This document provides information about an oil reservoir in West Africa and enhanced oil recovery techniques being considered to increase production. It summarizes: 1) The reservoir began production in 1977 with 6 platforms and 49 wells currently. Polymer flooding is being evaluated as an enhanced oil recovery method. 2) Simulations of polymer flooding were run on two extended sectors, with better results in Sector B. The best strategies were HPAM injection and xanthan polymer injection. 3) An economic analysis found polymer flooding in Sector B could be profitable over the evaluation period, while polymer flooding was not advantageous compared to water flooding in Sector A. Future work may include laboratory tests and full field implementation in Sector B

2. West Africa Reservoir: Basic Information
WEST AFRICA
1977:
Production starts
2013:
6 platforms
44 production wells
5 injection wells
1

3. West Africa reservoir layout
2

4. Reservoir Characteristics
3

5. Index
_Overview on the most important EOR techniques
_What is polymer flooding
_Reservoir sectors models
_Simulation results on extended sector in level A
_Simulation results on extended sector in level B
_Economic evaluation
_Conclusions
_Future perspectives
4

6. Information about Ehanced Oil Recovery (EOR)
WHAT?
_Enhanced oil recovery (EOR) is the oil recovery obtained with injection in the
reservoir of:
Miscible gases
Chemicals
Thermal energy
WHEN?
_EOR is not restricted to a specific phase of the production life of a reservoir
WHY?
_The application of EOR processes is fundamental for big oil companies in order
to maximize the oil recovery factor from conventional reservoirs
5

7. Oil Recovery Techniques
6

8. Oil Recovery Techniques
7

9. Why to apply a chemical EOR technique?
_Very low recovery factor (≈18%) achieved after more than 30 years of
oil production
_High value of water production (water cut ≈ 82%)
_Low efficiency of the current peripheral water flooding
8

10. EOR Technique: Polymer Flooding
_The aim is to reduce the mobility of the water injected in the reservoir mainly by increasing
its viscosity
_A lower mobility ratio brings to a higher value of the efficiency of the water flood thanks to
an improved volumetric sweep efficiency and a more uniform displacement front
9

11. Most important polymers available for chemical EOR
SYNTHETIC POLYMERS
Hydrolyzed polyacrilamide
(HPAM)
10

12. Most important polymers available for chemical EOR
BIOPOLYMERS
Xanthan
11

13. Properties of polymer mixtures
VISCOSITY
_Polymer viscosity depends on:
_Polymer concentration
‫ ܭ‬ൌ
ܸ݅‫݊݋݅ݐݑ݈݋ݏ ݎ݁݉ݕ݈݋݌ ݂݋ ݕݐ݅ݏ݋ܿݏ‬
ܸ݅‫ݎ݁ݐܽݓ ݂݋ ݕݐ݅ݏ݋ܿݏ‬
Viscosity coefficient (K)
40
35
30
K [-]
25
20
15
10
5
0
0
1
2
3
4
Polymer concentration [kg/Sm^3]
5
12

14. Properties of polymer mixtures
VISCOSITY
_Polymer viscosity depends on:
_Polymer concentration
_Salinity
Xanthan
concentration: 1 kg/Sm^3
26M Dalton HPAM
concentration: 1,5 kg/Sm^3
20M Dalton HPAM
concentration: 1,5 kg/Sm^3
8M Dalton HPAM
concentration: 1,5 kg/Sm^3
13

15. Properties of polymer mixtures
VISCOSITY
_Polymer viscosity depends on:
_Polymer concentration
_Salinity
_Shear rate
Shear rate ≈ Velocity of propagation of the mixture
HPAM
concentration 1 kg/Sm^3
HPAM
concentration 1,5 kg/Sm^3
HPAM
concentration 2 kg/Sm^3
Polymer solution viscosity [cP]
HPAM solution Viscosity vs.Velocity
7
6
5
4
3
2
1
0
0
0,2
0,4
0,6
0,8
Velocity of propagation of the mixture
[m/day]
1
14

16. Properties of polymer mixtures
ADSORPTION
_Adsorption refers to the interaction, through physical adsorption, Van
Der Waals forces and hydrogen bonding, between polymer molecules and
porous media surfaces
_Adsorption causes a reduction in rock permeability
Polymer adsorption [g/grock]
HPAM adsorption curve
0,00003
0,000025
0,00002
0,000015
0,00001
0,000005
0
0
1
2
3
4
Polymer concentration [kg/Sm^3]
5
15

17. Reservoir Simulator: Eclipse
_Eclipse simulator has been used to forecast future performance of the
scenarios considered
_Eclipse uses the finite difference approach and the black oil model. The model
consists of reservoir description, fluid and rock property description, initial
conditions and wells and their phase flow rates
_Black oil model basic assumption is that at most three distinct components can
be described in the reservoir: oil, water and gas
_In polymer flooding applications, the polymer injected into water represents the
4th component in aqueous phase
_Within the model, the reservoir is assumed to be at constant temperature
during the simulation period
_The basic equations used in black oil models are the mass conservation law and
Darcy’s law (one equation for each component)
16

18. Extended sectors extraction
_The sectors extracted for the evaluation of polymer flooding performance
have been taken from the full field model deactivating the other cells
_On the boundaries of the sectors the mass flux has been fixed equal to
zero
_Initial pressures and saturations were known in each cell of the sectors
(history matching)
ܵܽ‫ ݊݋݅ݐܽݎݑݐ‬ൌ
ܸ‫ ݀݅ݑ݈݂ ܽ ݂݋ ݁݉ݑ݈݋‬
ܲ‫݁݉ݑ݈݋ݒ ݁ݎ݋‬
17

19. Location of the extended sectors
18

20. Extended Sectors: Reservoir Characteristics
Sector in level B shows much better petro-physical properties compared to
level A
19

21. Scenarios considered in extended sectors
Do-nothing scenario:
_No injectors in the extended sector considered, production due to
natural driving mechanism (13 years)
Water flooding scenario:
_Injection of water through two injectors (13 years)
Polymer flooding scenario:
_Injection of polymer solution slugs/water (13 years)
20

22. Location of the injectors
SECTOR IN LEVEL A
Production wells
SECTOR IN LEVEL B
Injection wells
21

23. Results of simulations run on extended sector level A
1/1/2025
FOE = RECOVERY FACTOR
0,4
Do-nothing
Water Flooding
Polymer Flooding
0
0,08
0,16
0,24
0,32
0,4
Polymer Concentration
[kg/Sm^3]
22

24. Best polymer flooding strategies in extended sector (level B)
XANTHAN + FORMATION WATER
HPAM + SEA WATER
23

25. Results of simulations run on extended sector level B
Field Oil Production Rate - Xanthan
Production interrupted
Do-nothing
Water Flooding
Polymer Flooding
24

26. Results of simulations run on extended sector level B
Field Oil Recovery Factor - Xanthan
5,7
Do-nothing
Water Flooding
Polymer Flooding
25

27. Results of simulations run on extended sector level B
Field Oil Recovery Factor - HPAM
6,4
Polymer Flooding
Water Flooding
26

28. Economic analysis of most attractive strategies applied in
level B
RESULTS:
_The contribution of taxes and royalties has been neglegcted within this
analysis
27

29. Conclusions
_Dispersed polymer injection applied on the extended sector in level B appear to be
promising, with a substantial increase in the oil recovery
_The scenario with HPAM injection is preferable to Xanthan injection mostly
due to technical reasons
_The petro-physical properties of the reservoir appear to be foundamental for
the success of the polymer flooding technique
_The best strategies found for polymer flooding in level B appear to be
economically profitable in the period considered
28

30. Future Perspectives: Full Field Implementation
From the current study level B appears to be more interesting to perform a
full field polymer injection implementation
Laboratory tests are necessary in order to evaluate:
_The most appropriate polymer according to the field conditions
_The effect of salinity and shear rate on polymer solution viscosity
(rheology)
_The polymer solution long term stability (chemical, mechanical and
biological)
_The polymer adsorption on reservoir porous medium
The polymer plant design must be considered as key point for the
realization of the project
29

31. Future Perspectives: Polymer Plant Design
30

32. Thanks for your attention

33. Best polymer flooding strategies in extended sector (level A)
XANTHAN + FORMATION WATER

34. Results of simulations run on extended sector level A
Field Oil Production Rate - Xanthan
Do-nothing
Water Flooding
Polymer Flooding

35. Economic analysis of most attractive strategies applied in
level B
_The economic evaluation has been performed only on polymer injection
in level B
_The results obtained with simulations on the extended sector in level A
revealed that polymer flooding is not technically convenient if compared
with the water flooding scenario
Economic data used to evaluate CAPEX and OPEX: