Assessing the Potential for Future 

Reserve Growth in the Western 

Canadian Sedimentary Basin 

By Mahendra K. Verma 

Open-File Report 2005-1179 
 

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U.S. GEOLOGICAL SURVEY 
U.S. Department of the Interior 

Gale A. Norton, Secretary 

U.S. Geological Survey 

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U.S. Geological Survey, Reston, Virginia 2005 

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Preface 

This presentation ─ Assessing the Potential for Future Reserve Growth in the 

Western Canadian Sedimentary Basin ─ was prepared for a meeting of the 

Conference Board of Canada in Calgary, Canada, on May 24-25, 2005. The 

material is based on a paper entitled “Historical and Potential Reserve Growth in 

Oil and Gas Pools in Saskatchewan” by Mahendra K. Verma and Mitchell E. 

Henry. It was first presented at the 12th Williston Basin Horizontal Well and 

Petroleum Conference, held in Minot, North Dakota on May 3-5, 2004, which 

was organized jointly by North Dakota Geological Survey and Saskatchewan 

Industry and Resources. The paper was published in Summary of Investigations, 

2004, Volume 1, Miscellaneous Report 2004-4.1, by the Saskatchewan 

Geological Survey, Canada. 

The topic of the presentation at the meeting in Calgary is the reserve growth in 

Western Canadian Sedimentary Basin (WCSB), which includes southwestern 

Manitoba, southern Saskatchewan, Alberta, northeastern British Columbia and the 

southwest corner of the Northwest Territories. Of the provinces within the 

WCSB, Alberta and Saskatchewan have most of the oil and gas accumulations. 

Therefore, the reserve growth study in these two provinces should capture the true 

reserve growth trend for the WCSB. At this time, only Saskatchewan has been 

evaluated for a detailed reserve growth study, and the results are being presented 

at the Calgary meeting. A similar study of Alberta is underway. 

The presentation includes a definition of reserve growth, and the reasons for 

choosing Canada for reserve growth study. The objectives are to evaluate reserve 

growth at the pool and field levels, develop models for forecasting additional 

reserves from reserve growth, and determine reserve growth sensitivity to various 

parameters, such as pool size, oil gravity, and porosity. The presentation also 

includes a brief description of geology, reserve analysis (change in oil-in-place, 

oil reserves, gas-in-place, gas reserves, and recovery factors with time), reserve 

growth models for oil and gas, and a short-term forecast of additional reserves 

from reserve growth. 
Assessing the Potential for Futu

Reserve Growth in the Western Canadian Sedimentary Basin 

Mahendra K. Verma, Ph.D. U.S. Geological Survey, Denver, ColoradoThe Conference Board of Canada, CalgaryMay 24-25, 2005 U.S. Department of the Interior U.S. Geological Survey 
Reserve Growth

 Reserve (or field) growth is defined as the

increase in successive estimates of recovcrude oil, natural gas, and gas liquids indiscovered accumulations. 

 Reserve-growth models contribute to real

estimates of potential reserves of a field/province/country. 

 Because of different field development po

reserve reporting systems, infrastructure, levels of investment, each petroleum provaround the world requires its own reserve model for a better estimate of potential re
Western Canadian Sedimenta

Basin (WCSB) and Reserve Gro

 The WCSB covers an area of 1.4 million k

southwestern Manitoba, southern SaskatcAlberta, northeastern British Columbia, ansouthwest corner of the Northwest Territo

 Of all the provinces in WCSB, Alberta and 

Saskatchewan have the most oil and gas reserves and resources. 

 A reserve growth study has been complet

the Saskatchewan Province, and is descrihere. A similar study is ongoing for the AlProvince. 
Why Canada’s Reserve Growth S

 Few known studies are available on reserv

growth in Canadian oil and gas pools.

 Canada is strategically important to the U

States for energy needs.

 Other considerations for selecting Saskat

first for this study: 

 Generally well-kept, long historical records, an

opportunity to study reserve growth at both pofield levels 

 Smaller number of pools in Saskatchewan com

Alberta 
What is a pool and a field ?

Definitions by Canadian Gas Potential Com(2001): 

 Pool 

─ a porous and permeable undergroun

formation that contains a natural accumulatcrude oil or natural gas and related substancombination of them, that is confined byimpermeable rock or water barrier, and that individual and separate from other reservoir

 Field 

─ a geographically defined area in whi

accumulations of crude oil, natural gas, and substances occur. 
Study Objectives for the 

Saskatchewan Province

 Evaluate reserve growth both at the pool 

field levels and develop models for forecaadditional potential reserves from reserve in Saskatchewan Province. 

 Determine reserve growth sensitivity to v

parameters, such as pool size, oil gravity, porosity. 
Data

Data includes estimates of oil-in-place/gas-iand oil/gas reserves, as well as pertinent reproduction and geologic information.  Source 

 Saskatchewan Industry and Resources 

 Length of records 

 1954 to 1984 hard copy  1985 to 2001 digital records

 Measurement units 

 1954 to 1977 Customary (American oilfield  1978 to 2001 Metric 
Methodology

Two methods were employed to estimate reserv Original method proposed by Arrington in early M

Arrington method – 1960s has been modified , aslightly different approach to calculate cumulatifactors, that requires summing recoverable pooreserves by year starting from the first productiindividual pools/fields. 

 Group Growth method – It was first used for grow

in the oilfields in Volga-Ural and W. Siberia provrequires a grouping of pools based on the lengtrecords (11 years minimum in the 1st group) foll

summing of recoverable reserves by year, beforcumulative growth factors are calculated. 
Geologic Setting

The following two sedimentary basins contribhydrocarbon (HC) accumulations in Saskatch Williston Basin – At least four total petroleum syste

contributed to HCs in the southeast part of the pro

 Three mature source rocks of Ordovician, Devonian, and D

Mississippian age 

 One immature source rock of Late Cretaceous age 

 Alberta Basin – At least four thermally matured tot

petroleum systems within this basin have provided the southwestern and west-central parts of Saskat

 Source rocks include thermally mature Devonian to Mississ

shale, Jurassic shale, Upper Cretaceous shale, and possib

Cretaceous shale and coal. 

 Timing for peak generation in the Alberta Basin is reported 

from about 60 Ma for Devonian to about 25 Ma for Cretaceo
OOil and Gas Pools and Produc

Areas, Saskatchewan Provin

Source: Saskatchewan Industry and Resou
Generalized Stratigraphic 

Chart for Southern Saskatchewan Source: Saskatchewan 

Industry and Resources 
1 2 3 4 

Distribution of Oil-In-Place 

Reserves by Age of Reservoir R

Saskatchewan Province

0 

lions of barrels) 

Age of reservoir rocks 

2,000 4,000 6,000 8,000 

10,000 12,000 14,000 16,000 18,000 

20,000

 Early

 Cretaceous 

Jurassic Early 

Carboniferous

 Devonian-

 Mississippian 

Oil in-place P ro ved o il res

Recoverable oil reserves (mil 
Oil-In-Place, Proved Oil Re

Place, Proved Oil Re

Recovery Factor Recovery Factor

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

1950 1955 1960 1965 1970 1975 1980 1985 1990 

Year

OIP, Oil Reserves, billion barrels

Oil-in-place (OIP)

Recoverable Oil Reserves

Recovery Factor
Gas-In-Place, Proved Gas 

Place, Proved Gas 

and Recovery Fact

and Recovery Fact

0

1,000

2,0003,0004,000

5,000

6,000

7,000

8,0009,000

10,000

1950 1955 1960 1965 1970 1975 1980 1985 199

Gas-in-place (GIP)

Recoverable G

Recovery Factor

GIP, Gas Reserves, in BCF

Years
Pool Selection Criteria

Modified Arrington Method: 

 All pools with reserve data through 2001 

Group Growth Method: 

Pools with at least 11 years of proved rese

Recoverable reserve data must extend into 

Cumulative production at the end of 1st ye

-About half of what is reported at the end of 2nd y

-Less than 10 percent depletion rate. 
Analysis Results

256 out of 648 oil pools and 51 out of 175 g

pools qualified for reserve growth analysis

 These pools represent about 70 percent of 

and 62 percent of gas recoverable reserve

the entire province. 

Of the 

51 gas pools, 45 are nonassociated 

are associated gas pools. 
Cumulative Growth Factor fo

Cumulative Growth Factor fo

Based on Modified Arrington and Group G

Based on Modified Arrington and Group G

1.

0

1.

5

2.

0

2.

5

3.

0

3.

5

4.

0

4.

5

5.

0

5.

5

0

5 10 15 2

0

256 pool

s

221 pool

s

187 pools

154 pool

s

M

odif ie

d Arri

Cumulative Growth Factor

Multiple of Initial Oil 

Estimate

Years Since First Production
Pool-size Distribution of 256 p

0 

10 

20 30 40 50 60 70 

1-2 4 8 64 

Number of Oil Pools 

Class Size, Million Barrels 

<0.5 0.5-1.0 2- 4- 8-16 16-32 32- 64-128 
Cumulative Growth Factor: Oil 

154 with 25 years growth; for pools with reserves 

≤ or > 

0 5 10 15 

l

Multiple of Initial Oil Estimate 

1.0 1.5 

2.0 2.5 3.0 3.5 4.0 

20 

All 154 Pools, 25 years 

68 Pools, >8 M illion bbls 

86 Pools, <8 M illion 

Cumu ative Growth Factor (CGF) 

Years Since First Production 
Cumulative Growth Factor: 

Cumulative Growth Factor: 

154 with 25 years growth; 154 with 25 years growth; for pools with reserv

for pools with reserv

1.

0

1.

5

2.02.53.03.54.04.55.05.5

0

5 10 15

All 1

54 Pool

s, 25 y

e

a

4 l

arg

e

st pool

s (

>100 M

M bbl)

150 S

m

aller po

Cumulative Growth Factor (CGF)

Multiple of Initial Oil Estimate

Years Since First Production
Cumulative Growth Factor: 

Cumulative Growth Factor: 

154 with 25 years growth; 154 with 25 years growth; subsets based 

subsets base

1.

0

1.

5

2.

0

2.

5

3.

0

3.

5

4.

0

0

5 10 15

H

e

avy Oil, 35 pools

Li

g

ht Oil, 65 pool

s

Cumul M e

diu

m Gravity Oil, 5

4 p

o

o

ative Growth Factor (CGF)

Multiple of Initial Oil Estimate

Years Since First Production
Cumulative Growth Factor: 

Cumulative Growth Factor: 

154 with 25 years growth; 154 with 25 years growth; subsets base

subsets base

123456789

1011121314

0

5 10 15 

P

oro

sity >30 %

Poro

sity <10 %

P

oro

sity 20-

30 

Cumulative Growth Factor (CGF)

Multiple of Initial Oil Estimate

Years Since First Production
Reserve Growth at Pool and Field 

 256 oil pools, which have adequate data 

reserve growth study, form 207 oil field207 fields, 42 contain two or more pool

 The 42 multiple-pool fields contain a tot

individual 91 pools (out of the total of 2pools).

 Reserve growth for the group of 91 poo

been compared with the growth for the 

of 42 fields. 
Cumulative Growth Factor for 

Reserve growth at field level

1 

2 3 4 5 6 7 8 9 

10 

0 5 25 

42 f ields 42 f ields 36 f ields ields 24 f ields 

Years Since First Production 

10 15 20 

27 f 

Cumulative Growth Factor (CGF) 

Multiple of Initial Oil Estimate 
Cumulative Growth Factor for 

Reserve growth at pool level

2.0 3.0 4.0 5.0 6.0 7.0 

0 5 20 25 

ls ls 

Years Since First Production 

1.0 

10 15 

91pools 85 poo 70 pools 50 poo 44 pool

Cumulative Growth Factor (CGF) 

Multiple of Initial Oil Estimate 
Reserve Growth in Gas Pool

 Of the 175 gas pools, 51 have adequate d

reserve growth study. 

 Of the 51 pools, 45 are nonassociated gas 

pools and 6 are associated gas pools.

 Of the 45 nonassociated gas pools, only 

have at least 25 years of reserve growth history. These 12 gas pools include the tlargest:

–Hatton Milk River with 1.8 TCF gas rese

–Hatton Medicine Hat with 0.7 TCF gas re
Cumulative Growth Factor fo

Cumulative Growth Factor fo

Based on Modified Arrington and Group G

Based on Modified Arrington and Group G

1.

0

1.

5

2.

0

2.

5

3.

0

3.

5

4.

0

4.

5

5.

0

0

5 10 15 20

Year

s Since First Production

Cumulative Growth Factor (CGF)

Multiple of Initial Gas Estimate 45

P

ool

s, 1

0 yrs

22 Pool

s, 1

5

yrs

12 P

ool

s, 20-2

5

yrs

8 P

ool

s, 30

M

o

difie

d Arri

n

gto

n
Cumulative Growth Factor: 

Cumulative Growth Factor: 

12 nonassociated nonassociated gas pools; s pools; 

for pools with rese

or pools with rese

0

1

23456789

10

11

12

0

5 10 15

H

at t on Milk

Riv

er, 1,802

B

C

F

G

All 12 Po

ols, 3,15

0 BC

F

G

H

at t o

n Me

Cumulative Growth Factor (CGF)

Multiple of Initial Gas Estimate

Years Since First Production
Model Development

 Two methods 

–Modified Arrington and G

Growth – were used to calculate cumulat

growth factors (CGF). 

 Oil CGF data from the two methods were 

and regressed using the power function 

best fit to the transformed variables. 

Gas CGF data from the two methods wer

plotted and regressed using a linear functhe best fit. 
Cumulative Growth Factor: O

Data and Model Results

1.0 1.5 2.0 2.5 3.0 3.5 4.0 

0 5 10 15 20 

i ion 

l ( ) 

i i

 -

- i i 

Years Since F rst Product 

Cumu ative Growth Factor CGF 

Multiple of Initial O l Est mate CGF: Data, Model Group Grow th meth

CGF: Data, Model Modif ed Arr ngton method 
Cumulative Growth Factor: Ga

Data and Model Results

0 5 10 15 20 

i i

 ( ) 

i 

i 

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 

Years S nce F rst Production 

Cumulative Growth Factor CGF 

Multiple of Initial Est mate 

CGF: Data and M o del - M o dif ed A rringto n 

CGF: Data, M o del - Gro up Gr
Model Equations

 Oil Pools: Power function used

CGF = 1.0191(YSFP)0.3485

...Group Growth 

CGF = 0.9890(YSFP)0.4278

...Modified Arring

Gas Pools:Linear Function

CGF = 0.0835*YSFP + 1.0375

...Group Growt

CGF = 0.0775*YSFP + 1.2033

...Modified Arri

CGF: Cumulative growth factorYSFP: Years since first production
Discussion:Based on Mod

Oil Pools:- Group Growth method: 3.13 - fold over 25 yr.= 4.

-Modified Arrington method: 3.92-fold over 25 yr.

Annual pool growth for Saskatchewan pools is hi

for fields in U.K. (2.3%), W. Siberia (2.8%); similar 

Norway (4.6%), Volga-Ural (5.3%) and U.S. Gulf of 

offshore (5.5%); and smaller than for fields in U.S

7.2%).

Gas Pools:

-Both the methods give similar growth: 3.18-fold = 

-Annual reserve growth smaller than fields in con

U.S.
Gas-in-place and Size of Develo

Area as a Function of Time 

0 

1 

2000 20

e 

,000 

2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 

10,000 

1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 

Year 

Recoverable Gas Reserves, Gas-in-plac

 Billion cubic feet 

Gas-in-place (GIP) 

Developed area (acres) 
Forecast of potential increases in Saskatc

oil and gas pool reserves, based on the mArrington method and the Group growth m

Total hydrocarbon volumes (oil volumes are in milbarrels and gas volumes in billions of cubic feet) Year of Reserve Oil Reserves, Grown Oil Volume, Gas Reserves GroEstimate/ million barrels million barrels Billion cubic feet BiForecast Mod. Arrington Group Growth Mod. Arrin2001 4,926.176 6,864.635 

2006 5,384.7 5,293.6 7,782.5 

2011 5,773.3 5,598.5 8,693.6 2016 6,121.0 5,867.9 9,604.7 
Forecast of potential increases in Saskatc

oil and gas pool reserves, based on the MoArrington method and the Group Growth m

Incremental hydrocarbon volumes (oil volumes amillions of barrels and gas volumes in billions of Year of Reserve Oil Volume, 

Forecast Million barrels 

Mod. Arrington Group Growth 

Grown Gas Volume 

Billion cubic feet 

Mod. Arrington Group G

2006 458.6 367.5 917.9 1002011 847.1 672.3 1829.0 2002016 1194.8 941.7 2740.1 300
Conclusions

Oil Pools:

 Overall growth in oil pools from models:

- Group Growth method: 3.13 - fold over 25 yr.= 4.7%/

- Modified Arrington method: 3.92- fold over 25 yr.=5.

Reserve growth sensitivity to various paramet

on CGF data and 25 years of growth: 

- Heavy and light oil pools show similar growth (5.6%

medium gravity oil pools show lower growth (3.7% 

- Smaller pools (reserves <8 MM bbl) show lower gro

compared to larger pools (reserves >8 MM bbl) (5.3

-Thefour largest oil pools(reserves >100 MM bbl) gre

6.9%/yr , and the remaining smaller pools by4.9%/y

-Growth at pool and field level for oil: Reserve growt

is about 50 percent higher than at the pool level, ov

25 years. 
CoConclusions Conclusions

 Oil Pools (Continued): 

 Average recovery factor for oil pools is abou

percent. 

Difference in 5 -and 15 - year forecasts for a p

increase in oil reserves by the two methods from 1.9 to 5.1 percent, respectively. 

Non- associated Gas Pools: 

 Recovery factor is about 70 percent.  Both methods gave similar growth 3.18 -fold 

 Difference in forecasts from the two models 

4 percent even at 15 years. 
Reserve Growth Study for th

Alberta Province

 It is the province with the largest volumes 

and gas accumulations in Canada. Alberta some light but mostly heavy oil, and gas. estimates have been offered over the yearRecent estimate of Canada’s reserves inc175 billion barrels of heavy oil from tar sadeposits. 

 Data obtained from Alberta Energy and Ut

Board (EUB), Calgary. 

 Earlier data (1955 -1977) are available on micro

incomplete or missing for some years. 

 Remaining data (1978-1998) are in digital form Recent data from 1999 to 2003 or 2004 will be 

from EUB. 
Alberta’s Oil and Gas Volum

(Source: Alberta Energy and Utilities Board, 1978

Year Oil-in-place 

billion bbl 

1978 56.8 

1998 85.4 

Initial Oil Reserves 

(Cum prod + remaining reserves) 

billion bbl 

17.3

23.8

Gas-in-place 

Trillion cubic feet 

155.3

245.5

Initial 

(Cum prod 

Tril