Design features of offshore oil production platforms influence their susceptibility to biocorrosion

Transcription

1 Design features of offshore oil production platforms influence their susceptibility to biocorrosion Kathleen E. Duncan University of Oklahoma

2 Outline Introduction and Background Technical approaches to identifying and evaluating microbially influenced corrosion (MIC) Microbial communities associated with oil/gas production Case study: a tale of two offshore oil production platform designs Result of alterations in operations

3 Identification and evaluation of MIC Rule out other types of corrosion Corrosive products, damage consistent with MIC Multiple lines of evidence needed before altering operations High # microbes: serial dilutions, ATP, qpcr Corrosive activity: sulfate reduction activity assay, chemical analysis ID corrosive microbes: serial dilutions, DNA sequencing

4 Potential microbial metabolic interactions inside an oil production platform Carbohydrates Proteins Nucleic Acids Lipids Hydrocarbons Food source fermenters thiosulfate reducer Simpler forms of carbon fermenters Sulfur reducer sulfate reducer Volatile fatty acids and alcohols syntrophic bacteria H 2 & CO 2 Acetate methanogen sulfate reducer CH 4 H 2 S

5 Constraints on Microorganisms Who s there and their level of activity is shaped by operational and environmental parameters Oxygen, Temperature, Salinity, ph Energy sources: electron acceptors and donors Control chemicals: biocides, corrosion and scale inhibitors, etc. Flow rate, surfaces for biofilms

6 MIC and microbial biofilms Localized pitting starts with formation of bacterial biofilms 3D communities adhere to surfaces MIC: Variety of mechanisms and organisms H 2 S production by sulfate-reducing prokaryotes (SRP) Acid production (fermenters) Direct electron transfer from metals Fig. 2D. SEM of steel studs showing biofilm deposit. Bryant et al AEM 57:2804

7 Design features of offshore oil production platforms influence their susceptibility to biocorrosion Kathleen E. Duncan, Irene A. Davidova, Heather S. Nunn, Blake W. Stamps, Bradley S. Stevenson, Pierre J. Souquet, Joseph M. Suflita. Appl Microbiol Biotechnol. DOI /s

8 Three offshore oil platforms: Assets A, B, C Asset Reservoir Temperature ( o C) API gravity Salinity (g/l NaCl) A o B o C 70/ o (*141)

9 Schematic Design of Oil/Water Separation ASSET A / ASSET B Closed drains Asset B Closed drains Asset A Combined water/oil/gas production from Reservoir 1st stage Separator Desalter/Desander /Deoiler Crude oil storage in CARGOS Degasser + PW Clean up Produced Water Reinjection

10 Schematic Design of Oil/Water Separation ASSET A / ASSET B Closed drains Asset B Closed drains Asset A Combined production from Reservoir 1st stage Separator Desalter/Desander /Deoiler Crude oil storage in CARGOS High water flow rate: up to 700 m 3 /hour Short fluid retention time: ~ 10 minutes Recirculated fluids only from Closed Drains Degasser + PW Clean <0.3% volume from Closed up Drains Produced Water Reinjection

11 Schematic Diagram of Oil/Water Separation: ASSET C Co-mingled production from Reservoir 1st stage Separator Desalting Tank Crude oil storage in CARGOS Closed drains Degasser Oily water recycling upstream 1st stage separator Produced Water Decantation Tank Produced Water Reinjection

12 Schematic Diagram of Oil/Water Longer retention time: 3-5 hours Large Produced Separation: Water Decantation ASSET Tank: C 7000 m 3 Recirculated fluids from Produced Water Decantation Tank ~ 20% of 1 st stage separator Commingled production from Reservoir 1st stage Separator Desalting Tank Crude oil storage in CARGOS Closed drains Degasser Oily water recycling upstream 1st stage separator Produced Water Decantation Tank Produced Water Reinjection

13 Suspected Types of Corrosion Asset Corrosion observed Estimated ph CO2 corrosion Erosion corrosion A Not significant No No No B C Internal high fluid velocity areas (2-4 mm/year) Localized pitting corrosion (4-6 mm/year) MIC Yes Yes Low # SRB 5.3 Yes in high flow sites No High # SRB H 2 S SRB: sulfate-reducing bacteria

14 CO 2 corrosion control in B and C Increased corrosion inhibitor level in B and C B: stopped corrosion C: decreased corrosion only in high flow sites But still significant localized corrosion at other sites, suggesting MIC Investigate for MIC

15 Each Asset sampled at many sites Samples collected for: Genomics Sulfate Reduction Activity Parameters obtained: Temperature Sulfate Salinity

16 Types of analysis Rule out other types of corrosion Corrosive products, damage consistent with MIC Multiple lines of evidence needed before altering operations High # microbes: qpcr Corrosive activity: sulfate reduction activity assay ID corrosive microbes: DNA sequencing

17 Assets A/B: Where do we find high # microbes? Low temperature 35 o C 30 o C Closed drains Asset B Closed drains Asset A Combined production from Reservoir 1st stage Separator 6 Desalter/Desander /Deoiler Crude oil storage in CARGOS # bacterial 16S rrna copies > <10 5 *: per ml sample Degasser + PW Clean up Produced Water Reinjection

18 ASSET C: Fewer sites with high #s Co-mingled production from Reservoir 1st stage Separator Desalting Tank Crude oil storage in CARGOS 30 o C Closed drains Degasser Oily water recycling upstream 1st stage separator Produced Water Decantation Tank Produced Water Reinjection # bacterial 16S rrna copies > <10 5 *: per ml sample

19 High sulfate-reducing activity found in closed drains Closed drain temperatures <35 o C ASSET C

20 DNA sequencing used to identify bacteria Stars=closed drains Asset A Asset B Asset C Data obtained from NGS sequencing of 16S rrna genes

21 Many have potential for MIC: Sulfide-producers: thiosulfate-, sulfate-reducers Acid producers (fermenters) Iron reducers Asset A Asset B Asset C

22 But which microbes are different in Asset C? Stars=closed drains Asset A Asset B Asset C

23 Desulfonauticus (SRB, Desulfovibrionales) detected only in Asset C Stars=closed drains Asset A Asset B Asset C

24 Only Asset C has the right conditions: Desulfonauticus can t tolerate high salinity or high temperatures (>65 o C) Desulfonauticus, a SRB found only in Asset C Assets A and B: high salinity Asset C: like seawater

25 Why MIC in Asset C? 1. Suitable environmental parameters for Desulfonauticus But Assets A and B also had SRBs 2. Long retention times and large volume tanks allow #s to build 3. Recycling from SRB-rich tank distributes SRB throughout Commingled production from Reservoir 30 o C Closed drains 1st stage Separator Degasser Oily water recycling upstream 1st stage separator Desalting Tank Produced Water Decantation Tank Crude oil storage in CARGOS Produced Water Reinjection

26 Change in operations: no more failures in Asset C Stopped recirculation from Produced Water Decantation Tank Biocide treatment: THPS (500 ppm) every week for 5 hours Environmental parameters changed too Higher temperatures Later genomics samples did not detect Desulfonauticus

27 Acknowledgements OU Biocorrosion Center and Total S.A. OU coauthors Irene A. Davidova Heather S. Nunn Blake W. Stamps Bradley S. Stevenson Joseph M. Suflita Total S.A. coauthor: Pierre J. Souquet