3/17/2010

File Title

Copyright: Shell Exploration & Production Ltd.

Shell Exploration & Production

Copyright: SIPC

Construction and Testing of Shell’s Freeze Wall

Shell Exploration & Production

Wolfgang Deeg, Sepehr Arbabi, Richard

Mykitta, Jeffrey Smith, Larry Crump

29th Oil Shale Symposium

Golden, Colorado

Oct. 19-23, 2009

2

Outline

• Purpose of freeze wall

• The freeze wall test

� Test site location

� Process design

� Subsurface construction and

freezing

� Freeze wall test layout

� Current status

� Future plans

Artistic

rendering of

the freeze wall.

3

An Effective Containment System

• Required to protect ground water

during oil shale in-situ conversion

• Ideal candidate: A freeze wall

� Ice forms an impermeable seal

• Shell’s Freeze Wall Test will

� Confirm freeze wall can be formed

across ENTIRE oil shale interval

� Establish freeze wall’s reparability

4

Freeze Wall Test Site

• Location

� Piceance Creek Basin in Rio Blanco County, Colorado

� On a 15 acre parcel of Shell’s private property

• Test site incorporates

� The freeze ring covering 1.2 acres

� Associated monitoring wells

� 3 refrigeration units and associated circulation systems

� Control room, process and data acquisition buildings, offices, and warehouse

• Serves as a laboratory to:

� Establish a freeze wall across the ENTIRE oil shale interval

� Demonstrate utility of freeze wall as a containment system

� Establish reparability of freeze wall containment system

5Freeze Holes

Pumps

Refrigeration Units (3.8 megawatts each)Tank

The Freezing System

• Combined cooling capacity:

� 3,242 tons (15,288 HP) of cooling

� 7,500 gpm circulation rate

• Circulation pumps rated at 3,500 gpm each

• Chilled aqua ammonia circulated through

136 freeze holes

� Total cooled subsurface length: 212,800 feet

6

Subsurface Construction

• Accurate well placement

� Tight well spacing (8’)

� Exceptional directional tolerance

� Required to ensure closure

• The results

� Successfully drilled all freeze holes within 2’ radius circular cylinder

� Successfully installed freeze equipment

• Confirmed by temperature logs

7

Freeze Wall Construction

• Circulation of chilled fluid

through each freeze hole

� Aqua ammonia at 25 to 50 gpm

• Higher rate at start-up

� Freeze hole inlet temperatures

as low as –54 degrees F

• Freezes water in formation

� Ice creates impermeable seal

across entire frozen interval

Chilled aqua

ammonia solution

Carbon steel

freeze tube

(closed end)

Water bearing zone

Water bearing zone

Inlet

HDPE - carbon steel

freeze tube annulus

HDPE inner

freeze tubeRich layer

Rich layer

Rich layer

Rich layer

Rich layer

Outlet

Water bearing zone

Water bearing zone

Chilled aqua

ammonia solution

Carbon steel

freeze tube

(closed end)

Water bearing zone

Water bearing zone

Inlet

HDPE - carbon steel

freeze tube annulus

HDPE inner

freeze tubeRich layer

Rich layer

Rich layer

Rich layer

Rich layer

Outlet

Water bearing zone

Water bearing zone

8

The Freeze Wall Test Layout

9

Current Status

• Actively freezing

� All freeze holes on line

� Freeze wall closure over 86% of interval being frozen

� A few holes remain in the wall in the hottest, deepest zones

• Wall thickness varies from about 16 feet to more than 40 feet

� Zone dependent

� Established based on

• Temperature logs in freeze temperature and other monitoring holes

• Numerical simulations Temperature (deg F)

Dep

th (

ft)

32 deg F

10/22/2007

11/12/2007

11/26/2007

12/10/2007

1/7/2008

2/18/2008

3/31/2008

5/12/2008

7/7/2008

8/18/2008

10/6/2008

1/5/2009

4/6/2009

6/1/2009

6/15/2009

7/6/2009

8/10/2009

9/7/2009

Temperature in Freeze Temperature Monitor Well

About 9 Feet from Freeze Wall Center Line

10

Field Data Confirms Simulations

-20

-10

0

10

20

30

40

50

60

70

80

0 90 180 270 360 450 540 630 720 810 900

Time (days)

Tem

pera

ture

(d

eg

. F

)

Field data

Field data

Simulation

Simulation

11

Freeze Wall Closure in Shallow Zones

• Confirmed by:

� Pressure rise within containment

area relative to that outside

� Lack of external pressure response

when changing water level inside

the containment area

� Lack of internal pressure response

inside the containment area to

external pressure transients

Water Level Changes at Freeze Wall Closure

Time

Wate

r le

vel ch

an

ge

Inside Containment Cell

Outside Containment Cell

12

Observations to Date

• Confirmed freeze wall can be

constructed over 86% of oil shale

interval we are freezing

� Anticipate closure over remaining

intervals in near term

• Confirmed activities that increase flow

velocities subsurface adversely affect

freeze wall construction

• Calibrated models using subsurface

temperature data and freezing

behavior

• Demonstrated leak tightness of wall

by

� Lowering or raising of fluid level within

test cell

� Saw no response outside test cell

13

Artistic

rendering of

the freeze wall.

Future Plans

• Complete freezing

� Establish freeze wall across entire oil

shale interval

• Monitor progress via temperature and

pressure data

• Closure expected in near future

• Test various containment system

configurations

• Establish freeze wall performance

� Break wall and repair