AVAILABILITY OF BOOKS AND MAPS OF THE U.S. GEOLOGICAL SURVEY 

Instructions on ordering publications of the U.S. Geological Survey, along with prices of the last offerings, are given in the 

current-year issues of the monthly catalog "New Publications of the U.S. Geological Survey." Prices of available U.S. Geological 

Survey publications released prior to the current year are listed in the most recent annual "Price and Availability List." Publications 

that are listed in various U.S. Geological Survey catalogs (see back inside cover) but not listed in the most recent annual "Price 

and Availability List" are no longer available. 

Prices of reports released to the open files are given in the listing "U.S. Geological Survey Open-File Reports," updated 

monthly, which is for sale in microfiche from the U.S. Geological Survey, Books and Open-File Reports Section, Federal Center, 

Box 25425, Denver, CO 80225. Reports released through the NTIS may be obtained by writing to the National Technical 

Information Service, U.S. Department of Commerce, Springfield, VA 22161; please include NTIS report number with inquiry. 

Order U.S. Geological Survey publications by mail or over the counter from the offices given below. 

BY MAIL 

Books 

Professional Papers, Bulletins, Water-Supply Papers, Techniques of Water-Resources Investigations, Circulars, publications of 

general interest (such as leaflets, pamphlets, booklets), single copies of 

Earthquakes & Volcanoes, Preliminary Determination of Epicenters, 

and some miscellaneous reports, including some of the foregoing series 

that have gone out of print at the Superintendent of Documents, e 

obtainable by mail from 

U.S. Geological Survey, Books and Open-File Reports 

Federal Center, Box 25425 

Denver, CO 80225 

Subscriptions to periodicals (Earthquakes & Volcanoes and 

Preliminary Determination of Epicenters) can be obtained ONLY from 

the 

Superintendent of Documents 

Government Printing Office 

Washington, D.C. 20402 

(Check or money order must be payable to Superintendent of 

Documents.) 

Maps 

For maps, address mail orders to 

U.S. Geological Survey, Map Distribution 

Federal Center, Box 25286 

Denver, CO 80225 

Residents of Alaska may order maps from 

Alaska Distribution Section, U.S. Geological Survey 

New Federal Building - Box 12 

101 Twelfth Ave., Fairbanks, AK ~9701 

OVER THE COUNTER 

Books 

Books of the U.S. Geological Survey are available over the 

counter at the following U.S. Geological Survey Public Inquiries 

Offices, all of which are authorized agents of the Superintendent of 

Documents: 

• WASHINGTON, D.C.-Main Interior Bldg., 2600 corridor, 

18th and C Sts., NW. 

• DENVER, Colorado-Federal Bldg., Rm. 169, 1961 Stout St. 

• LOS ANGELES, California-Federal Bldg., Rm. 7638, 300 N. 

Los Angeles St. 

• MENLO PARK, California-Bldg. 3 (Stop 533), Rm. 3128, 345 

Middlefield Rd. 

• RESTON, Virginia-503 National Center, Rm. 1C402, 12201 

Sunrise Valley Dr. 

• SALT LAKE CITY, Utah-Federal Bldg., Rm. 8105, 125 South 

State St. 

• SAN FRANCISCO, California-Customhouse, Rm. 504, 555 

Battery St. 

• SPOKANE, Washington-U.S. Courthouse, Rm. 678, West 920 

Riverside Ave. 

• ANCHORAGE, Alaska-Rm. 101, 4230 University Dr. 

• ANCHORAGE, Alaska-Federal Bldg., Rm. E-146, 701 C St. 

Maps 

Maps may be purchased over the counter at the U.S. Geological 

Survey offices where books are sold (all addresses in above list) and at 

the following U.S. Geological Survey offices: 

• ROLLA, Missouri-1400 Independence Rd. 

• DENVER, Colorado-Map Distribution, Bldg. 810, Federal 

Center 

• FAIRBANKS, Alaska-New Federal Bldg., 101 Twelfth Ave . 
Definition and World Resources of Natural 

Bitumens 

By RICHARD F. MEYER and WALLACE DE WITT, JR. 

Definitions of the main types of natural bitumens, 

with emphasis on natural asphalt, the most significant 

quantitatively and economically, and its world distribution 

U.S. GEOLOGICAL SURVEY BULLETIN 1944 
DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, Jr., Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

Any use of trade, product, or firm names in this publication is for descriptive purposes 

only and does not imply endorsement by the U.S. Government 

UNITED STATES GOVERNMENT PRINTING OFFICE: 1990 

For sale by the Books and Open-File Reports Section, 

U.S. Geological Survey, Federal Center, 

Box 25425, Denver, CO 80225 

Library of Congress Cataloging in Publication Data 

Meyer, R.F. (Richard F.), 1921-

Definition and world resources of natural bitumen I by Richard F. Meyer and 

Wallace de Witt, Jr. 

p. em. - (U.S. Geological Survey Bulletin ; 1944) 

Includes bibliographical references. 

Supt. of Docs. no.: I 19.3:1944 

1. Bitumen. 2. Asphalt. I. De Witt, Wallace, 1920- II. Title. 

Ill. Series. 

QE75.B9 no. 1944 

[TN850] 

553.2'4-dc20 90-3856 

CIP 
CONTENTS 

Abstract 1 

Introduction 1 

Acknowledgments 1 

Definitions of Natural Bitumens and Related Substances 1 

Natural Bitumens 1 

Components of Natural Bitumens 2 

Types of Natural Bitumens 3 

Crude Oil 5 

Coal 6 

Classification Systems of Natural Bitumens 6 

Differentiating Natural Bitumens and Crude Oil 9 

Usage of Natural Bitumens 9 

Natural Asphalt Resources 10 

Natural Asphalt Deposits 10 

Resource Evaluation 11 

References 13 

FIGURES 

1. Chart showing classification of natural bitumens, crude oil, and coals 3 

2. Chart showing solvent fractionation of natural bitumens and topped crude oil 4 

3-6. Graphs showing: 

3. Atomic ratios of coals and natural bitumens 5 

4. Correlation of absolute viscosity and API gravity for gas-free crude oil at 

various reservoir temperatures 6 

5. Grade conversions for natural asphalt deposits 12 

6. Sensitivity of discounted cash flow rate of return to natural asphalt grade for 

three different processing plant sizes 12 

TABLES 

1. Physical and chemical limits of natural bitumen and petroleum 7 

2. Comparison of petroleum and natural bitumen classification systems 8 

3. World natural asphalt resources 10 

Contents Ill 
Contents IV 

METRIC CONVERSION FACTORS 

For readers who wish to convert measurements from the inch-pound system of units to the metric system of 

units, the conversion factors are listed below: 

Multiply 

Foot (ft) 

Mile (mi) 

Square mile (mi2

) 

Centipoise ( cP) 

Degrees API (

0 API) 

Barrel per day (bbl/d) 

Short ton per year (ton/yr) 

Degrees Fahrenheit (°F) 

By 

0.3048 

1.609 

2.59 

.001 

141.5 

131.5+0API 

.159 

.907 

5/9(°F-32) 

To obtain 

Meter (m) 

Kilometer (km) 

Square kilometer (km2

) 

Pascal second (Pa· s) 

Grams per cubic centimeter (g/cm3

) 

Cubic meter per day (m3 /d) 

Megagram (metric ton) per year (Mg/a) 

Degrees Celsius (°C) 

API gravity: A standard adopted by the American Petroleum Institute for expressing the specific weight of oils. 

API gravity = 141.5/specific gravity at 60 °F-131.5. Measured in °API. 
Definition and World Resources of Natural Bitumens 

By Richard F. Meyer and Wallace de Witt, Jr. 

Abstract 

Natural bitumens, semisolid or solid mixtures of 

hydrocarbons and as much as 50 percent heterocyclic 

compounds, are composed largely of carbon and hydrogen but have substituents of nitrogen, oxygen, sulfur, and 

trace metals, especially iron, nickel, and vanadium. Bitumens are soluble in organic solvents such as toluene or 

chloroform. The natural bitumens are differentiated from 

less viscous crude oils on the basis of their absolute 

viscosity of more than 10,000 centipoises. Natural asphalt, 

commonly known as oil sand or tar sand, is the only 

natural bitumen variety of quantitative and economic 

significance and today serves as a source of road metal 

and as raw material for synthetic fuels. 

Canada's Alberta Province dominates world resources of natural asphalt; it has demonstrated and 

inferred resources totaling more than 2,500 billion barrels. 

Resources ranging from 10 billion to 70 billion barrels are 

in the U.S.S.R., the People's Republic of China, Venezuela, and the United States. Smaller amounts of natural 

asphalt resources are present in numerous other countries. At present, little use is being made of many of these 

deposits. However, with the depletion of conventional 

crude oil, natural asphalt will become more important as a 

source of hydrocarbon~s'' for fuels and petrochemicals. 

INTRODUCTION 

Bitumen, asphalt, and related substances were used in 

the Middle East before historical records. Study of archeological sites (Abraham, 1960a; Forbes, 1964; Bilkady, 

1984) showed that, as long ago as 4000 B.C., bitumen was 

used to waterproof reed roofs and boats. Between 3200 

B.C. and 2500 B.C., bitumen was used for mortar, pavement, insulation, joints, and water courses. The source of 

the bitumen was oil seeps and asphalt deposits, some of 

which were quarried until recently. In historic times, 

methods were developed to distill oil from the bitumen to 

recover naphtha and kerosene for illumination, cooking, 

heating, and military uses. 

Manuscript approved for publication May 22, 1990. 

Acknowledgments 

We gratefully acknowledge t~e critical reviews of the 

manuscript by Dona B; Dolan, Christopher J. Schenk, and 

Gregory F. Ulmishek and the preparation of illustrations by 

Maura J. Hogan. 

DEFINITIONS OF NATURAL BITUMENS AND 

RELATED SUBSTANCES 

Natural Bitumens 

Hydrocarbons are molecules composed of hydrogen 

and carbon atoms and form a continuous series of organic 

compounds ranging from coal (the heaviest), to crude oil, to 

methane (the lightest). In nature, hydrocarbons form complex mixtures with nonhydrocarbons; these mixtures are 

distinguished on the basis of their atomic hydrogen-carbon 

(H/C) and oxygen-carbon (0/C) ratios, as well as by the 

amount of included nitrogen, ~xygen, sulfur, and trace 

metals. One such mixture is the natural bitumens. 

Physically, these complex mixtures are defined by 

their solubility in various organic solvents, such as carbon 

disulfide, and by their fusibility, the fusing or softening 

point that indicates a gradual transition from a solid to a 

liquid state, through a considerable range of temperatures. 

In contrast, many substances, particularly metals having a 

definite composition, melt quickly, within a narrow range 

of temperatures (Abraham, 1960b). Various definitions and 

classifications of natural bitumens, crude oil, petroleum, 

and coal are given by Abraham (1960a), Carman and Bayes 

(1961), Bell and Hunt (1963), Wen and others (1978), Hunt 

(1979), Speight (1980), and Cornelius (1987). 

There are no standard definitions for the basic commodities discussed in this bulletin. Terms generally have 

been adapted to suit particular requirements of geologists, 

engineers, refiners, or lawyers. The following definitions 

are from Hunt (1979). 

Bitumens. -Native substances of variable color, 

hardness, and volatility, composed principally of the elements carbon and hydrogen, and sometimes associated with 

mineral matter. The nonmineral constituents are largely 

soluble in carbon disulfide. 

Definitions of Natural Bitumens and Related Substances 
Coal. -A readily combustible rock containing more 

than 50 percent by weight, and more than 70 percent by 

volume, of organic material formed from the compaction or 

induration of variously altered plant remains. Humic coals 

form from plant cell or wall material deposited under 

aerobic conditions, whereas sapropelic coals form from 

spores, pollen, and algae deposited under anaerobic conditions. 

Crude oil. -A petroleum that is removed from the 

Earth in liquid state or is capable of being so removed. 

Kerogen.-The disseminated organic matter of sedimentary rocks that is soluble in nonoxidizing acids, bases, 

and organic solvents. The organic matter initially deposited 

with unconsolidated sediments is not kerogen but a precursor that is converted to kerogen during diagenesis. Sapropelic kerogens yield oil and gas on heating, whereas humic 

kerogens yield mainly gas. Kerogen includes both marineand land-derived organic matter; the latter is the same as the 

components of coal. 

Petroleum.-A species of bitumen composed principally of hydrocarbons and existing in the gaseous or liquid 

state in its natural reservoir. 

Although petroleum is a species of bitumen, it is 

convenient to consider it as a separate commodity possessing many of the attributes of bitumen; this practice is 

followed by most geologists. Refiners (Neumann and 

Rahimian, 1984) define petroleum as the liquid mixture of 

hydrocarbons and nonhydrocarbons in a reservoir and 

define crude oil as the recovered petroleum at the surface; 

crude oil serves as the feedstock for refineries. In legal 

terms, Williams and Meyers (1964) defined petroleum as a 

complex mixture of hydrocarbon compounds, oily and 

inflammable in character. They defined crude oil, or crude, 

as liquid petroleum as it comes out of the ground, as 

distinguished from refined oils manufactured from crude. 

The natural bitumens are essentially free of gas; 

therefore, the species of petroleum considered in this report 

is crude oil (crude), the term that will be used throughout 

this bulletin. Distinctions between crude oil and the natural 

bitumens are arbitrary but useful for categorizing individual 

deposits. Most of the natural bitumens are the result of the 

alteration of a crude oil, but some are simply an immature 

step in the evolution of a mature crude oil. The term "oil" 

is used in the sense of Speight (1980) for the oily constituent 

of some natural bitumens, the proportion of which may be 

used to distinguish natural bitumens from crude oil. Figure 

1 shows the relations among coals, crude oil, and natural 

bitumens. 

Natural bitumens are semisolid or solid mixtures of 

hydrocarbons and as much as 50 percent heterocyclic 

compounds constituted largely of carbon and hydrogen but 

having substituents of sulfur, oxygen, nitrogen, and trace 

metals, especially iron, nickel, and vanadium, in the carbon 

network (Yen, 1984). In sedimentary rocks, natural bitumen is the soluble (in organic solvents) portion of the 

2 Definition and World Resources of Natural Bitumens 

disseminated organic matter; kerogen is the insoluble portion. Part or all of the bitumen may be expressed from 

sedimentary rock (the source bed or rock) through primary 

migration to form natural bitumen deposits (Tissot and 

Welte, 1978). The natural bitumen deposits may be subsequently altered to form different varieties of natural bitumens, crude oil, or natural gas. Some crude oil or gas also 

can evolve in the source rocks and subsequently migrate to 

form oil or gas reservoirs (pools). The oil or gas thus 

accumulated may be altered to create reservoir bitumens or, 

ultimately, natural gas or graphite. Oil shale is rock that 

contains at least 33 percent ash; its organic matter is 

normally insoluble but will yield oil upon destructive 

distillation. Tar is an artificial product of the destructive 

distillation of coal or wood; therefore, it is excluded from 

this discussion. 

Components of Natural Bitumens 

The principal components of topped crude oil or 

natural bitumens can be determined by fractionation with 

organic solvents (fig. 2). Crude oil is topped if the volatile 

components are removed to a temperature of 300 °F, above 

which cracking of large molecules may commence. Extraction with solvents provides a ready means of physically 

separating the components in a way that reflects their 

chemical differences. It also provides a way to determine 

the relative proportions of components, such as the asphaltics and oil, in a natural bitumen sample. 

Natural bitumens consist mostly of hydrocarbons 

(paraffinic, naphthenic, and aromatic) but also include 

various amounts of nonhydrocarbon heterocyclic compounds, which incorporate nitrogen, oxygen, sulfur, and 

trace metals as substituents. The preasphaltenes, asphaltenes, and resins constitute the heavy (high molecular 

weight) constituents of natural bitumens and crude oil and 

are referred to as the asphaltics (Yen, 1984). Preasphaltenes 

(carbenes and carboids) (Yen, 1984) are present in very 

small amounts, usually less than 2 percent, are insoluble in 

pentane, and are commonly disregarded. Asphaltenes are 

very large molecules, most often incorporating heteroatoms 

and trace metals, and are soluble in carbon disulfide but 

insoluble in normal pentane. Nitrogen, sulfur, and oxygen 

form hydrocarbon heterocyclic compounds, termed N-S-0 

compounds, which are strongly polar. These compounds 

commonly result from the complexing of N-S-0 heteroatoms and trace metals in the asphaltene structure. 

Resins are also large molecules that are strongly 

polar; they are soluble in both carbon disulfide and normal 

pentane (n-pentane). The polar compounds (such as the 

resins and heterocyclic compounds) are significant because 

of their attraction to water and clay. Because of this 

attraction, polar compounds adversely affect the rheological 

properties of petroleum or bitumens that contain large 

proportions of polar compounds, and they make recovery of 
CRUDE OIL 

NATURAL BITUMENS 

COALS 

I 

I I 

I ALLOCHTHONOUS I I AUTOCHTHONOUS I 

Viscosity< 10,000 cP I Viscosity> 10,000 cP 

I I I 

I CRUDE OIL I NATURAL BITUMEN I I COALS I 

cs2 soluble I cs2 insoluble I 

I I I I 

SOLUBLE NATURAL PYROBITUMENS SAPROPELIC HUMIC 

BITUMENS (Anaerobic) (Aerobic) 

I I 

-I RESERVOIR BITUMEN 1-- Cannel Peat 

Bog head Lignite 

(Torbanite) Bituminous 

Fusible Difficult to fuse (Coorongite) Anthracite 

I I I 

MINERAL WAX NATURAL ASPHALT ASPHALTITE 

I I I 

Ozocerite Athabasca Gilsonite 

Scheererite Trinidad Lake Grahamite 

Tabbyite Glance pitch 

H/C>1 H/C<1 

I 

Elate rite 

lngramite lmpsonite 

Wurtzilite Anthraxolite 

Albertite Shungite 

Figure 1. A classification of natural bitumens, crude oil, and coals. H/C, hydrogen-carbon ratio. Modified from Rogers and 

others, 1974; Hunt, 1979; and Cornelius, 1987. 

petroleum or natural bitumens from reservoir rocks difficult. The n-pentane-soluble constituents are called the 

maltenes. The maltenes may be treated with propane; the 

resins are insoluble in propane, and the remainder of the 

constituents constitutes the oily fraction. 

Types of Natural Bitumens 

The natural bitumens are mostly allochthonous and 

may be divided into two main groups on the basis of their 

solubility in carbon disulfide. One group, the pyrobitumens, is dark colored, hard, and insoluble in carbon 

disulfide. The pyrobitumens are divided into two subgroups-those whose HIC is smaller than unity and those whose 

H/C is larger than unity. The impsonite-anthraxoliteshungite subgroup is metamorphosed and has H/C of about 

0.1 to 0.8. The elaterite-wurtzilite-ingramite-albertite subgroup is characterized by H/C as great as 1. 6. Elaterite and 

wurtzilite contain 3-4 weight percent sulfur and have 

undergone various degrees of vulcanization; the sulfur 

imparts an elastic constitution. Albertite and ingramite are 

low in sulfur, have H/C only slightly greater than unity, and 

appear to be more highly indurated forms of natural asphalt 

(Hunt, 1979). 

The soluble natural bitumens form the other group of 

bitumens; its members are soluble in carbon disulfide and 

are composed mostly of hydrocarbons. However, these 

hydrocarbons frequently are in combination with heterocyclic compounds of nitrogen, sulfur, oxygen, and trace 

metals, most notably nickel and vanadium. The soluble 

natural bitumens generally contain various amounts of 

admixed mineral matter from their host rocks. Soluble 

bitumens fall into three subgroups defined by their relative 

fusibility-mineral waxes, natural asphalts, and asphaltites. 

Definitions of Natural Bitumens and Related Substances 3 
NATURAL BITUMEN 

TOPPED CRUDE OIL 

PENTANE INSOLUBLE 

I I 

I 

I 

PENTANE SOLUBLE 

(MALTENE) 

I 

PROPANE INSOLUBLE 

(RESIN) 

I 

I 

PROPANE SOLUBLE 

(OIL) 

BENZENE SOLUBLE 

(ASPHAL TENE) 

BENZENE INSOLUBLE 

(PREASPHAL TENE) 

I 

I I 

CARBON DISULFIDE 

INSOLUBLE 

(CARBOID) 

CARBON DISULFIDE 

SOLUBLE 

(CARBENE) 

Figure 2. Solvent fractionation of natural bitumens and topped crude oil. Modified from Yen, 1984. 

The mineral waxes are similar to the pyrobitumens 

that have H/C greater than unity (fig. 1). However, they 

differ from the pyrobitumens and from the other soluble 

natural bitumens chemically because the waxes are mostly 

normal paraffins and cycloparaffins, whereas pyrobitumens 

consist substantially of asphaltics, and the other natural 

bitumens are composed almost entirely of aromatic hydrocarbons and asphaltics, to the virtual exclusion of paraffins. 

Ozocerite, the most common mineral wax, is easily fusible, 

has H/C of. about 1.5, and is made up almost entirely of 

paraffins. 

The natural asphalts are black, easily soluble, fuse at 

50-160 °F, frequently contain admixed mineral matter, and 

are usually composed in part of nitrogen-sulfur-oxygen 

heterocyclic compounds and trace metals. Characteristically, natural asphalt occurs in lenticular deposits at or near 

the Earth's surface. Deposits of natural asphalt, with or 

without admixed mineral matter, may be very small areally 

or may underlie many square miles. Conversely, the other 

natural bitumens generally occur in dikes a few feet or tens 

of feet in thickness and as much as several miles in length. 

Because only natural asphalt is of quantitative importance 

or of economic significance, the general term natural 

bitumen is frequently, although incorrectly, used as a 

synonym for natural asphalt. Rogers and others (1974) 

concluded that the term natural asphalt may be used when a 

bitumen's origin from crude oil by nonthermal degradation 

4 Definition and World Resources of Natural Bitumens 

is evident. Connan and van der Wiede ( 1978) used natural 

asphalt to signify altered, but not immature, crude oil. 

The asphaltites are very dark colored solids that will 

fuse, but only at temperatures above about 230 °F, and are 

almost completely soluble. 

Reservoir bitumens (figs. 1 and 3) are black, solid, 

graphitic or asphaltic particles or coatings within the pores 

of oil- or gas-bearing reservoir rocks, having been derived 

from the petroleum contained therein. Such bitumens are 

frequently seen in cores and well cuttings and are described 

by Rogers and others (1974) from Paleozoic carbonate 

reservoir rocks lying unconformably below the Cretaceous 

sandstones of the western Canada basin. The reservoir 

bitumens are derived from the reservoir oil by two different 

processes, thermal alteration and deasphalting; the derivation from two processes leads to variations in solubility in 

carbon disulfide. They are distinguished from other bituminous substances by being predominantly composed only of 

hydrogen and carbon. The insoluble reservoir bitumens 

mostly have H/C of less than 1 and densities of about 

1.15-1.40, whereas the soluble forms have H/C of about 

1. 2-1.5 and densities of 1. 02-\ .14. Figure 3 shows that the 

reservoir bitumens form a distinct grouping, based on their 

H/C, which are lower than the ratios of all the natural 

bitumens except impsonite and anthraxolite, and their 

(N +S)/0, which are considerably higher than those of the 

latter two pyrobitumens. 
2.0 

1.8 

1.6 

1.4 

lngramite• 

0 

Tabbyite 

, 

Wurtzilite!, 

Athabasca 0

Trinidad O 

0 Texas Rozel Point 

Gilsonite'$---------- __ ; -~ 

,'' *Ragusa 

,' Athabasca * I 

I 1.2 Boghead coal 

/ ~ Cannel coal 

~1.0-/ 

0.8 

0.6 

0.4 

0.2 

0 

~# United States 

Germany # " 

( 

# 

1 e . # Australia 

mpsomte 

# South Africa 

# 

# 

I 

0.2 

New Zealand 

# 

e Anthraxolite 

# 

0.3 0.5 1 

(N+S)/0 

* Lagunillas 

* Baxterville 

I I 

2 4 

I 

7 10 

EXPLANATION 

~ Sapropelic coal # Humic coal 0 Asphalt $ Asphaltite 

* Petroleum asphaltene [J Reservoir bitumens • Mineral wax e Pyrobitumens 

Figure 3. Atomic ratios of coals and natural bitumens. H/C, hydrogen-carbon ratio; (N+S)/0, (nitrogen+sulfur)-oxygen 

ratio. From Hunt 1979. 

Crude Oil 

Crude oil is allochthonous (fig. 1) and is composed 

mainly of hydrocarbons. It is distinguished from natural 

bitumens by its viscosity of less than 10,000 centipoises 

(cP) (fig. 4). Petroleum is divided into conventional, heavy, 

and extra heavy oil on the basis of API gravity. Conventional oil is lighter than 20 o API. The gravity of heavy oil is 

Definitions of Natural Bitumens and Related Substances 5 
1,000 

~ en 

0 

u 

(/) 

> 10 L.U 

1-

:::> 

_J 

0 

(/) 

co 

<( 

0.1 L__--J... _ _L...__.._____._ _ __.___.L_---l. _ ___j_ _ __!___L____J 

10 15 20 25 30 35 40 45 50 55 60 65 

API GRAVITY, IN °API 

Figure 4. Correlation of absolute viscosity and API gravity 

for gas-free crude oil at various reservoir temperatures. 

Modified from Beal, 1946. 

between 10 and 20 °API. Extra heavy oil has a gravity less 

than 10 o API; that is, a specific gravity greater than 1. These 

definitions differ from those of the World Petroleum Congress (WPC) (Martinez and others, 1987) only in that the 

congress sets the upper limit of heavy oil at 22.3 °API 

(specific gravity of 0.920). The heaviness of a crude oil is 

a function of increasing size of the hydrocarbon and 

asphaltic molecules, especially the asphaltenes, that make 

up the crude oil. The number of hydrogen atoms decreases, 

and the number of carbon and heteroatoms increases. 

Heavy oil and natural bitumens owe their character to 

their deficiency of light paraffinic and naphthenic molecules, the most volatile components of an oil, and their 

resultant aromaticity. Heavy oil and natural bitumens 

(except the mineral waxes) consist of 50 percent or more 

aromatic hydrocarbons and N-S-0 compounds (Cornelius, 

1987). This composition may result from immaturity of an 

oil or from degradation of a mature oil. Alteration of oil by 

water washing or biodegradation results in loss of light 

hydrocarbons, especially paraffins. Alteration by deasphalting through contact with natural gas leads to heavy oil and 

natural bitumens. Thermal alteration results in production 

of methane and pyrobitumens or equivalent reservoir bitumen. The class "aromatic asphaltic oil" (Tissot and Welte, 

1978) is the quantitatively most important of all classes of 

oil and includes the extra heavy and heavy oil of Venezuela 

6 Definition and World Resources of Natural Bitumens 

and the U.S.S.R. and the natural bitumens of Alberta, 

Canada, the U.S.S.R., and the United States. 

Coal 

Coal is mostly autochonous, readily combustible, and 

composed of at least 50 weight percent and 70 volume 

percent organic matter. The sapropelic coals evolved anaerobically from algae, spores, and pollen, whereas the humic 

coals formed aerobically from plant cell and wall material. 

Coals expel volatile hydrocarbons with increasing thermal 

maturity and ultimately are composed only of fixed carbon 

and inorganic ash. On the basis of their ratios of hydrogen 

to carbon, sapropelic coals (fig. 3) are comparable to the 

asphalts, asphaltites, and petroleum asphaltenes but differ 

in having higher oxygen contents (Hunt, 1979). The humic 

coals have H/C similar to those of the reservoir bitumens of 

the western Canada basin. The bitumens, however, differ in 

having higher oxygen contents than humic coals. Humic 

coals are similar to impsonite and anthraxolite but have 

higher devolatilization temperatures. 

CLASSIFICATION SYSTEMS OF NATURAL 

BITUMENS 

Today, except for natural asphalt and petroleum, 

which are commercially important substances, natural bitumens are mostly of interest to organic geochemists. Connan 

and van der Weide (1978) recognized that physical 

attributes of the deposits of bitumens revealed little of their 

origin because the asphaltic character may be due either to 

immaturity or alteration of the bitumen. Because most 

asphaltic deposits result from degradation, indicated by 

severe depletion of the normal paraffin hydrocarbons, 

Connan and van der Weide (1978) refer to altered crude oils 

as natural asphalt. Curiale ( 1986) discounted bitumen classifications based on solubility, fusibility, and H/C in favor 

of molecular and bulk maturation data. He contrasted 

immature bitumens, which have migrated short distances 

from presumably rich source rocks, with altered oils, which 

were generated by and migrated from mature source rocks. 

Once formed, all solid bitumens may be subject to the same 

modification processes. 

A difficulty with purely geochemical classification 

techniques is that they require methods and analytical 

abilities beyond the expertise of most geologists. Their 

advantages lie in the great amount of additional information 

that geochemical methods may provide relative to a substance's origin and maturity to aid in the search for 

additional deposits of bitumens or petroleum or both. 

However, classifications based upon physical attributes, 

such as solubility in organic solvents, fusibility, hardness, 

and color, together with viscosity and density measurements, provide the simplest means of acquiring comparable 

worldwide resource information. 
Table 1. Physical and chemical limits of natural bitumen and petroleum (from 

Khalimov and others, 1983) 

Class Oil Asp hal tics 

(percent) (percent) 

High viscosity oil 

[Heavy oil] 75 <25 

Maltha 

[Extra heavy oil] 40-75 25-60 

Asphalt 

[Natural bitumen] 25-40 60-75 

Asphaltite <25 >75 

Kerite 

[Pyrobitumen] 1

3-5 90 

Anthraxolite 

[Pyrobitumen] e) 100 

Ozocerite 

[Mineral wax] e) <50 

'Rarely as high as 10. 2

Hard, partly soluble in chloroform. 3

Not available. 4

Hard, insoluble in chloroform. 5

If pure, 100 percent; if impure, 50 percent. 6

Semihard paraffinic structure. 

Definitions applied to natural bitumens vary in different places, frequently for legal purposes. The Energy 

Resources Conservation Board (ERCB) of Alberta, Canada, 

uses subjective definitions and makes special adjustments 

for market variations (ERCB, 1984). Although heavy oil is 

separated from conventional oil at 900 kg/m3 (a specific 

gravity of about 0. 900 or about 25 o API), the ERCB uses no 

physical or chemical parameter to distinguish heavy oil 

from bitumen. 

The U.S. Department of Commerce uses 25 o API as 

the criterion for identifying heavy oil (in Lundberg Survey, 

Incorporated, 1989). This standard probably derives from 

Hawkins (1967, p. 5), who defined heavy oil as follows: 

"Heavy oil and low-gravity oil are used interchangeably and 

include all crude oils with a measured API gravity of 25° 

or less. However, only oil which is mobile at reservoir 

conditions is included in the study. Recovery of oil by 

primary methods was considered evidence of oil mobility." 

The U.S. Department of Energy (Ruth M. Davis, written 

commun., 1980) defined tar sand as "any consolidated or 

unconsolidated rock (other than coal, oil shale, or gilsonite) 

that contains a hydrocarbonaceous material with a gas-free 

viscosity greater than 10,000 centipoises at reservoir temperature." 

In the U.S.S.R., a more complex terminology for 

describing natural bitumens has evolved, but the fundamental basis for subdivision (percent of oil and of asphaltics, 

viscosity, and density) is very useful. The classes of 

bitumens and a summary of their physico-chemical characteristics (table 1) are adapted from Khalimov and others 

(1983). In their classification, "high-viscosity oil" is most 

closely comparable to heavy oil (Lisovsky and others, 

1984) and "maltha" to extra heavy oil. However, Khalimov 

Viscosity Density 

(cP) (specific gravity) 

50-2,000 0.935-0.965 

2,000-20,000 0.965-1.030 

20,000-1 ,000,000 1.030-1.100 

>1,000 1.050-1.200 

(!) 1.070-1.350 

(4) 1.300-2.000 

(6) 0.850-0.970 

and others (1983) refer to maltha as viscous bitumen, as 

distinct from the other natural bitumens and from heavy oil. 

Kerite and anthraxolite seem to correspond most closely 

with the pyrobitumens, whereas ozocerite is clearly a 

mineral wax. Gol'dberg and IUdin (1979) and Gol'dberg 

( 1981) further proposed that bitumens be broken into two 

categories: naphthides and naphthoids. Naphthides include 

petroleum, gas condensate, natural gas, and their natural 

derivatives. Naphthoids are the pyrogenic or tectonogenic 

analogs of naphthides; that is, the flammable products of 

destructive distillation induced by contact metamorphism. 

Although the term naphthoid is encountered in tables of 

classification, it is found infrequently in the literature. 

U.S.S.R. classification is based upon three genetic series: 

hypergenous (oxidizing), phase-migrational, and thermal 

metamorphic. ( 1) Deposits of the oxidizing series result 

from reactions with water at or near the Earth's surface; the 

reactions include water washing, bacterial degradation, and 

natural deasphalting. (2) Phase-migrational deposits result 

from differentiation of the fluids during migration by 

precipitation or deasphalting. Fluids differentiated during 

upward migration result in the early deposition of the 

molecules of highest molecular weight and give rise to vein 

deposits (Gol'dberg, 1981). (3) The thermal-metamorphic 

series may result from contact metamorphism or the pyrolysis of rocks fairly rich in organic matter. 

Bitumens of the same class may occur in all three 

series in the U.S.S.R. system, depending upon perceptions 

of the bitumens' origin. Apparently, the degree of thermal 

maturity and the structural style of a basin are used by 

U.S.S.R. geologists as a guide to the class and series of a 

natural bitumen, rather than the thermal maturity and 

alteration of the bitumen indicating the maturity of a basin 

Classification Systems of Natural Bitumens 7 
Table 2. Comparison of petroleum and natural bitumen classification systems 

Viscosity 

Source Oil Asphaltics at reservoir 

(percent) (percent) temperature 

(cP) 

Heavy oil 

UNITAR1 

WPC2 

U.S.S.R. 3 >75 <25 

People's Republic of China 

<10,000 

<10,000 

50-2,000 

4

50-100 5

<10,000 

10.0-20.0 

10.0-22.3 

15.1-19.8 

17.0-22.0 

17.0-22.0 

Extra heavy oil 

UNITAR 

WPC 

U.S.S.R. 6 40-75 

People's Republic of China 

<10,000 

<10,000 

25-60 2,000-20,000 5 10,000-50,000 

<10.0 

<10.0 

5.9-15.1 

<17.0 

Natural bitumen 

UNITAR 

WPC 

U.S.S.R. 7 

People's Republic of China 

5-40 60-75 

>10,000 

>10,000 

20,000-1 ,000,000 

5>50,000 

-2.9-5.9 

<13.0 

1

United Nations Institute for Training and Research/United Nations Development Programme Information 

Centre for Heavy Crude and Tar Sands. 2

World Petroleum Congress. 3

High viscosity oil in U.S.S.R. terminology. 4

At reservoir temperature. 5

Gas free. 

~altha in U.S.S.R. terminology. 7

Asphalt in U.S.S.R. terminology. 

in terms of organic source material and its alteration, 

sedimentary rocks, structural evolution, and degree of 

metamorphism. The nature of the bitumen's original source 

material, whether organic matter, petroleum, or another 

natural bitumen, is intrinsic to U.S.S.R. classification 

schemes. 

Natural asphalt is known from a number of places in 

Venezuela, but Venezuela is best known for its enormous 

deposits of extra heavy oil in the Orinoco Oil Belt. In 

Venezuela, the United Nations Institute for Training and 

Research/United Nations Development Programme Information Centre for Heavy Crude and Tar Sands (UNITAR) 

definitions generally are followed. 

In the People's Republic of China, heavy oil and 

natural bitumen, as defined by Liu (1989), represent a 

special case. China's nonmarine oil is relatively low in 

asphaltene, sulfur, and trace metal content but high in resin. 

Thus, it has both high viscosity and high API gravity (Liu, 

1989; Xu and Niu, 1989). 

Table 2 compares the preceding classifications. Data 

sources are UNITAR (Cornelius, 1987), WPC (Martinez 

and others, 1987), U.S.S.R. (see table 1), and the People's 

Republic of China (Liu, 1989). The UNITAR and WPC 

definitions are clear and unequivocal. U.S.S.R. heavy oil is 

8 Definition and World Resources of Natural Bitumens 

limited by about 15 °API but fits within the UNITAR and 

WPC gravity and viscosity limits and approximates the 

chemical composition of comparable Venezuelan heavy oil. 

Chinese heavy oil fits within the UNIT AR and WPC 

viscosity limits but has higher gravity boundaries. U.S.S.R. 

maltha (extra heavy oil) closely matches in chemical composition the Venezuelan heavy and extra heavy oil within 

the same gravity range; however, the viscosity and gravity 

limits are different from those of UNIT AR and WPC. 

Chinese extra heavy oil is both higher in gravity and more 

viscous than the UNITAR and WPC limits. Natural bitumen 

is defined by UNIT AR and WPC as any oil heavier than 

10,000 cP. The U.S.S.R. definition imposes a lower range 

of viscosities, the lower limit of which is twice as high as 

that of UNITAR and WPC but also includes a gravity range; 

gravity is not a part of UNIT AR and WPC definitions. The 

Chinese definition is anomalous in that the gravity is as high 

as 13 °API, but the viscosity is more than 50,000 cP. The 

UNITAR and U.S.S.R. definitions are similar, but the 

Chinese definitions differ greatly from other definitions 

because of the different chemical character of the nonmarine oils. Of significance is the absolute need for stating the 

definitions being used in any particular instance. In resource 

compilations, for example, the assignment of maltha is 
important not merely for the numbers involved but for 

implications as to its ease of recoverability, transportation, 

and upgrading and its intended end use. 

DIFFERENTIATING NATURAL BITUMENS AND 

CRUDE OIL 

The dividing line between crude oil and natural 

bitumens is of interest scientifically and in the estimation of 

resource recoverability. The boundary is of critical importance with respect to regulation and its economic impacts. 

The United Nations Information Centre for Heavy Crude 

and Tar Sands (Martinez, 1984) and the 12th World 

Petroleum Congress (Martinez and others, 1987) chose a 

viscosity of 10,000 cP, as shown graphically in figure 1, to 

separate natural bitumen from the less viscous oils. Danyluk 

and others ( 1984) recognized that such a demarcation is not 

precise because the two otherwise essentially indistinguishable materials, heavy oil and natural bitumen, may be 

alternatively defined, depending upon the reservoir temperature. They recommended standard viscosity measurement 

techniques and suggested that the demarcation zone lies 

between 5,000 and 15,000 cP. Gibson (1984) described five 

viscosity measurement methods and urged that one, such as 

that based on the commonly used rotational viscometer, be 

selected for a worldwide standard. 

Briggs and others (1988) defined heavy oil as that 

more viscous than 100 cP, their rationale being that production rates for pumped cold oil will be less than 10 barrels 

per day (bbl/d) if the oil's viscosity exceeds 100 cP. They 

did not distinguish between heavy oil and bitumen but 

considered all deposits that normally occur at depths of 

1 ,000 to 4,000 ft and that can be exploited in situ to be 

heavy oil. Cornelius (1987) drew the line between heavy 

and conventional crude at 300 cP because he expected oil to 

flow in the reservoir at that viscosity or less. 

If possible, the limits of natural bitumen and heavy 

oil should be based upon physical and chemical attributes 

that can be easily measured and will reflect the requirements 

for recovery. Viscosity is the principal factor involved with 

recovery, and, although it can be measured with precision, 

it is fundamentally dependent upon temperature. Although 

customarily calculated at reservoir temperature, the viscosity at surface temperature is also critically important in 

transporting the material following its extraction. Viscosity 

data are not routinely available for most deposits, but 

density information is reported for oils and bitumens in 

nearly all reservoirs. Furthermore, density is not very 

sensitive to temperature variations. A correlation between 

viscosity and density is thus very desirable. 

Physical attributes such as density and viscosity 

generally reflect the chemical composition of a natural 

bitumen or petroleum. Natural bitumen and heavy and extra 

heavy crude oil contain a large proportion-as much as 50 

weight percent-of asphaltenes, resins, and heterocompounds. These high proportions lead to high molecular 

weights and content of constituents such as sulfur and trace 

metals, which are undesirable impurities in the refining 

process. In a reservoir, natural bitumen and the heavier oils 

have very low ratios of gas to oil, being essentially gas free 

(dead oil), and so any entrained gas will not appreciably 

affect the viscosity. In addition, their density is close to the 

specific gravity of water, so that whether viscosity is 

reported as absolute in centipoises or kinematic in centistokes (centipoises times density) is not a serious consideration in assessing the reservoir behavior of the bitumen. 

The correlations between density and viscosity at 

different temperatures are given in figure 4. The correlations are maintained even as the viscosity decreases as a 

result of increased temperature. Oil at reservoir temperatures of 100-130 °F will have an absolute viscosity of 100 

cP at about 18-20 °API. Oils having a gravity of 10 °API, or 

a specific gravity of 1 (that of water), will have a viscosity 

of about 10,000 cP at 130 °F and will be even more viscous 

at lower temperatures. This relation places 10 °API oils in 

the category of natural asphalt. Figure 4 clearly suggests the 

temperature increments required to produce oil (that is, to 

reduce viscosity to at least 100 cP, so that oil will flow). 

Precise boundaries do not exist between crude oil and 

natural bitumens. The various species within the natural 

bitumens can be defined by both physical and chemical 

parameters. The most important demarcation, between 

natural asphalt and crude oil, occurs at a viscosity of about 

10,000 cP. The need to use enhanced recovery methods, 

usually heat, begins at a viscosity of about 100 cP, or about 

18 °API, the boundary between heavy and conventional oil 

(Briggs and others, 1988; Lisovsky and others, 1984). The 

effectiveness of known in situ recovery methods declines at 

about 10,000 cP. At most localities, natural bitumens, 

including natural asphalt, must be mined and upgraded to 

pipeline quality for transportation and refining. 

We recommend that the natural bitumens be defined 

on the basis of their solubility, fusibility, hardness, color, 

density, and viscosity and that they be distinguished from 

crude oil by having an absolute (dynamic) viscosity in 

excess of 10,000 cP. 

USAGE OF NATURAL BITUMENS 

Except for natural asphalt, natural bitumens (fig. 1) 

are only of local economic interest. Because the other 

natural bitumens are minor in quantity and commercial 

importance, the term "natural bitumen" is generally considered to be synonymous with natural asphalt. The term 

"natural asphalt" displaces the etymologically incorrect 

terms oil sand and tar sand, which are not always sand and 

never tar, although they may contain oil. However, because 

of past usage, the terms "oil sand" and "tar sand" will 

undoubtedly continue in use indefinitely. 

Usage of Natural Bitumens 9 
The chief interest in natural asphalt is as a source of 

synthetic oil. Natural asphalt has been virtually displaced as 

a construction material by commercial asphalt processed 

from crude oil, usually heavy, in refineries, where quality 

can be closely controlled. However, natural asphalt is 

mined locally for construction purposes in Albania, Indonesia, Trinidad and Tobago, Turkey, and the U.S.S.R. 

Natural asphalt has been mined for paving, mastic, 

and other uses, but the natural material has now been almost 

wholly displaced by asphalt manufactured from heavy oil 

and refinery residua. Some mines, quarries, and deposits 

are still in operation, but at a low level of activity. Miller 

(1938), Redfield (1949), and Armanet (1962) reviewed 

production activity for all the natural bitumens, and the 

U.S. Bureau of Mines (Coumbe and Avery, 1956) reported 

on the use of natural asphalt and related bitumens for 1953, 

the latest year for which statistics were available, when the 

market was essentially one of manufactured asphalt. In 

1953, the production of gilsonite was still being reported. In 

1986, native asphalt was being produced by three companies in Texas and Utah, and gilsonite was being mined by 

two firms in Colorado and Utah (Johnson, 1986). No later 

production reports are available. 

Minor mining of ozocerite and pyrobitumens (kerite, 

anthraxolite, and shungite) continues in the U.S.S.R., in 

addition to small amounts of natural asphalt produced for 

road building (Beskrovnyi and others, 1985). Asphaltites 

and some asphalt are mined in Turkey (Heavy Oiler, 1989). 

Attempts are being made to use the asphaltic limestone on 

Buton Island, Indonesia, as road material (Corne and 

Soehartono, 1989). 

In 1962, according to Armanet (1962), the important 

bitumen mines were the mines of Gard (A vejan and 

Saint-Jean-de-Maruejols), Auvergne (Puy-de-Dome), and 

Ain and Haute-Savoie (Seyssel, Bourbogne, and Gardebois 

and Montrottier) in France; Vorwohle in Germany; Caxito 

in Angola; Maestu in Spain; Abruzzi and Ragusa in Italy; 

Val de Travers in Switzerland; Latakia in Syria; Uvalde in 

Texas, U.S.A.; and Pitch Lake, in Trinidad and Tobago. 

Other significant mines include Bombay Island, India (Fox, 

1922), Selenitza, Albania (Miller, 1938), Leyte Island, the 

Republic of the Philippines (Palacio, 1957), and Buton 

Island, Indonesia (Warga Dalem and Padmosubroto, 1988; 

Corne and Soehartono, 1989). 

NATURAL ASPHALT RESOURCES 

Natural Asphalt Deposits 

A list of world resources of natural asphalt (table 3) is 

derived from Meyer and Duford (1989), with the exception 

of U.S.S.R. asphalt, the source for which is Gol'dberg 

(1981). The quantities listed are only the amounts from 

deposits that contain at least 1 million barrels of natural 

asphalt in situ; these deposits are considered to be suffi10 Definition and World Resources of Natural Bitumens 

Table 3. World natural asphalt resources (in million barrels) 

Area Demonstrated Inferred 

NORTH AMERICA 

United States 22,823 33,709 

Canada 1,685,725 831,100 

Total 1,708,548 864,809 

SOUTH AMERICA 

Trinidad 60 

Venezuela 50,400 

Total 50,460 

EUROPE 

Albania 371 

Italy 1,260 

Romania 25 

U.S.S.R. 18,837 

-- Total 20,493 

ASIA 

People's Republic of China 10,050 

U.S.S.R. 66,213 

Total 76,263 

AFRICA 

Madagascar 35 31 

Nigeria 1,000 

Zaire 30 

Total 1,065 31 

MIDDLE EAST 

Syria 13 

Total 13 

SOUTHEAST ASIA 

Indonesia 10 

Republic of the Philippines 

Total 11 

WORLD TOTAL 1,856,853 864,841 

ciently large to have at least the potential to serve as a 

source for synthetic oil. This choice of size is based 

primarily on economics, not technology. Most probably, 

deposits even as large as 100 million barrels of natural 

asphalt in situ will not be exploited for oil in the foreseeable 

future. 

Giant deposits, for convenience, may be considered 

to be those containing at least 1 billion (1 ,000 million) 

barrels of natural asphalt in situ. Natural asphalt in Alberta, 

Canada, in the western Canada basin (1 ,686 billion barrels 

demonstrated and 831 billion barrels inferred) completely 

dominates the world's natural asphalt resource. The deposits contain about 91 percent of the demonstrated and 96 

percent of the inferred natural asphalt resources of the 

world. These resources are found in Lower Cretaceous 

sandstones in the Athabasca, Cold Lake, and Peace River 

deposits and in Upper Devonian limestones of the Carbonate Triangle area. 
In the United States, there are eight giant natural 

asphalt deposits: 

1. Arctic Coastal Plain basin, Alaska, Kuparuk deposit, 

Paleocene and Upper Cretaceous U gnu sandstones 

(Werner, 1987), 11 billion barrels inferred; 

2. Cherokee basin, Kansas and Missouri, sandstones of 

the Middle Pennsylvanian Bluejacket and Warner 

Sandstone Members of the Krebs Formation, 2. 7 

billion barrels, measured and inferred; 

3. Gulf Coast basin, Texas, San Miguel deposit, sandstones of the Upper Cretaceous San Miguel Formation, 2 billion barrels demonstrated and inferred; 

4. Illinois basin, Kentucky, Upper Mississippian Big 

Clifty Sandstone Member of the Golconda Formation, 

2.1 billion barrels demonstrated and inferred; 

5. Paradox basin, Utah, Tar Sand Triangle deposit, 

Lower Permian White Rim Sandstone Member of the 

Cutler Formation, 2. 9 billion barrels demonstrated 

and inferred, and Circle Cliffs deposit, sandstones of 

the Middle Triassic Moenkopi Formation, 1. 7 billion 

barrels demonstrated and inferred; 

6. Santa Maria basin, California, Foxen deposit, sandstones of the Pliocene Foxen Formation, 1.9 billion 

barrels inferred, and Casmalia field, diatomaceous 

mudstone of the Miocene and Pliocene Sisquoc Formation, 1.5 billion barrels demonstrated; 

7. Uinta basin, Utah, P.R. Spring deposit, sandstones of 

the Paleocene and Eocene Green River Formation, 

4.3 billion barrels demonstrated and inferred, and 

Sunnyside deposit, sandstones of the Paleocene and 

Eocene Green River Formation, 6.1 billion barrels 

demonstrated and inferred; 

8. Black Warrior basin, Alabama, Upper Mississippian 

Hartselle Sandstone, 7. 8 billion barrels inferred. 

These deposits represent nearly 80 percent of the total U.S. 

demonstrated and inferred resource, the other 20 percent 

being distributed among numerous deposits of less than 1 

billion barrels each. 

In South America, only the natural asphalt deposits of 

Venezuela appear to qualify as giant. Mendez (1988) gave 

a total for Venezuela of 50.4 billion barrels, most of which 

occurs in eight deposits along the southwestern flank of the 

eastern Venezuela basin. Whether any of the individual 

deposits is as large as 1 billion barrels of asphalt in situ is 

not known; the best known deposit, Guanoco (Bermudez) 

Pitch Lake, evidently is not that large (Abraham, 1960a). 

Giant natural asphalt deposits in Europe are confined 

to Italy and the U.S.S.R .. In Italy, Miocene calcarenites of 

the Ragusa area on the Ragusa Platform appear to contain as 

much as 1.3 billion barrels demonstrated. 

Herein, the U.S.S.R. is divided into an eastern 

portion, whose resources are assigned to Asia, and a 

western portion, whose resources are assigned to Europe. 

For the U.S.S.R. as a whole, the resource level is drastically reduced from that given in Meyer and Duford (1989), 

which was taken from Meyerhoff and Meyer ( 1987). For 

the European portion, the reduction is more than 100 billion 

barrels, and for the Asian portion, more than 570 billion 

barrels. Savinkin (1989, p. 11) stated that "the current best 

estimate of bitumen [natural asphalt] resources [in the 

U.S.S.R.] is up to 60 billion tons [378 billion barrels]." The 

estimate given here for the U.S.S.R. as a whole is 85.1 

billion barrels (Gol'dberg, 1981); this estimate excludes 

nearly 105 billion barrels of maltha, which fits the category 

of extra heavy oil and is comparable to oils in the Venezuelan Orinoco Oil Belt. Savinkin (1989) probably included 

maltha in his total, and maltha was included in the estimate 

of Meyerhoff and Meyer (1987). The sizes of individual 

deposits are not known. 

The largest occurrences of natural asphalt in European U.S.S.R. are in Lower Mississippian clastic and 

carbonate and Upper Devonian carbonate rocks of the 

Timan-Pechora province and in Lower Permian carbonate 

rocks of the Volga-Urals province, most importantly the 

Melekess basin-South Tatar arch district. In the VolgaUrals province, however, by far the greatest quantity of oil 

is maltha, herein excluded from natural asphalt resources. 

The total amount of natural asphalt for European U.S.S.R. 

is 18.8 billion barrels. 

In Asia, the sizes of individual deposits are unknown, 

but collections of natural asphalt deposits in close proximity 

constitute giant deposits in Asian U.S.S.R. and the People's 

Republic of China. Two such collections of deposits contain 

70 percent of the 66.2 billion barrels of natural asphalt that 

have been identified in Asian U.S.S.R.-the Central Anabar and the Olenek-Udzha areas, on the Siberian platform in 

the Lena-Tungusska province. The natural asphalt is concentrated in rocks of Late Proterozoic, Cambrian, Permian, 

and Early Jurassic age. 

At least two areas in the People's Republic of China 

have very large collections of natural asphalt deposits. 

These two areas contain total resources of as much as 5 

billion barrels each in lower Paleozoic rocks on the Y angzi 

platform of the Yellow Sea province and in the Junggar, 

Tarim, and other western China basins. 

In Africa, the most notable occurrence is the 1-

billion-barrel deposit in the Benin embayment (Dahomey 

basin) in Nigeria. The natural asphalt occurs in Upper 

Cretaceous sandstones. One or more giant deposits probably occur in Angola, but necessary volumetric data are not 

available in the resource literature. 

Although many seeps and natural asphalt quarries are 

located in the Middle East, none of these is of giant size. 

Resource Evaluation 

Any evaluation of resources necessitates consideration of the individual deposits, their size, and grade. Some 

natural asphalt deposits are essentially pure; they contain 

Natural Asphalt Resources 11 
LITERS PER METRIC TON 

0 40 80 120 160 200 

20 3800 

~ 

u 

0 1-

0:: 0 

~ 0 

L.L. 

.....J w 

0:: 0 u 1- <X: 

a:i 10 1900 E5 u c.. 0:: (/) w 

c.. .....J 

w 1- 0:: 

:I: 0:: 

(.!J <X: 

i:i:i co 

$ 

0 0 

0 10 20 30 40 50 

GALLONS PER TON 

Figure 5. Grade conversion chart for natural asphalt deposits. From Earley, 1987. 

very small amounts of mineral matter such as sand, silt, or 

clay. In these deposits, the grade is close to 100 weight 

percent natural asphalt. Other deposits are composed of 

natural asphalt in a matrix of sand, sandstone, or limestone; 

this composition makes their grade (that is, the weight 

percent natural asphalt) critically important in determining 

economic exploitability. 

Earley (1987) examined the effects of the amount of 

overburden (stripping ratio) and grade upon economic 

recoverability of a natural asphalt deposit. He used the 

discounted cash flow rate of return (DCFROR) as a measure 

of profitability and therefore a measure of incentive to 

exploit a deposit. Earley (1987) found that, by using drag 

lines to remove overburden, the stripping ratio (the ratio of 

waste rock to ore) had little effect on the DCFROR to an 

overburden thickness of about 300 ft. With greater thicknesses of overburden, the cost of stripping rapidly 

increases. Because 300 ft is too shallow to attempt thermal 

recovery with steam, a zone of presently unrecoverable ore 

between about 300 and 600 ft is left for recovery by a new 

technology, such as shaft and tunnel. 

Figure 5 is a conversion chart for the common ways 

in which grade is expressed. Figure 6 gives the sensitivity of 

DCFROR to grade for three different natural asphalt processing plant sizes. For plants processing more than 15,000 

bbl/d, grade does not appreciably affect profitability, but an 

obvious loss in profitability occurs below 10,000 bbl/d at 

lower grades. A grade of about 7 weight percent natural 

asphalt is close to the lower limit of exploitability; a grade 

of 12 weight percent or greater is desirable. 

Average in situ recovery of natural asphalt from rock 

asphalt deposits may be expected to be about 15 weight 

percent of asphalt in situ, by using thermal methods. By 

12 Definition and World Resources of Natural Bitumens 

25 

a: 20 0 

a: 

u.. 

u 

0 15 

10 

5 

8.1 10.0 12.1 14.1 16.2 18.2 

ORE GRADE [WEIGHT PERCENT ASPHALT] 

Figure 6. Sensitivity of discounted cash flow rate of return 

to natural asphalt grade for three different processing 

plant sizes. DCFROR, discounted cash flow rate of return; 

bbl/d, barrels per day. From Earley, 1987. 

using mining methods, asphalt recovery may be as high as 

95 percent. Thus, a deposit of 1 billion barrels of natural 

asphalt in situ may yield from 150 million to 950 million 

barrels of raw natural asphalt, before processing losses. A 

perspective may be obtained from the efforts to exploit 

natural asphalt as a source of synthetic oil in the western 

Canada basin. There, 1987 annual production was about 

126 million barrels or 345,000 bbl/d (ERCB, 1987). 

Approximately two-thirds of this production was from two 

surface-mining operations (Athabasca deposit), and the 

remainder from three major commercial in situ projects 

(Cold Lake) and numerous smaller or experimental 
projects. Cumulative production to the end of 1986 totaled 

755 million barrels from the two Athabasca deposit surfacemining operations, 88 million barrels from the Cold Lake in 

situ projects, and 2.5 million barrels from the Peace River 

in situ project. These three deposits constitute 4,465 million 

barrels of original reserves (proved reserves plus cumulative 

production). Because the reserves are based on the amount 

of bitumen recoverable with existing wells and facilities, 

the figures represent only a small portion of the in situ 

natural asphalt resources (table 3) (Meyer and Duford, 

1989). 

REFERENCES 

Abraham, Herbert, 1960a, Historical review and natural raw 

materials (v. 1), in Asphalts and allied substances, 6th ed.: 

New York, Van Nostrand, 370 p. 

---1960b, Methods of testing, Part 1 (v. 4), in Asphalts 

and allied substances, 6th ed.: New York, Van Nostrand, 

435 p. 

Armanet, J., 1962, Les mines d'asphalte dans le monde: Paris, Le 

Syndicat des Producteurs & Entrepreneurs d' Asphalte and 

!'Office des Asphaltes, 48 p. 

Beal, Carlton, 1946, The viscosity of air, water, natural gas, crude 

oil and its associated gases at oilfield temperatures and 

pressures: American Institute of Mining and Metallurgical 

Engineers Transactions, v. 165, p. 94-115. 

Bell, K.G., and Hunt, J.M., 1963, Native bitumens associated 

with oil shales, in Breger, I.A., ed., Organic geochemistry: 

New York, Macmillan, p. 333-366. 

Beskrovnyi, N.S., Gol'dberg, I.S., Makarov, K.K., Sobolev, 

V.S., and Taliev, S.D., 1985, Prirodnye tverdye bitumy i 

SSSR-Vazhnyi syr'evoi reverv narodnogo khoziaistva [Natural solid bitumens in the USSR-An important raw material 

res.erve for the national economy]: Geologiia Nefti i Gaza, 

no. 4, p. 14-20. 

Bilkady, Zayne, 1984, Bitumen-A history: Aramco World Magazine, November-December, p. 2-9. 

Briggs, P.J., Baron, R.P., Fulleylove, R.J., and Wright. M.S .. 

1988, Development of heavy-oil reservoirs: Journal of Petroleum Technology, v. 40, no. 2, p. 206-214. 

Carman, E.P., and Bayes, F.S., 1961. Occurrence, properties, 

and uses of some natural bitumens: U.S. Bureau of Mines 

Information Circular 7997. 42 p. 

Connan, J.M., and van der Weide, B.M., 1978, Thermal evolution of natural asphalts, in Chilingarian. G.V., and Yen, 

T.F., eds., Bitumens, asphalts, and tar sands: Amsterdam, 

Elsevier, p. 27-55. 

Corne, C.P .. and Soehartono, Ir, 1989, Utilization ofButon Island 

rock asphalt in road pavements, in Meyer. R.F., and Wiggins, E.J., eds., The UNITAR/UNDP International Conference on Heavy Crude and Tar Sands. 4th, Edmonton, 1988. 

Proceedings, v. 2: Edmonton. Alberta Oil Sands Technology 

and Research Authority. p. 397-412. 

Cornelius, C.D., 1987. Classification of natural bitumens-A 

physical and chemical approach, in Meyer, R.F., ed .. Exploration for heavy crude oil and natural bitumen: American 

Association of Petroleum Geologists Studies in Geology, 

no. 25, p. 165-174. 

Coumbe, A.T., and Avery, I.F., 1956, Asphalt and related 

bitumens: U.S. Bureau of Mines Minerals Yearbook, Fuels, 

V. 2, 1953, p. 297-302. 

Curiale, J.A., 1986, Origins of solid bitumens, with emphasis on 

biological marker results: Organic Geochemistry, v. 10, nos. 

1-3, p. 559-580. 

Danyluk, A.M., Galbraith, B., and Omana, R., 1984, Toward 

definitions for heavy crude and tar sands, in Meyer, R.F., 

Wynn, J.C., and Olson, J.C.. eds., The Future of Heavy 

Crude and Tar Sands, International Conference, 2d, Caracas, 

1982: New York, McGraw-Hill, p. 3-6. 

Earley, J. W., 1987, Economic factors in near-surface heavyoil/tar-sand mining. in Meyer, R.F., ed., Exploration for 

heavy crude oil and natural bitumen: American Association 

of Petroleum Geologists Studies in Geology, no. 25, 

p. 669-671. 

Energy Resources Conservation Board [Alberta], 1984, Alberta's 

reserves of crude oil, oil sands, gas, natural gas liquids, and 

sulphur: ERCB ST 85-18, p. 1-3-1-4. 

---1987, Alberta oil sands annual statistics: ERCB ST 87-43. 

Forbes, R.J., 1964, Studies in ancient technology (v. 1): Leiden, 

Brill, 199 p. 

Fox, C.S., 1922, The occurrence of bitumen in Bombay Island: 

Geological Survey of India Records, v. 54, pt. 1, 

p. 117-128. 

Galarraga, F.A., 1986, Organic geochemistry of the heavy oils in 

the eastern Venezuela basin: College Park, Maryland, University of Maryland, Ph. D. dissertation, 343 p. 

Gibson. B.J., 1984, Methods of classifying heavy crude oils using 

the UNITAR viscosity-based definition, in Meyer, R.F., 

Wynn. J.C.. and Olson, J.C.. eds., The Future of Heavy 

Crude and Tar Sands, International Conference, 2d, Caracas, 

1982: New York, McGraw-Hill, p. 17-21. 

Gol'dberg, I.S., ed., 1981, Prirodnye bitumy SSSR [Natural 

bitumens of the USSR]: Leningrad, "Nedra," 195 [223] p. 

Gol' dberg, I. S., and ill din, G. T., 1979. Voprosy klassifikatsii, 

obrazovaniia i razmeshcheniia skoplenii bitumov [Problems 

of the classification, formation and distribution of bitumen 

accumulations], in Ditmar, V.I., ed., Geologiia bitumov i 

bitumovmeshchaiushchikh porod [Geology of bitumens and 

bituminous rocks]: Moscow, "Nauka," p. 15-20. 

Heavy Oiler, 1989, Turkey: No. 29, p. 6-7. 

Hunt, J.M., 1979, Petroleum geochemistry and geology: San 

Francisco. Freeman, 617 p. 

Johnson, Wilton, 1986, Asphalt (native): U.S. Bureau of Mines 

Minerals Yearbook, 1986, v. 1. p. 1035. 

Khalimov, E.M., Klimushin. I.M., Ferdman, L.I., and 

Gol'dberg, I.S., 1983. Geological problems of natural bitumen: World Petroleum Congress, 11th, Proceedings, v. 2, 

p. 57-70. 

Lisovsky, N.N., Khalimov, E.M., Ferdman, L.I., andKlimushin, 

I.M., 1984. The formation and spatial distribution of viscous 

and solid naphthides in the oil and gas-bearing basins of the 

USSR: International Geological Congress, 27th, Proceedings, v. 13, p. 85-104. 

Liu Wenzhang, 1989, Classification standard of heavy oil, screening criterion for steam thermal recovery and reserves classiReferences 13 
fication, in Meyer, R.F., and Wiggins, E.J., eds., The 

UNIT AR/UNDP International Conference on Heavy Crude 

and Tar Sands, 4th, Edmonton, 1988, Proceedings, v. 2: 

Edmonton, Alberta Oil Sands Technology and Research 

Authority, p. 215-233. 

Lundberg Survey, Incorporated, 1989, Bottom of the barrel: v. 4, 

no. 3, p. 7. 

Martinez, A.R., 1984, Report of working group on definitions, in 

Meyer, R.F., Wynn, J.C., and Olson, J.C., eds., The Future 

of Heavy Crude and Tar Sands, International Conference, 2d, 

Caracas, 1982: New York, McGraw-Hill, p. lxvii-lxviii. 

---1987, The Orinoco Oil Belt, Venezuela: Journal of Petroleum Geology, v. 10, no. 2, p 125-134. 

Martinez, A.R., Ion, D.C., De Sorey, G.J., Dekker, H., and 

Smith, Shofner, 1987, Classification and nomenclature systems for petroleum and petroleum reserves: World Petroleum 

Congress, 12th, Preprint, 16 p. 

Mendez, Jose, 1988, Natural asphalt in Venezuela [abs.]: UNIT ARIUNDP International Conference on Heavy Crude and 

Tar Sands, 4th, Edmonton, 1988, Conference Program, 

p. 26. 

Meyer, R.F., and Duford, J.M., 1989, Resources of heavy oil and 

natural bitumen worldwide, in Meyer, R.F., and Wiggins, 

E.J., eds., The UNITAR/UNDP International Conference on 

Heavy Crude and Tar Sands, 4th, Edmonton, 1988, Proceedings, v. 2: Edmonton, Alberta Oil Sands Technology and 

Research Authority, p. 277-307. 

Meyerhoff, A.A., and Meyer, R.F., 1987, Geology of heavy 

crude oil and natural bitumen in the USSR, Mongolia, and 

China, in Meyer, R.F., ed., Exploration for heavy crude oil 

and natural bitumen: American Association of Petroleum 

Geologists Studies in Geology, no. 25, p. 31-101. 

Miller, J.S., 1938, Native asphalts and bitumens, in Dunstan, 

A.E., ed., The science of petroleum: London, Oxford University Press, v. 4, p. 2710-2727. 

Neumann, Hans-Joachim, and Rahimian, Iradj, 1984, Petroleum 

refining, in Beckmann, Heinz, ed., Geology of Petroleum, 

v. 7: Stuttgart, Ferdinand Enke, 126 p. 

Palacio, D.N., 1957, Preliminary report on the geology and rock 

asphalt deposits of Balite, Villaba, Leyte: Philippine Geologist, v. 11, no. 3, p. 69-100. 

Redfield, A.H., 1949, Native bitumens, in Industrial rocks and 

minerals (2d ed.): New York, American Institute of Mining 

and Metallurgical Engineers, p. 637-642. 

14 Definition and World Resources of Natural Bitumens 

Rogers, M.A., McAlary, J.D., and Bailey, N.J.L., 1974, Significance of reservoir bitumens to thermal-maturation studies, 

western Canada basin: American Association of Petroleum 

Geologists Bulletin, v. 58, no. 9, p. 1806-1824. 

Savinkin, P. T., 1989, Status of natural bitumens and heavy oil 

development, in Meyer, R.F., and Wiggins, E.J., eds., The 

UNITAR/UNDP International Conference on Heavy Crude 

and Tar Sands, 4th, Edmonton, 1988, Proceedings, v. 2: 

Edmonton, Alberta Oil Sands Technology and Research 

Authority, p. 11. 

Speight, J. G., 1980, The chemistry and technology of petroleum, 

in Heinemann, Heinz, ed., Chemical Industries: New York, 

Marcel Dekker, v. 3, 498 p. 

Tissot, B.P., and Welte, D.H., 1978, Petroleum formation and 

occurrence (1st ed.): New York, Springer-Verlag, 538 p. 

---1984, Petroleum formation and occurrence (2d ed.): New 

York, Springer-Verlag, 699 p. 

Warga Dalem, M.A., and Padmosubroto, Soegianto, 1988, The 

occurrence of heavy crude and tar sands in Indonesia, in 

Meyer, R.F., ed., The Third Unitar/UNDP International 

Conference on Heavy Crude and Tar Sands, Long Beach, 

California, U.S.A., 1985: Edmonton, Alberta Oil Sands 

Technology and Research Authority, p. 171-183. 

Wen, C.S., Chilingarian, G.V., and Yen, T.F., 1978, Properties 

and structure of bitumens, in Chilingarian, G. V., and Yen, 

T.F., eds., Bitumens, asphalts, and tar sands: Amsterdam, 

Elsevier, p. 155-190. 

Werner, M.R., 1987, Tertiary and Upper Cretaceous heavy oil 

sands, Kuparuk River Unit area, Alaskan North Slope, in 

Meyer, R. F. , ed. , Exploration for heavy crude oil and natural 

bitumen: American Association of Petroleum Geologists 

Studies in Geology, no. 25, p. 537-548. 

Williams, H.R., and Meyers, C.J., 1964, Manual of oil and gas 

terms: New York, Matthew Bender, 449 p. 

Xu Shubao and Niu Jiayu, 1989, The petroleum thickening 

mechanism and characteristics of terrestrial heavy oil pools in 

China, in Meyer, R.F., and Wiggins, E.J., eds., The 

UNIT AR/UNDP International Conference on Heavy Crude 

and Tar Sands, 4th, Edmonton, 1988, Proceedings, v. 2: 

Edmonton, Alberta Oil Sands Technology and Research 

Authority, p. 3-9. 

Yen, T.F., 1984, Characterization of heavy oil, in Meyer, R.F., 

Wynn, J.C., and Olson, J.C., eds., The Future of Heavy 

Crude and Tar Sands, International Conference, 2d, Caracas, 

1982: New York, McGraw-Hill, p. 412-423. 


Periodicals 

Earthquakes & Volcanoes (issued bimonthly . 

Preliminary Determination of Epicenters (issued montllcy). 

I 

Technical Books and Reports 

Professional Papers are mainly comprehensive scie tifi re ' orts 

of wide and lasting interest and importance to professio al scie 

an engineers. Included are reports on the results o resdurce s 

and of topographic , hydrologic, and geologic investigations. he 

include collections of related papers addressing different aspec 

single scientific topic. 

Bulletins contain significant data and interpretations that re of I lasting scientific interest but are generally more li ited ri n sea e or 

geographic coverage than Professional Papers. They inclu e the ,;e ults 

of resource studies and of geologic and topographic · ves igatio 

weU as collections of short papers related to a specific to ·c. 

Water-Supply Papers are comprehensive reports that p 

significant interpretive results of hydrologic investigations of 

interest to professional geologists, hydrologists, and engineer 

series covers investigations in all phases of hydrolog , inc utling 

hydrogeology' availability of water' quality of water' and use of at r. 

Circulars present administrative in ormatio or imp _rtant 1 ·entifiG information of wide popular interest in a format esigned or 

distribution at no cost to the public . Information is usually Qf short-te 

Maps 

Geologic Quadrangle Maps are multicolor geolo ic rna s on 

topographic bases in 7.5- or 15-minute quadrangle fo ats (s ale 

mainly 1:24,000 or: 1:621

500) showing bedrock, surficial, or engi 1 e,ring geology. Maps generally include brief texts; so e maps i oJu e 

stru ture and columnar sections only. 

Geophysical Investigations Maps are on topograpbtc or Ia ·-

metric bases at various scales; they show results of surveys sing 

geophysical techniques, such as gravity, magnetic, seismic, or r di -

activity, which reflect subsurface structures that are of e,conomic or 

geologic significance. Many maps include correlations w"th the eology. 

Miscellaneous Investigations Series Maps are on planim bliic or 

topographic bases of regular and irregular areas at various scales· they 

present a wide variety of format and subject matter. Th series also 

includes 7 .5-minute quadrangle photogeologic maps on lanj tdc 

bases that show geology as interpreted from aerial photographs. Se ·es 

also includes maps of Mars and the Moon. 

eas. 

Oil and Gas Investigations ChartS show stratigraphic information for certain oil and gas fields nd o 1:1er area having petroleum 

otential. 

Miscellaneous Field Studies Maps are multicolor or black-

, d-white maps on topographic or lanime ric bas s on quadrangle or 

irregular areas at various scales. Pre,-1971 aps sh w bedrock geology 

in relation to specific mining or m·neraHileposit oblems; post-1971 

maps are primarily black-and-white maps on vari us subjects such as 

environmental studies or wilderness mineFal inves gations. 

Hydrologic Investigations Atlases are mu ticolored or blackand-white maps on topographic or planimetric bas s presenting a wide 

range of geohydrologic data of oth regular atPd irregular areas; 

p, incipal scale is 1:24,000, and reg'onal s udies ar at 1:250,000 scale 

or smaller. 

1 

Permanent catalogs, as well s som others, giving comprehens 've listings of U.S. Geological Sur e y pulJ ·cations are available under 

tlie conditions indicated below fr m th U.S. eological Survey, 

Books and Open-File Reports Sec ion, !Federal enter, Box 25425, 

enver, CO 80225. (See latest Price and vailability List.) 

"Publications of the Geolo~ical S rvey, 79-1961" may be 

purchased by mail and over the cou ter in aperbao book form and as 

a set of microfiche . 

"Publications of the Geological rvey, 1962-1970" may be 

P. rchased by mail and over the counter in aperbaok book form and as 

a set of microfiche. 

"Publications of the U.S. G ological Surve , 1971-1981" may 

oe purchased by mail and over the co nter paperback book form (two 

v lumes, publications listing and intlex) a d as a et of microfiche. 

Supplements for 1982, 1983, 198 1 1985, 986, and for subsequent years since the last permanent catalog m y be purchased by 

mail and over the counter in paperbfick book form 

State catalogs, "List of U.S .. Geological Su vey Geologic and 

Water-Supply Reports and Maps , or (S te)," ay be purchased by 

ail and over the counter in papertl,ack booklet fo 1 only. 

"Price and Availability List of U. . . Geological Survey Publications," issued annually, is available ree of charge in paperback 

booklet form only. 

Selected copies of a monthly catalog "New Publications of the 

U.S. Geological Survey" are available free of ch ge by mail or may 

be obtained over the counter in paperbac~ bookie form only. Those 

wishing a free subscription to the monthly catalog " ew Publications of 

t)ie U.S. Geological Survey" should wr"te to the U.S. Geological 

S rvey, 582 National Center, Reston, VA 2.2092. 

Note.-Prices of Governmen publications I' sted in older catalogs, announcements, and publicat"ons m y be incorrect. Therefore, 

the prices charged may differ from the pliices in catalogs, announcements, and publications.