American Oil and Gas Reporter - February 2017 - 70

SpecialReport: Enhanced Oil Recovery
be a difficult problem to overcome for CO2 flooding. Increasing
the average reservoir pressure in a WAG project much above the
current 1,100 psi also likely would result in gas containment issues.
FIGURE 6A
East Texas Waterflood and Ethane WAG Results
450
400
350

Ethane WAG
EOR, Mstb
GI, MMscf
GP, MMscf
Mscf/stb

300
250

CUM PRD OIL

200

(MSTB)

OIL PRD RATE

(STB/DAY)

OIL PRD RATE

(STB/DAY)

CUM INJ GAS

(MMSCF)

CUM PRD OIL

150

(MSTB)

CUM PRD OIL

100

50.1
357.4
281.7
7.13 Gross
1.51 Net

(MSTB)

50
0

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

FIGURE 6B
East Texas CO2 and Ethane WAG Comparison
450

450

400

400

350
300
250

(STB/DAY)

OIL PRD RATE

(STB/DAY)

OIL PRD RATE

200

CUM INJ GAS

150

CUM INJ GAS

100

CUM PRD OIL
CUM PRD OIL

50
0
3,500

OIL PRD RATE

CUM PRD OIL

4,000

4,500

(STB/DAY)
(MMSCF)
(MMSCF)
(MSTB)
(MSTB)
(MSTB)

5,000

Ethane WAG
EOR, Mstb
GI, MMscf
GP, MMscf
Mscf/stb
CO2 WAG
EOR, Mstb
GI, MMscf
GP, MMscf
Mscf/stb
5,500

350
300

50.1
357.4
281.7
7.13 Gross
1.51 Net

250
200
150

13.6
250.9
205.8
18.43 Gross
3.31 Net
6,000

100
50

6,500

7,000

0

FIGURE 7
East Texas Field Ethane and CO2 WAG Oil Saturation
And Oil Viscosity Simulations
SO

VISO

Slim tube simulations were again run to determine the MMP
of both ethane and CO2 using an oil composition of 39 degrees
API gravity and a reservoir temperature of 146 degrees. The MMP
for ethane in the East Texas Field was 1,150 psi, while the MMP
for CO2 was 1,900 psi. The slim tube simulation comparison with
the CO2 Berea Sand core flood and slim tube experimental data
was quite good.
A quarter-five-spot model was again built using the SPE3 solution and reasonable estimates of depth, initial pressure, reservoir
thickness, well spacing, fluid composition, average porosity, and
average permeability. Injection pressure was limited to 1,600 psi
to reduce gas containment issues. A 10-acre spacing base model
was waterflooded for 20 years. The model was placed on waterflood for 4,000 days, and then 12 WAG cycles of ethane and water were injected at 1,600 psi (Figure 6A). A similar procedure was
followed to inject 12 WAG CO2 cycles and 12 methane cycles.
The ethane WAG recovered an additional 10.9 percent of OOIP
at a gross efficiency of 7.1 Mcf of ethane per barrel. The net efficiency was a very attractive 1.5 Mcf/bbl. The CO2 WAG recovered an additional 3.0 percent of OOIP at a gross efficiency of
18.4 Mcf/bbl. Net efficiency was 3.3 Mcf/bbl. The methane WAG
again did not recover significant additional oil.
Figure 6B compares the ethane and CO2 results. Figure 7 shows
oil saturation and oil viscosity maps from the ethane and CO2 WAG
runs. The ethane WAG was miscible and reduced oil viscosity significantly. The CO2 was near-miscible at the injection well, but
did not effectively reduce the residual oil saturations at the average pattern pressure of 1,100 psi.
Table 1 shows a summary of the EOR performance, and the
gross and net solvent efficiencies for the three example fields at
assumed costs of $4.15 an Mcf of ethane and $2.00 an Mcf of CO2.
In many locations, ethane is available for less than $1.00 an Mcf
because of transportation costs to a sales hub.
As these evaluations demonstrate, ethane's higher solubility
in oil and lower MMPs allow ethane EOR to recover more oil than
CO2 EOR in shallow reservoirs such as the Lawrence Field and
low-pressure settings such as the East Texas Field. Both gasses
work well in higher-pressure fields such as Cushing Field, allowing ethane to play a potentially important new role in higher-pressure cases where CO2 supply is limited or unavailable.
The enormous increase in ethane production from shale plays, in
concert with expanding ethane pipeline infrastructure, is creating new
opportunities to leverage plentiful and low-cost ethane in higher-value applications such as recovering a portion of the billions of bar-

TABLE 1
EOR Performance and Gross/Net Solvent Efficiencies for Three Example Fields
Lawrence Field
Ethane
CO2
EOR (Mbbl)

103.0

26.1

Gas injection (MMcf)

180.0

Gas production (MMcf)

84.2

Mcf/bbl (gross)

Cushing Field
Ethane
CO2
224.6

162.1

190.8

841.7

94.7

472.4

1.75

7.32

Mcf/bbl (net)

0.93

Cost per Mcf
Cost per bbl EOR

East Texas Field
Ethane
CO2
50.1

13.6

691.9

357.4

250.9

237.3

281.7

205.8

3.75

4.27

7.13

18.43

3.69

1.64

2.80

1.51

3.31

$4.15

$2.00

$4.15

$2.00

$4.15

$2.00

$3.86

$7.37

$6.82

$5.61

$6.27

$6.63

70 THE AMERICAN OIL & GAS REPORTER



American Oil and Gas Reporter - February 2017

Table of Contents for the Digital Edition of American Oil and Gas Reporter - February 2017

Contents
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