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Bacteria Population Density is a Key Performance Indicator for Oilfield Water Handling Systems

Authors:
  • Infra-Tech Consulting LLC

Abstract

In the oil & gas industry, key performance indicators (KPI) are used to track the efficiency of the prevailing corrosion risk management strategy for the preservation of pipeline integrity. This includes the integration of corrosion monitoring, process monitoring, inspection, mitigation, environmental control, and materials management. At Kuwait Oil Company (KOC), internal corrosion monitoring activities are carried out in 22 gathering centers, early production facilities, 5 booster stations (operating), 3 effluent water disposal plants, seawater treatment plant, seawater injection plant, and pipeline network carrying different products. Corrosion and corrosivity trends are monitored using weight-loss coupons, electronic probes, bioprobes, hydrogen patch probes, galvanic probes as well as the measurement of iron content (total and dissolved) and manganese content. Corrosivity trend is also monitored using pH, conductivity, total dissolved solids, total hardness, dissolved oxygen, H2S concentrations, CO2 concentrations, bacterial population density and corrosion inhibitor residuals. These activities consume significant resources that could otherwise be conserved. The present paper identifies bacterial population density as a key performance indicator. That is, minimizing bacterial population density could enable greater cost effectiveness, efficiency, and reliability. It would certainly enable the control of the state of corrosion integrity of oilfield water handling systems.
Bacteria Population Density is a
Key Performance Indicator for Oilfield Water
Handling Systems
Dr. Olagoke Olabisi
Director, Internal Corrosion Engineering
Corrpro Companies, Inc., Houston, Texas
Abdul Razzaq Al-Shamari
TL (S&E) Inspection & Corrosion Team
Kuwait Oil Company, Ahmadi, Kuwait
Ashok Mathew
Corrosion Chemist, Inspection & Corrosion
Kuwait Oil Company, Ahmadi, Kuwait
Presentation outline
Types of water handling systems considered in
this study
Corrosion monitoring methods
Significance of fluid parameters as corrosion
control metrics
Field data analyses
Corrosivity severity ranking of oilfield waters
Corrosion severity ranking of oilfield waters
Bacteria population density severity ranking of
oilfield waters
Concluding remarks
3
Water systems considered in this study
Three water handling systems were selected based on
fluid type
Fluid TDS, mg/L Fluid type Monitoring locations
1 5,000-
18,000 Brackish
Water 2nd Stage Desalter Inlet
2 6,000-
20,000 Recycle
Water 1st Stage Desalter Inlet
3 45,000-
150,000 Effluent Water 1st Stage Desalter Outlet, Effluent
Balance Tank Inlet & Outlet
4
Corrosion monitoring in water systems
Corrosion monitoring methods:
Mass loss corrosion coupons
General & pitting corrosion rates measurements
Deposits collection (includes sessile bacteria)
LPR probes (corrosion rates measurements)
Galvanic probes (oxygen concentration)
Bio probes (sessile bacteria population density)
XRD analyses (pig deposits & other solids)
Fluid analyses
Chemical analyses of water solubles
Chemical analyses of acid solubles
Treatment chemical residual analyses
Electrolyte conductivity
Planktonic bacteria population density 5
S/N Parameter Significance
1 pH pH of <7 indicates acidity of the fluid. A lower value of pH
indicates higher corrosivity.
2 Conductivity A high conductivity of the fluid generally indicates high
corrosivity.
3 Chloride Chloride acts as electrolyte in corrosion reactions.
Corrosivity of the fluid generally increases with an
increased chloride content
4 Sulfate
Sulfate acts as electrolyte in corrosion reactions. However,
sulfate contributes less to Corrosivity than Chloride.
Sulfate Reducing Bacteria (SRB) grow in sulfate containing
water
5 Hydrogen
Sulphide (H2S) H2S increases corrosivity of the fluid by providing H+ ions.
6 Total Hardness As the hardness of the fluid increases, scaling tendency
increases. This may contribute to under-deposit corrosion.
Significance of Fluid Parameters as Corrosion Control Metrics
S/N Parameter Significance
7 Dissolved
Oxygen (DO)
High DO content indicates high corrosivity. Typically the
DO content is kept at <10 ppb by the use of oxygen
scavengers.
8 Dissolved Iron Dissolved iron content is a measure of corrosion. An
increasing trend of iron content might be indicative of
increasing corrosion.
9 Total Iron
Total Iron indicates the sum of dissolved iron and insoluble
iron compounds. The difference between total and
dissolved iron indicates the amount of iron compounds
formed due to corrosion.
10 Manganese
(Mn)
Mn is a major alloying element in carbon steel. A high Mn
content indicates high corrosion. Also, the ratio Mn:Fe
indicates whether the Fe content is due to corrosion
11 Corrosion
Inhibitor (C.I.)
Residual
A higher content of C.I. Residual indicates decreased
corrosivity.
Significance of Fluid Parameters as Corrosion Control
Metrics (contd.)
Trend of pH and Corrosion rates in Effluent Water
(1mpy = 0.0254 mm/y)
8
GC-08 Effluent Water
0
2
4
6
8
10
Jan-06
Jan-07
Jan-08
Jan-09
Jan-10
Jan-11
Jan-12
Jan-13
Jan-14
Period
0.1
1
10
100
1000
Corrosion Rate and
Ptting Rate (mpy)
Corrosion Rate (mpy) Pitting Rate (mpy) pH
Trend of Conductivity and Corrosion rates in Effluent Water
(1mpy = 0.0254 mm/y)
9
GC-08 Effluent Water
0
100000
200000
300000
400000
500000
Jan-06
Jan-07
Jan-08
Jan-09
Jan-10
Jan-11
Jan-12
Jan-13
Jan-14
Period
Conductivity (µs/cm)
0.1
1
10
100
1000
Corrosion Rate and
Ptting Rate (mpy)
Corrosion Rate (mpy) Pitting Rate (mpy) Conductivity (µs/cm)
Trend of Chloride and Corrosion rates in Effluent Water
(1mpy = 0.0254 mm/y)
10
GC-08 Effluent Water
0
20000
40000
60000
80000
100000
Jan-06
Jan-07
Jan-08
Jan-09
Jan-10
Jan-11
Jan-12
Jan-13
Jan-14
Period
Chloride (ppm)
0.1
1
10
100
1000
Corrosion Rate and
Ptting Rate (mpy)
Corrosion Rate (mpy) Pitting Rate (mpy) Chloride (ppm)
Trend of Dissolved Oxygen and Corrosion rates in Effluent Water
(1mpy = 0.0254 mm/y)
11
GC-08 Effluent Water
0
10
20
30
40
50
Jan-06
Jan-07
Jan-08
Jan-09
Jan-10
Jan-11
Jan-12
Jan-13
Jan-14
Period
Dissolved Oxygen (ppb)
0.1
1
10
100
1000
Corrosion Rate and
Ptting Rate (mpy)
Corrosion Rate (mpy) Pitting Rate (mpy) Dissolved Oxygen (ppb)
Trend of Hydrogen Sulfide and Corrosion rates in Effluent Water
(1mpy = 0.0254 mm/y)
12
GC-08 Effluent Water
0
2
4
6
8
Jan-06
Jan-07
Jan-08
Jan-09
Jan-10
Jan-11
Jan-12
Jan-13
Jan-14
Period
Hydrogen Sulphide (ppm)
0.1
1
10
100
1000
Corrosion Rate and
Ptting Rate (mpy)
Corrosion Rate (mpy) Pitting Rate (mpy) Hydrogen Sulphide (ppm)
Trend of total hardness and corrosion rates
(1mpy = 0.0254 mm/y)
13
GC-08 Effluent Water
0
10000
20000
30000
40000
Jan-06
Jan-07
Jan-08
Jan-09
Jan-10
Jan-11
Jan-12
Jan-13
Jan-14
Period
Total Hardness (ppm)
0.1
1
10
100
1000
Corrosion Rate and
Ptting Rate (mpy)
Corrosion Rate (mpy) Pitting Rate (mpy) Total Hardness (ppm)
Trend of dissolved iron and corrosion rates
(1mpy = 0.0254 mm/y)
14
GC-08 Effluent Water
0
2
4
6
8
Jan-06
Jan-07
Jan-08
Jan-09
Jan-10
Jan-11
Jan-12
Jan-13
Jan-14
Period
Dissolved Fe (ppm)
0.1
1
10
100
1000
Corrosion Rate and
Ptting Rate (mpy)
Corrosion Rate (mpy) Pitting Rate (mpy) Dissolved Fe (ppm)
Trend of total iron and corrosion rates
(1mpy = 0.0254 mm/y)
15
GC-08 Effluent Water
0
2
4
6
8
Jan-06
Jan-07
Jan-08
Jan-09
Jan-10
Jan-11
Jan-12
Jan-13
Jan-14
Period
Total Fe (ppm)
0.1
1
10
100
1000
Corrosion Rate and
Ptting Rate (mpy)
Corrosion Rate (mpy) Pitting Rate (mpy) Total Fe (ppm)
Trend of manganese and corrosion rates
(1mpy = 0.0254 mm/y)
16
GC-08 Effluent Water
0
1
2
3
4
5
Jan-06
Jan-07
Jan-08
Jan-09
Jan-10
Jan-11
Jan-12
Jan-13
Jan-14
Period
Manganese (ppm)
0.1
1
10
100
1000
Corrosion Rate and
Ptting Rate (mpy)
Corrosion Rate (mpy) Pitting Rate (mpy) Manganese (ppm)
Trend of corrosion inhibitor and corrosion rates
(1mpy = 0.0254 mm/y)
17
GC-08 Effluent Water
0
10
20
30
40
Jan-06
Jan-07
Jan-08
Jan-09
Jan-10
Jan-11
Jan-12
Jan-13
Jan-14
Period
CI Residual (ppm)
0.1
1
10
100
1000
Corrosion Rate and
Ptting Rate (mpy)
Corrosion Rate (mpy) Pitting Rate (mpy) CI Residual (ppm)
Trend of sulfate and corrosion rates
(1mpy = 0.0254 mm/y)
18
GC-08 Effluent Water
0
500
1000
1500
Jan-06
Jan-07
Jan-08
Jan-09
Jan-10
Jan-11
Jan-12
Jan-13
Jan-14
Period
Sulphate (ppm)
0.1
1
10
100
1000
Corrosion Rate and
Ptting Rate (mpy)
Corrosion Rate (mpy) Pitting Rate (mpy) Sulphate (ppm)
Field Data Analysis
All the figures indicate that general and pitting
corrosion rates are impacted somewhat by the fluid
parameters in effluent, brackish, and recycle water
systems.
However, a distinct correlation is not discernible.
Let us now compare the values of the fluid
parameters for the three different fluids.
We tabulate the highest values for each parameter
for each fluid, except for pH (where the lowest value
is the most acidic).
Summary of Analytical Results of Different Fluid Streams
S/N
Parameter Values Obtained for Different Fluids
Brackish
Water Recycle Water Effluent Water
1 pH 6.2 6 5
2 Conductivity (µs/cm) 5800 15,000 320,000
3 Chloride (mg/L) 1250 6400 95,000
4 Dissolved Oxygen (DO) (ppb) 10 5 20
5 Hydrogen Sulphide (mg/L) 0.1 4.2 5
6 Total Hardness (mg/L) 2500 4000 35,000
7 Dissolved Iron (mg/L) 2 4.5 5
8 Total Iron (mg/L) 2 4.5 5
9 Manganese (mg/L) 0.5 0.5 2.5
10 Corrosion Inhibitor (C.I)
Residual (mg/L) 50 20 30
11 Sulphate (mg/L) 2200 1500 1000
Corrosivity Ranking of Different Fluid Streams
Based on the 2010-2013 data of eleven different
fluid parameters, the corrosivity severity ranking of
the water handling systems is in the following
decreasing order:
Effluent Water > Recycle Water > Brackish Water
MENT PROTOCOLS
ENT PROTOCOLS
NACE RP0775 guidelines
*mpy = mil per year (1 mil = 0.001 inch = 0.254 mm)
General Corrosion
Category
Corrosion Rate
(mpy) Pitting Corrosion
Category Pitting Rate
(mpy)
Low < 1 Low < 5
Moderate 1 to 4.9 Moderate 5 to 7.9
High 5 to 10 High 8 to 15
Severe > 10 Severe > 15
Corrosion Severity Classification
Summary of Corrosion and Pitting Rates of
Different Fluid Streams
23
S/N Parameter
Incidents of severe
corrosion (%)
Brackish
Water Recycle
Water
Effluent
Water
1
General corrosion Rate
(above 10 mpy or 0.254
mm/y) 67 20 9
2
Pitting Rate
(above 15 mpy or 0.381
mm/y)) 92 86 57
Based on the above tabulated results, the corrosion severity
ranking of the water handling system is in the following
decreasing order:
Brackish Water > Recycle Water > Effluent Water
Paradoxical observation about:
Corrosion Severity & Corrosivity Ranking
24
Based on Corrosion and Pitting Rates, the
corrosion severity ranking of the water handling
systems is in the following decreasing order:
Brackish Water > Recycle Water > Effluent Water
This is paradoxically the complete opposite of the
corrosivity severity ranking:
Effluent Water > Recycle Water > Brackish Water
That is, there is no direct correlation between the
analytical results from fluid sampling and
corrosion data from mass-loss corrosion coupons
Corrosivity Vs. Corrosion Severity Rankings
What could be responsible for the reduced
corrosion severity when fluid corrosivity is high?:
Presence of a durable film layer of corrosion
inhibitor on the coupon
Presence of a passive layer of iron oxide on the
coupon
Presence of scaling compounds that form a
protective layer on the coupon
Reduced or limited MIC susceptibility
Corrosivity Vs. Corrosion Severity Rankings
(Cont’d.)
Under the current production scenarios, what is
responsible for the reduced corrosion severity when
the bulk corrosivity is high?
We did not observe any passive layer of iron oxide
on the corrosion coupons
We did not observe any protective layer of
scaling compounds on the corrosion coupons
On the other hand, we are unable to eliminate the
possibility of a durable film layer of corrosion
inhibitor on the coupon.
However, what about the MIC susceptibility of the
fluid streams?
Data Analysis by Serial Dilution (NACE TM0194)
KOC guidelines are used for handling bacteria data
KOC 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/APB
<102 counts/cm2 <104 counts per ml
Number of Bacteria Incidents Categorized Per
Company Guidelines
FLUID
TYPE
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
Brackish
Water 3 27 0 30 0 30
Recycle
Water 13 12 7 18 7 18
Effluent
Water 18 2 16 4 9 11
Key Performance Indicator
The data presented in the previous 2 slides illustrates
that both the corrosion severity as well as the bacteria
population density severity of the streams are in the
following decreasing order:
Brackish Water > Recycle Water > Effluent Water
That is, there is a direct correlation of corrosion severity
with bacteria population density severity
But there is NO correlation of corrosivity severity with
corrosion severity.
Hence, bacteria population density is a Key
Performance Indicator (KPI) for oilfield waters
29
The corrosivity severity ranking of the oilfield water
handling systems is in the following decreasing order:
Effluent Water > Recycle Water > Brackish Water
The corrosion severity ranking of the oilfield water
handling systems is in the following decreasing order:
Brackish Water > Recycle Water > Effluent Water
Bacteria population density severity ranking of the
oilfield water handling systems is in the following
decreasing order:
Brackish Water > Recycle Water > Effluent Water
Summary and Conclusion
Under the current production scenarios, Brackish Water is
less saline and more susceptible to MIC.
The paradoxical observation that Brackish Water is
characterized by the lowest fluid corrosivity and the highest
corrosion severity could be ascribed to its MIC susceptibility.
Bulk corrosivity is NOT an appropriate performance
indicator in the presence of effective corrosion inhibitor
Bacteria population density is the key performance indicator
in a bacteria-infected, MIC-susceptible water-handling
systems.
Summary and Conclusion (Cont’d)
Olagoke Olabisi, PhD
Director, Internal Corrosion Engineering
Corrpro Companies, Inc., Houston, Texas
Abdul Razzaq Al-Shamari
TL (S&E) Inspection & Corrosion Team
Kuwait Oil Company, Ahmadi, Kuwait
Ashok Mathew
Corrosion Chemist, Inspection & Corrosion
Kuwait Oil Company, Ahmadi, Kuwait
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