Design for optimal treatment of produced water Design for optimal treatment of produced water33rd rdInternational Seminar on Oilfield Water ManagementInternational Seminar on Oilfield Water Management Rio de Janeiro, 7Rio de Janeiro, 7 -- 9 June 2010 9 June 2010Anne Finborud, Mator AS Anne Finborud, Mator ASDesign for optimal treatmentDesign for optimal treatment what does it mean? what does it mean? Flexible regards to increasing produced water flow rate during field lifetime, both total flow rate and flow rate from individual separators. Robust regards to higher than expected amount of water from low pressure separators.R b d d i fi l l h hifi d id ib i Robust regards to production of particles although specified in a design basis as not expected. Robust regards to treatment and routing of already separated streams (rejects) toRobust regards to treatment and routing of already separated streams (rejects) to minimize negative effects. Flexible regards to utilization of the pressure and temperature balance in the t system. Robust regards to account for the total oily water system including open drain, closed drain and jetting water. closed drain and jetting water. Flexible to handle future low pressure production. Robust regards to a control philosophy with increased focus on constant flowRobust regards to a control philosophy with increased focus on constant flow instead of constant interfaces.Input data for design and equipment selection Input data for design and equipment selection? Characteristics and thereby treatability of produced water prior to treatment depends on: the type of fluid to be producedthe specification, design and operation of the separation trainthe production chemicals used the production chemicals used Having knowledge about factors such as droplet break-up, coalescence, physical and chemical properties, effects from process components etc. related to your specificyapplication, greatly increases the possibility for making good design solutions.Input data for design and equipment selection (contd) Input data for design and equipment selection (contd)System information: Field frame conditionsProcess information: Pressure Gas/condensate, oil, heavy oil Production profilesS ti t iPressure Pressure drop choke valves Temperatures Separation train Product spec Production chemicals Gas lift / high GLR Slugging Well workoversFluid properties: Oil and water densitites Solids Separator design Oil and water densitites Oil and water viscosities Oil/water interfacial tension Water phase salinity TAN WAT WAT OiW-concentration Oil droplet sizesHigher number of factors having negative influence on produced water requires a more robust process.Conventional technologies for oily water treatment Conventional technologies for oily water treatmentClass of technology Type of technologyDriving force General area of applicationMain technology Hydrocyclone Enhancedgravity Oilfields with high/low water flow, high/lowgy(Primary and secondary treatment)y y g y g , gOiW.Degasser Dissolvedflotation/gravityAll fields with high/low water flow, low OiW.Flotationunit Inducedflotation/gravity All fields with high/low water flow, low OiW.Compact flotation unitInducedflotation/gravity All fields with high/low water flow, low/medium OiW.Centrifuge Enhancedgravity Gas/condensate fields and open drain. Low water flow and high/low OiW.Enhancing/polishingtechnologyExtraction unit(e.g. CTour)Coalescence/extraction Oilfields with high/low water flow with available condensate. Special attentiondissolved technology(Tertiary treatment)(e.g. CTour) condensate. Special attention dissolved components.Extraction unit(e.g. MPPE)Coalescence/extraction All fields with low water flow, low OiW, and low solids and scale potential. Special attention di l d t dissolved components.Coalescing unit(e.g. MaresTail, PectF)Coalescence Oilfields (with hydrocyclones), and with low solids and scale potential.)Filters(e.g. CrudeSorb, TORR, nutshell)Coalescence/extraction Gas/condensate fields with low water flow, low OiW, and low solids and scale potential.Examples: treatment of oilfield produced water Examples: treatment of oilfield produced waterHow to combine the technologies into an overall system? How to combine the technologies into an overall system?Oily water and sand treatment philosophy Oily water and sand treatment philosophy Best Available Techniques (BAT), with built-in robustness against operational variations. PWRI applications require treatment PWRI applications require treatment. Two treatment stages to meet World Bank discharge limit of 29 mg/l oil in PW. Three treatment stages to meet stricter project requirements. g p j qThis also to apply for treatment of PW from 2nd stage/3rd stage/coalescer. Separate out PW from the oil train as early as feasible / possible. Avoid direct recycling of reject streams and skimmed oil streams as this may impair oil/water separation over time. Reject streams should be treated in a reject treatment stage with: Skimming of the oil phase for routing to export or last stage separator/coalescer Skimming of the oil phase for routing to export or last stage separator/coalescer. Treatment of the water phase in the PW system with possibility for recycling for increased flexibility.Or rejects should be routed to a slop system with dedicated treatment system. For pumping of PW prior to treatment use screw pumps (mono) or low speed centrifugal pumps. PW systems benefit from having constant flow rates. Include possibility for cleaning in place (CIP).Oily water and sand treatment philosophy (contd) Oily water and sand treatment philosophy (contd) When PW is used as jetting water it shall be taken downstream of the final treatment stage. Use sand cyclones on jetting water return. Water overflow to be returned to the PW system. Sand underflow to be treated according to sand management strategy Sand underflow to be treated according to sand management strategy. Online oil in water measurement is a valuable tool for optimization and troubleshooting. Cl d d i l Closed drain vessel: To be separate from the reject treatment stage. Skimming of the oil phase for routing to export or last stage separator/coalescer. Treatment of the water phase in the PW system with possibility for recycling for increased flexibility.Or closed drain should be routed to a slop system with dedicated treatment system.Od i Open drain: Skimming of the oil phase for routing to export or last stage separator/coalescer. Water from non-hazardous open drain can be discharged directly to sea. Water from hazardous open drain can be injected, sent onshore or discharged to sea after dedicated treatment.Oily water and sand treatment philosophy (contd) Oily water and sand treatment philosophy (contd)Case: produced water pump Case: produced water pump Screw pumps are far more gentle to the oil droplets thang phigh speed centrifugal pumps, thereby more suitable as produced water pumps. For centrifugal pumps increasing dP increases droplet break-upScrew pumps do notbreak up. Screw pumps do not show such correlation. Case: low pressure produced water Case: low pressure produced water Low pressure produced water is often more stabilised by particles and chemicals (lower interfacial tension thereby lower oil droplet coalescence), thereby more difficult to treat difficult to treat. However, treatment systems for low pressure water are often less equipped than high pressure water low pressure water has negative influence on the discharge.Case: sand cycloneCase: sand cyclone Oil content200u/s sand cycloneSolids content1200u/s sand cyclone140160180d/s sand cycloned/s hydro cycloned/s flash tank80090010001100d/s sand cycloned/s hydro cycloned/s flash tank80100120Oil, [mg/l]500600700Solids, [mg/l]20406010020030040002 min 7 min 20 min BaselineTime f r om st ar tjet t ing01002 min 7 min 20 min BaselineTime f r om st ar tjet t ing Solids d/s sand cyclone little affected by solids u/s sand cyclone, i.e. high solid content at the start of jetting is effectively removed by the sand cyclone. Solids and oil d/s hydrocyclone and degasser are somewhat higher during jetting, and lowest at baseline one day after jetting. Case: cleaning in place (CIP) Case: cleaning in place (CIP)Before CIP: After CIP:Case: recycling of rejects Case: recycling of rejects Rejects are often a mix of oil, particles and chemicals. Direct recycling of rejects to the separation train may impair oil/water separation. Many installations experience accumulation of rag-layers in the separators with resulting need for frequent carry-over procedures, and close follow-up of unforeseen process up-sets over time both on the oil and produced water side. p p p Negative effects from direct recycling of rejects occur over time, and are difficult to prove by short time testing. However, we strongly believe that alternative solutions than direct recycling of rejects in many cases would make a large difference especially on unforeseen and difficult to explain increased discharge of oil in water to sea. Case: recycling of rejects (contd) Case: recycling of rejects (contd) Direct recycling of rejects via the 57-tank high OiW and particles to 3stage separator Direct recycling of rejects via the 57-tank high OiW and particles to 3. stage separator. Results in bad quality water from 3. stage separator, however, better than the stream from the 57-tank. Intermittent return directly to the degasser, i.e. treated by only one treatment stage. Large negative influence on discharge to sea.Case: recycling of rejects (contd) Case: recycling of rejects (contd)Online OiW: Build-up of rag-layer in coalescer and intermittent (on/off) return of bad quality watere e (o /o ) e u o bad qua y a ewith flocculant and particles to 1. stage separator.P i d i hlf fl li j i Periods with control of flocculant injection, reduced skimming from degasser thereby reduced recycle, and improved pumping freq encofater ret rn from coalescer to frequency of water return from coalescer to1. stage separator.Case: recycling of rejects (contd) Case: recycling of rejects (contd) Reject water phase treated by dedicated centrifuge. Discharge < 10 ppm OiW with clean centrifuge requires CIP and optimized continuous operation optimized continuous operation. Recycling of water phase from closed drain has some negative effect on water from the separatorhowevereasy manageable byseparator, however, easy manageable by the hydrocyclones and degasser. Improved solution for reject treatment! All produced water discharge problems solved...? All produced water discharge problems solved...?Thank you! Thank you!