Wellbore Leakage Potential in CO2 Storage or EOR

Fourth Wellbore Integrity Network MeetingParis, France

March 19, 2008

Theresa WatsonT.L. Watson & Associates Inc.theresa.watson@tlwatson.com

Dr. Stefan BachuEnergy Resources Conservation Board

Stefan.Bachu@gov.ab.ca

Introduction• Wellbore Leakage• Shallow Leakage • Tool Development• Deep Leakage• Case Studies• Risk Analysis

Wellbore Leakage• Wellbore leakage is separated

into two distinct areas of the wellbore

• Shallow leakage generally due to poor cementing practices

• Deep leakage generally due to stimulation or perforating

• Only deep leakage is generally associated with CO2

• CO2 leakage in the shallow areas are due to secondary events

Example of Cement and Casing Quality in a Well in the Haynes Field, Alberta

Shallow Leakage• Surface Casing Vent Flow• Gas Migration• Casing Failure

Factor with Significant Impact on Shallow Well Leakage

• Well Type (Open Hole or Cased Hole) • Regulatory Change • Spud Date (Historical Impacts)• Geographic Area• Wellbore Deviation• Cement Top• Cased Hole Abandonment Method

Tool Development• Data gathering

– ERCB well data• Depths, sizes, location, type, dates, H2 S/CO2 levels, SCVF/GM, CF, etc.

– Alberta Environment• Groundwater depth• Water well location

• Database creation– All data for Alberta dumped into SQL database– Data manipulated to calculate various fields such as; required cement

top, proximity to water wells, well density, exposure to H2 S • User interface

– Choose a smaller subset (Spawned Database) to work with– Set the values to be assigned to various factors

• Output Analysis– Small database created in Access to allow for easy analysis or special

manipulation of the data.

Factors Used in Shallow AnalysisShallow leakage factors.

Factor Criterion MeetsCriterionValue

DefaultValue

Spud Date 1965-1990 3 1

Abandonment Date <1995 5 1

Surface Casing Size ≥244.5 mm 1.5 1

Well Type Cased 8 1

Geographic Location Special Test Area 3 1

Well Total Depth >2500 m 1.5 1

Well Deviation 1.2-1.8 1.5 1

Cement to Surface No 5 1

Cement to Surface Unknown 4 1

Additional Plug No 2 1

Additional Plug Unknown 1.5 1

Deep Leakage• To adjacent zones• To groundwater• To atmosphere

Deep Leakage

Deep Leakage Factors• Stimulation• Perforated intervals• Abandonment mode• Cement type

Photograph courtesy of Halliburton Energy Services

Potential to create pathways in wellbore cement during perforating, acidizing or fracturing.

High pressure fracturing may also affect zonal isolation near the wellbore within the reservoir itself.

Multiple perforated intervals may increase the potential for cement sheath damage as well as provide leak pathways within the wellbore for zone to zone communication.

Stimulation and Perforating

Cement plug set across perforations.

Cement squeeze with retainer to perforations.

Bridge plug capped with 8 meters of cement.

Zonal Abandonment

Zonal Abandonment Failure

Cement Type

Data and photograph courtesy Barbara Kutchko, DOE

Deep leakage factors.

Factor Criterion Meets Criterion Value

Default Value

Fracture count =1 1.5 1

Fracture count >1 2 1

Acid count=1 1.1 1

Acid count=2 1.2 1

Acid count>2 1.5 1

Perforations count>1 2 1

Abandonment type Bridge Plug 3 1

Abandonment type Not abandoned

2 1

Cement types and values.

Cement Type Assigned Value Description

1:1 POZ MIX 1 Cement and fly ash

1:1:# POZ3 Cement, fly ash and various quantities

of bentonite

BLACKGOLD 1 Unknown

CAP (NEAT)1 Cap pumped on top of foam cement,

not applicable.

CLASS X NEAT 1 Various neat cements

FILL ECP1 Cement to fill annular packer, not

applicable

FOAMED 1 Cement foamed with nitrogen

G + # PC SALT1 Cement with various percent salt

additive

G + # PC SAND1 Cement with various percent silica

sand additive

GPSL/GPCEM/THX 3 Gypsum and gel additives

LIGHT WEIGHT 3 Assumed gel additive to reduce density

SELF STRESS3 No cement, hole allowed to slough in

on casing

SLAG1 Blast furnace slag, reduces cement

porosity

SLOTTED LINER 3 No cement

SLURRY 6D 1 Unknown

TAPERED CASING 3 No cement

TH CEM/CEM FNDU1 Thermal cement, usually sand or silica

additive

UNCEM CSG/LINER 3 No cement

Deep Leakage Factors

Scores

Deep leak potential.

Deep Leak Potential (DLP) Score

Low <2

Medium 2-6

High 6-10

Extreme >10

Shallow leak potential.

Shallow Leak Potential (SLP) Score

Low <50

Medium 50-200

High 200-400

Extreme >400

DLS= v(fracture count) X v(acid count) X v(perforated interval count) X v(aban type) X v(cement type)

SLP = v(spud date) X v(aban date) X v( SC size) X v(well type) X v(location) Xv( TD) X v(dev) X v(cement top) X v(additional plugs)

Case Studies

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Zama Field

Pembina Field

Edmonton

Calgary

ALBERTA

Field data and results summary.

Pembina Zama

Number of cased wells 9860 607

Number of wells drilled and abandoned 1050 106

% of wells with cement data 40% 64%

% of wells with high DLP cement score 28% 20%

% of wells fractured 75% 2%

% of wells acidized 47% 80%

% of wells abandoned 12% 13%

% of wells with multiple completions 11% 55%

% of wells with extreme DLP 14% 28%

% of wells with extreme SLP 7% 18%

% of wells with extreme SLP and DLP 1.6% 4.3%

Zama Deep Leakage Potential

0

20

40

6080

100

120

140

0 5 10 15 20 25 30+

DLP Score

Num

ber o

f Wel

ls w

ith D

LP

Scor

e

ExtremeHighMediumLow

3

u4

u1

u

u

u4

3

43

3 u

14

4 u

4

4

34 u

bu4

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3 1413

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415

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4 uu1

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3413 E 44*1451

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Zama Shallow Leakage Potential

0

50

100

150

200

250

300

100200300400500600700800900

1000+SLP Score

Num

ber o

f Wel

ls w

ith S

LP

Scor

e

ExtremeHighLowMedium

3

u4

u1

u

u

u4

3

43

3 u

14

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4

4

34 u

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3 1413

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Pembina Deep Leakage Potential

0200400600800

10001200140016001800

0 5 10 15 20 25 30+

DLP Score

Num

ber o

f Wel

ls w

ith D

LP

Scor

e

ExtremeHighMediumLow

Pembina Shallow Leakage Potential

0

1000

2000

3000

4000

5000

6000

100200

300

400500

600

700800

9001000

+

SLP Score

Num

ber o

f Wel

ls w

ith S

LP

Scor

e

ExtremeHighLowMedium

Potential Risk• Groundwater exposure• Proximity to groundwater well• Proximity to other oil and gas wells• Toxic gas release • Encroaching population

Increase in Water Wells Associated with Population Increase

An increase in the number of water wells increases the likelihood that gas, due to migration through shallow zones, can accumulate in buildings.

Deep Leakage to Surface and Groundwater in Central Alberta

Increasing Wellbores

It is estimated that there will be 959,000 wells in the province by 2056 compared to 343,000 in 2006.

Wellbore Strike by Farming Equipment

Toxic Gas Release• The program calculates which wells

penetrate horizons that contain H2 S.• This information can be used in

conjunction with the potential for leakage to determine the risk to a population in the event of a leak from the well.

Urban Encroachment

City

Well 2

Well 1

2006 City Boundary

Estimated 2056 City Boundary

2 people per km2

8 people per km2 100 people

per km2

Population growth by expanding urban centres

Population Growth

Population is expected to increase from 3,000,000 to almost 6,000,00 people by 2056This growth will take place in the large urban centres such as Calgary, Edmonton, Red Deer etc.

Wellbore Strike during Development

Conclusions• The development of this tool provides the ability

to evaluate large numbers of wells on a first pass look.

• Will enable operators/regulators to zoom in on wells or areas with high potential for leakage.

• Can be used to determine risk, not only due to CO2 but also other toxic gas releases.

• More work needs to be done to verify the factors that contribute to deep well leakage.