Oil-gas geological features and exploration direction in the Qingxi Sag, Jiuquan Basin

doi:10.13745/j.esf.sf.2022.8.20

Abstract

Abstract:

Petroleum exploration in the Jiuquan Basin begins in the 1920s with the successive discoveries of the Laojunmiao, Yaerxia and Danbei oilfields. The basin is a fault/depression superimposed basin formed through two-stage evolution—Early Cretaceous fault depression and Mesozoic-Cenozoic foreland, where a set of laminar argillaceous dolomite and dolomitic mudstone deposited in the Lower Cretaceous Chijinbao and Xiagou formations during the fault depression period. The relatively developed algal dolomite is high-quality source rock, and rapid basin subsidence during the depression period lead to the quick maturation of source rock and efficient hydrocarbon generation, which provides strong driving force for oil and gas migration. At the same time, compression and thrust play a key role in the generation of structural traps and migration channels as well as improvement of reservoir physical properties. Many positive structural belts, such as the Kulongshan mountain range, are favorable areas for oil and gas enrichment. There are three types of crude oil in the Qingxi Sag according to thermal maturity. The low-maturity crude oil is only found in the upper Xiagou-Zhonggou formations; mature crude oil, capable of large-scale migration, are distributed in the Liugouzhuang, Yaerxia, Laojunmiao and Shiyougou oilfields; and deep high-maturity crude oil, largely confined below the medium and shallow layers, presents promising resource potential. The above results provides a valuable reference for the petroleum exploration in the Lower-Cretaceous Qingxi Sag.

Key words: Jiuquan Basin, fault-depression superimposed, algal lamina, source rocks, compression, thrust, migration channels, positive structural belts, resource potential

CLC Number:

TE132

WEI Haoyuan, ZHU Zongliang, XIAO Wenhua, WEI Jun, WEI Deqiang, YUAN Bochao, XIANG Xin. Oil-gas geological features and exploration direction in the Qingxi Sag, Jiuquan Basin[J]. Earth Science Frontiers, 2023, 30(1): 69-80.

Figures/Tables 17

Fig.1 Simplified tectonic setting of the Jiuquan basin region

Fig.2 Tectonic division of the Jiuquan Basin

Fig.3 Schematic section of the Jiuxi Sag along the JX06316-QXLP-JX85334 line illustrating its tectonic evolution

Fig.4 Structural map of the Uppermost Cretaceous Xiagou Formation, Qingxi Sag

Fig.5 Organic maceral components in source rock in the Qingxi Sag

Fig.6 Burial history and thermal evolution of source rock in well Liu 9, Qingxi Sag

Fig.7 Simulation results showing the oil generation percentage of K1c (left) and K1g formations, Qingxi Sag during different geological periods

Fig.8 Mass spectra of steranes in low-maturity (top), mature (middle) and high-maturity oil samples from Qingxi Sag

Fig.9 Fine correlation of Cretaceous oil sources in the Qingxi Sag

Fig.10 Casting thin sections (a-c) and coring photos (d,e) showing fracture developments in the Qingxi Sag

Fig.11 Detrital quartz particles corroded by deep fluid in the Qingxi Sag

Fig.12 Microcrystalline quartz particle aggregates in coarse-grained clastic rock of the Qingxi Sag

Fig.13 Albite crystal particles in coarse-grained clastic rock of the Qingxi Sag

Fig.14 Deep fluid action modes in Early Cretaceous Qingxi Sag

Fig.15 Source-reservoir-cap combination and distribution of oilfields in the Jiuquan Basin

Fig.16 Reservoir accumulation pattern of the Kulongshan structural belt, Qingxi Sag

Fig.17 Model of oil and gas migration in the Qingxi-Laojunmiao structural belt

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