11

Hearing How An Operator

Monitored Individual

Producing Well Pump Intake

Pressures To Maximize The

Areal Sweet In A CO2

Flooding Operation In The

SACROC Unit, San Andres

Presented by: Kim Lomeli

8/26/2015

SACROC Unit

Discovered – 1948

Unitized for wtr flood 1952

First CO2 injection – 1973

(immiscible, little tertiary recovery)

K-M CO2 injection – 2000

(fully miscible, good tertiary recovery)

Patterns 10 Ac. to 90 Ac.

Average K – 30 mD

Most wells have ESP’s

Pressure & Rate Rebalancing

P Q

D’Arcy’s Law

w

e

wfe

rr

ppKhQ

ln

2

dr

dPKAQ

Radial FlowDifferential Form

Calculated Pressure Gradients, SWCL

Incremental Oil ResponseNeeds ESP UpsizeHigh GOR Well CTF/SI

Pressure & Rate Re-balancing

0

500

1000

1500

2000

2500

3000

3500

0 1000 2000 3000 4000 5000

Pu

mp

Inta

ke P

ress

ure

(P

SI)

Inflow Relationships

2

max

8.02.01

R

wf

R

wf

P

p

p

p

q

q

Productivity Index (PI)

0

500

1000

1500

2000

2500

3000

3500

0 2000 4000 6000 8000

q (bbls/day)

q (bbls/day)

Vogel’s IPR

wfR pp

qIP

..

Operating Point:

2000 bbls/day @ 2400 psi

An “Ideal” Pattern for CO2 Flooding

• Symmetrical Pattern

• Equal pressure gradients

• All layers take fluid

• Constant thickness

• Uniform permeability

• Laterally continuous

The Unfortunate Reality

• Asymmetrical Patterns

• Variable gradients

• Multiple layers

• Thickness varies

• Permeability varies

• Discontinuities

10

Step-Rate Testing

An initial SRT is run when the well is placed on initial water

injection to determine BHP, and the injectivity index.

Subsequent SRT’s are run annually, when on water during

WAG cycles

Key objectives:

• 48-hr shut-in prior to test gives a good estimate for reservoir pressure.

• Injectivity index is calculated from BHP vs. rate curve.

• Determination of the formation parting pressure (if observed).

• Pressure fall-off after last step gives an indication of perm and skin.

11

Step-Rate Testing

Skin

Note the near-wellbore skin effect

12

Rapid Pressure Drawdown (IWR < 1)

13

Rapid Pressure Drawdown (IWR < 1)

All ESP’s are equippedto record Pwf andmotor temp.

This data is availablein real-time and canalso be used to trackreservoir pressure

ESP Bottom-hole Gauge

14

Effect of Pressure Re-Balancing

Two Months on Injection/Production.

Boundary wells are drawing down reservoir pressure, flow

paths toward the interior

Nine Months on Injection/Production.

Reservoir pressure has decreased in boundary region, flow

paths realigned, improved sweep

Two months on injection.

No support to the western half of

pattern 261-2 (prior water curtain)

Nine months on injection.

Large ESP draw down pressure,

flowlines rearranged, support to west

15

Pattern 261-2 (showing delayed response)

16

Rate Re-balancing

Direct Channel

A direct channel from injector 212-2 to producer 271-3A

overwhelmed the support from adjacent patterns

17

Rate Re-balancing

With injector shut-in support from adjacent patterns

contributed to the response in producer 271-3A

18

Rate Re-balancing

212-2

Shut-in

Response

271-3A Response to shutting in 212-2

19

Pressure and Rate Re-balancing

Water Curtain

Overran 294-1

294-1 shows the effect of too much water curtain

20

Pressure and Rate Re-balancing

Water Curtain

shut-in

After water curtain shut-in well began receiving CO2 support

294-1 Production After Water Curtain Scaled Back

Decrease

in PIP

Increase in

Oil, GOR

Shut-in Water

Curtain

21

Response to Pressure & Rate Re-balancing

New Patterns Affect on “Nearby” Wells

“Nearby” Well Performance Data

Conclusions

• Successful optimization of a CO2 EOR project requires intensive

and continuous reservoir surveillance.

• Changing withdrawal in producing wells can have a significant

effect on the streamlines between the injector and producers within

a pattern.

• High GOR wells can be managed by downsizing the ESP or by

converting to flow.

• A relatively high processing rate is desirable so that the effects of

rebalancing can be observed in a reasonable time frame.

• High processing rates mean that individual patterns will have a

short producing life so adjustments need to be made as soon as

the opportunities are identified.

Questions