National and Global Petroleum Assessment

Assessment of Undiscovered Conventional Oil Resources of the 

East Gobi, Nyalga, Tamtsag-Hailar, Erlian, and Yingen Basins of 

Mongolia and China, 2018

Using a geology-based assessment methodology, the U.S. Geological Survey estimated undiscovered, technically recoverable mean

conventional resources of 187 million barrels of oil and 85 billion cubic feet of gas in the East Gobi, Nyalga, Tamtsag-Hailar, Erlian, and 

Yingen basins of Mongolia and China.

Introduction

The U.S. Geological Survey (USGS) quantitatively assessed the 

potential for undiscovered, technically recoverable conventional oil

resources in the East Gobi, Nyalga, Tamtsag-Hailar, Erlian, and Yingen 

basins of Mongolia and China (fig. 1). These basins, which represent groups 

of subbasins, share a similar tectonic history and development of petroleum 

systems (Meng, 2003; Meng and others, 2003; Windley and others, 2007; 

Wilhem and others, 2012). Middle Jurassic and Late Jurassic–Early 

Cretaceous extension formed a regional system of extensional basins 

that was filled with synrift nonmarine facies, including alluvial, fluvial, 

deltaic; marginal lacustrine sandstones; and shallow-to-deep-water 

lacustrine shales (Changsong and others, 2001). In these five basins, 

petroleum source rocks are organic-rich, deep-water lacustrine shales 

(Traynor and Sladen, 1995; Graham and others, 2001; Johnson and 

others, 2003; Johnson, 2004; Prost, 2004; Ding and others, 2015; 

Luo and others, 2018). Following cessation of rifting, a thermal sag 

phase led to increased accommodation space and deposition, resulting 

in local source-rock maturation and petroleum migration. However, 

the sag phase of deposition was interrupted by regional compression, 

uplift, and erosion in the Late Cretaceous that inverted many of 

the extensional structures, largely curtailed the thermal maturation 

process, and may have caused remigration of oil or loss of oil from 

conventional traps.

Total Petroleum System and Assessment Units

The Mesozoic Composite Total Petroleum System was defined 

to encompass petroleum generated from synrift, Lower Cretaceous 

lacustrine source rocks and from lacustrine shales such as in the 

Middle Jurassic Eedemt Formation (Hasegawa and others, 2018). 

Although geochemical parameters for source rocks are variable across 

the basins, the lacustrine source rocks contain Type I kerogen (with 

minor Type III kerogen), are as much as 700 m thick, are as much 

as 10 weight percent total organic carbon, and have hydrogen index 

values that are as much as 600 milligrams of hydrocarbon per gram 

organic carbon. In each basin, an assessment unit was defined to 

include all potential undiscovered conventional oil accumulations 

sourced by these lacustrine rocks.

The geologic model is that oil was generated from synrift 

lacustrine source rocks in those subbasins that have reached the 

thermal maturity window for oil generation. Once generated, this 

oil may have migrated into synrift reservoirs and may have been 

trapped only to possibly remigrate during Late Cretaceous inversion. 

Remigration may have resulted in the loss of oil from conventional 

traps. The range of uncertainty on the assessment input (table 1) 

reflects the level of uncertainty on the extent of source-rock facies 

U.S. Department of the Interior

U.S. Geological Survey

within the grabens, the level of thermal maturation of lacustrine source 

rock, and the retention of oil within traps following compression and 

inversion. Assessment input data are summarized in table 1.

Undiscovered Resources Summary

The USGS quantitatively assessed conventional oil and associated 

gas resources in five assessment units (table 2) in the East Gobi, Nyalga, 

Tamtsag-Hailar, Erlian, and Yingen basins of Mongolia and China. For 

undiscovered, technically recoverable resources, the mean totals are 

187 million barrels of oil (MMBO) with an F95–F5 fractile range from 

0 to 453 MMBO and 85 billion cubic feet of associated gas (BCFG) 

with an F95–F5 fractile range of 0 to 212 BCFG. Of the mean total of 

187 MMBO, about 86 percent, or 162 MMBO, is estimated to be in the 

Tamtsag-Hailar basin (100 MMBO) and Erlian basin (62 MMBO).

0 150 300 MILES

0 300 KILOMETERS 150

Base map from U.S. Department of the Interior National Park Service

YELLOW SEA

 LAKE

BAIKAL

CHINA

RUSSIA

MONGOLIA

100° E 105° E 110° E 115° E 120° E

55° N

50° N

45° N

40° N

35° N

Map area

MNG

CHN

PRK

KOR

JPN

RUS EXPLANATION

East Gobi Basin Conventional Oil AU

Nyalga Basin Conventional Oil AU

Tamtsag-Hailar Basin Conventional Oil AU

Erlian Basin Conventional Oil AU

Yingen Basin Conventional Oil AU

Figure 1. Map showing five conventional assessment units (AUs) in the 

East Gobi, Nyalga, Tamtsag-Hailar, Erlian, and Yingen basins of Mongolia 

and China.

Fact Sheet 2018–3041

August 2018
Table 1. Key input data for five conventional assessment units (AUs) in the East Gobi, Nyalga, Tamtsag-Hailar, Erlian, and Yingen basins of Mongolia 

and China.

[AU, assessment unit; MMBO, million barrels of oil. Shading indicates not applicable]

Assessment input data—

Conventional AUs

East Gobi Basin Conventional Oil AU Nyalga Basin Conventional Oil AU

Minimum Median Maximum Calculated mean Minimum Median Maximum Calculated mean

Number of oil fields 1 5 15 5.3 1 5 20 5.5

Size of oil fields (MMBO) 0.5 1 40 1.8 0.5 1 40 1.8

AU probability 0.8 0.8

Assessment input data—

Conventional AUs

Tamtsag-Hailar Basin Conventional Oil AU Erlian Basin Conventional Oil AU

Minimum Median Maximum Calculated mean Minimum Median Maximum Calculated mean

Number of oil fields 1 20 40 20.5 1 20 40 20.5

Size of oil fields (MMBO) 0.5 1.5 300 5.4 0.5 1.5 100 3.4

AU probability 0.9 0.9

Assessment input data—

Conventional AUs

Yingen Basin Conventional Oil AU

Minimum Median Maximum Calculated mean

Number of oil fields 1 5 15 5.3

Size of oil fields (MMBO) 0.5 1 100 2.5

AU probability 0.7

Table 2. Results for five conventional assessment units (AUs) in the East Gobi, Nyalga, Tamtsag-Hailar, Erlian, and Yingen basins of Mongolia and China.

[MMBO, million barrels of oil; BCFG, billion cubic feet of gas; NGL, natural gas liquids; MMBNGL, million barrels of natural gas liquids. Results shown are fully risked 

estimates. F95 represents a 95-percent chance of at least the amount tabulated; other fractiles are defined similarly. Fractiles are additive under the assumption of perfect 

positive correlation. Shading indicates not applicable]

Total petroleum system 

and assessment units (AUs)

AU

probability

Accumulation 

type

Total undiscovered resources

Oil (MMBO) Gas (BCFG) NGL (MMBNGL)

F95 F50 F5 Mean F95 F50 F5 Mean F95 F50 F5 Mean

 Mesozoic Composite Total Petroleum System

East Gobi Basin Conventional Oil AU 0.8 Oil 0 6 21 8 0 3 9 3 0 0 0 0

Nyalga Basin Conventional Oil AU 0.8 Oil 0 6 23 8 0 2 9 3 0 0 0 0

Tamtsag-Hailar Basin Conventional Oil AU 0.9 Oil 0 84 249 100 0 41 127 50 0 0 0 0

Erlian Basin Conventional Oil AU 0.9 Oil 0 59 128 62 0 23 54 25 0 0 0 0

Yingen Basin Conventional Oil AU 0.7 Oil 0 6 32 9 0 2 13 4 0 0 0 0

Total undiscovered conventional resources 0 161 453 187 0 71 212 85 0 0 0 0

References Cited

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Mongolia and China Basins Assessment Team

Christopher J. Schenk, Tracey J. Mercier, Janet K. Pitman, Thomas M. Finn, Cheryl A. Woodall, Kristen R. Marra, Phuong A. Le, 

and Heidi M. Leathers-Miller

For More Information

Assessment results are also available at the USGS Energy Resources Program website at https://energy.usgs.gov.

ISSN 2327-6916 (print) ISSN 2327-6932 (online) https://doi.org/10.3133/fs20183041