Wettability alteration of carbonate rock mediated by biosurfactant produced from

high-starch agricultural effluents

University of Kansas: Mehdi Salehi, Stephen Johnson and Jenn-Tai Liang

Idaho National Laboratory: Sandra Fox and Gregory Bala

9th International Wettability Symposium

Bergen, Norway. 18-19 September 2006

Outline

Introduction Surfactin and benchmark surfactants Static adsorption Aging procedure Wettability tests Conclusions Future and ongoing work Acknowledgments

Introduction

Spontaneous imbibition of water is the main production mechanism in naturally fractured reservoirs (NFR)

NFRs are mostly oil-wet or mixed-wet (Roehl et al. 1985).

Secondary production is very low, especially if the fractures form a connected network (Allan et al. 2003)

Low-concentration surfactants can change the wettability of the reservoir rock to a more water-wet state, promoting the spontaneous imbibition of water

Cheap biosurfactant may be an economical option

Effectiveness of surfactant-based EOR depends on surfactant propagation through reservoir

Dilute solutions of biosurfactant assessed for:– effectiveness in mediating wettability of carbonate rocks– adsorption

Compared to similar benchmark chemical surfactant

Oil

Surfactant

Biosurfactant

Surfactin– anionic cyclic lipopeptide – surfactant and antibiotic

properties Bacillus subtilis

– grow on high-starch medium (agro-industry waste stream)

– centrifuge to remove cells– HCl to precipitate surfactin– centrifuge and freeze-dry– re-dissolve in RO-water as

required Characterized by Schaller et al.

(INL)

O

N O

N

O

NO

N

O

NO

N

O

N

OO

O

OO

OGlu

Leu

Leu

Val

Asp

Leu

Leu

Benchmark chemical surfactants

Similar charge Comparable tail length Prior study and/or use Candidates:

– sodium dodecylbenzene sulfonate (BIO-SOFT D40)

– sodium dodecyl sulfate (STEPANOL)

– sodium laureth sulfate (STEOL CS-330)

O

S

O

OO

Na+

S

O

OO

Na+

O

O

O

O

SO

O

O

Na+

Selecting the chemical surfactant

IFT between surfactants and Soltrol 130

Materials

Benchmark surfactant: STEOL CS-330 (Stepan Co.) Biosurfactant: Crude surfactin (INL) Adsorbents (53 to 300 m) :

– Miami oolitic outcrop (MI)– Bethany Falls oomoldic outcrop (BF)– Lansing-Kansas City oomoldic reservoir material (L7) from the

Hall-Gurney Field in Russell County, KS.

Surfactant-ion selective combination electrode used to determine concentration of anionic surfactants in aqueous solution by potentiometric titration with Hyamine 1622.

Potentiometric titration

mV

--

mV

--

++

mV

--

++

++

A: Before equivalence B: At equivalence C: After equivalence

Modified after DIN EN 14480

Surfactant electrode

.

-20

0

20

40

60

80

100

120

140

160

0 1

0.05 M Hyamine 1622, ml

E, m

V

0

100

200

300

400

500

600

De

riv

ati

ve

E, mV

First Derivative

A B C

Static adsorption

Procedure: – 2.0 g crushed rock– 30 ml surfactant solution– shake for 24 h– centrifuge @ 3000 rpm for 30 min.– measure surfactant concentration before and after

equilibrating with crushed rock– calculate specific adsorption (mg/g)

0

5

10

15

20

25

0 1 2 3 4

Rock Mass (g)

Sp

ec

ific

Ad

so

rpti

on

(m

g/g

)

0.37 mmol/l Surfactin on Miami

0.37 mmol/l Surfactin on BF

1.44 mmol/l STEOL on Miami

1.44 mmol/l STEOL on BF

Specific adsorption at various surfactant/adsorbent mass ratios

0

1

2

3

4

5

0 0.5 1 1.5 2 2.5 3

Initial Concentration (mmol/l)

Sp

ecifi

c A

dso

rptio

n (m

g/g

)

0.5 g

1.0 g

2.0 g

3.0 g

STEOL CS-330 isotherms on BF rock

STEOL and surfactin isotherms on 2.0 g BF and L7 rocks

.

0

1

2

3

4

5

6

0 0.5 1 1.5 2

Initial Concentration (mmol/l)

Sp

ecif

ic A

dso

rpti

on

(m

g/g

)

Surfactin & BFSTEOL CS-330 & BFSurfactin & L7STEOL CS-330 & L7

STEOL and surfactin (30 ml) adsorption isotherms on 2.0 g BF and L7 rocks

Adsorption results (I)

Higher adsorption on oomoldic material– higher specific surface area

Specific adsorption as rock mass – settling of crushed rock in the test tubes reduced contact with

surfactant? higher shaking rates adsorption

– mechanical scouring of surface

Adsorption results (II)

Specific adsorption– surfactin > STEOL CS-330– maximum adsorption density reached at a lower

concentration reflects the lower CMC of surfactin

Surfactin and STEOL CS-330 on both L7 and BF rocks exhibit the four regions seen in a typical adsorption isotherm

Four regions of adsorption isotherm

.

0

1

2

3

4

0 0.5 1 1.5 2 2.5 3

Concentration

Sp

ec

ific

Ad

so

rpti

on

(m

g/g

)

I

II

IIIIV

Regions of typical adsorption isotherm

After Tabatabai et al. (1993)

HMC

CMC

Explanation for regions of adsorption isotherms

After Somasunduran et al. in Sharma (1995)

Wettability change

Clean crushed rocks– THF, chloroform, methanol, water– strongly water-wet

Age crushed rocks in crude oil – two weeks at 90C – strongly oil-wet

Change in wettability due to surfactants– contact aged rock with surfactants – assess wettability

Qualitative wettability tests

Two-phase separation (Somasundaran & Zhang 1997)– 0.2 g of crushed rock– 20 ml RO-water – 20 ml Soltrol 130– shake for 1 min by hand and allow to settle– material partitions between aqueous/non-aqueous phases

Flotation test (Wu et al. 2006)– 0.2 g of crushed rock– RO-water– oil-wet material floats

LKC reservoir rock – two-phase separation and flotation tests

Bethany Falls oomoldic outcrop - two-phase separation and flotation tests

.

Wettability tests results

Two-phase separation and flotation tests agree Surfactin more effective than STEOL CS-330 in

reversing the wettability of oil-wet crushed carbonate rocks.

Conclusions

Standardize and report mass of rock and volume of surfactant solution used to develop adsorption isotherms

STEOL CS-330 and surfactin exhibit typical adsorption isotherms with four distinct regions

Surfactin has higher specific adsorption on carbonate rocks than STEOL CS-330

Surfactin is more effective than STEOL CS-330 in altering wettability of crushed BF and LKC carbonates from oil-wet to water-wet state.

– on both molar and w/w bases

Ongoing and future work

Ongoing– Assess other chemical surfactants– Spontaneous/forced imbibition in cores

Future– Dynamic adsorption/desorption experiments– Economic analysis

Acknowledgements

Co-authors:– Mehdi Salehi (PhD candidate, KU)– Jenn-Tai Liang (PI, KU)– Gregory Bala (Co-PI, INL) – Sandra Fox (INL)

Other team members– Karl Eisert (MS candidate, KU)– Vivian Lopez (Undergraduate, KU)

Financial support– Grant # DE-FC26-04NT15523

United States Department of Energy (National Energy Technology Laboratory/Strategic Center for Natural Gas and Oil)

Contact details

Stephen J. Johnson The University of Kansas

Tertiary Oil Recovery Project Learned Hall, Room 4165E 1530 W. 15th Street Lawrence, KS 66045-7609

+1 (785) 864-3654 +1 (785) 864-4967 sjohn@ku.edu