Sea Water Treatment Plant (SWTP), Central Injection Plant Facility
©2013 by NACE International.
Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to
NACE 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.
4
(CIPF), and Sea Water Injection Headers & Wells (SWIH&W). Whenever upset conditions
occur, more frequent monitoring takes place.
The success of corrosion and bacteria monitoring in the seawater system has been aided by
the fact that pigging is carried out on a regular schedule for piggable lines equipped with flush-
disk corrosion coupons. Significant effort is focused on fluid sampling for corrosion and
bacteria of pig runs and on determining the water quality from every run. Suspended solids are
analyzed. Dissolved oxygen, pH, and sulfides are also monitored.
Figure 1 illustrates the trend of bacteria count and general corrosion rate in seawater system
and Figure 2 illustrates the same trend for bacteria and pitting corrosion rate.
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Corrosion Rate (mpy)
Corrosion Rate SRB GAB GAnB
Figure 1: Trend of bacteria count and general corrosion rate in Seawater System
(1 mpy = 0.0254 mm/y)
It is generally observed that the coupons installed at SWIH&W are comparatively more
corroded than the coupons installed in other locations in the seawater system. This is perhaps
due to the fact that SWIH&W is the farthest location from the Seawater Treatment Plant.
Brackish Water System.
The TDS of brackish water from different supply wells vary from ~5,000 mg/L to 18,000 mg/L.
The water is chemically treated with oxygen scavenger, corrosion inhibitor, and scale inhibitor
prior to arriving at the de-salter where it is used for wet crude washing purposes at Gathering
Centers (GCs). Routine water sampling locations are: Brackish Water Inlet to Storage Tank,
Storage Tank Outlet and Inlet to 1st Stage De-salter. Fluid sampling for chemical analysis and
planktonic bacteria is conducted routinely at 45-day intervals. Dissolved oxygen, pH, and
sulfides are monitored. It is generally observed that planktonic bacteria levels at the outlet of
©2013 by NACE International.
Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to
NACE 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.
5
brackish water tank are considerably higher than at the inlet. This is probably due to the
presence of suspended matter, which settles at the tank bottom and provides breeding
environment for bacteria.
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Counts/cm
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(Scale =
Logarithm)
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Corrosion Ra te (mpy)
Pitting Rate SRB GAB GAnB
Figure 2: Trend of bacteria count and pitting corrosion rate in Seawater System
(1 mpy = 0.0254 mm/y)
Because the pipelines and tanks are internally coated, concern for MIC and pitting corrosion is
minimized. Nonetheless, knowledge of the presence of bacteria is essential for asset integrity
considerations. Figure 3 illustrates the trend of bacteria count and general corrosion rate in
brackish water system and Figure 4 illustrates the same trend for bacteria and pitting corrosion
rate.
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Logarithm)
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Corrosion Rate (mpy)
Corrosion Rate SRB GAB GAnB
Figure 3: Trend of bacteria count and general corrosion rate in Brackish Water System
(1 mpy = 0.0254 mm/y)
©2013 by NACE International.
Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to
NACE 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.
6
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Pitting Rate SRB GAB GAnB
Figure 4: Trend of bacteria count and pitting corrosion rate in Brackish Water
System (1 mpy = 0.0254 mm/y)
Effluent Water System
The primary constituents of effluent water are the produced water and the brackish water. The
wash water coming from the 1st Stage De-Salter Outlet combines with the produced water
from wet crude to make the Final Effluent Water. The TDS at the 1st stage de-salter is 45,000-
50,000 mg/L depending on the oil-water ratio of the crude and the produced water quality
The produced water is highly saline, but the brackish water is relatively low in salinity.
However, the presence of the highly saline produced water does not reduce the propensity for
bacteria infection in effluent water. For example, GAnB grows in large numbers in the effluent
waters in all GCs; whereas, the SRB and GAB population are comparatively lower. The routine
water sampling locations are: 1st Stage De-Salter Outlet, Effluent Water Balance Tank, Outlet
of Effluent Water Treatment System (EWTS) and Effluent Water Disposal Plant (EWDP).
Figures 5 illustrates the trend of bacteria count and general corrosion rate in the effluent water
system from the 1st Stage De-Salter Outlet and Figure 6 illustrates the same trend for bacteria
and pitting corrosion rate
Recycle Water System.
Brackish water used for desalting crude at the 2nd stage de-salter becomes the recycle water.
It is then used for 1st stage desalting of wet crude operating at around 80oC. Consequently,
the recycle water contains varying amounts of oil, it is slightly more saline and higher in
temperature (around 80oC) than the brackish water which came in at ambient temperature.
The propensity for bacteria activity in recycle water is lower than that of the brackish water.
There is routine sampling at the Recycle Water Pump Outlet. Figure 7 illustrates the trend of
bacteria count and general corrosion rate in recycle water system and Figure 8 illustrates the
same trend for bacteria and pitting corrosion rate.
©2013 by NACE International.
Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to
NACE 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.
7
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Corrosion Rate SRB GAB GAnB
Figure 5: Trend of bacteria count and general corrosion rate in Effluent Water
System (1 mpy = 0.0254 mm/y)
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Logarithm)
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2000
2500
Corrosion Rate (mpy)
Pitting Rate SRB GAB GAnB
Figure 6: Trend of bacteria count and pitting corrosion rate in Effluent Water System
(1 mpy = 0.0254 mm/y)
©2013 by NACE International.
Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to
NACE 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.
8
1
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Corrosion Rate (mpy)
Corrosion Rate SRB GAB GAnB
Figure 7: Trend of bacteria count and general corrosion rate in Recycle Water
System (1 mpy = 0.0254 mm/y)
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Counts/cm
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(Scale = Logarithm )
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100
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400
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600
Corrosion Ra te (mpy)
Pitting Rate SRB GAB GAnB
Figure 8: Trend of bacteria count and pitting corrosion rate in Recycle Water System
(1 mpy = 0.0254 mm/y)
©2013 by NACE International.
Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to
NACE 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.
9
Firewater Water System
All Gathering Centers and Gas Booster stations have fire water tanks, which are fed by
brackish water pipelines. The tanks and pipelines are all coated, and currently, they do not
have corrosion coupons installed. However, the fire water system is sampled. Fluid sampling is
used for chemical analysis and planktonic bacteria monitoring during system flushing.
Suspended solids are analyzed and attention is focused on determining the presence or
otherwise of iron sulfide and sulfates. It has been shown during shut-down that the bacteria
levels are as high as SRB (106 counts/ml), GAB/APB (106 counts/ml) and GAnB (106
counts/ml).
DATA ANALYSIS
According to NACE RP0775-20052 corrosion severity classification is in terms of corrosion
rates in mils per year (1 mil = 0.001 in) or mm/y as illustrated in Table 2. On the other hand,
certain morphology of corrosion pits is sometimes used to be a sign of MIC. For example, a
terraced pit is accepted as indicative of SRB but ‘pits within pits’ and/or tunneling is accepted
as indicative of APB/GAB. Because such morphologies could be elucidated in terms of abiotic
mechanisms as well, corroboration is normally sought for biotic mechanisms based on bacteria
growth analyses. Serial Dilution Test Method outlined in NACE International Standard
TM0194-20041 is the method of choice to study bacteria growth. Additional evidence may
include sampling for metabolic products such as sulfides.
Table 2
Classification of General and Pitting Corrosion Rates
General Corrosion Pitting Corrosion
Low < 1.0 mpy (< 0.0254 mm/y) Low < 5.0 mpy (0.127 mm/y)
Moderate 1.0- 4.9 mpy
(0.0254-0.12446 mm/y)
Moderate 5.0 – 7.9 mpy
(0.127-0.20066 mm/y)
High 5 – 10 mpy
(0.127-0.254 mm/y)
High 8 – 15 mpy
(0.2032-0.381 mm/y)
Severe > 10 mpy (0.254 mm/y) Severe > 15 mpy (0.381 mm/y)
Bacteria Population Density and MIC.
Consider, for example, a system that has been experiencing increased corrosion over a period
of time. If the trend of corrosion rate versus time parallels the corresponding plot of sessile
bacteria population density over that same period of time, the general assumption is to ascribe
the source of the corrosion to the prevailing sessile bacteria population density. It is because
of this pragmatic correlation that oil companies normally develop in-house guidelines for
quantifying bacteria proliferation. For example, the Operator guideline for quantifying sessile
and planktonic bacteria proliferation is presented in Table 3.
©2013 by NACE International.
Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to
NACE 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.
10
Table 3
Target Bacteria Population Density
Bacteria Type Sessile Bacteria Planktonic Bacteria
SRB <102 counts/cm2 <1 counts per ml
GAB/APB <102 counts/cm2 <104 counts per ml
GAnB <102 counts/cm2 <104 counts per ml
This guideline implies that the population of the different strains of bacteria in an operating
system should be kept under the target values. If the target values are exceeded, then
aggressive biocide treatment of the system is indicated. The target values also provide a
means of assessing the efficacy of the biocide treatment program and serve as a basis for
biocide dosage control. This approach admits the fact that it is nearly impossible to kill all
bacteria. Minimization, destabilization and/or regular disruption of biofilm activity provide the
key to preventing significant MIC damage.
Although, the presence of planktonic populations is indicative of the presence and type of
sessile bacteria population, it can not provide proof for the effect of sessile bacteria population
density on corrosion, nor the effectiveness of biocide treatment. That is, biofilm matrix with its
bacteria community represent the primary cause of MIC, planktonic bacteria population density
is only corroborative. Sessile bacteria, which are responsible for MIC, are well protected by the
matrix of gelatinous extra-cellular polymeric substances (EPS) generally referred to as
biofilms. Corrosion, occasioned by sessile bacteria, is characterized by:
Microbial break down of passive metal film and accelerating corrosive attack
Microbial communities creating biofilms that could cause under-deposit corrosion
Microbial metabolic products that could cause pitting
Because biofilms are never completely destroyed by treatment chemicals, sessile bacteria
readily re-colonizes the system as long as nutrients are available. Consequently, the trick for
mitigating MIC is to continuously disrupt biofilm formation. If the biofilm-bound sessile bacteria
community is effectively disrupted, corrosion rates would be significantly reduced even if serial
dilution microbial culture indicates the presence and type of live planktonic bacteria. On the
other hand, conditions that are friendly to biofilm formation are nearly impossible to eliminate in
oil field water systems, namely, nutrients, low velocity, particulate loading, scale formation, and
water stagnancy. The effects of selected environments on bacteria and corrosion in the
Operator oilfield water handling systems is summarized in Table 4.
Specifically, the introduction of oxygen accelerates microscopically induced corrosion of iron
leading to the conversion of primary iron sulfide product mackinawite (FeS) to pyrite (FeS2)
and elemental sulfur5. Under anaerobic conditions SRB creates a galvanic couple with the iron
surface acting as a cathode and the iron as an anode. The open circuit potential of the iron
increases and moves to more positive values as long as the bacteria is active. Bacteria do
influence the type and concentrations of ions, pH, and oxygen levels resulting in significant
variations in the chemical and physical characteristics of the environment thereby accelerating
©2013 by NACE International.
Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to
NACE 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.
11
the corrosion rate.
Table 4
Effects of a Selected Environment on Bacteria and Corrosion
Effects of pH Effect of Dissolved Oxygen Effect of Ionic strength
Neutral pH
favors bacteria
growth.
Low pH
increases
corrosion.
High DO increases corrosion.
High DO supports GAB/APB
growth, which assists the
survival of other bacteria (SRB
and GAnB) by symbiosis.
DO-free environment favors
SRB and GAnB growth
High ionic strength
(conductivity), especially
chloride, increases
corrosion.
High salt content slows
bacteria growth
Lower salt content
favors bacteria
DO = dissolved oxygen
BACTERIA POPULATION DENSITY AS CORROSION CONTROL METRIC
Corrosion risk management for an operation is the systematic application of policies, practices,
and resources to control risk and provide reliable safeguards against unexpected failures and
leaks, occasioned by corrosion, which can jeopardize mechanical integrity, operation, health,
safety and environment (HSE). A corrosion control metric is a performance measure that can
be used to assess the efficiency of the prevailing corrosion risk management strategy4. For
bacteria population to be used as a corrosion control metrics, some empirical correlation is
required, however tenuous, that could relate bacteria population to corrosion.
Figures 1 to 8 validate that the trend of the general and pitting corrosion rates are strongly
impacted by sessile bacteria population density trend. However, a distinct correlation is not
discernable except for a rather tenuous relationship in Figures 3 and 4. To interpret the field
data in terms of the corrosion severity classification given in Table 2 as well as the target
population density depicted in Table 3, we resort to elementary statistics for a 5-year period
(2007-2011). For each of the Operator oilfield water handling systems, the number of incidents
of ‘Low’, ‘Moderate’, ‘High’, and ‘Severe’ corrosion for the 5-year period is tabulated in Table 5.
The corresponding number of incidents of (<102 counts/cm2), and (>102 counts/cm2) for SRB,
GAB/APB, and GAnB for each fluid type is tabulated in Table 6.
According to API 580-20026, relative risk is the comparative risk of a system to other systems,
among others and the establishment of relative risk is the key to prioritization. This entails the
comparative risk analysis of a system in a facility to a similar system in order to differentiate
and provide a relative priority for integrity assessment. Risk-based inspection (RBI) is focused
on a systematic determination of relative risks. Indeed, this concept is focused on inspection,
but inspection and monitoring are the two key processes by which the onset of internal
corrosion, external corrosion and stress corrosion cracking can be detected. If inspection
techniques are used to measure corrosion rates, significant measurable corrosion (about 10
mils or 0.254 mm) has to occur to the base materials, before it can be detected.
©2013 by NACE International.
Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to
NACE 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.
12
Table 5
Number of Corrosion Incidents Categorized Per Table 2 (NACE Severity Classification)
FLUID
TYPE pH DO,
ppb
TDS,
mg/L
Incidents For General Corrosion Incidents For Pitting Corrosion
LOW MODERATE HIGH SEVERE LOW MODERATE HIGH SEVERE
1 6.0-
7.5
10-
300
0
5,000-
18,000 1 7 11 17 0 0 0 32
2 5.5-
7.0 10 6,000-
20,000 13 5 6 10 0 0 3 25
3 5-6.5 10
45,000-
50,000 4 2 3 13 0 0 2 24
4 6-7.5 10
40,000-
45,000 9 23 5 3 9 3 5 13
Where: Fluid type 1=Brackish water; Fluid type 2=Recycle Water; Fluid type 3=Effluent Water; Fluid type 4=Seawater
Table 6
Number of Bacteria Incidents Categorized Per Table 3 (i.e. Operator Target Bacteria Population Density)
FLUID
TYPE
DO,
ppb
TDS,
mg/L
Incidents For SRB Incidents For GAB Incidents For GAnB
<102 per cm2 >102 per cm2 <102 per cm2>102 per cm2<102 per cm2>102 per cm2
1 10-
3000
5,000-
18,000 3 27 0 30 0 30
2 10
6,000-
20,000 13 12 7 18 7 18
3 10
45,000-
50,000 18 2 16 4 9 11
4 10
40,000-
45,000 12 20 11 21 5 27
Where: Fluid type 1=Brackish water; Fluid type 2=Recycle Water; Fluid type 3=Effluent Water; Fluid type 4=Seawater
©2013 by NACE International.
Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to
NACE 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.
13
That loss of base metal is normally irreplaceable and the loss will have an effect upon all
subsequent MAOP (maximum allowable operating pressure), structural integrity, and
remaining life calculations. On the other hand, corrosion monitoring is able to detect corrosion
significantly quicker (less than 1.0 mil equal to 0.0254 mm). This “early detection” of the onset
of corrosion enables a quick response to the changing operational environment, and, when
appropriate, enables increasing the quantity of treatment chemicals applied to the process
fluids, thereby enhancing protection. Thus, corrosion monitoring helps to minimize the extent
of damage to the base metal and helps to maintain the structural integrity of the production
systems.
Risk assessment process identifies the conditions that could lead to asset failure. Risk,
understood in its technical sense, is a combination of the probability that an event will occur
and the consequences of the occurrence. When probability and consequence are expressed
numerically, risk is the product. For the four oilfield water handling systems, the leak impact
factor, representing the consequence, is essentially identical. Hence the risk factor is highest
for the oilfield water handling systems that has the highest probability of negative outcome
occasioned by bacteria population. That is the probability of failure could be used as a
surrogate to establish a relative risk ranking for maintenance action. This enables the framing
of the bacteria impact question in terms of probability. That is, which of the four oilfield water
handling systems has the highest probability of failure, and therefore the highest relative risk,
of negative outcome occasioned by bacteria population and the attendant corrosion?
The data presented in Tables 5 and 6 essentially establish an asset integrity risk ranking for
the four oilfield water handling systems under study. The risk to each system is in the following
decreasing order:
Brackish Water > Seawater > Recycle Water > Effluent Water
With this prioritization scheme, inspection activities may be deployed to confirm whether actual
damage has occurred. When appropriate, mitigation actions may be deplored thereby
enhancing asset integrity. That is, the scheme is within the realm of corrosion risk
management, namely, the identification, assessment, and prioritization of risks followed by
coordinated and systematic application of policies, practices, and resources to minimize the
impact of corrosion. The scheme assists corrosion risk criticality assessment, helps to ensure
reliability of production, and enables the avoidance of losses from operational failures.
SUMMARY AND CONCLUSION
1 The Brackish water indicated a larger proportion of high and severe general
corrosion than the Recycle, Effluent water and Sea water. This is correlated with a
similar larger proportion of brackish water samples showing SRB, GAB and GAnB
above the target levels.
2 The incidence and severity of pitting corrosion is higher than general corrosion in all
the water systems, although the effect is more pronounced in Brackish water
3 Although all the water systems are de-aerated and treated with oxygen scavenger,
brackish water contains dissolved oxygen (DO) that is as much as 75 times the
Operator compliant level. In combination with bacteria, corrosion severity is
©2013 by NACE International.
Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to
NACE 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.
14
exacerbated.
4 Scale deposit was not observed in any of the scale coupons, but matrixes of
gelatinous extra-cellular polymeric substances (biofilms) are observed on scale and
corrosion coupons along with pitting corrosion.
5 Effluent water, with its lower pH and higher ionic strength, did not exhibit the highest
corrosion. Brackish water, with its highest bacteria population, exhibited the highest
corrosion underscoring the elevated corrosive effects of bacteria in brackish water.
6 The effects of bacteria population density on general and pitting corrosion has been
utilized to establish an asset integrity risk ranking for four oilfield water handling
systems. The risk to each system is in the following decreasing order:
Brackish Water > Seawater > Recycle Water > Effluent Water
REFERENCES
1. Field Monitoring of Bacteria Growth in Oil and Gas Systems, NACE International, NACE
TM0194-2004
2. Preparation, Installation, Analysis, and Interpretation of Corrosion Coupons in Oilfield
Operations, NACE International, NACE RP0775-2005.
3. ASTM G1 – 03, “Standard Practice for Preparing, Cleaning, and Evaluating Corrosion
Test Specimens,” American Society for Testing and Materials, PA, 2003
4. O. Olabisi. “Corrosion/Erosion Management Strategy in the North Slope: Use of
Corrosion Rate as Key Performance Indicator (KPI)”. CORROSION/2012, Paper No.
C2012-0001180, (Houston, TX: NACE 2012)
5. H. A. Videla, L. K. Herrera. “Influence of Microorganisms on the Corrosion and
Protection of Metals: An Overview”. CORROSION/2011, Paper No. C2011-0011218,
(Houston, TX: NACE 2011)
6. API RP 580 - Risk Based Inspection, First Edition, May 2002.
©2013 by NACE International.
Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to
NACE 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.
15
... seawater, brackish water, effluent water, and firewater are available. 4 Because of this pragmatic correlation, oil companies normally develop in-house guidelines for quantifying bacteria proliferation. For example, the Kuwait Oil Co. guidelines for quantifying sessile and planktonic bacteria proliferation are presented in Table 2. ...
... However, a distinct correlation is not discernable-not only for the recycle water data shown in Figures 1 and 2, but for the data corresponding to all the other water handling systems as well. 4 To interpret the field data in terms of the corrosion severity classification given in Table 1, as well as the target population density depicted in Table 2, elementary statistical analysis was adopted for the five years' worth of data. For each of the oilfield water handling systems studied, the number of corrosion incidents classified as "Low," "Moderate," "High," and "Severe" for the five-year period is summarized in Table 3. ...
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... Once defined by a major company, KPI values often replicate across the industry and are used to assess the efficacy of mitigation programs (El-Sherik, 2017). Typical empirical KPIs used by field operators in the Oil and Gas sector can range between 1 and 10,000 bacteria per milliliter or cm 2 , being in most cases 100 bacteria per ml or cm 2 the maximum tolerable concentration for cultivable sulfate reducers (Al-Shamari et al., 2013). Yet, ideally, the definition of microbial KPIs should be made in a case-by-case basis, taking into account trends of the microbiological, physicochemical and operational context, rather than adopting a generic figure (NACE-International, 2018). ...
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... The average CRs for groups of 60 BBs in duplicate columns 1 to 24 subjected to flow conditions for 45 days are summarized in Table 2. The averages for untreated columns 1 and 2, 7 and 8, and 13 and 14 were 0.101 ± 0.004, 0.107 ± 0.005, and 0.0962 ± 0.0004 mm/year, respectively, which is a moderate MIC rate (Al-Shamari et al. 2013). Columns 23 and 24 injected with sterile CSBK for 45 days had an average CR = 0.020 ± 0.002 mm/year (Table 2). ...
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Installation, Analysis, and Interpretation of Corrosion Coupons in Oilfield Operations
Preparation, Installation, Analysis, and Interpretation of Corrosion Coupons in Oilfield Operations, NACE International, NACE RP0775-2005.
Standard Practice for Preparing, Cleaning, and Evaluating Corrosion Test Specimens
ASTM G1 – 03, " Standard Practice for Preparing, Cleaning, and Evaluating Corrosion Test Specimens, " American Society for Testing and Materials, PA, 2003