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

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

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

Hig

h w

ater

co

ncen

trat

ion

Low

wat

er

conc

entr

atio

n

Flow induced by water concentration gradient

Flow induced bypressure gradient=

Slide 3

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

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.

SPE 168998 • The Effect of Chemical Osmosis on Improve Oil Recovery from Fractured Shale Formations • P. Fakcharoenphol

Slide 6

OSMOTIC EFFICIENCY IN SHALE

Theoretical 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 =

SPE 168998 • The Effect of Chemical Osmosis on Improve Oil Recovery from Fractured Shale Formations • P. Fakcharoenphol

Slide 7

OSMOTIC EFFICIENCY IN SHALESlide 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)

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.

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.

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

SPE 168998 • The Effect of Chemical Osmosis on Improve Oil Recovery from Fractured Shale Formations • P. Fakcharoenphol

Slide 11

Bakken brine282,000 ppm salinity

KCL brine20,000 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

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.

SPE 168998 • The Effect of Chemical Osmosis on Improve Oil Recovery from Fractured Shale Formations • P. Fakcharoenphol

Slide 13

11-12-201211-05-2012

High Salinity Experiment Start: 11-01-2012 Low Salinity Experiment Start: 11-07-2012

LABORATORY RESULTS

After 5 days soaking in 282,000 ppm high-salinity brine

After 6 days soaking in 20,000 ppm KCL-brine

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

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

, / / , /w f m f m m w f m op f f m mk E C C

, // /, /

/

z f mpf m m wf m of om cowf cowm w wf wmw f m

f m

k p p p p h h

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:

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

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

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

Acknowledgements

MCERS, EMG,

and UNGI at Colorado School of Mines

Richard Rosen, Tobi Kosanke,

and William Mickelsonat Marathon Technical Laboratory

Slide 19

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