Polymer flooding improved sweep efficiency for utilizing IOR - - PowerPoint PPT Presentation

Polymer flooding –improved sweep efficiency for utilizing IOR potential

Force seminar April 2016

8 April 2016

Classic polymer screening

› Viscosifying effect

• Solution preparation
• Bulk rheology

› Flow properties in porous media

• Filterability
• Screen factor
• Mobility reduction
• Permeability reduction
• Inaccessible pore volume
• Retention

› Stability

• Shear stability
• Thermo‐chemical stability

8 April 2016

IOR mechanism – Improve sweep by reducing mobility ratio

›

• ·

⁄ ›

• › Water‐cut depends on polymer

viscosity and permeability › Will polymer alter Sor?

• Lab scale – correctly interpret fw = 1,

if not recovery increases by reducing M

• Field scale – the existence of critical fw at

which above production is not economic

8 April 2016

0.25 0.50 0.75 1.00 0.01 0.1 1 10 100 1000 Recovery Mobility ratio fwc=0.95 fwc=0.99 fwc=0.999 fwc=0.9999

0.0 0.2 0.4 0.0 0.2 0.4 0.6 0.8 1.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 krw fw, kro Sw

kro Brine Polymer RRF = 1.5 Polymer RRF = 2.0 Polymer RRF = 2.5 fw=0.22 Lab data kro fw - Brine fw - Polymer krw Lab data krw

How to optimize mobility ratio

› Polymer viscosity depends on Mw, concentration and salinity

• 1
• Intrinsic viscosity, ·
• Intrinsic viscosity depends on

effective salinity, C

• ∑
• › Non‐Newtonian fluids
• Rheology in porous media differs from bulk rheology

– Slip flow – Depleted layer – Fåhræus‐Linquist effect

8 April 2016

1 10 100 0.001 0.01 0.1 1 10 Intrinsic viscosity Effective salinity, MIS, M

How to optimize

› Polymer 1 ‐ Regular HPAM‐ based polymer

• Relatively shear stable

viscsosity at moderate shear rates

› Polymer 2 ‐ Biopolymer

• Shear thinning polymer

› Polymer 3 ‐ HPAM‐based polymer with hydrophobic co‐monomers (Associative polymer)

• Highly shear thinning at

moderate shear rates

8 April 2016

1 10 100 1000 10000 0.1 1 10 100 1000 10000 Mobility reduction Shear rate, 1/s POL 1 HMW POL 1 LMW POL 2 MC POL 2 LC POL 3 HMW POL 3 LMW 1 10 100 1000 0.1 1 10 100 1000 10000 Viscosity, mPas Shear rate, 1/s POL 1 HMW POL 1 LMW POL 2 MC POL 2 LC

Shear degradation in porous media

› Synthetic polymers are shear senstive › Onset of degradation above critical shear rate, which depends on Mw › LMW polymers are more shear stable than HMW › Replacing HMW polymer with LMW will not improve viscosity,

• nly injectivity

8 April 2016

0.25 0.5 0.75 1 5 10 15 20 1.0E+02 1.0E+03 1.0E+04 1.0E+05

Normalized viscosity Viscosity Shear rate, 1/s

LMW MMW HMW

Polymer transport in porous media

› Polymer retention

• Assume Langmuir isoterms
• Adsorption depends strongly on wettability

› Inaccessible porevolume (IPV)

• Fraction of pores too small for polymer

invasion, depleted layer

• Here, IPV = 0.20

› Effective transport properties

• Oil‐wet reservoir (low adsorption)

vp/vT > 1 for c > 500 ppm

• Water‐wet reservoir

vp/vT < 1, critical only at ultra‐low concentration (e.g., in low salinity water)

› Minimize produced polymer

• Use retention and injected

concentration as design criterion

8 April 2016

0.25 0.5 0.75 1 1.25 500 1000 1500 2000 Polymer to tracer velocity Polymer concentration, ppm

Water‐wet Water‐wet‐Langmuir Oil‐wet Oil‐wet‐Langmuir

10 20 30 40 50 60 500 1000 1500 2000 Adsorption, g/g rock Polymer concentration, ppm

Water‐wet Oil‐wet

Vertical sweep efficiency

Delay breakthrough time

• Example:
• = 100, at unit mobility

reduction,

• 1
• 0.505

and at infinity viscosity

• 1
• 0.55

– Selective viscosity will dramatically improve sweep efficicency – Selectivity exploited by salinity, temperature and permeability contrasts

8 April 2016

0.001 0.01 0.1 1 0.1 1 10 100 1000 Displacement in low permeability layer at bt Mobility reduction

Selective 1 0.5 0.2 0.1 0.05 0.02

The new class of EOR polymers

› Hydrophobically modified water solubles copolymers

• Hydrophobic groups added to regular polymer

backbone reacts with each other leading to intermolecular polymer network

• Mobility reduction can in porous media due

to formation of polymer network increase significantly

• Mobility reduction depends at least on amount of

associative groups, Mw, salinity and temperature

8 April 2016

Mobility reduction in porous media

› Constant rate vs. constant differential pressure

• Flow behaviour at low flow rates deviates strongly from classic Darcy law flow
• Demonstrate the possibility of maintaining nearly constant differential pressure at flow rates

varying more the two order of magnitude – and the behaviour is reversible

8 April 2016

Mobility reduction – effect of oil

› In presence of oil the associative interactions are weakend resulting in less mobility reduction and lower RF compared to Sw = 1 (dotted lines)

8 April 2016

Effect on oil recovery

› High mobility reduction will improve the sweep efficiency towards piston‐like displacement and reduce the tail‐end production › High mobility reduction may be utilized to increase the capillary number /, with the possibility of lowering Sor › Exp I

• Brine, followed by regular

ATBS followed by 1000 ppm associative polymer

› Exp II

• Brine followed by 500 ppm

associative polymer

8 April 2016

Oil recovery vs. capillary number

8 April 2016

Optimization

› Define assosiative polymers which at injection condition behave as regular polymers (low mobility reduction and good injectivity) while high mobility reduction is triggered by temperature

8 April 2016

Conclusions

›Main mechanisms for EOR polymer flood are understood

• Sweep improvement by lowering mobility ratio

›The wide variety of EOR polymers allowing for optimization, e.g.,

• Injectivity vs. mobility reduction
• EOR potential vs. mobility reduction
• Type of injection brine
• Polymer loss vs. produced polymer
• Why always choose HMw HPAM polymer?

›Commercial simulators are not fully ready for polymer – does however only partly explain lack of field experience

8 April 2016