What is Chemical EOR, Different types of chemical EOR, favorable Characteristics, the problems associated with it, advantages and disadvantages.

1. Enhanced Oil Recovery Techniques
Topic – Chemical EOR
Kavan Bhatt (500065783)
Manjil Nath (5000657670
Srivalsan (500071866)
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2. Introduction to Chemical EOR
• It is injection of various chemical which are usually dilute solution those have been use to enhanced
mobility and reduce surface tension.
• Types of Chemical EOR are –
a. Polymer Flooding –
 Consists of mixing long-chain polymer molecules with the injected water to increase the water
viscosity.
 Improves the vertical and areal sweep efficiency there by improving the water/oil Mobility ratio.
b. Surfactant Flooding –
 Decreases the surface tension between oil and water which reduces residual oil saturation and
improves the macroscopic efficiency of the process.
c. Alkali Surfactant Polymer Flooding –
 Caustic flooding lowers the surface tension, reverse the rock wettability, mobilize the oil and helps in
drawing the oil out of the rock.

3. Polymer Flooding
• The objective of polymer flooding as a mobility control agent is to provide better displacement and volumetric
sweep efficiencies during a water flood.
• The range of recovery with polymer is 5% to 30% of OOIP and efficiency is in the range of 0.7lb to 1.75 lb of
polymer per bbl of incremental oil production.
• Applicable to light and medium gravity oils
• Mature method with 40 years of commercial applications.
• Largest current polymer flood is in the Daqing field with about 220,000 bbl/day increment in oil production
from polymer flooding and 12% OOIP incremental recovery as of 2005.
• Hydrolyzed polyacrylamide (HPAM) is used in the field, up to about 185 F depending on the brine hardness.

4. Polymer Flooding

5. Favorable Characteristics for Polymer Flooding
• High remaining oil saturation
• Low water flood residual oil saturation
• High permeability and porosity
• Sufficient vertical permeability to allow polymer to induce crossflow in reservoir and good geological continuity.
• High polymer concentration and slug size.
• High injectivity due to favorable combination of high permeability, wells, or injection of parting pressure.
• Fresh water and soft water.
• Reservoir temperatures less than 220 F.

6. Structure and Behaviour Partially Hydrolyzed Polyacrylamide
(HPAM)

7. Polymer Implementation Problem
• Don't inject enough polymer.
• Open up high mobility paths by injecting water for a long time before polymer.
• Shear degrade the polymer.
• Plug the rock with low quality solution or polymer too large for small pores.
• Use biodegradable polymer such as xanthangum without effective biocide.
• Inject polymer in wells without geological continuity.

8. SURFACTANT FLOODING
• A small amount of surfactant is added to the displacing fluid injected to sweep the reservoir.
• The presence of surfactant reduces the interfacial tension between the oil and water phases and also alters the
wettability of the reservoir rock and improve oil recovery.
• The interfacial tension (IFT) is reduced by the creation of microemulsions at the interface between crude oil
and water
• Surfactants are used in conjunction with polymers.

9. SURFACTANT FLOODING

10. CHALLENGES OF SURFACTANT FLOODING
• Adsorption of surfactant to the rock during the injection
• Separation of the surfactant and co-surfactant(co-solvent softens up the surfactant film at oil/water interface
and increases the equilibration rate and formation of low viscosity microemulsions) in the reservoir
• High temperature
• High pressure
• High salinity

11. Favorable Characteristics for Surfactant Flooding
• High permeability and porosity
• High remaining oil saturation (>25%)
• Good geological continuity
• Good source of high quality water
• Reservoir temperatures less than 300 F for surfactant and less than 220 F if polymer is used for mobility control
• Surfactants with an equal attraction to the oil and water are optimum

12. TYPES OF SURFACTANTS
• Anionic surfactants
 Low adsorption at neutral to high pH on both sandstones and carbonates
 Can be used for a wide range of conditions
 Low cost
 High temperature applications
• Cationic surfactants are generally used as co-surfactants
• Non-ionic surfactants have not performed as well for EOR as anionic surfactants.

13. Some Surfactants used for surfactant flooding
• Alkyl benzene sulfonate
• Alkyl aryl sulfonate
• Alkyl sulfate
• Sodium dodecyl sulfate (SDS)
• Alcohol Propoxy Sulfate (APS)
• Ethoxy Sulfate (AES)

14. Winsor Type I Behavior
• Oil-in-water microemulsion
• Surfactant stays in the aqueous phase
• Difficult to achieve ultra-low interfacial tension

15. Winsor Type II Behavior
• Water-in-oil microemulsion
• Surfactant lost to the oil and observed as surfactant retention
• Should be avoided in EOR

16. Winsor Type III Behavior
• Separate microemulsion phase
• Bi-continuous layers of water and dissolved hydrocarbons
• Ultra-low interfacial tensions ~ 0.001 dynes/cm can be achieved
• Desirable for EOR

18. Alkaline flooding
• In alkaline flooding , a high PH (>7) chemical system is injected during polymer flooding or water flooding.
• It increase the relative permeability to oil and decreasing residual oil saturation by reducing IFT between oil
and water phase.
• Mobility control can improves displacement efficiency in alkaline floods.
• In most case, polymer is used as mobility buffer to displace primary slug.
• Chemicals used and in-situ formation of surfactant: alkaline agents are NaOH, Ammonium hydroxide,
Na2CO3, Ammonium carbonate.

19. How it works ?
• Alkaline chemical react with certain type oil which forming surfactant inside reservoir.
• Eventually, the surfactant reduce the IFT between oil and water and trigger an increase the oil production.
• Wetting characteristics also change due to formation of surfactant inside reservoir

20. When not to use ?
• Alkaline flooding is not suggested for carbonate reservoir due to presence of calcium.
• The chemical reaction between alkaline chemical and calcium ions may produce hydroxide precipitations that
may occur damage to formation

21. Criteria for Using and Effect of Diff. chemical
• Crude oil
 Gravity:13-35 API
 Viscosity: <200cp
• Reservoir
 AVG. permeability: >20md
 Depth: <9000ft
 Temp : < 200 degree F
Chemicals Effectiveness
Sodium othosillicate Up to 100%
Sodium carbonate Up to 65%
Sodium Hydroxide Up to 80%

22. Advantage and modification of technique
• It is usually more effective and efficient when acid content of reservoir is very high.
• In addition of new modification where surfactant and polymer to alkali which give a rise to Alkaline-
surfactant-polymer (ASP) EOR method
• This method is an effective and inexpensive form of micellar-polymer flooding.

23. Disadvantages
• Scaling and plugging in producing wells.
• High caustic consumption.