10 Appraisal and Economics

1 0 APPRA I S A L AND ECONOMICS The appraisal

economic basis

may

of

of a

efficiency shall

for any

planned project and the evaluation of its be illustrated

economic considerations

be recovered

in the

following.

The

is the additional oil that

as compared to a water flood, and the total cost

investments, chemicals, operation and maintenance. Examples are

ciilcul~ted for a

viscosities.

typical five-spot

Incremental oil

with regard

recovery by

to different oil

polymer flooding due to

reservoir heterogeneities are not considered.

10 1 Numerical simulation of a five-spot pattern

The performance of water flooding and polymer flooding was cal-

culated

using numerical

block

was

voir

parameters

pattern

was sized

permeabilities in

Fig. 10.1.

ties

reservoir simulation.

A closed reservoir

chosen with one injection and four production wells. The

of the

300 x 300 m , the thickness was 10 m . The reser

are

that have

listed

in

Table

10.1,

the

relative

been used for the simulation are plotted

The simulation was performed for different viscosi-

reservoir oil

( 5 , 1 5 , and 30 mPa’s). The calculation

was only done for one quarter of that five-spot pattern, so that Table 1 0 . 1 Parameters used five-spot pattern Grid system: d i r e c t i on )

Reservo4r:

for the Block

numerical simulation

length:

Water:

a

and

y-

Block thickness: 10 m Number of blocks: 25 (one quarter of 5-spot) Number of layers: 1 Depth:

Dip:

1000 m sub sea level 0 0 %

Porosity : 25 Permeability: 1 Pore volume: 56 250 OOIP: 39 375

Oil:

30 m (in x-

of

Bo: Viscosity:

R,

:

urn2 m3 m3

1 5 , 1 5 , 3 0 mPa’s 16 m3(Vn)/m3

at 2 MPa

1 mPa’s

Viscosity:

(The model was set up in a way that the oil-water contact and gas-oil contact were below and above the reservoir limits. PVT-data were simplified, Bo was set to 1 to simplify material lance and the pressure in the reservoir was always kept above bubble point.)

162

the The ba-the

the

values given

was

modelled using

plete

five-spot. A

be,low should

THAM ( 1 9 7 2 )

be multiplied by four for the com-

black oil model was used, and polymer flooding the theory

proposed by

BONDOR, HIRASAKI, and

L

B

c aJ

2 0

Water saturation, 5,

1 0 . 1 Relat ive permeabilities to oil and water

Fig

Fig.

The results

water

three

cases was

started after 6 years of water injection, polymer

was chosen

in the

viscous the

= 5 , 1 5 , and 30 mPa.s) is shown for polymer flooding. Polymer injection in all

cases (oil viscosity

flooding and

viscosity water

of the simulation runs are shown in Fig. 10.2 and

1 0 . 3 . In Fig. 1 0 . 2 the development of water cut for the three

different

that

(%I

case of

equal to

breakthrough occurs oils. Hence

the oil

the reservoir

viscosity. It

with the

earlier than

in

is obvious

highly viscous oil,

the

cases

of

lower

the benefit of polymer flooding is greater in

case of the high viscous oil than if viscosity were lower. The

decrease

in water

significant.

In the

cut during

polymer flooding is in all cases case of the 30 mPa s oil, water cut decreases

about 95 % to about 5 0 % . This is in good agreement with the results of the case histories dicussed in Chapter 9 . from

163

100

80

20

0

1

2

5

4

3

I

6

. I

I

7

I

8

9

I

10

I

Time, (years)

11

1

I

1213

I

14

I

15

10.2 Water cut versus time for three different reservoir Results of a numerical reservoir simulation for water flooding and polymer flooding for a quarter of a five-spot.

Fig.

oils.

- 250

m

E

N

s

.-

u

200 150

L

a

0

e

a 100

.-0 d

A E = 18

15 m P a . s

A E = 15 % OOlP

5 mPa.s

g 50

AE =

OOlP

9 ’1- OOlP

~ l , l l j , l l

Start o f polymer injection

=I U

0

30 m P a . s

I

1

I

2

I

3

I

4

I

5

6

7

8

Time,

9

1011

1 2 1 3 1 4 1 5

(years)

Fig. 10.3 Cumulative oil production versus time for three different oil viscosities. Results of a numerical reservoir simulation for water flooding and polymer flooding for a quarter of a five-spot.

164

Figure 1 0 . 3 shows the results of the simulation runs with res-

pect

could

to 4 8 38

%

to cumulative

For the 5 mPa’s case, 19,000 m 3

oil recovery.

be recovered by water flooding after 11 years, which amounts

%

of

of the original oil in place. In the 3 0 mPa’s the original

oil in

place could

case

only

be recovered. By using

polymer

flooding, an additional 9 % of the OOIP could be recovered

geneous

reservoir, the

in the 5 mPa.s case, and 18 % in the 3 0 mPa’s case. Though water flood recovery is already excellent in this homoadditional oil

by polymer flooding is remarkable.

that may still be recoverd

1 0 . 2 Economics

the

For an example calculation of the economics of a polymer flood, case with the 3 0 mPa’s oil was chosen. This does not mean that

polymer

flooding in

covered

is not

economical.

worthwhile

reservoirs having lower viscosity oils is not

Though the so

as well,

such

since the

viscosity is also lower. The production

amount of

high,

data for

a

additional oil project

cost for

the

30

discussed here are listed in Table 1 0 . 2 .

may

a polymer

mPa’s

case

that may be re-

be

economically

slug of lower that

will

be

Table 1 0 . 2 Net oil production for water flooding and pol mer flooding. 30 mPa’s case. Wet oil production rate 3 0 m B / d , injection rate 3 0 m3/d. Quarter of a 5-spot.

Waterflood 7 11 12 13 13

9 10

11 12 13 14

*

7 600 3 600

600 200 300 000

900 700

500

13 9 0 0 14 2 0 0

8

Polymerflood

1 4 500 2 4 750 15 000 15 200 15 400 1 5 570

15 730 1 5 880

Annual oil production m3 Waterflood Polymer f loo(

500 400 300 300

14 200 1 5 150 1 9 200 21 2 0 0 2 2 000 22 400 2 2 650 22 8 5 0 23 000

250 250 200 200

170 160

150

Start of polymer flood at January lSt of year 7 165

0 950 4 050 2 000 800 400 250 200 150

1 0 . 2 . 1 Valuation of the produced oil

The investment

before for

any

any incremental

simulated

calculation

calculated in

Table

incremental

the

4960

for a polymer flood has to be made 2 - 3 years

above, the

of

oil is produced. This has to be considered profitability.

value of

Thus,

the incremental

the

example

produced oil

was

for the time at the start of the polymer flood as shown

At

10.3.

an

oil produced

polymer flood m3. For

interest in the

would not

the

10

of

%,

be that

total five-spot

Table 10.3 Net present value of polymer flood. Interest 10 % .

I

Incremental oil product ion m3 0 650 3800 1750 600

7 8 9

10

11

6860

1 0 . 2 . 2 Investments

the

value

of

the

first 5 years after the start of

of 6860 m3 but only that of

which is

further calculations, this figure is 1 9 , 8 4 0 m3.

Year

for

dealt with

incremental oil

Di s coun t factor

at

in

start

the

of

Present value (at start of polymer in.i.) m3

0,9091 0.8264 0.7513 0.6830 0.6209

1

0 537 2855 1195 - - 373 - .. - 4960

Investments in this example are only necessary for storage and

mixing might

of the

polymer. The

be necessary

for a

costs for

project like

the mixing facilities that

the 5-spot described here

a r e , according to the author s experience, about US $200,000.

Other investments, e . g . for water treatment and filtration, are

not considered. Such costs should be borne by the whole field.

166

10.2.3 Lifting costs

Lifting costs m a y , b e a controversially discussed factor, mainly

when these costs are already high, because the oil field is already producing at a high water cut. I t is evident that if the field

should

is only

also be

operated with

polymer flooding

credited with

the lifting

polymer flood economically unattractive. On

the other

windfall,

hand, the

tertiary oil

the

tertiary

oil

costs. This can make a may be

regarded as a

oil that is lifted instead of water. This may reduce the

specific production costs significantly.

Reduction of water cut from 99 % to 98 % is a reduction of the water-to-oil ratio from 100 to 5 0 , or a reduction in lifting costs

by

a factor

So polymer

of 2 .

flooding may

economic i f

also be

water cut is only decreased slightly.

In the following lifting costs are not considered.

1 0 . 2 . 4 Chemical costs

1 0 . 4 the

In Fig.

viscosity yield

of two typical xanthans is

shown. T o obtain a viscosity equal to the oil viscosity in the above-mentioned 30 m P a . s case, a polymer concentration of 800-1000 LO

l

'I

1

.

0

Fig. 10.4 at 54 OC.

~

100

.

I

l

200

~

300

~

LOO

I

,

500

l

600

,

~

700

.

800

~

,

900

~

1000

Polymer concentration, (ppm) Viscosity yield of two xanthann in a 2 0 0 g/l TDS water

167

,

~

ppm at a tcmpei,ature of 54 ’C is necessary. The price of xanthan is

about US $3

costs. some for

--

4 / h n , depending on the product and transportation

S o at a concentration of 1 kg/m3, and also considering

that

other chemicals like biocides are needed, a price of US $ 6 / m 3

a 30

mPa.s polgmer

solution seems

to be

realistic.

case of polyacrylamide the cost may be slightly lower. 1 0 . 2 . 5 Specific costs Calculations for

the following

In the

specific costs of incremental

oil are based on the costs given above.

us

Investment:

Lifting costs:

$200 0 0 0

Chemical costs (Slug of 0 . 5

vp

= 112 5 0 0 in3; 6 US $ / m 3 ) :

US $675 000 4 4 US $/m3

= = > Specific costs:

7 US $/bbl

1 0 . 3 Outlook of

is

and

The calculations made above show that total costs of 7 US $/bbl incremental oil

produced by

polymer flooding are neoded. This

of course a rough figure and not representative for every field case, but

it illustrates

that polymer

flooding

may

be

attractive enhanced oil recovery method even at low oil prices.

For the

temperat’ures

futuro, polymer of more

then 90

flooding may OC, when

be extended

other

an

to higher

temperature-stable

products

have been

polymers

at lower prices, so that polymer flooding might become as

oil

industry may

developed. A more intensive application by the

also enable

the chemical

industry

to

provide

common a technique in the oil field as i t is water flooding today.

REFERENCES Bondor, P.L.,Hirasaki, G . J . ,Them, M . J . : "Mathematical simulation of polymer flooding in complex reservoirs", SPE reprint series no. 11 (1972)

168