National and Global Petroleum Assessment

Assessment of Undiscovered Conventional Oil and Gas 

Resources in the West Korea Bay–North Yellow Sea Basin,

North Korea and China, 2017

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

conventional resources of 1.1 billion barrels of oil and 2.2 trillion cubic feet of gas in the West Korea Bay–North Yellow Sea Basin, 

North Korea and China.

Introduction

The U.S. Geological Survey (USGS) completed an assessment of undiscovered, technically recoverable, conventional oil 

and gas resources within the West Korea Bay–North Yellow Sea 

Basin of North Korea and China (fig. 1). The West Korea Bay–

North Yellow Sea Basin is part of a structurally complex area that 

underwent multiple phases of extension and compression since 

the Triassic (Hao and others, 2007; Wan and Hao, 2010), producing a complex mosaic of horsts, grabens, and half grabens with 

varying degrees of structural inversion (Li and others, 2012). 

Crustal extension created synrift accommodation space that was 

filled with alluvial, fluvial, and lacustrine sediments that range 

from conglomerates to organic-rich black shales. Compression 

following thermal maturation of shales resulted in uplift and 

erosion that may have affected the preservation of conventionally 

trapped oil and gas. However, considerable geologic uncertainty 

remains in understanding the tectonic evolution of this region 

(Metcalfe, 2006). Organic-rich synrift lacustrine shales of the 

Upper Jurassic, Lower Cretaceous, and possibly Paleogene are 

potential petroleum source rocks in the basin, with the Upper 

Jurassic lacustrine shales of the Sim Uuju Formation cited as 

the most viable source rock for the conventional oil and gas 

resources based on total organic carbon, thickness, and levels 

of thermal maturation (Massoud and others, 1991; Massoud 

and others, 1993). Based on limited drilling and sampling, total 

organic carbon is as much as 6.87 weight percent with an average of 1.6 weight percent; thickness of the source-rock interval 

is as much as 550 meters; and thermal maturation is in the oil 

window for shallower areas and in the gas window for the deeper 

subbasins (Massoud and others, 1991; Massoud and others, 

1993; Stewart, 1999).

Total Petroleum System and Assessment Unit

For the West Korea Bay–North Yellow Sea Basin, the 

USGS defined the Mesozoic–Cenozoic Composite Total 

Petroleum System (TPS) and the West Korea Bay–North 

Yellow Sea Conventional Oil and Gas Assessment Unit (AU) 

within this TPS. The geologic model for the assessment is 

for oil and gas generated from organic-rich, lacustrine source 

rocks to have migrated along faults or carrier beds into structural traps or to have migrated into reservoir-quality facies 

in stratigraphic traps. The source of geologic risk in the AU is the 

potential for loss or remigration of petroleum from conventional 

traps during subsequent phases of uplift and erosion (Massoud 

and others, 1993; Cheng and others, 2015; Son and Park, 2015; 

Cheng and others, 2015). Assessment input data for the West Korea 

Bay–North Yellow Sea Conventional Oil and Gas AU are shown in 

table 1.

Undiscovered Resources Summary

The USGS quantitatively assessed undiscovered conventional 

oil and gas resources within the West Korea Bay–North Yellow 

Sea Basin (table 2). The estimated means are 1,136 million barrels 

of oil (MMBO), or 1.1 billion barrels of oil, with an F95–F5 range 

from 0 to 2,610 MMBO; 2,156 billion cubic feet of gas (BCFG), 

40°

121° 122° 123° 124° 125° 126°

41°

39°

38°

37°

CHINA

NORTH

KOREA

CHINA

SOUTH KOREA YELLOW SEA

BO HAI GULF

KOREA BAY

Source: U.S. Department of the Interior National Park Service

West Korea Bay–North Yellow Sea 

 Conventional Oil and Gas AU

EXPLANATION

0 25 50 MILES

0 25 50 KILOMETERS

MONGOLIA

CHINA

NORTH KOREA

RUSSIA

SOUTH KOREA

JAPAN

Map

area

Figure 1. Location of the West Korea Bay–North Yellow Sea, North 

Korea and China, and the assessment unit (AU) defined in this study.

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2017–3041

July 2017
or 2.2 trillion cubic feet of gas, with an 

F95–F5 range from 0 to 5,503 BCFG; 

and 37 million barrels of natural gas 

liquids (MMBNGL) with an F95–F5 

range from 0 to 103 MMBNGL. The zero 

values for the F95 fractiles reflect the AU 

probability of 0.8, which suggests there 

is a possibility for no undiscovered oil 

or gas fields of minimum size (5 million 

barrels of oil equivalent) preserved in the 

assessment unit.

References Cited

Cheng Yanjun; Wu Zhiping; Yan Shiyong; Xu Changgui; Li Wei; Zhang Jing; Zhang Shao-Chen; Ren Jian; Su Wen; and Zhang Jiang-Tao, 

2015, Cenozoic tectonic evolution of Liaodong dome, northeast Liaodong Bay, Bohai, offshore China—Constraints from seismic 

stratigraphy, vitrinite reflectance, and apatite fission track data: Tectonophysics, v. 659, p. 152–165.

Hao T.-Y.; Xu Y.; Suh M.; Xu Y.; Liu J.-H.; Zhang L.-L.; and Dai M.-G., 2007, East marginal fault of the Yellow Sea—A part of the conjunction zone between Sino-Korea and Yangtze blocks?, in Zhai M.-G.; Windley, B.F.; Kusky, T.M.; and Meng Q.R., eds., Mesozoic 

sub-continental lithospheric thinning under eastern Asia: The Geological Society of London, Special Publication No. 280, p. 281–292.

Li Wenyong; Lu Wenfen; Liu Yanxu; and Xu Jianchun, 2012, Superimposed versus residual basin—The North Yellow Sea Basin: 

Geoscience Frontiers, v. 3, no. 1, p. 33–39.

Massoud, M.S., Killops, S.D., Scott, A.C., and Mattey, D., 1991, Oil source rock potential of the lacustrine Jurassic Sim Uuju Formation, 

West Korea Bay Basin, Part I—Oil source rock correlation and environment of deposition: Journal of Petroleum Geology, v. 14, no. 4, 

p. 365–386.

Massoud, M.S., Scott, A.C., Killops, S.D., Mattey, D., and Keeley, M.L., 1993, Oil source rock potential of the lacustrine Jurassic 

Sim Uuju Formation, West Korea Bay Basin, Part II—Nature of the organic matter and hydrocarbon-generation history: Journal of 

Petroleum Geology, v. 16, no. 3, p. 265–284.

Metcalfe, Ian, 2006, Paleozoic and Mesozoic tectonic evolution and paleogeography of East Asian crustal fragments—The Korean 

Peninsula in context: Gondwana Research, v. 9, p. 24–46.

Son B.-K., and Park Meesook, 2015, Petroleum system analysis of west Korea Bay Basin, North Korea: Journal of the Geological Society 

of Korea, v. 51, no. 5, p. 433–449.

Stewart, Alex, 1999, Glimmers of hope seen in North Korean basins, markets: Oil and Gas Journal, January 4, 1999, p. 62–65, accessed 

March 16, 2017, at http://www.ogj.com/articles/print/volume-97/issue-1/in-this-issue/exploration/glimmers-of-hope-seen-in-northkorean-basins-markets.html.

Wan Tianfeng, and Hao Tianyao, 2010, Mesozoic-Cenozoic tectonics of the Yellow Sea and oil-gas exploration: Acta Geologica Sinica, 

v. 84, no. 1, p. 77–90.

For More Information

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

West Korea Bay–North Yellow Sea Basin Assessment Team

Christopher J. Schenk, Marilyn E. Tennyson, Tracey J. Mercier, Sarah J. Hawkins, Thomas M. Finn, Stephanie B. Gaswirth, 

Kristen R. Marra, Timothy R. Klett, Phuong A. Le, Heidi M. Leathers-Miller, and Cheryl A. Woodall

Table 1. Key assessment input data for one conventional assessment unit in the West Korea 

Bay–North Yellow Sea Basin, North Korea and China.

[AU, assessment unit; MMBO, million barrels of oil; BCFG, billion cubic feet of gas. Shading indicates not 

applicable]

Assessment input data West Korea Bay–North Yellow Sea Conventional Oil and Gas AU

Minimum Median Maximum Calculated mean

Number of oil fields 1 50 150 53.2

Number of gas fields 1 14 50 15.2

Sizes of oil fields (MMBO) 5 10 1,200 26.8

Sizes of gas fields (BCFG) 30 60 4,000 127.9

AU probability 0.8

Table 2. Assessment results for one conventional assessment unit in the West Korea Bay–North Yellow Sea Basin, North Korea 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. For gas accumulations, all liquids are included in the NGL category. 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–Cenozoic Composite Total Petroleum System

West Korea Bay–North Yellow Sea 

Conventional Oil and Gas AU 0.8 Oil 0 1,101 2,610 1,136 0 586 1,416 608 0 9 26 10

 Gas 0 1,347 4,087 1,548 0 20 77 27

Total undiscovered 

conventional resources 0 1,101 2,610 1,136 0 1,933 5,503 2,156 0 29 103 37

ISSN 2327-6916 (print) ISSN 2327-6932 (online) https://doi.org/10.3133/fs20173041