Polymer injection eor

West Africa Reservoir: Basic Information

1977: Production starts

2013: 6 platforms44 production wells5 injection wells

WEST AFRICA

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West Africa reservoir layout

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Reservoir Characteristics

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_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

Index

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WHAT?

_Enhanced oil recovery (EOR) is the oil recovery obtained with injection in thereservoir 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 orderto maximize the oil recovery factor from conventional reservoirs

Information about Ehanced Oil Recovery (EOR)

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Oil Recovery Techniques

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Oil Recovery Techniques

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_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

Why to apply a chemical EOR technique?

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_The aim is to reduce the mobility of the water injected in the reservoir mainly by increasingits viscosity

_A lower mobility ratio brings to a higher value of the efficiency of the water flood thanks toan improved volumetric sweep efficiency and a more uniform displacement front

EOR Technique: Polymer Flooding

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SYNTHETIC POLYMERS

Hydrolyzed polyacrilamide (HPAM)

Most important polymers available for chemical EOR

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BIOPOLYMERS

Xanthan

Most important polymers available for chemical EOR

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0

5

10

15

20

25

30

35

40

0 1 2 3 4 5

K [-]

Polymer concentration [kg/Sm^3]

Viscosity coefficient (K)

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Properties of polymer mixtures

VISCOSITY_Polymer viscosity depends on:_Polymer concentration

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VISCOSITY_Polymer viscosity depends on:_Polymer concentration_Salinity

Xanthanconcentration: 1 kg/Sm^3

26M Dalton HPAMconcentration: 1,5 kg/Sm^3

20M Dalton HPAMconcentration: 1,5 kg/Sm^3

8M Dalton HPAMconcentration: 1,5 kg/Sm^3

Properties of polymer mixtures

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VISCOSITY_Polymer viscosity depends on:_Polymer concentration_Salinity_Shear rate

0

1

2

3

4

5

6

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0 0,2 0,4 0,6 0,8 1

Polymer solution viscosity [cP]

Velocity of propagation of the mixture [m/day]

HPAM solution Viscosity vs. Velocity

HPAMconcentration 1 kg/Sm^3

HPAMconcentration 1,5 kg/Sm^3

HPAMconcentration 2 kg/Sm^3

Properties of polymer mixtures

Shear rate ≈ Velocity of propagation of the mixture

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ADSORPTION_Adsorption refers to the interaction, through physical adsorption, VanDer Waals forces and hydrogen bonding, between polymer molecules andporous media surfaces

_Adsorption causes a reduction in rock permeability

0

0,000005

0,00001

0,000015

0,00002

0,000025

0,00003

0 1 2 3 4 5

Polymer adsorption [g/grock]

Polymer concentration [kg/Sm^3]

HPAM adsorption curve

Properties of polymer mixtures

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Reservoir Simulator: Eclipse

_Eclipse simulator has been used to forecast future performance of thescenarios considered

_Eclipse uses the finite difference approach and the black oil model. The modelconsists of reservoir description, fluid and rock property description, initialconditions and wells and their phase flow rates

_Black oil model basic assumption is that at most three distinct components canbe described in the reservoir: oil, water and gas

_In polymer flooding applications, the polymer injected into water represents the4th component in aqueous phase

_Within the model, the reservoir is assumed to be at constant temperatureduring the simulation period

_The basic equations used in black oil models are the mass conservation law andDarcy’s law (one equation for each component)

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Extended sectors extraction

_The sectors extracted for the evaluation of polymer flooding performancehave been taken from the full field model deactivating the other cells

_On the boundaries of the sectors the mass flux has been fixed equal tozero

_Initial pressures and saturations were known in each cell of the sectors(history matching)

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Location of the extended sectors

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Extended Sectors: Reservoir Characteristics

Sector in level B shows much better petro-physical properties compared tolevel A

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Do-nothing scenario:_No injectors in the extended sector considered, production due tonatural 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)

Scenarios considered in extended sectors

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Location of the injectors

Production wells Injection wells

SECTOR IN LEVEL BSECTOR IN LEVEL A

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Do-nothing

Water Flooding

Polymer Flooding

0,4

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0 0,16 0,24 0,32 0,40,08

1/1/2025

Polymer Concentration[kg/Sm^3]

Results of simulations run on extended sector level A

FOE = RECOVERY FACTOR

XANTHAN + FORMATIONWATER

HPAM + SEA WATER

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Best polymer flooding strategies in extended sector (level B)

Results of simulations run on extended sector level BField Oil Production Rate - Xanthan

Do-nothing Water Flooding Polymer Flooding24

Production interrupted

Results of simulations run on extended sector level BField Oil Recovery Factor - Xanthan

5,7

Do-nothing Water Flooding Polymer Flooding25

Results of simulations run on extended sector level BField Oil Recovery Factor - HPAM

6,4

Polymer Flooding Water Flooding26

Economic analysis of most attractive strategies applied in level B

RESULTS:

_The contribution of taxes and royalties has been neglegcted within thisanalysis

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Conclusions

_Dispersed polymer injection applied on the extended sector in level B appear to bepromising, with a substantial increase in the oil recovery

_The scenario with HPAM injection is preferable to Xanthan injection mostlydue to technical reasons

_The petro-physical properties of the reservoir appear to be foundamental forthe success of the polymer flooding technique

_The best strategies found for polymer flooding in level B appear to beeconomically profitable in the period considered

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From the current study level B appears to be more interesting to perform afull 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 andbiological)

_The polymer adsorption on reservoir porous medium

The polymer plant design must be considered as key point for therealization of the project

Future Perspectives: Full Field Implementation

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Future Perspectives: Polymer Plant Design

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Thanks for your attention

Best polymer flooding strategies in extended sector (level A)

XANTHAN + FORMATIONWATER

Results of simulations run on extended sector level AField Oil Production Rate - Xanthan

Do-nothing Water Flooding Polymer Flooding

Economic analysis of most attractive strategies applied in level B

_The economic evaluation has been performed only on polymer injectionin level B

_The results obtained with simulations on the extended sector in level Arevealed that polymer flooding is not technically convenient if comparedwith the water flooding scenario

Economic data used to evaluate CAPEX and OPEX: