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WorksheetsEnhanced Oil Recovery (EOR) Worksheet
Total questions: 40
Worksheet time: 30mins
A reservoir contains light oil (6 cp). Thermal EOR such as steam is usually used for very high-viscosity oils (hundreds to thousands of cp). Which statement is correct?
Thermal EOR is ideal for 6 cp oil
Thermal EOR is unnecessary for such low viscosity
Steam will increase viscosity
Steam cannot be injected into any reservoir
Chemical EOR (surfactant/polymer) typically degrades above 150°F. If a reservoir is 215°F, what does this imply?
Chemical EOR is ideal
Chemicals will be more active
Chemicals may degrade and lose effectiveness
Surfactant flooding becomes miscible
A reservoir has pressure = 2000 psi and the minimum miscibility pressure (MMP) for CO₂/H₂S mixture is 1000 psi. Which EOR method is most suitable?
Polymer
Miscible gas flooding
Steam flooding
Nitrogen injection
When CO₂/H₂S was injected, production fell quickly after a short time. What is the most likely reason?
Oil viscosity increased
Early gas breakthrough
Wellbore collapse
Formation became water-wet
In a WAG process, the gas-water ratio was reduced from 1.0 to 0.7 to improve performance. Why?
To improve vertical sweep efficiency
To reduce corrosion
To avoid asphaltene precipitation
To increase MMP
A reservoir is dipping at 30°. For CO₂ flooding, what is the best well placement?
Injector above producer (updip injection)
Injector below producer (downdip injection)
Horizontal wells only
No relation to dip
In a reservoir with a strong bottom aquifer, what is the usual effect on oil production?
Oil rate increases continuously
Water breakthrough reduces oil production
Gas breakthrough increases oil production
Viscosity is reduced
How can oil production be maintained when aquifer water rises?
Shut in all producers
Drill horizontal wells higher in structure
Inject steam
Reduce GOR
A carbonate reservoir at 15,000 ft depth and 50° API oil has high pressure. Which EOR method is favored?
Polymer
Surfactant
Miscible gas injection
Steam
Why is polymer flooding difficult in a 225–250°F reservoir?
Polymer becomes more viscous
Polymer degrades at high temperature
Water salinity decreases
Oil becomes heavier
An unconsolidated reservoir with strong edge water shows 89% water cut. Why is WOR so high?
Oil is too viscous
High permeability channels allow early water influx
Pressure is too high
Polymer was added
Polymer was injected as 1200 ppm → 1000 ppm → 600 ppm slugs. Why taper the concentration?
To reduce scaling
To reduce cost while maintaining mobility control
To increase injectivity
To change wettability
Injector pressures increased and injectivity decreased during polymer injection. What does it indicate?
Polymer degradation
Plugging or reduced permeability
Gas breakthrough
Improved sweep
A sandstone reservoir: 120 cp oil, permeability 8–25 D, temperature 46°C. Which EOR method is most suitable?
CO₂ miscible
Polymer flooding
Steam
Nitrogen
Before polymer flooding, low-salinity preflush was injected. Why?
To reduce polymer viscosity
To avoid polymer precipitation
To increase oil viscosity
To raise reservoir pressure
16. In a carbonate formation, after polymer flooding, water cut increased from 88% to 94%. Why?
Polymer was too viscous
Presence of channels
Oil viscosity was too low
Injectors were shut in
A gel system (HPAM + aluminum citrate) caused sharply increasing injection pressure.
What does it mean?
Formation damage
Gas influx
Water salinity decreased
Gel diluted
Surfactant was injected to a sandstone with high kaolinite and montmorillonite, the surfactant concentration at the producer was very low. Why?
Surfactant evaporated
Heavy oil consumed surfactant
High surfactant adsorption
GOR was too high
What is the biggest challenge of surfactant flooding in most reservoirs?
Weak wettability alteration
Strong surfactant adsorption
No change in IFT
Surfactant reaction with oil
What can reduce surfactant adsorption?
Higher temperature
Preflush of alkali
Lowering the pH
Increasing formation salinity
In a sandstone reservoir, oil viscosity is 4.7 cp and no gas is available. Which EOR is suitable?
Miscible gas flooding
Steam flooding
Surfactant/Polymer flooding
In-situ combustion
Severe injectivity loss occurred when seawater was used to prepare polymer solution. What is the likely cause?
Polymer precipitation
reaction of polymer with water
Gas generation due to the reaction
Low salinity effect
Formation water salinity is very high and around 90–120 g/L. Oil viscosity is 38 cp, and the formation is water wet. which is not very high. Which EOR method do you recommend?
Alkaline-surfactant-polymer
Steam flooding
Low salinity water flooding
CO₂ foam flooding
What is the main concern of injecting CO₂ to a formation with thief zones?
Pressure can be too high
CO₂ dissolves oil too fast
CO₂ channeling
low microscopic sweep efficiency
What is the best way to evaluate the performance of an EOR method in the field scale?
Coreflood tests
Tracer flooding
Satellite images
Well logging
During water flooding, a tight field shows fast increase in water cut. What is the reason?
Blocking of pores by water
Presence of fractures between wells
Reaction of water with the rock
High salinity of water
In a tight field, after alkali–surfactant injection, injectivity increased for more than two times. What is the reason?
Reaction of surfactant with the oil in porous media
Changes in IFT and relative permeability
Breakthrough of water
Lowering the viscosity of oil
Polymer broke through a nearby well with very high concentration (890–1100 ppm), causing oil rate reduction. Is it a problem, if yes, what is it?
Yes, we used too much polymer
Yes, polymer channeled and did not changed the sweep efficiency
Yes, polymer changed the relative permeability
There is no problem, everything is as we designed.
A chalk reservoir is strongly oil-wet, yet seawater flooding gave 55% recovery. Why?
Seawater changed the oil/water IFT
Wettability alteration occurred due to low salinity effect
Seawater contained surfactant molecules
Sea water reacted with the formation water and blocked the pores
Lab studies show that in a reservoir viscosity drops from 4000 cp → 15 cp at 250°F. Which EOR method is best for this field?
Polymer
Steam
Surfactant
CO2
In average in which type of EOR projects, the high water cut is the main reason to start this type of EOR method?
Miscible flooding
Immiscible gas flooding
Polymer flooding
Surfactant flooding
IIn which type of EOR projects, presence of clays is a big challenge?
Steam flooding
Miscible flooding
Surfactant flooding
Thermal combustion
Which condition most strongly suggests the use of mobility-control treatments such as gels or foams?
High oil viscosity with low water production
Presence of high-permeability streaks
Low reservoir temperature and shallow depth
Strong crossflow between layers
When screening EOR methods for multiple reservoirs with limited data, what should be the first priority?
Selecting the cheapest chemical
Identifying reservoir properties that immediately eliminate unsuitable methods
Running full-field simulation models
Collecting all laboratory data
In average in which type of EOR projects, mobility control is the primary reason for success?
Polymer flooding
Steam flooding
Miscible flooding
Thermal combustion
In average in which type of EOR projects, wettability alteration by injected ions is most significant?
Steam flooding
Surfactant/polymer
Low-salinity waterflooding
CO₂ miscible process
Which reservoir characteristic most strongly influences the choice between thermal and non-thermal EOR methods?
Reservoir depth and temperature
Well spacing
Availability of surface chemical storage
Tubing diameter
When an operator wants to reduce excessive water production without affecting oil zones, which strategy is possible?
Increase gas injection rate
Apply relative permeability modifiers
Drill horizontal producers
Inject seawater at higher salinity
In a reservoir where gas availability is limited and gas breakthrough is occurring frequently, a viable approach to improve gas sweep efficiency is:
Increase injection pressure above fracture pressure
Alternate gas injection with water or foam to improve mobility control
Reduce the number of producers
Replace the gas with a lighter hydrocarbon
When performing an initial EOR screening, which economic factor is most important
Number of drilling rigs available
Long-term oil price sensitivity for the proposed method
Number of reservoir engineers on the team
Cost of surface heaters
