1. SPE 168998
The Effect of Chemical Osmosis on Improve Oil
Recovery from Fractured Shale Formations
P. Fakcharoenphol*, Colorado School of Mines; B. Kurtoglu, Marathon
Oil; H. Kazemi, S. Charoenwongsa**, Y. Wu, Colorado School of Mines
* now with Shell
** now with Chevron

2. SPE 168998 • The Effect of Chemical Osmosis on Improve Oil Recovery from
Fractured Shale Formations • P. Fakcharoenphol
Slide 2
AGENDA
• Chemical-induced osmotic pressure
• Membrane efficiency in shale
• Laboratory study
• Mathematical model
• Numerical simulation study
• Conclusions
Slide 2

3. SPE 168998 • The Effect of Chemical Osmosis on Improve Oil Recovery from
Fractured Shale Formations • P. Fakcharoenphol
Slide 3
CHEMICAL-INDUCED OSMOTIC PRESSURE
Flow induced by water
concentration gradient
Highwater
concentration
Lowwater
concentration
Flow induced by water
concentration gradient
Flow induced by
pressure gradient=
Slide 3

4. SPE 168998 • The Effect of Chemical Osmosis on Improve Oil Recovery from
Fractured Shale Formations • P. Fakcharoenphol
Slide 4
OSMOTIC PRESSURE IN SUBSURFACE
• Osmotic pressure causes drilling operation problems
• High-salinity brine in shale formations due to reverse
osmosis (de Sitter; 1947 and Bredehoeft et al.; 1963)
• High pressure anomaly in subsurface formations
(Marine and Fritz, 1981)
Slide 4

5. SPE 168998 • The Effect of Chemical Osmosis on Improve Oil Recovery from
Fractured Shale Formations • P. Fakcharoenphol
Slide 5
T = 285 F
Bakken brine
Fracturing fluid
OSMOTIC PRESSURE IN SHALE
Theoretical osmotic pressure between Bakken brine and fracturing
fluid could be higher than 4000 psi.

6. SPE 168998 • The Effect of Chemical Osmosis on Improve Oil Recovery from
Fractured Shale Formations • P. Fakcharoenphol
Slide 6
OSMOTIC EFFICIENCY IN SHALE
Theoretica
l osmotic
pressure
Measured osmotic
pressure
Ideal membrane
Neuzil and Provost (2009) reported low osmotic efficiency (<5%).
Measured osmotic pressure
Theoretical osmotic pressure
Leakage membrane
Osmotic efficiency =

7. SPE 168998 • The Effect of Chemical Osmosis on Improve Oil Recovery from
Fractured Shale Formations • P. Fakcharoenphol
Slide 7
OSMOTIC EFFICIENCY IN SHALE
Slide 7
Membrane character in shale is created by
the electrical charge at clay surface.
Ion-milled SEM image in kerogen and in clay
for a Barnett shale sample
(Milner et al., 2010)
Diagram showing electric double layer (EDL) next to the clay surface, the
diffuse layer (DL), and the neutral zone (NZ)
(adopted from Mitchell; 2005 and Keijzer; 2000)

8. SPE 168998 • The Effect of Chemical Osmosis on Improve Oil Recovery from
Fractured Shale Formations • P. Fakcharoenphol
Slide 8
OSMOTIC EFFICIENCY IN SHALE
Heterogeneity causes low membrane efficiency.
Salt ions and water molecules leak through wide gaps between clay surfaces, thus
reducing the pore pressure which is observed as low osmotic pressure in laboratory.

9. SPE 168998 • The Effect of Chemical Osmosis on Improve Oil Recovery from
Fractured Shale Formations • P. Fakcharoenphol
Slide 9
CHEMICAL OSMOSIS IN MULTIPHASE SYSTEM
The leakage mechanism promotes water-oil counter-
current flow.
The invaded low-salinity water dilutes salt concentration in the formation brine and causes
detachment of the molecular bridge (Ca2+/Na+) between the clay surface and oil, thus
increasing water wetting of the surface.

10. SPE 168998 • The Effect of Chemical Osmosis on Improve Oil Recovery from
Fractured Shale Formations • P. Fakcharoenphol
Slide 10
THE CHEMICAL OSMOSIS EFFECT
ON ENHANCE OIL RECOVERY IN SHALE
Low-salinity brine injection could improve oil recovery in
oil-bearing shale formation by:
• Counter-current oil flow induced by osmoticity and capillarity
• Increased water wetting due to invaded low-salinity brine

11. SPE 168998 • The Effect of Chemical Osmosis on Improve Oil Recovery from
Fractured Shale Formations • P. Fakcharoenphol
Slide 11
Bakken brine
282,000 ppm salinity
KCL brine
20,000 ppm salinity
Soaking a preserved core
from Middle Bakken
in high-salinity brine
Soaking the same core
in low-salinity brine
a preserved core sample
from Middle Bakken
LABORATORY SETUP

12. SPE 168998 • The Effect of Chemical Osmosis on Improve Oil Recovery from
Fractured Shale Formations • P. Fakcharoenphol
Slide 12
Dolomite
Dolomite
Illite/clay-size
grain in pore
Ion-milled SEM of oil producing zone in Middle Bakken (Kurtoglu, 2013).
PORE STRUCTURE OF MIDDLE BAKKEN
Pore space is filled with Illite and clay-size grain.

13. SPE 168998 • The Effect of Chemical Osmosis on Improve Oil Recovery from
Fractured Shale Formations • P. Fakcharoenphol
Slide 13
LABORATORY RESULTS
After 5 days soaking in
282,000 ppm high-salinity brine
After 6 days soaking in
20,000 ppm KCL-brine

14. SPE 168998 • The Effect of Chemical Osmosis on Improve Oil Recovery from
Fractured Shale Formations • P. Fakcharoenphol
Slide 14
Modeling Approach
• Fractured shale formations are represented by dual-
porosity system
• Osmotic pressure is defined as a function of salt
concentration
• Salt concentration is calculated as single component
solute transport
MATHEMATICAL MODEL

15. SPE 168998 • The Effect of Chemical Osmosis on Improve Oil Recovery from
Fractured Shale Formations • P. Fakcharoenphol
Slide 15
MATHEMATICAL MODEL
, / , /, /
p
w f m w f mw f m
π
τ τ τ= +
( ) ( ), / / , /w f m f m m w f m op f f m mk E C Cπ
τ σ λ π π = − −
 
( ) ( ) ( ), /
/ /, /
/
z f mp
f m m wf m of om cowf cowm w wf wmw f m
f m
k p p p p h h
σ
τ σ λ γ
σ
 
= − − − + − 
  
Extending dual-porosity model (Kazemi and Gilman, 1993) to account for
osmotic pressure (π)
Water transfer function:
Induced by osmoticity:
Induced by viscous force, capillarity, and gravity:

16. SPE 168998 • The Effect of Chemical Osmosis on Improve Oil Recovery from
Fractured Shale Formations • P. Fakcharoenphol
Slide 16
SIMULATION STUDY
One-simulation-grid, dual-porosity model
Assumptions:
•Oil reaches a producer well once leaving the
matrix
•Constant Pf, Swf, and Cf
•Oil rate is scaled to 1 sq.mi drainage area
•No wettability alteration effectFracture:
100% Swf
10000 ppm brine
Matrix:
Oil + water
280000 ppm brine
Relative permeability Capillary pressure Osmotic pressure

17. SPE 168998 • The Effect of Chemical Osmosis on Improve Oil Recovery from
Fractured Shale Formations • P. Fakcharoenphol
Slide 17
SIMULATION RESULTS
Production rate Recovery factor
Osmotic pressure promotes oil production

18. SPE 168998 • The Effect of Chemical Osmosis on Improve Oil Recovery from
Fractured Shale Formations • P. Fakcharoenphol
Slide 18
DISCUSSIONS AND CONCLUSIONS
• Low-salinity brine injection could improve oil recovery in oil-
bearing shale formation by:
• Counter-current oil flow induced by osmoticity and capillarity
• Increased water wetting due to invaded low-salinity brine
• In gas-bearing shale formations, osmotic pressure may be the
reason for enhanced gas production when a newly stimulated
well is shut in for several months
• The mathematical model presented in this paper simulates
chemical osmosis effect for oil- and gas-bearing fractured
shale formations
Slide 18

19. Acknowledgements
MCERS,
EMG,
and UNGI
at Colorado School of Mines
Richard Rosen,
Tobi Kosanke,
and William Mickelson
at Marathon Technical Laboratory
Slide 19

20. SPE 168998 • The Effect of Chemical Osmosis on Improve Oil Recovery from
Fractured Shale Formations • P. Fakcharoenphol
Slide 20
Osmotic pressure is pre-calculated using TOUGHREACT. It is used in the same
manner as capillary pressure and relative permeability saturation functionality
MATHEMATICAL MODEL