aquateam A Review of PWRI experience: Souring Mitigation, MIC Control and Monitoring

Transcription

1 A Review of PWRI experience: Souring Mitigation, MIC Control and Monitoring TEKNA Produced Water Management Conference 2011, Stavanger, Norway Anthony J Dinning, PhD Microbiologist Aquateam

2 The next 25 mins PWRI history on the NCS Reservoir souring Souring mitigation Nitrate mediated souring mitigation Case review of knowledge Successful nitrate based souring mitigation Road map to sustainable PWRI

3 PWRI NCS: Field studies, Aquateam Ula pilot & full scale Snorre full scale Stopped 2006 Ongoing Statfjord C pilot risk of souring Ekofisk pilot risk of souring Draugen pilot: NO 3 High MIC PWRI delayed Petromaks PWRI JIP 2007 to 2010 Sustainable PWRI-developing biotoolbox Developing PWRI Guidelines

4 PWRI drivers & obstacles Drivers Legislation Company profile Environmental profile Reduce discharge Reduce chemical use Cost effectiveness Reduce volume PW discharged PW becomes a resource Obstacles Cost Reservoir integrity Corrosion Biofouling MIC occurrence RESERVOIR SOURING

5 PWRI Studies Studies performed for: ConocoPhillips Statoil Norske Shell BP Petrocanada OGPT Petrobras Enterprise Oil Competance areas: Solids handling Microbiology Water treatment Corrosion Most studies do not reach the field due to high risk of souring Particularly mature fields

6 Souring mechanism Definition: Increase in hydrogen sulphide (H 2 S) in reservoir fluids Mediated by Sulphate reducing prokaryotes (SRP previously known as SRB) Detrimental: Limits reservoir exploitation Economy, HS&E, Integrity Carbon + SO H + Biomass + H 2 S + CO 2 + H 2 0 Observed in: Seawater flooded reservoirs Reservoirs utilising PWRI

7 Reservoir scavenging Producing well Injector well Authigenic iron minerals present in the reservoir (ie: siderite) Lower [H 2 S] High [H 2 S] Initially lower H 2 S concentration in the water due to hydrocarbon partitioning and mineral interaction H 2 S conc increases with number of pore volumes Biofilm area and H 2 S production Production Flow

8 PWRI & souring The implementation of successful PWRI may be dependent upon controlling souring The inevitability of souring provides the demand for a successful mitigation strategy Mitigation strategies have to be reviewed, including new data

9 Souring mitigation available tools Biocide dosing Too intensive, costly Ineffective in the reservoir Require 1500 times more biocide to kill a biofilm Biofilm Survives biocide dosing Planktonic Doesn t survive Sulphate removal Nutrient limitation Molybdate / anthraquinone Inhibit SO 4 reduction to H 2 S Low sulphate concentration Low souring levels Nitrate dosing Steer metabolism from S to N NO 3 SO 4 S 2- NO 2, N 2, NH 4

10 Nitrate based souring mitigation Nitrate / nitrite Environmentally acceptable chemical (completely broken down) Shown to work well in SWI systems Halfdan (but corrosion reported topsides at receiving platform??) Gulfaks Norne Etc Effects the microbial community composition in the IW, reservoir and producing wells Lots of different organisms can utilise nitrate/nitrite

11 Nitrate based souring mitigation Who does what? NR-SOB nitrate reducing-sulphide oxidising bacteria reduce nitrate and oxidise sulphide (most likely not in one single step) 8 NO H HS - 4 N H 2 O + 5 SO 4 2 NRB reduce nitrate through to N 2 (most likely not in one single step) Denitrification - - NO 3 NO 2 NO N 2 O N 2 SRP NRB NR-SOB + NH 4 NR-SOB NRB Dissimilatory nitrate reduction to ammonia (DNRA) NRB dissimilate NO 3 to NH 4 via NO 2 SRP dissimilate NO 3 to NH 4 (detox process)

12 Partial NO 3 reduction = Partial S 2- oxidation The partial reduction of nitrate may result in partial oxidation of sulphide These species (polysulphides, elemental sulphur) are corrosive A clue in the nitrate-mic mechanism Involvement of NR-SOB in MIC process NO 3 NO 2, N 2 O, NO N 2 S 2- S - n SO 4 CORROSION

13 PWRI & Nitrate case studies Glauc C Field (Alberta) H 2 S levels were mitigated successfully No corrosion observed Brage (NCS) Corrosion rates increased 1,4 1,2 ER Probe B Draugen (NCS) Souring mitigated successfully Corrosion rates increased Pitting & MIC increased Corrosion rate [mm/year] 1,0 0,8 0,6 0,4 0,2 ½ NO 3 NO B B 0,

14 Laboratory findings NR-SOB were present in the Draugen produced water In systems with established sulphidic biofilm, corrosion rates increased as the nitrate to carbon ratio increased Elemental sulphur was found in nitrate treated biofilm This suggests the involvement of NR-SOB in the MIC process in nitrate dosed biofilms Corrosion control can be achieved Elemental sulphur

15 MIC control PW & NO 3 Nitrate : Carbon is important Nitrate : Carbon < 1:1 improved MIC control Souring was compromised Play off Souring v MIC Dependent upon bacterial populations Use of pigging / biocide had a positive effect on MIC Corrosion inhibitor had a positive effect in clean systems Corrosion inhibitor had no effect in systems with existing SRB biofilm (ie, sulphidic activity)

16 Use of laboratory tests (JIP) Maintenance of the Draugen (sitespecific) biofilm was time consuming The laboratory work did: Confirm Draugen results Aid understanding of the nitrate- MIC mechanisms Allow testing many variables Lab tests are good but can: Be time consuming (to gain the correct information > years) Give extensive error sources NCO s, contaminant enrichment Change microbial community Maintaining relevant biofilm Support understanding experiences gained in the field - SMC

17 Nitrate, PWRI & Biotoolbox The onset of corrosion with nitrate dosing is FIELD SPECIFIC Field monitoring is crucial The biotoolbox includes Applicable monitoring procedures Physicochemical methods Microbiological methods Corrosion studies Procedures for application of nitrate Monitoring secondary effects MIC & Biofouling Evaluating mitigation strategies Defining sustainable PWRI Laboratory screening Lab long term Pilot field scale Cost of testing Full scale

18 The biotoolbox a biochemical solution Microbiology NRB / NR-SOB Pyrosequencing / MPN Chemistry Nutrients SO 4, NO 3, NO 2, NH 4, tot-n, PO 4, C S 2- formation Corrosion Pitting increase Testing Offshore real time Independent of PWRI Corrosion Microbes Successful souring mitigation Sustainable PWRI Chemistry The Biotoolbox

19 Nitrate based souring mitigation for sustainable PWRI Logical steps required for mitigation and control Analysis of water quality to be injected Performance of pre-studies to monitor the reactivity of the PW with nitrate (biotoolbox, independent of LIVE PWRI) Aid in the prediction of MIC Allow for MIC mitigation to be fine tuned Pilot well should have a short pore volume (ie, days or weeks) This provides monitoring with respect to effects of nitrate breakthrough increased MIC risk potential biofouling Analysis of the near well & PW microbiology prior to nitrate injection Quality control of nitrate injection in a pilot well Quality control of nitrate injection, full scale

20 Acknowledgements The Research Council of Norway and our industry partners Nils-Kåre Birkeland, Marit Madsen, Håkon Dahle and Jeffery Keen Joseph Arensdorf Eilen Vik, Carsten Schwermer, Frøydis Garshol, Ocelie Kjønnø and Liv Bruås

21 Thank you for your attention!