Investigation of Polymer Adsorption on

Rock Surface of High Saline Reservoirs

Mohammed M. AmroPetroleum & Natural Gas Eng. Dept.

King Saud University

2008 SPE Saudi Arabia Section Technical Symposium

Outline

• Introduction• Oil Recovery Methods

– EOR Mechanisms– EOR Processes

• Experimental WorkExperimental Procedures

Material Used

Results and Discussion

• Summary

• Physical Reasons:Existence of the interfacial tension between oil

and water, and wettability (capillary forces)High mobility ratio between water and oil

(viscous forces)

• Geological Reason:The heterogeneities in the reservoir rock

Causes for Poor Recovery

EOR Mechanisms

• The mechanisms of EOR:Eliminate or reduce capillary and Interfacial

tension to improve the displacement efficiency

Improve sweep efficiency by reducing the mobility ratio between injected and displaced fluids (Polymer, Thermal)

Act on both phenomena at same time (Nc)

CN

Capillary number

Displacing fluid velocity [m/day]

Displacing fluid viscosity [mPa.s]

Interfacial tension [mN/m]

For waterflooding, Nc is 10-6 to 10-7 (under certain assumptions)

If the Nc can be increased to 10-4 to 10-2,

the residual oil saturation will be reduced significantly.

Pk

L

Ratio of viscous forces to capillary forces

Apr 18, 2023

EOR Processes

Tertiary Recovery

Thermal ChemicalMiscible/

ImmiscibleOther

Steam drive

Steam stimulation

Hot water

In-situ combustion

Polymer

Surfactant

Caustic

Combination

CO2

Inert gas

Miscible Solvent

Flue gas

Microbial

Vibration

Electrical

• Offers good opportunity to maximizing the reserves in many depleted and waterflooded reservoirs

• Opportunities exist under economic conditions and current oil prize

Chemical Properties Desirable:• Good solubility (low concentration)• High injectivity• Long-term stability against:

– Electrolytes, - Bacteria, - Temperature– Oxidation, - pH-Value changes

• Low adsorption on the rock, special focus on carbonate reservoirs (Polymer flooding)

• Simple handling and Low cost

Chemical Flooding

• Decreasing the mobility ratio (M)

• Influence on volumetric sweep efficiency EV

EV =EA EI

Therefore, ED→Sorw will be reached more faster

EA = Areal efficiency and

EI = vertical sweep efficiency

Polymer Flooding

Apr 18, 2023

Mathematical Description of Polymer Rheology

*w w

ww

K P

V l

*

, (Resistance Factor)

w pa

w

pa wf

w w p

K P

V l

PTherefore R

P

Effective water viscosity

Effective polymer viscosity

Assumption: Vw = Vp (No ‘‘Inaccessible Pore Volume‘‘ for polymer)

Case 1: Only viscosity increase : Kw = Kp

*p p

pp

K P

V l

w pK K

*, (Resistance Factor)

*w pw

fp p w

KTherefore R

K

Case 2: Viscosity increase and permeability decrease:

Residual resistance factor (RRF)

1 2

2 1

(Residual Resistance Factor)w wrf

w w

PR

P

Mathematical Description of Polymer Rheology

0

2

4

6

8

10

12

14

16

0 1 2 3 4 5 6 7 8 9 10

Injected PV

RF

& R

RF

Resistance factor (RF) and Residual resistance factor (RRF)

RF & RRF are important factors to determine the concentration of polymer needed to perform polymer flooding (e.g. RF = 7 - 8 &

RRF = 1.5) or water shut off (Rf = 6 & RRF = 4).

Experimental Procedure

• Polymer solutions were prepared and evaluated at different salinities, shear rates, temperatures and concentrations.

• Core samples were flooded with polymer solutions (const. flow rate = 2.5 ft/day) until full adsorption (const. Pressure drop and const. effluent viscosity); RF was calculated

• The core samples were flooded with brine (Pressure drop and effluent viscosity were monitored); RRF was calculated.

Experimental Work

• Polymers (Xanthan, PAA),

• Biocide (Formaldehyde)

• Brine (83% NaCl and 17% CaCl2)

• Core samples (Berea SS with different Kranged from 200 – 1300 mD)

• Flooding apparatus.

Results and Discussion

Effect of Shear Rate and Salt Concentration on Polymer Solution

Viscosity

Viscosity of polymer solution of different xanthan concentrations in 10% brine.

Effect of Salt concentration on Xanthan viscosity (14.7 s-1)

Effect of Salt concentration on PAA viscosity (14.7 s-1)

Resistance Factor (RF) & Residual Resistance Factor (RRF); Xanthan

Resistance Factor (RF) & Residual Resistance Factor (RRF); PAA

Effect of Injection Rate (Xanthan)

Effect of Injection Rate (PAA)

3000 ppm & 5% Brine

Effect of Temperature

RF & RRF (60 °C)

Polymer Accumulation

Conclusions

• The viscosity decreases with increasing the shear rate up to a certain value beyond which it becomes almost constant.

• Xanthan viscosity is more affected by the shear rate rather than salt concentration, while PAA viscosity depends strongly on both factors.

• A reduction of permeability using polymer solution depends on the porous medium, the particular polymer, concentration of polymer, salinity, and injection rate.

• Polyacrylamide (PAA) can reduce the heterogeneity in reservoir at low salinity. High PAA concentration will be needed to tolerate the high salinity.

Cont. Conclusions

• Partially reversible adsorption (physical) from the rock surface occurred by brine flooding (RRF).

• The flooding velocity and the permeability have great effect on the adsorption.

• The temperature increase leads to delay the full adsorption on the rock surface. Therefore, more PV of solution is necessary .

• Thus, xanthan can be recommended, as a good polymer candidate to be used in high salinity reservoirs.