Polymer Flooding – Factors That May Impact the EOR Potential

Lunch and Learn seminar

27 January 2016

Some highlights from reasearch in The National IOR Centre of Norway

› Sweep efficiency is one of the main EOR mechanisms• Polymer flooding and how to demonstrate EOR potential• Do polymer alter residual oil saturation• How do polymers alter fractional flow curves• How to calculate polymer permeability – permeability damaging Non‐Newtonian fluids

27 January 2016

Polymer flooding in reservoir core1. Recieved NCS reservoir core material from operator2. Established initial conditions3. Steady state oil‐water injection at fw = 0 to 0.22 – predict water fractional flow curve4. Steady state oil‐polymer injection at fw = 0.22 to 1.0

a) Observe saturation shift at fw = 0.22

b) Polymer fractional flow curve shifted to higher water saturation

c) Viscosity corrected fractional flow curves matched experiment

5. Results confirm classic understanding and make interpretation of polymer flooding simple

3

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, k

roSw

krofw=0.22Lab data kroSw VB [frac.]Sw VB [frac.]krwLab data krwLab data krwkrw2krw3krw4

What affect the polymer viscosity

› Mobility ratio and EOR potential depends on effective polymer viscosity› For some polymers, the viscosity depends strongly on salinity

• Polymer viscosity in low salinity brine can be significantly higher than in high salinity brine, effective salinity• Introduce the existence of optimized brine salinity, which may differ from convential smart water recipee

• 1 )

• 1

• Effective salinity defined as C ∑

• Shear dependcy e.g., Carreau model 1 /

› Deviation between apparent viscosity in porous medium and bulk viscosity measured on rheometer

27 January 2016

Polymer stability and lack thereof

› Mechanical degradation • During mixing, flow through choke valves and flow line restrictions

• At sand face

› Thermochemical degradation

› Degradation by bacterial attack

27 January 2016

Mechanical degradation› Synthetic polymers are sensitive to shear degradation (i.e., high stretch rate)

• Depends on polymer structure, Mw and salinity– Will chokes and valves be show stoppers for some polymers?

– Does low shear chokes exist, i.e., shear rate < 1E+04 s‐1 at differential pressure > 30 bar?

– How to scale lab experiments to field conditions

– If the existence of low shear chokes, polymers may be degraded when entering the formation

› Will it be possible to relate shear degradation to bulk properties

27 January 2016

Productiveinterval

(m)

Shear rate at K= 1 D

(s-1)

Shear rate at K= 5 D

(s-1)

100 10 000 5 000

1 000 1 000 500

Field scale (5000 m3/d)Shear rate in matrix formation

1 34 /4

With fractures, maxium shear rateis well below critical shear rate

Polymer shear degradation – effect of scaling

› Large scale polymer shear degradation tests performed Autumn 2015 including standard and fixed choke valves, as well as SNF LPR (Linear Pressure Reducer)

› Synthetic polymers were severely degraded in standard choke valves at differential pressures of 50 bar 

› From capillary tube (and core flood) experiments degradation is understood by appliedshear rate, which from Poiseuoilleflow is  ⁄ 4 /

› No match when scaling to larger tube size

› Reynolds number 2 /varied from 10 to > 105

› Then,    where coefficient of resistance, which for laminar flow 64/and  / / for turbulent flow

27 January 2016

0

0.2

0.4

0.6

0.8

1

1.2

1.00E+03 1.00E+04 1.00E+05 1.00E+06

Normalize

d viscosity

Shear rate = 4<v>/R

0.0000625 0.0000635 0.000875 0.00229 0.00229 0.003

0.00397 0.00476 0.00622 0.00635 0.00699 0.00940

0.0124 0.0159 0.01754 0.0254 Series12

Polymer shear degradation

0

0.2

0.4

0.6

0.8

1

1.2

1.00E+03 1.00E+04 1.00E+05 1.00E+06 1.00E+07

Normalize

d viscosity

Shear rate = /w

0.0000625 0.0000635 0.000875 0.00229 0.002290.003 0.00397 0.00476 0.00622 0.006350.00699 0.00940 0.0124 0.0159 0.017540.0254 Model 1 Standard choke 2000 ppm 10000 ppm

27 January 2016

1.0E‐03

1.0E‐02

1.0E‐01

1.0E+00

1.0E+01

1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06 1.0E+07

Resistance coefficient, f

Reynold number

LaminarBlasiusCurrent Prediction

Proper match by setting a= 0.155 and = 2.51.0E+00

1.0E+01

1.0E+02

1.0E+03

1.0E‐01 1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06

Viscosity, m

Pas

Shear rate, 1/s

Viscosity at 20°C

1 000 ppm

2 000 ppm

10 000 ppm

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(ref. SPE 179801, Reichenbach‐Klinke et al. 2016)

– Bulk viscosity increases (increased [] and k’)

– Mobility reduction can in porous media due to formation of polymer network increase significantly

27 January 2016

Mobility reduction in porous media› Regular ATBS polymer › ATBS polymer with associative 

groups

Mobility reduction in porous media› Viscosity and mobility reduction for associative polymer when flowing through porous media and capillary tube• Mobility reduction > relative polymer viscosity

• Mobility reduction increases by increasing temperature

• Mobility reduction increases by increasing the amount of associative groups

Mobility reduction in porous media› Constant rate vs. constant differential pressure

• At low flow rates (deep into the formation) flow behaviour deviates strongly from classicDarcy law flow

• Demonstrate the possibility of maintaining nearly constant differential pressure at flowrates varying more the two order of magnitude – and the behaviour is reversible

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Step P, mbar q, ml/min1 520 1.00 2 513 0.20 3 500 0.15 4 700 5.14 5 600 4.10 6 500 0.16 7 550 0.88 8 400 0.03 9 450 0.13

10 500 0.31 11 300 0.02 12 500 0.80

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)

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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 regularATBS followed by 1000 ppmassociative polymer

› Exp II• Brine followed by 500 ppmassociative polymer

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Oil recovery vs. capillary number

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Optimization

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

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