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Seismic Stimulation for Enhanced Oil Recovery

Steve Pride, Mike Kowalsky, Valeri Korneev LBNL, Earth Sciences Division, Geophysics Department, Berkeley, CA, USA

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Todays Talk:

The basis of a physical model. A theoretical “stimulation criterion”. Lattice-Boltzmann simulations of seismically

stimulated two-phase flow at the pore scale. The Foraker test site for the RPSEA project. Conclusions

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Context: As much as 60% of the world’s oil is in known reservoirs but is trapped on capillary barriers and is effectively “stuck”.

Seismic Stimulation:A seismic wave is to “shake the stuck oil loose” and get it flowing again toward a production well.

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Increase in Oil Production after Stimulationat Occidental’s Elk Hills Field, California

stimulation applied

Oil

Pro

duct

ion

(B/d

ay)

Oil

cut

%

Oil Production

Oil Cut

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The condition for a stuck oil bubble:

updown

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RRP

The production pressure drop along the bubble is just balanced by a capillary-pressure increase.

Beresnev et al. (2005)Pride et al. (2009)

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The production-gradient force that always acts on the fluids:

“acceleration of grains”

HPF /0

Poroelasticity determines the seismic force acting on the fluids:

U

fpS KG

BcF

341

“wavelength-scale fluid-pressure gradient”

where

is the seismic strain rate.

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The seismic force adds to the production gradientand can overcome the capillary barrier whenever:

F0 Fs

Fc

1, when F0 / Fc 1.

“stimulation criterion”

where

khFc

2

cos Capillary force resisting

bubble movement at the barrier (constriction).

When the bubble does not become trapped on the barrier.

S F0 / Fc 1

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NOTES•No green arrow = no applied forcing•Single green arrow = production-gradient only•Double green arrow = two periods of seismic stress + production-gradient

“when stimulation is applied, bubbles coalesce creating a longer stream of oil that flows even in absence of stimulation”

Lattice-Boltzmann Movie

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Snapshots and average oil speed during the four stages of a typical “production run”:

a. Oil separates from water without applied forcing.b. Production gradient applied; oil flows some, then gets stuck.c. Two periods of seismic stimulation applied that frees bubbles.d. Stimulation turned off and new steady-flow state emerges.

running average

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Volume of produced oil when no stimulation applied (dependence on )cFFS /0

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• Filled symbols / solid lines = stimulation appliedo Open symbols / dashed lines = stimulation not applied.

Volume of produced oil is increased when stimulation applied (wave strain )610

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Foraker Field in Osage County, OklahomaReservoir is a fractured chert called the “Chat Formation”

Simple Seismic Model at Foraker

Seismic Velocity (vertical section)

Peak particle acceleration

(plan view)

Fc = capillary force

hFc

2

cos

Used values 15.0

310 2 N /m

porosity

surface tensionpermeabilitycontact angleoil bubble lengthmh 5

030D110

3/6163 mNFc

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Maps of Stimulation Potential Created Using:

1),,(1

)()(

)( 0

x

x

xsxu

l

Z

Z

T

R

tzdtdzTH

where

otherwise0and1if00

sF

vF

v

sc

f

c

f

Ft

Ft

gradient production background velocity,particle =

trace,ofduration time=

layer,reservoir of surfacelower depth to =

layer,reservoir of surfaceupper depth to =

layer,reservoir of thicknessaverage =

0 Fv

T

Z

Z

H

l

u

R

Pressure gradientaround the 20 wells to be stimulated at the Foraker site.

Stimulation PotentialThe closer to 1, the greater the potential for liberating oil. Characteristic stuck bubble length of h = 10 cm.

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Conclusions of the modeling to date:

• Stimulation criterion successfully verified by the 2D Lattice-Boltzmann simulations so far conducted.• Need to extend the simulations to 3D and to larger systems.• Over a significant and realistic range of seismic amplitudes and reservoir conditions, seismic stimulation seems to work• The Foraker test site will be the first field test of the capillary threshold model and one of the most definitive tests to date. • The Foraker site is still being monitored for the pre-stimulation well-by-well production statistics. Stimulation is expected to begin by March of 2011.