Tertiary Recovery

Key Takeaways

• Thermal EOR dominates heavy oil and oil sands recovery — steam injection methods work by heating high-viscosity crude oil from tens of thousands of centipoise at reservoir temperature to a few hundred centipoise at steam temperatures (300-350°C), reducing viscosity by several orders of magnitude and making it mobile enough to flow to producing wells; SAGD (steam-assisted gravity drainage), used extensively in Alberta's Athabasca oil sands, uses paired horizontal wells — a steam injector above a producer — to create a steam chamber that grows upward and outward through the bitumen, with the heated oil draining by gravity to the producer; SAGD recovers 40-70% of bitumen in place in favorable reservoir conditions, far exceeding what any other method could achieve in viscosities of 1 million centipoise and higher.
• CO2 miscible flooding has become the most widely deployed tertiary recovery method in conventional reservoirs — CO2 injected at pressures above the minimum miscibility pressure (MMP) with the reservoir oil undergoes a multi-contact miscibility process, dissolving into and vaporizing components from the oil until the injected CO2 and reservoir oil reach a single-phase miscible state; this miscibility eliminates the capillary trapping that causes residual oil saturation and allows the CO2 to mobilize and displace oil that water flooding cannot touch; the Permian Basin in West Texas and New Mexico hosts the most extensive CO2 EOR operations in the world, with hundreds of millions of cubic feet of CO2 injected daily through a pipeline network connecting CO2 source fields (natural CO2 reservoirs and industrial sources) to EOR fields; CO2 EOR also provides a path for geological carbon sequestration, as a portion of the injected CO2 is permanently trapped in the reservoir.
• Polymer flooding improves water flooding sweep efficiency by increasing the viscosity of the injection water — conventional water flooding suffers from poor sweep efficiency when water is significantly less viscous than reservoir oil (typical in medium and heavy oil reservoirs), causing the water to "finger" through the most permeable paths and bypass significant oil volumes; adding high-molecular-weight polymers (partially hydrolyzed polyacrylamide, HPAM, or xanthan biopolymer) to the injection water increases its viscosity and improves the mobility ratio, resulting in a more piston-like displacement front that sweeps a larger fraction of the reservoir; polymer flooding is commercially mature and has been deployed at massive scale in China (particularly in the Daqing field, where it increased recovery by several percentage points above water flood baseline), improving cumulative recovery by 10-15% incremental oil in favorable applications.
• Alkaline-surfactant-polymer (ASP) flooding combines three chemical mechanisms to attack both sweep efficiency and residual oil saturation — the alkaline component (sodium carbonate or sodium hydroxide) reacts with acidic crude oil components to generate natural surfactants in-situ, reducing the chemical cost of surfactant flooding; the synthetic surfactant component reduces interfacial tension to near-zero, mobilizing residual oil trapped in swept pore spaces; the polymer component provides mobility control for improved sweep efficiency; ASP combinations achieve the best theoretical efficiency of any chemical EOR method by simultaneously addressing both recovery mechanisms, but require careful formulation for each specific reservoir-oil-brine system and have historically suffered from surfactant adsorption losses and operational challenges including produced water treatment of the recovered chemical-laden fluids.
• The economics of tertiary recovery depend critically on oil price, reservoir quality, and method-specific operating costs — thermal methods have high energy costs (steam generation consumes natural gas or produces its own fuel from the produced oil); CO2 flooding requires sourcing, compressing, and recycling large volumes of CO2 with significant infrastructure investment; chemical flooding requires polymer and surfactant costs that increase linearly with water volume injected; the breakeven oil price for most EOR methods ranges from $40-80+ per barrel depending on method and reservoir quality, which explains why EOR activity expands dramatically at higher oil prices and contracts when prices fall; the 2014-2016 oil price downturn delayed numerous planned EOR projects that were economic at $100/bbl but not at $50/bbl.