Water Treatment & Production Challenges

Table of Contents

Introduction

In tertiary floods—and, to a lesser extent, secondary floods—the most effective way to minimize the impact of polymer breakthrough (BT) on the production side is to delay BT by injecting at sufficiently high viscosity to improve the mobility ratio and keep polymer out of water fingers and high-permeability streaks. This lowers back-produced polymer loading on the water-treatment plant, preserves hydrocyclone and flotation efficiency, and reduces sludge formation with cationic programs. If early BT is detected at separators (rising polymer ppm), interpret it as a subsurface conformance signal: based on concentration and trend, screen and deploy profile control to re-balance flux before escalating topside mitigations. As a rule of thumb, <100–300 ppm at the water-treatment inlet is generally manageable with operational tuning; above that, prioritize conformance first, then refine chemicals and process settings.

What changes when polymer arrives at surface

Depending on concentration/molecular weight/degradation:

  • Higher water viscosity & elasticity: slower droplet rise (Stokes), tighter emulsions, altered coalescence.

  • Anionic charge: interacts with cationic chemicals, can stabilize oil droplets; raises cationic demand for deoilers.

  • Interactions with divalent ions (Ca²⁺/Mg²⁺, Fe): precipitation/fouling risk, sticky sludge.

  • Facility impacts: artificial-lift derating/wear, separator performance loss, cyclone/flotation efficiency drop, filtration/membrane fouling.

Primary separation (FWKO / first stage)

Possible impact of polymer Increased rag, carry-under/over, slow dehydration.

Levers:

  • Raise residence time; adjust internals for non-Newtonian μ–T–shear behavior measured on actual PFPW.

  • Demulsifier program: re-screen on polymerized emulsions; avoid unproven cationics upstream; prefer non-ionic/anionic packages validated in field brine.

Deoiling train

Hydrocyclones

  • Effect: drag reduction / altered flow ⇒ efficiency loss; pronounced >~800 ppm polymer.

  • Actions: pre-break viscosity (controlled shear/chemical), raise reject ratio, tune ΔP/flow, pair with flotation (CFU).

Flotation (IGF/DGF)

    • Principle: bubbles attach to droplets; polymer can hinder attachment or cause channeling.

    • Actions: combine DGF (denser, smaller bubbles) + IGF for robustness; re-tune gas fraction and contact; validate with polymerized streams

Coalescers

      • Dual behavior: small polymer can aid coalescence; high polymer inhibits film drainage.

      • Actions: increase surface area (media + plates), tune shear to avoid nano-droplets; add targeted coalescing chemicals.

Filtration & polishing

  • Media filters / nutshell: risk of polymer adsorption → ∆P rise, poor backwash. Use oil-selective media (not polymer-adsorbing), enlarge area, sequence backwashes (saline/alkaline surfactant; low oxidant only if materials allow).

  • Cartridges/bags: as safety polish; expect shorter life → plan spares.

  • Membranes (UF/ceramic): polymers pass but rapidly increase TMP, reduce flux; require frequent backwash/CIP and robust pretreatment (de-oiling + low-shear media + dose control). Pilot under worst-case polymer loads.

Heaters / electrostatic treaters

Heaters: polymer/oil-wet fines deposit on hot surfaces; limit wall temperature/heat flux; favor larger area/∆T step-down; implement polymer-aware cleaning (not just carbonate acid). Avoid exceeding polymer cloud-point regimes (HPAM issues escalate as wall temps rise; failures reported above ~220 °C). Consider ATBS-based polymers.

Electrostatic: polymer changes conductivity/coalescence kinetics; map field strength × water-cut window with and without polymer; adjust temperature, demulsifier timing, residence; consider dual-stage with inter-heating if fouling is controlled.

Chemical program (selection & compatibility)

  • Demulsifier (oil phase) + Deoiler (water phase): re-select on polymerized matrices; target minimal viscosity loss and acceptable filterability: ≤10% viscosity drift and ≤20% filter ratio change vs blank as screening criteria.

  • Cationic deoilers: dose carefully—high sludge risk with anionic polymer; plan sludge handling (stickier/heavier flocs).

  • H₂S scavengers: avoid strong oxidants in water line (polymer degradation, by-products). Prefer liquid-phase scavengers (e.g., MEA-triazine / newer oxazolidines) with deposition risk managed.

  • Biocides/others: verify no polymer degradation (viscosity loss, filterability). Some aldehydes lose efficacy with polymer hydrolysis by-products (ammonia). Always jar/bottle-test in field brine with returned polymer present.

Breaking the Polymer

  • Mechanical shear: simple, but may stabilize finer droplets/emulsions—apply judiciously.

  • Oxidation/radical routes (e.g., NaOCl): effective viscosity cut; design dedicated contactor with pH control, residual monitoring, materials compatibility, and safe containment; note potential corrosive by-products and waste.

  • Coagulation approaches: can aid downstream clarification but add sludge; test for compatibility

Artificial lift & upstream handling

  • SRP/PCP: higher energy, eccentric wear; mitigate with centralizers, continuous rods, GRE-lined tubing.

  • ESP: head derating possible (reports up to 60–70% at 6–11 cP); test curves in polymer fluids; avoid overheating (favors polymer precipitation); manage scale on hot surfaces.

Do / Don't

Do

  • Re-screen demulsifier/deoiler on polymer-rich matrices; calibrate dosages & injection points.

  • Combine DGF + IGF, and cyclones + flotation after viscosity-break where needed.

  • Upgrade filters/media to oil-selective, plan strong backwash sequences, and CIP fit-for-polymer.

  • Limit heater wall temperature; instrument for skin-temp alarms.

  • Budget for higher sludge volumes; pre-plan handling.

Don’t

  • Don’t introduce unproven cationic chemicals upstream of water line.

  • Don’t run hydrocyclones at polymer loads beyond tested thresholds without pre-breaking.

  • Don’t send polymer-rich streams to membranes without robust pretreatment and a CIP plan.

  • Don’t assume Newtonian design curves (cyclones, pumps, separators) apply unchanged.

Typical Outcomes & Expectations

  • With tuned chemistry, combined coalescence + flotation, and oil-selective media, spec water is achievable even with low-to-moderate polymer loads; high loads require a viscosity-break step and careful sludge management.

  • Keeping polymer in the water loop (PWRI), even degraded, often reduces overall OPEX (lower fresh chemical make-up, less waste). Deployment should be phased, with progressive upgrades tied to measured polymer back-production.

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