Geological characteristics and accumulation mode of the Jurassic deep coal-rock gas in Junggar Basin

doi:10.3969/j.issn.1672-7703.2025.04.006

Abstract

Abstract: The Jurassic coal measures were well developed in Junggar Basin, which served as both good source rock and reservoir. A Well
CT1H was drilled in Baijiahai Bulge, and high-yield gas flow was obtained in the Jurassic Xishanyao Formation coal rock reservoir, breaking through the traditional depth forbidden zone for CBM exploration and development at a depth greater than 2000 m, which indicated a new type of natural gas resource for increasing reserves and production on a large scale. Based on the exploration results of the Jurassic coal-rock gas in Junggar Basin, and combined with experimental methods such as casting thin section, scanning electron microscope, and nuclear magnetic resonance, a systematic study has been conducted on the geological characteristics and hydrocarbon accumulation pattern of deep coal-rock gas, and the future exploration orientation has been clarified. The study results show that two sets of main coal rocks, namely, coal rock No.2 in Xishanyao Formation and coal rock No.5 in Badaowan Formation, were developed in Junggar Basin. Xishanyao Formation coal rocks in the basin hinterland are characterized by low rank and primary structure, an average porosity of 17.25%, and poor gas generation capacity, while those in the southern basin margin are composed of medium-rank coal, with good connectivity of pores and a high proportion of free gas. Badaowan Formation coal rocks are characterized by medium rank and primary structure, with an average reservoir porosity of 3.12% and a proportion of adsorption gas of 89.75%. There are three main types of hydrocarbon accumulation patterns of the Jurassic deep coal-rock gas in the basin, i.e., allogenetic structural type, authigenic stratigraphic type, and authigenic structural type. The comprehensive study of geological conditions and gas accumulation control factors indicates that the favorable exploration area of deep coal-rock gas is 2385 km², and the predicted coal-rock gas resources are 4260×10⁸ m³ in Junggar Basin. The future exploration orientation of coal-rock gas includes Xishanyao Formation and Badaowan Formation in Dinan–Baijiahai area in the hinterland basin and Xishanyao Formation in the southern margin of the basin.

Key words: Junggar Basin, Jurassic, coal-rock gas, geological characteristics, hydrocarbon accumulation pattern, resource potential, exploration orientation

CLC Number:

TE122.2

He Wenjun, Pan Jin, Liu Chaowei, Wang Qiuyu, Li Hui, Chen Mengna, Li Peng, Wang Ning. Geological characteristics and accumulation mode of the Jurassic deep coal-rock gas in Junggar Basin[J]. China Petroleum Exploration, 2025, 30(4): 78-91.

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