A Holistic Approach to Produced Water Management. Case Study. Jacqueline Geddes-Smith / 19 th June

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1 A Holistic Approach to Produced Water Management Case Study Jacqueline Geddes-Smith / 19 th June

2 Produced Water Typical Concerns > Physical and chemical properties of produced water vary considerably depending on: geographic location, geologic formation type of hydrocarbon product being produced. > The major constituents of concern are: Salt content (salinity, conductivity, or total dissolved solids (TDS). > Oil and grease. Free oil: large droplets - readily removable by gravity separation methods Dispersed oil: small droplets - somewhat difficult to remove Dissolved oil: hydrocarbons and other similar materials dissolved in the water stream - very challenging to eliminate. > Inorganic and organic toxic compounds. > Naturally occurring radioactive material (NORM). 2

3 Produced Water What can we do to manage it? > What is the fate of produced water from our fields? Injected for enhanced oil recovery (EOR) Discharged to environment Off-site waste commercial disposal. > How do we treat our produced water? > Why is residual oil in this produced water a concern? Plugging of disposal wells Plugging of lines, Corrosion due to acid gases and electrochemical reactions Growth of bacteria. Significant environmental risks. Removal of Oil, Grease and Organics Removal of metals and Inorganics Removal of salts Microbial Control Gravity separation Physical separation (filters, hydrocyclones, centrifuges) Coalescence Floatation Combined physical and chemical processes Adsorption Oxidation ph adjustment and clarification Membrane processes (RO) Ion exchange Electrocoagulation Membrane processes (RO) Thermal distillation Crystallization Use of biocides UV treatment Treatment with ozone Is this the whole picture though??? 3

4 Synopsis North Sea Operating Facility > Facility had experienced water quality issues for a protracted period of time. Light crude; GOR scf/stb API 34 Significant water production from wells Injection supported reservoir Gas lifted wells > Designed for 41 platform wells Less than half now producing Subsea field tie-back, 7mbd Oil in Water Concentrations (PPMV) Heather Daily Oil In Water Concentrations > Numerous types of treatment vessels applied Compact Floatation Unit (CFU) Hydrocyclones WEMCO - Mechanically induced floatation unit 0 01-Jan Feb Apr May Jul Sep Oct Dec-12 Date Daily Oil In Water Concentrations Maximum Oil In Water Limit None successfully alleviated the issue. 4

5 Facility Produced Water Handling Framing the Problem > Limiting the period of production review to current system arrangement 3 month period selected. > Fishbone approach to root cause analysis. > Four key areas of analysis identified: Solids management Process debottlenecks Chemical Treatment Process Troubleshooting > Xodus Study Approach included: Production Chemistry Flow Assurance Process Dynamics 5

6 Period of Review > Focus on High period operation line-up of wells which showed the greatest excursion from the OIW specification. 6

7 Problem Solving Approach Study approach focused on a 3-pronged approach > Production Chemistry Review > Process Topside Review > Flow Assurance review. Summary of approach > All studies commenced with information sharing. > Oil in water likely to be caused by slugging from the 3-phase pipelines (8-inch and 10-inch) > Solution likely to be by: Remedy of slugging to 1 st stage separator Chemical means or identify an alternative separation process. 7

8 Production Chemistry Review Aim of review > Achieve consistent OIW discharge figures < 30 mg/l Stretch target for daily discharge at < 15 mg/l > Identify potential process, equipment, well fluid and / or chemical issues impacting the produced water system > Analysis effects to determine their influence on the system performance > Implement recommendations to ensure controls put in place to enable proactive and controlled changes. Key findings > Solids management issues related to iron sulphide as a surfactant > Changes needed to chemical treatment philosophies > Possible process bottlenecks and oversizing of hydro-cyclones and CFUs Recommendations > Assess whether iron sulphide was being recycled to the upstream system. > Monitor all wells regularly for sediment analysis > Improve record keeping from well test data. No conclusive cause of oil in water quality issues identified. 8

9 Flow Assurance / Slugging Review Pipeline Performance > Single point benchmarking of pipeline hydraulics (both 8-inch and 10-inch) > Focus on well line-up with significant OIW excursions > Confirmation of slugging in both the 8-inch and 10-inch production pipelines terrain induced mechanism Slug Mitigation Potential to Stabilise Flow to CFU > Inlet choking at platform > Applying +2 bar on 8-inch flowline reduced surge volumes Liquids by 18-33% Water by 8 to 36% Impact to production rates from wells. > Applying +2 bar on 10-inch flowline increased liquid surge volumes Liquids by % Water by % Choking of 10-inch not a suitable option. So, what can we do now? 9

10 Process Topside Review Produced Water Facilities Performance > Oversized equipment CFU designed for 50,000 bbl/d Current operation 23,000 bbl/d > Issue being caused by cycling of water flow to the CFUs Vortices disturbed within unit Separation efficiency negatively impacted Separator Performance > Riser 1 and Riser 2 pressures show significant fluctuations for on spec and off spec production days Level of pressure swing noted to be larger on days where water quality off spec. > Control instabilities induced by slugging Separator (C01) pressure swings Separator pressure floats on compressor suction Instabilities in separator pressure therefore only dampened by volume effects. Level fluctuations leads to LCV movement coupled with pressure results in larger flow fluctuations of water stream from vessel. Control band noted to be 20% Separator (C-02) adequately sized for current duty Level and pressure control valve movement minimal - little carryover from the separator Raising interface level of C-01 to use separation capacity of C-02 10

11 Process Solution Solution and Recommendations > Improved monitoring and record keeping > Interface level raised (C-01) > Revisit of control scheme on separator (C-01) to open level control band > Re-instate control scheme on compressors. Reviewed control arrangement implemented. > Vortices stabilised in water treatment and significant improvement achieved in OIW content. Problem solved! 11

12 > Thank you 12