U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet FS–070–03

August 2003

Heavy Oil and Natural Bitumen—Strategic Petroleum Resources

Figure 1. Distribution of the world’s known

recoverable oil resources and reserves by

type. Technically recoverable oil in known

heavy oil and natural bitumen accumulations

is about equal to reserves of light oil (API

gravity greater than 22°) in known conventional accumulations. BBO, billion barrels

of oil.

Table 1. Regional distribution of estimated technically recoverable heavy oil and natural

bitumen in billions of barrels (BBO).

Heavy oil Natural bitumen 

Region Recovery Technically Recovery Technically

factor* recoverable BBO factor* recoverable BBO

North America 0.19 35.3 0.32 530.9

South America 0.13 265.7 0.09 0.1

W. Hemisphere 0.13 301.0 0.32 531.0

Africa 0.18 7.2 0.10 43.0

Europe 0.15 4.9 0.14 0.2

Middle East 0.12 78.2 0.10 0.0

Asia 0.14 29.6 0.16 42.8

Russia 0.13 13.4 0.13 33.7**

E. Hemisphere 0.13 133.3 0.13 119.7

World 434.3 650.7

*Recovery factors were based on published estimates of technically recoverable and in-place

oil or bitumen by accumulation. Where unavailable, recovery factors of 10 percent and 5 percent of

heavy oil or bitumen in place were assumed for sandstone and carbonate accumulations, respectively.

**In addition, 212.4 billion barrels of natural bitumen in place is located in Russia but is

either in small deposits or in remote areas in eastern Siberia.

Introduction

Because conventional light oil can

typically be produced at a high rate and a

low cost, it has been used before other types

of oil. Thus, conventional oil accounts for a

declining share of the Earth’s remaining oil

endowment. In addition to assessing conventional oil resources, scientists of the

U.S. Geological Survey’s Energy Resources

Program collect data on the abundant energy

resources available as heavy oil (including

extra-heavy oil) and natural bitumen; see

definitions in sidebar on page 2. The data in

this Fact Sheet are compiled from commercial databases (NRG Associates, I.H.S.

Petroconsultants), unpublished government

data, and the published literature.

Natural bitumen (often called tar sands

or oil sands) and heavy oil differ from light

oils by their high viscosity (resistance to

flow) at reservoir temperatures, high density

(low API gravity), and significant contents

of nitrogen, oxygen, and sulfur compounds

and heavy-metal contaminants. They

resemble the residuum from the refining of

light oil. Most heavy oil is found at the

margins of geologic basins and is thought

to be the residue of formerly light oil that

has lost its light-molecular-weight components through degradation by bacteria,

water-washing, and evaporation.

The estimated volume of technically

recoverable heavy oil (434 billion barrels)

and natural bitumen (651 billion barrels) in

known accumulations is about equal to the

Earth’s remaining conventional (light) oil

reserves (table 1, fig. 1).

In spite of an immense resource base,

heavy oil and natural bitumen accounted

for only about 3 billion barrels of the 25

billion barrels of crude oil produced in

2000. Compared to light oil, these resources

are generally more costly to produce and

transport. Also, extra-heavy oil and natural

bitumen must usually be upgraded by

reducing their carbon content or adding

hydrogen before they can be used as feedstock for a conventional refinery. The extra

production, transportation, and upgrading

costs explain why development and production of extra-heavy oil and bitumen are still

limited. Their abundance, strategic geographic distribution, quality, and costs will

shape their role in the future oil supply.

Geographic Distribution

The Western Hemisphere has 69 percent of the world’s technically recoverable

heavy oil and 82 percent of the technically

recoverable natural bitumen. In contrast, the

Eastern Hemisphere has about 85 percent

of the world’s light oil reserves.

Heavy oil and natural bitumen are

present worldwide (table 1). Each category is dominated by a single extraordinary accumulation. The largest extraheavy oil accumulation is the Venezuelan

Orinoco heavy oil belt, which contains

90 percent of the world’s extra-heavy oil

when measured on an in-place basis.

Eighty-one percent of the world’s known

recoverable bitumen is in the Alberta,

Canada, accumulation. Together the two

deposits contain about 3,600 billion

barrels of oil in place.

In addition to extra-heavy Orinoco oil,

South America has an estimated 40 billion

barrels of technically recoverable heavy oil,

so that, in total, 61 percent of the known

technically recoverable heavy oil is in

South America.

Of the 35 billion barrels of heavy oil

estimated to be technically recoverable in

North America, about 7.7 billion barrels

are assigned to known producing accumulations in the lower 48 States, and 7

billion barrels are assigned to the North

Slope of Alaska.

The U.S. bitumen accumulations are

largely in Utah. No U.S. accumulations are

being produced commercially, although, in

total, they are estimated to contain 6.1 billion

barrels of recoverable bitumen.
Current Production Technology

Currently, producers target heavy oil

accumulations having better quality oil in

terms of chemistry and density. About 66

percent of the heavy oil produced annually

is lighter than 15° API gravity, but about

50 percent of the estimated technically

recoverable heavy oil is denser (less than

15° API gravity) (fig. 2).

In conventional production, reservoir

pressure from gas and water associated

with the oil is generally sufficient to cause

light oil to flow to a production well. If natural reservoir pressure becomes depleted,

then oil flow may be enhanced by injecting

gas or water into the reservoir to push the

residual oil to the production well.

Historically, heavy oil was found incidentally during the search for light oil and

was produced by conventional methods

when economically feasible. However, to

sustain commercial well production rates,

heavy and extra-heavy oil production

almost always requires measures to reduce

oil viscosity and to introduce energy into

the reservoir. When super-heated steam is

injected into a reservoir, oil viscosity is

reduced and reservoir pressure is increased

through displacement and partial distillation

of the oil. Steam may be injected continuously to form a flood or it may be injected

in cycles so wells are used alternately for

injection and production.

Extra-heavy oil commonly requires the

addition of diluents (gas condensate, natural

gas liquids, or light crude) to enable the oil to

be transported by pipeline. Extra-heavy oil

must also be chemically upgraded to reduce

density and remove contaminants before it

can be used as refinery feedstock. In recent

projects in the Venezuelan Orinoco heavy oil

belt, 1 barrel of diluents is required for every

3 or 4 barrels of extra-heavy oil produced.

Natural bitumen is so viscous that it is

immobile in the reservoir. For oil sand

deposits less than 225 feet deep, bitumen is

recovered by mining the sands, then separating the bitumen from the reservoir rock

by processing it with hot waters, and finally upgrading the natural bitumen onsite to

a synthetic crude oil. In deeper oil sand

deposits, where the bitumen is commonly

less viscous, steam is injected into the

reservoir to mobilize the oil for recovery

by production wells. The product may be

upgraded onsite or mixed with diluent and

transported to an upgrading facility.

Production Projections 

In the Orinoco heavy oil belt, horizontal wells and lateral branches that are

optimally positioned and equipped with

improved electrical submersible or progressing cavity pumps can deliver up to

2,000 barrels of oil per day. Such horizontal well costs have been reduced in recent

years, and thus this extra-heavy crude oil

is commercial. However, the costs associated with the diluents for reservoir injection and for facilitating transport to an

upgrading facility are still significant.

Concession operators plan to increase

Orinoco production to 600,000 barrels of

extra-heavy oil per day by 2005 and to

sustain that rate for 35 years (Petroleum

Review, 2001, v. 55, no. 653, p. 30). 

Natural bitumen is extracted from

Alberta oil sand deposits that are too deep

to surface mine by a process known as

steam-assisted gravity drainage (SAGD);

see fig. 3. Production wells could produce

in excess of 2,000 barrels of bitumen per

day. In 2001, about 735,000 barrels per day

were extracted by mining and by in-situ

production from Alberta oil sands, accounting for 36 percent of Canada’s total oil production. Projected 2011 production is 2.2

million barrels per day (Alberta Energy

and Utility Board, 2002, Alberta’s Reserves

2001 and Supply/Demand Outlook

2002–2011, Statistical Series 2002–98,

p. 2–8 to 2–9).

For more information, please contact:

Richard F. Meyer

Emil D. Attanasi

U.S. Geological Survey

956 National Center

Reston, VA 20192

Telephone: 703–648–6502

703–648–6129

E-mail: rfmeyer@usgs.gov

attanasi@usgs.gov

Figure 3. Stacked pair of horizontal wells for

steam-assisted gravity drainage (SAGD), a natural bitumen recovery process. Steam injected

through the upper well mobilizes bitumen, and

gravity causes the mobilized fluid to move

toward the lower well, where the bitumen is

pumped to the surface. Graphic copyright

Schlumberger “Oilfield Review”; used with

permission. From Carl Curtis and others, 2002,

Oilfield Review, v. 14, no. 3, p. 50.

Figure 2. Cumulative percentage of annual

production (blue) and cumulative percentage

of technically recoverable resources (brown)

of heavy oil as a function of oil density (API

gravity) in 2000. Less than 10 percent of the

heavy oil produced annually is extra-heavy oil

(API gravity of 10° or less), whereas 33 percent of the technically recoverable heavy oil

has an API gravity of 10° or less.

Definitions

Petroleum Types:

Light oil, also called conventional oil, has an API

gravity of at least 22° and a viscosity less than

100 centipoise (cP).

Heavy oil is an asphaltic, dense (low API gravity),

and viscous oil that is chemically characterized by

its content of asphaltenes (very large molecules

incorporating most of the sulfur and perhaps 90

percent of the metals in the oil). Although variously

defined, the upper limit for heavy oil has been set

at 22° API gravity and a viscosity of 100 cP.

Extra-heavy oil is that portion of heavy oil having

an API gravity of less than 10°.

Natural bitumen, also called tar sands or oil

sands, shares the attributes of heavy oil but is yet

more dense and viscous. Natural bitumen is oil

having a viscosity greater than 10,000 cP.

Other Terms:

Viscosity is a measure of the fluid’s resistance to

flow. It varies greatly with temperature. Viscosity

matters to producers because the oil’s viscosity

at reservoir temperature determines how easily

oil flows to the well for extraction.

Density is a measure of mass per unit volume and

interests refiners because it is an indicator of yield

from distillation. Oil density is expressed in degrees

of API gravity, a standard of the American Petroleum

Institute. API gravity is computed as (141.5/sp g) –

131.5, where sp g is the specific gravity of the oil

at 60°F.