Introduction 

The importance of field growth cannot be overemphasized, 

especially in the context of a mature petroleum province or a 

country, such as the U.S., with declining domestic production and 

increasing imports. This fact sheet has been prepared to discuss 

some of the important aspects of field growth, particularly the role 

of enhanced oil recovery (EOR) processes.

Field growth is the increase in total proved reserves of an 

existing field through time as a result of such factors as (1) 

application of enhanced oil recovery (EOR) processes and 

horizontal well technology, (2) discovery of new pools (or 

reservoirs) or extensions of known pools (or reservoirs) in the 

existing fields, (3) improvement in reservoir characterization, and 

(4) development of more sophisticated and efficient reservoir 

simulators and data processing capabilities. The term reserves, in 

field (or reserve) growth, refers to the total proved reserves or the 

estimated ultimate recovery (EUR), which is equal to the sum of 

remaining proved reserves and cumulative production at the time 

of reporting. 

In industry, reservoirs are periodically assessed for the 

remaining hydrocarbon reserves to optimize reservoir development 

strategies for better economic returns. These periodic assessments 

generally result in increased total proved reserves.

Potential additions to hydrocarbon (oil and gas) reserves come 

from two sources, new discoveries and existing fields. During the 

early phases of development in a petroleum province, new 

discoveries are the dominant source of reserve additions. Growth 

from existing fields (field growth) is somewhat obscure or 

insignificant in the early phases but becomes dominant in the final 

development phase. Attanasi and Root (1994) report that the 

growth of existing fields contributed about 90 percent of the 

additional U.S. reserves from 1978 through 1991. Field growth is 

crucial to the supply of petroleum to the U.S. and elsewhere in the 

world. 

Background 

Although the importance of field growth was first recognized 

by Arrington (1960), Attanasi and Root (1994) were the first to 

attempt to forecast the growth of oil and gas fields for the 

conterminous United States. Attanasi and Root (1994) used the 

proprietary Oil and Gas Integrated Field File (OGIFF) developed 

by the Energy Information Administration (EIA) of the U.S. 

Department of Energy (DOE), which estimates total reserves of 

crude oil and gas, to develop their model. A summary of the 

OGIFF was published in 1990 by the EIA (Energy and Information 

Administration, 1990). The 1993 version of the OGIFF database 

includes estimated total reserves (same as EUR) from 1977 

through 1991 for all discovered U.S. oil and gas fields. In a 

subsequent paper, Attanasi and others (1999) reported that in the 

period 1992 through 1996, oil reserve additions from field growth 

were 33 percent lower and gas reserve additions from field growth 

were 25 percent higher than predicted by their earlier model. These 

differences are attributed primarily to the lower oil prices and 

higher gas prices during this period (Attanasi and others, 1999). 

Schmoker and Attanasi (1996) discuss the importance of reserve 

(or field) growth to the U.S. natural gas supply. 

Importance of Field Growth Studies

During 1998, U.S. petroleum production and imports were 8.0 

and 10.38 million barrels per day, respectively (Energy 

Information Administration, 1998). Figure 1 shows the historical 

petroleum production (including crude oil, lease condensate and 

natural gas plant liquids) and petroleum imports (including crude 

oil and petroleum products) from 1949 through 1998. 

The decline of domestic production and increase of petroleum 

imports reminds us of our increasing dependence on foreign 

petroleum supplies. Combined with the fact that the probability of 

finding new discoveries is continually decreasing reinforces the 

need for domestic field growth, which in turn results mainly from 

successful application of proven technologies in all phases of oil 

and gas exploration and development. Moreover, the economics of 

EOR projects is significantly improved when the use of existing 

wells, including stripper wells (producing 10-15 barrels per day or 

less) and associated facilities, is maximized. Once wells and 

production facilities become inactive for a long term, putting them 

back into operation for either production or application of 

enhanced oil recovery (EOR) methods may not be economically 

viable, and opportunities for reserve growth are diminished.

Technologic advancements in various phases of the oil industry 

have contributed to an increase field growth. Some of the 

advancements include the use of 4-D seismic technique; improved 

drilling practices, particularly horizontal wells for low 

permeability and thin reservoirs; EOR techniques, such as thermal 

recovery for heavy oil, and carbon dioxide (CO2), hydrocarbon or 

chemical injection for lighter oil; improved logging and coring 

tools; and more sophisticated reservoir simulation models. Figure 

2 shows U.S. EOR average daily production from January 1, 1984 

(for 1983) through January 1, 2000 (for 1999). In 1999 (reported 

U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet FS–115–00

October 2000 Printed on recycled paper

The Significance of Field Growth and the Role of 

Enhanced Oil Recovery
Figure 1. U.S. petroleum production and imports, in million barrels per day from 1948 through 1998. Domestic 

petroleum production includes crude oil, lease condensate and natural gas plant liquids; petroleum imports include 

crude oil and petroleum products. Data from Annual Energy Review 1998, Energy Information Administration, 1999, 

p. 119.

2

4

6

8

10

12

1948 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998

YEAR

Domestic Petroleum Production

Petroleum Import

PETROLEUM, IN MILLION BARRELS/DAY

Figure 2. U.S. enhanced oil recovery (EOR) production using following methods: chemical, 

thermal, CO2 injection, flue gas injection, miscible/immiscible hydrocarbon gas injection and 

nitrogen injection processes. Data from Moritis, 2000, p. 39–61.

100

200

300

400

500

600

700

800

1984 1986 1988 1990 1992 1994 1996 1998 2000

YEAR

CO2 Flue gas injection injection

Nitrogen injection

PRODUCTION, IN 1000s BARRELS/DAY

HC gas injection

Thermal

Chemical

as of January 1, 2000), EOR processes contributed 748,000 barrels 

per day to U.S. oil production or, about 12 percent of U.S. oil 

production, a percentage that is consistent with 1997 levels 

(reported as of January 1, 1998) (Moritis, 2000). 

Thermal recovery, CO2 gas injection and miscible/immiscible 

hydrocarbon gas injection are the EOR techniques that have 

contributed the most to field growth. At the year-end 1999, 86 

thermal recovery, 64 CO2 injection, and 6 hydrocarbon 

miscible/immiscible gas injection projects were in operation in the 

U.S. (Moritis, 2000). It is important to note that despite the decline 

in number of EOR projects in the U.S. and the low price of oil 

during 1998-1999, the EOR production was still a significant 

portion of the U.S. total oil production (about 12 percent). Among 

the various thermal recovery techniques, steam flooding is the most 

widely used method. Of the various gas injection processes, 

miscible CO2 injection process has been a preferred option because 

it is usually more efficient in displacing oil than any other gas 

injection process. Miscible/immiscible hydrocarbon gas injection is 

technically complex and relatively more expensive. In the miscible 

gas injection process, the injection gas and the reservoir oil form a 

single phase, resulting in significantly higher oil recoveries. In the 

immiscible gas injection process, the injection gas and reservoir oil 

remain as two separate phases and the oil recoveries are not as high 

as in the miscible gas injection process. 

Thermal recovery and CO2 injection processes are technically 

and economically the most successful EOR techniques and will 

continue to play an important role in the field growth phenomenon. 

The key to expanding the use of the technically proven EOR 

processes is the reduction of implementation costs. One recent 

example is an innovative thermal recovery (steam-cogeneration) 

project in the Wilmington field, California where steam was used 

first to produce electricity generating extra revenue and then was 

injected into reservoirs to mobilize viscous oil for better recovery 

(Moritis, 1998).

Field Growth in Major Petroleum

Production Regions 

Field growth is seen in most of the petroleum provinces of the 

world. The results of detailed study by the USGS in two regions, 

the onshore United States and Russia, are briefly described.
Figure 3. U.S. cumulative reserve growth of oil and gas fields. Data from 1995 USGS National Oil and Gas 

Resource Assessment reported by Attanasi, and others, 1999, p. 79–81.

2

3

4

5

6

7

8

9

10

11

0 10 20 30 40 50 60 70 80 90

YEARS SINCE DISCOVERY

Oil

Gas

CUMULATIVE GROWTH FACTOR

United States

The onshore fields of the conterminous United States were 

studied as part of the 1995 USGS National Oil and Gas Resource 

Assessment (reported by Attanasi and others, 1999) and are 

summarized in figure 3. 

After 90 years of production, reserves continue to grow for 

both oil and gas. As part of their study, Attanasi and Root (1994) 

divided U.S. onshore fields into two groups, common and outlier 

fields. Outlier fields were defined as fields whose reserve growth 

deviated from the general trend of common fields. Fields with 

heavy oil, such as the Midway-Sunset field in California, where a 

sudden increase in recovery many years after discovery is 

attributed to the application of thermal recovery methods, are 

considered to be outliers. Fields with low permeability or 

continuous gas reservoirs, where development seems to be 

especially sensitive to gas price fluctuations, are also considered 

to be outlier. Because the expected growth rate for common and 

outlier fields are different, they were evaluated separately. 

Although outlier fields were defined differently by Attanasi and 

Root (1994) and in the 1995 National Oil and Gas Resource 

Assessment (Attanasi and others, 1999), the overall reserve 

growth trends are similar. Cumulative growth factors (multiples of 

reserve value at discovery) 90 years after discovery from the two 

studies were slightly different with results from Attanasi and Root 

(1994) and Attanasi and others (1999) shown as follows: 

cumulative growth factors of 10.8 and 10.0 for oil fields and 8.6 

and 9.2 for gas fields, respectively. 

Although the reserve growth in common fields, as shown 

above, is attributed primarily to water flood as well as to other 

EOR techniqes, it is not large enough to offset the decline in the 

remaining proved oil reserves caused by the ongoing production 

from the existing fields. The U.S remaining proved oil reserves 

grew from 22.02 billion barrels on January 1,1998 to 22.55 billion 

barrels on January 1, 1999 (Oil & Gas Journal, 1998), but the high 

oil production rate of 6.4 million barrels/day (or annual 

production of 2.3 billion barrels) in 1998 would deplete the 

remaining reserves fast without continued field growth. The 

application of EOR techniques has occurred in only a limited 

number of fields to date. Therefore, there is potential for 

additional reserves if EOR techniques are extended to 

other fields. Further studies are required to improve the economics 

of technically proven EOR techniques for their application to 

other fields including remote and even relatively smaller fields.

Russia

As part of the assessment of reserve growth, Verma and others 

(2000) evaluated field growth in the Volga-Ural province of 

Russia. In their ongoing study, they also noted similar reserve 

growth in the West Siberian province of Russia. The Volga-Ural 

province has shown cumulative reserve (field) growth factors of 

3-5 during the first 30 years since discovery of the oil fields. 

Because of the time required in Russia to develop a field, defining 

field growth is more complex than in the U.S. For the study on 

the Volga-Ural province, the field’s effective discovery years is 

redefined as either the year of first significant reserve reporting or 

the year of first production. 

Volga-Ural and West Siberia provinces show most of their 

reserve growth in the first 5-7 years after discovery and little or no 

growth thereafter. It is difficult to compare the growth in Russian 

fields with those of the U.S. fields where growth continues even 

after 90 years, because in Russia oil fields are first evaluated over 

a 5-7 year period before being produced whereas in the U.S. both 

the evaluation and production of fields start shortly after their 

discovery. To further complicate the comparison, proved reserves 

in Russia generally include only primary and secondary (water 

flood) recoveries, although in the U.S. the reserves are revised 

regularly and include water flood and EOR recoveries. Other 

factors such as the Russian oil industry’s lack of infrastructure, 

operational and economic problems in maintaining and 

developing fields, reporting requirements and documentation, and 

changes in the political system may have contributed to the 

difference in reserve growth. 
References 

Arrington, J.R., 1960, Size of crude reserves is key to evaluating 

exploration programs: Oil & Gas Journal, v. 58, no. 9, p. 

130–134.

Attanasi, E.D., and Root, D.H., 1994, The enigma of oil and gas 

field growth: American Association of Petroleum Geologists 

Bulletin, v. 78, no. 33, p. 321–332.

Attanasi, E.D., Mast, R.F., and Root, D.H., 1999, Oil, gas field 

growth projections—Wishful thinking or reality: Oil & Gas 

Journal, v. 97, no. 14, p. 79–81.

Conclusions

Field growth occurs in almost all petroleum provinces of the 

world primarily due to the advancement of technology in various 

aspects of petroleum exploration and development. 

Field growth is considered to be the most important source for 

additional reserves in the U.S. In order to maintain or raise the 

current level of field growth, research on various aspects of 

proven EOR methods, particularly the economics, would be of 

value. While talking about improving economics of EOR 

techniques, it is important to point out that if stripper wells 

(producing 10-15 barrels per day or less) and associated 

production facilities that are in reasonable mechanical condition, 

continue to be operated or suspended rather than shut-in for long 

periods of time or abandoned, the economic viability of EOR 

application in smaller fields or parts of larger fields will definitely 

improve. 

Opportunities exist to increase U.S. oil reserves, through the 

application of proven EOR processes.

Energy Information Administration, 1990, The domestic oil and 

gas recoverable resource base—Supporting analysis for the 

national energy strategy: U.S. Department of Energy, Energy 

Information Administration SR/NES/90-05, 56 p.

Energy Information Administration, 1999, Annual Energy 

Review 1998: U.S. Department of Energy, Energy 

Information Administration DOE/EIA-0384 (98), July, p. 119.

Moritis, Guntis, 1998, EOR production up slightly: Oil & Gas 

Journal, v. 96, no. 16, p. 49–56.

Moritis, Guntis, 2000, EOR weathers low oil prices: Oil & Gas 

Journal, v. 98, no. 12, p. 39–61.

Oil & Gas Journal, 1998, Worldwide look at reserves and 

production: Oil & Gas Journal, v. 96, no. 52, p. 38–68.

Schmoker, J.W. and Attanasi, E.D., 1996, The importance of 

reserve growth to the nation’s supply of natural gas: U.S. 

Geological Survey Fact Sheet FS-202-96, 2 p.

Verma, M.K., Ulmishek, G.F., Gilbershtein, A.P., 2000, Oil and 

Gas reserve growth—A model for the Volga-Ural Province, 

Russia: Proceedings of SPE/AAPG Western Regional 

Meeting, June 19-23, Long Beach, California, SPE no. 62616, 

10 p. 

For more information, contact:

Mahendra K. Verma 

Denver Federal Center, Box 25046, MS 939

Denver, CO 80225 

Phone 303-236-1746

E-mail mverma@usgs.gov