This document discusses water alternating gas (WAG) enhanced oil recovery. WAG involves alternating injections of gas and water to improve displacement and sweep efficiency. There are different classifications of WAG including miscible, immiscible, and hybrid WAG. The success of WAG depends on reservoir characteristics, fluid properties, well arrangement, and WAG parameters like slug size and ratio. Types of WAG include miscible, immiscible, hybrid, simultaneous, and selective simultaneous WAG. The document concludes that each reservoir is unique and laboratory experiments can help determine the most suitable WAG technique.

1. Water Alternating Gas (WAG)
EnhancedOil Recovery
Ibrahim Muhammad
African Universityof Science& Technology
December2015

2. Content
• Introduction
• Water Alternating Gas (WAG) flooding
• Classification of WAG
• Factors affecting WAG
• Types of WAG
• When to Initiate WAG
• Conclusion

3. Introduction
• Why is Enhanced Oil Recovery (EOR) needed
• Economic quantities left after primary and secondary recovery.
• To economically recover more oil
• Infrequent discoveries of major new reservoirs
• Different types of EOR techniques;
• Gas Injection e.g. WAG
• Microbial
• Thermal
• Chemical

4. Water Alternating Gas (WAG)
• Water Alternating Gas
• Involves Gas injection followed by water Injection
• Gas Injection increases displacement efficiency
• Water Injection increases sweep efficiency

5. WAG Basic classification
Miscible WAG (MWAG);
• Reservoir pressure
maintained above MMP.
• At MMP, gas-oil miscible at
all proportions
• In reality, not completely
achieved (hard to maintain
MMP)
• About 9.7% Improved oil
recovery (Touray, 2013)
Immiscible WAG (IWAG)
• Aim is to stabilize the sweep
front and increase contact of
un-swept areas.
• High microscopic efficiency
• Poorer macroscopic efficiency
due to high M.
• About 6.4% Improved oil
recovery (Touray, 2013).

6. Factors affecting WAG
Success of a WAG project depends largely on;
• Reservoir characteristics.
• Reservoir Heterogeneity
• Petrophysical properties (ф, k, Sw, So, wettability)
• Fluid properties
• Viscosity of oil f(T, P, SG).
• Injection and production well arrangement
• Optimum arrangement for optimum results f(cost)

7. Factors affecting WAG cont’d
• WAG parameters
• WAG slug size; Optimum size for better results
• WAG ratio; Too much water will affect micro ԑ, too much gas
affects macro ԑ.
• WAG cycles; Timing to switch from gas to water.

8. Factors affecting WAG cont’d
• Fundamental Equations
• Some equations driving the WAG process include Darcy’s law,
Mobility Ratio,

9. Types of WAG
• Miscible WAG (MWAG)
• Injected gas miscible with
reservoir oil at MMP or higher
• Decreases oil viscosity –
Increases oil mobility
• Immiscible WAG (IWAG)
• Not miscible with reservoir oil.
Occurs below MMP
• Displaces oil while maintaining
oil phase.
• Provides a front between the 2
phases

10. Types of WAG cont’d
• Hybrid WAG (HWAG)
• Begins with Injection of large slug of gas
• Followed by small slugs of water and gas

11. Types of WAG cont’d
• Simultaneous WAG (SWAG)
• Water and Gas Injected at the same time
• Water and gas mixed at the surface
• Single Injection well

12. Types of WAG cont’d
• Selective Simultaneous WAG (SSWAG)
• Dual completions in a single Injection well
WaterGas

13. When to Initiate WAG
• Initial WAG : Beginning of reservoir development
• Post Breakthrough WAG: Initiating WAG after Breakthrough.
Initial WAG shows slightly higher cumulative oil recovery
(Morais, 2012).

14. Conclusion
Every Reservoir is Unique and should be treated Independently
when deciding the type of EOR technique to be used for
optimum results. Laboratory experiments are important
processes which aid in making an informed decision.