EOR

Oil Displacement Processes •

Frontal advance theory

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Displacement efficiency

•

Areal and vertical sweep efficiencies

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Waterflood processes

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Factors that affect oil displacement -- M o b i l i t y r a t i o

- - Gravitation al forc es - - C ap ap i l l a r y f o r c e s

Frontal Advance Theory •

•

•

First introduced by Buckley and Leverett Related to advancement of displacement front when a given fluid displaces oil in a reservoir rock Requires relative permeability and viscosity data Displacement front

qo + qw A

Water

Oil

x

dx

Water fractional flow f w =qw / (qo +qw) Front velocity v  f  = x/ t = [(qo + qw) / A ]( f w/ Sw)

Frontal Advance Theory Saturation distribution

Sw

0

Distance

L

Water cut Water cut in reservoir = f w Producing water cut = f w / [f w + (1/Bo)(1 - f w)]

Fractional Flow Curves f w = qw / (qo + qw) qw = k rw k A (dP/dx) /

and

w

qo = k ro k A (dP/dx) /

o

hence; f w = M / (M + 1) where M =

w /

o

w =

k rw /

w 

and

o =

1

f w

0

0

Swc

Sw

1 - Sor

1

k ro /

o

Water Saturation Behind Front At Breakthrough 1

f wbt

f w

Slope = 1/tD

0

0

Swc

Swi

Sw

Swbt

1 - Sor

1

Water Saturation Behind Front After Breakthrough 1

Reservoir water cut Slope = 1/tD

f w

0

0

Swc

Sw

Swbf

1 - Sor

1

Displacement Analysis Injection volume Slope of tangent = 1 / tD = Vp Ev / Vinj where Vp = pore volume Ev = volumetric sweep efficiency

Displacement efficiency Oil saturation behind front So = 1  –  Swbf Displacement efficiency Ed = 1  –  (SoBoi / SoiBo) Ultimate displacement efficiency Edult= 1  –  (SorBoi / SoiBo)

Displacement Analysis Example Given data: Oil viscosity Boi Bo behind front Swi

4 cp 1.12 RB/STB 1.16 RB/STB 28%

Water viscosity Reservoir volume Porosity Ev 

0.7 cp 36 MMB 24% 70%

Sw

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

k rw

0

0.015

0.040

0.065

0.095

0.125

0.170

0.220

0.260

0.310

k ro

0.68

0.55

0.46

0.34

0.26

0.17

0.11

0.06

0.03

0

Required: •

•

•

Ultimate displacement efficiency Water cut, recovery factor and injected volume at breakthrough Recovery factor after injection of 7MMB water