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 1.0 kro › � � � � � Brine · � �� ⁄ � � � Polymer RRF = 1.5 0.8 0.4 Polymer RRF = 2.0 �� �� Polymer RRF = 2.5 � � � � � 0.6 › � � � � � �� � � � � �� � � fw=0.22 fw, kro krw �� �� � �� �� � � Lab data kro 0.4 0.2 fw - Brine fw - Polymer › Water ‐ cut depends on polymer krw 0.2 Lab data krw viscosity and permeability 0.0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Sw 1.00 0.75 › Will polymer alter Sor? Recovery fwc=0.95 • Lab scale – correctly interpret fw = 1, fwc=0.99 0.50 if not recovery increases by reducing M fwc=0.999 • Field scale – the existence of critical fw at fwc=0.9999 which above production is not economic 0.25 0.01 0.1 1 10 100 1000 Mobility ratio 8 April 2016
How to optimize mobility ratio › Polymer viscosity depends on Mw, concentration and salinity • � � � ��� �1 � � �� � � � � � 100 � • Intrinsic viscosity, � � � · � � Intrinsic viscosity • Intrinsic viscosity depends on � ���� � ∑ � � effective salinity, C ��� � � � 10 � 1 0.001 0.01 0.1 1 10 Effective salinity, MIS, M › Non ‐ Newtonian fluids • Rheology in porous media differs from bulk rheology – Slip flow – Depleted layer – Fåhræus ‐ Linquist effect 8 April 2016
How to optimize › Polymer 1 ‐ Regular HPAM ‐ 1000 POL 1 HMW POL 1 LMW based polymer POL 2 MC POL 2 LC Viscosity, mPas • Relatively shear stable 100 viscsosity at moderate shear rates 10 › Polymer 2 ‐ Biopolymer • Shear thinning polymer 1 › Polymer 3 ‐ HPAM ‐ based 0.1 1 10 100 1000 10000 Shear rate, 1/s polymer with hydrophobic POL 1 HMW POL 1 LMW 10000 co ‐ monomers (Associative POL 2 MC POL 2 LC polymer) Mobility reduction POL 3 HMW POL 3 LMW 1000 • Highly shear thinning at 100 moderate shear rates 10 1 0.1 1 10 100 1000 10000 Shear rate, 1/s 8 April 2016
Shear degradation in porous media › Synthetic polymers are 20 1 shear senstive › Onset of degradation 15 0.75 Normalized viscosity above critical shear rate, which depends on Mw Viscosity 10 0.5 › LMW polymers are more shear stable than HMW 5 0.25 › Replacing HMW LMW MMW HMW polymer with LMW will 0 0 not improve viscosity, 1.0E+02 1.0E+03 1.0E+04 1.0E+05 only injectivity Shear rate, 1/s 8 April 2016
Polymer transport in porous media › Polymer retention 60 50 • Assume Langmuir isoterms Adsorption, g/g rock • Adsorption depends strongly on wettability 40 Water ‐ wet Oil ‐ wet › Inaccessible porevolume (IPV) 30 20 • Fraction of pores too small for polymer invasion, depleted layer 10 • Here, IPV = 0.20 0 › Effective transport properties 0 500 1000 1500 2000 Polymer concentration, ppm • Oil ‐ wet reservoir (low adsorption) v p /v T > 1 for c > 500 ppm 1.25 • Water ‐ wet reservoir Polymer to tracer velocity 1 v p /v T < 1, critical only at ultra ‐ low concentration (e.g., in low salinity water) 0.75 › Minimize produced polymer 0.5 • Use retention and injected Water ‐ wet Water ‐ wet ‐ Langmuir 0.25 concentration as design criterion Oil ‐ wet Oil ‐ wet ‐ Langmuir 0 0 500 1000 1500 2000 Polymer concentration, ppm 8 April 2016
Vertical sweep efficiency Delay breakthrough time Selective 1 0.5 0.2 0.1 0.05 0.02 Displacement in low permeability layer at bt 1 � � • Example: � � = 100, at unit mobility � � � reduction, � � � � 1 � � 0.505 � � 0.1 and at infinity viscosity � � � � � � � 1 � � 0.55 � � 0.01 – Selective viscosity will dramatically improve sweep efficicency 0.001 – Selectivity exploited by salinity, temperature 0.1 1 10 100 1000 and permeability contrasts Mobility reduction 8 April 2016
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
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