Lithologic Reservoirs ›› 2026, Vol. 38 ›› Issue (5): 1-9.doi: 10.12108/yxyqc.20260501

• PETROLEUM EXPLORATION • Previous Articles     Next Articles

Influence mechanism of salt minerals on large-scale hydrocarbon generation from low-abundance source rocks: A case study of Paleogene Xiaganchaigou Formation in western Qaidam Basin

WANG Bo1,2(), ZHOU Fei1,2, TIAN Jixian3(), ZHANG Jing1,2, ZHANG Tong1,2, QI Yonggang4, QIAO Baihan1,2, FENG Dehao5   

  1. 1 Research Institute of Exploration and Development, PetroChina Qinghai Oilfield Company, Dunhuang 736202, Gansu, China
    2 Plateau Saline Lacustrine Basin Oil-Gas Geology Key Laboratory of Qinghai Province, Dunhuang 736202, Gansu, China
    3 PetroChina Research Institute of Petroleum Exploration and Development, Beijing 100083, China
    4 Supervision & Management Company, PetroChina Qinghai Oilfield Company， Dunhuang 736202, Gansu, China
    5 College of Earth Sciences, China University of Petroleum （Beijing）, Beijing 102249, China
  • Received:2026-01-19 Revised:2026-02-10 Online:2026-09-01 Published:2026-09-04
  • Contact: TIAN Jixian E-mail:wboqh@petrochina.com.cn;tjx69@petrochina.com.cn

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Abstract:

Paleogene-Neogene saline lacustrine basin source rocks in western Qaidam Basin are with relatively low abundance organic matter, but multiple large-scale oil and gas reservoirs have been discovered. Saline inorganic minerals in source rocks have important impacts on the hydrocarbon generation of low abundance source rocks. Through conducting simulation experiments on hydrocarbon generation from organic matter with NaCl, the influence of inorganic salts on hydrocarbon generation from organic matter in Paleogene of western Qaidam Basin was systematically evaluated, influence machenism of salt minerals was clarified, and the hydrocarbon generation model for saline lacustrine basins was established. Research results show that: （1） Paleogene-Neogene saline minerals in western Qaidam Basin are developed, with rock salt, gypsum, and glauberite as the main types, and with single layer thicknesses ranging from several centimeters to over ten meters. Salt layers are interbedded with source rock organic matters, which provides favorable conditions for the catalytic effect of salt substances. （2） Thermal simulation experiments have confirmed that the addition of chloride salts significantly promotes the hydrocarbon generation of source rocks, which can significantly enhance the generation of liquid hydrocarbons in the oil window stage and gaseous hydrocarbons in the gas window stage. With the increase of salinity, the peak yields of gaseous and liquid hydrocarbons gradually increase, and the cracking rate of liquid hydrocarbons accelerates simultaneously. （3） During the pyrolysis process of kerogen, the addition of chloride salts clearly reduces the breaking energy of C-C and C-H bonds in kerogen molecules, thereby enhancing hydrocarbon generation. The underlying mechanism may involve the alteration of molecular surface charge distribution through electronic induction effects, which accelerates specific reaction pathways and influences the pyrolysis reaction rate of kerogen. （4） Compared with the conventional hydrocarbon generation model, source rocks in saline environments have the characteristic of early hydrocarbon generation. The hydrocarbon generation of shallow soluble organic matter and deep kerogen follow a relay. When Ro is 0.5%, the secondary peak of soluble organic matter oil generation occurs, and when Ro is 0.9%-1.1%, the peak of kerogen oil generation occurs. The participation of saline substances greatly promotes the hydrocarbon generation efficiency of organic matter, ultimately achieving large-scale hydrocarbon generation from low abundance source rocks, which enable source rocks from saline lacustrine basins of western Qaidam Basin to generate a large amount of oil and gas even under the condition of low organic matter abundance.

Key words: saline lacustrine basin, hydrocarbon generation mechanism, saline minerals, thermal simulation experiment, activation energy, hydrocarbon generation rate, Xiaganchaigou Formation, Paleogene, Qaidam Basin

CLC Number: 

  • TE122.112

Fig. 1

Sedimentary facies distribution (a) and comprehensive stratigraphic column (b) of the upper member of Xiaganchaigou Formation (E32) in Paleogene of western Qaidam Basin"

Fig. 2

Core photos, microscopic features and EDS spectrum of salt layer and salt minerals of Paleogene E32 in western Qaidam Basin"

Fig. 3

Planar distribution of salt-bearing stratum thickness of Paleogene E32 in western Qaidam Basin"

Fig. 4

Organic matter abundance (a) and types (b) of Paleogene E32 in western Qaidam Basin"

Table 1

Sample data of source rock hydrocarbon generation simulation experiment of Paleogene in western Qaidam Basin"

井名 层位 深度/
m		 TOC/% Tmax/
℃		 HI/
(mg HC·g-1·TOC-1)		 （S1 + S2）/
(mg·g-1)		 实验
类别
英探1 E31—E32 4 552.4 1.13 432 295 3.58 高压釜
绿参1 E31—E32 4 305.7 0.66 423 98 1.18 黄金管

Fig. 5

Hydrocarbon generation rate of the autoclave pyrolysis experiment for source rocks under different salinity conditions of Paleogene in western Qaidam Basin"

Fig. 6

Hydrocarbon generation rate of the gold-tube pyrolysis experiment of source rocks under different salinity conditions of Paleogene in western Qaidam Basin"

Fig. 7

Distribution characteristics of activation energy for Type Ⅲ organic matter hydrocarbon generation under different salinity conditions in the gold-tube limited system of Paleogene source rocks in western Qaidam Basin"

Fig. 8

Schematic diagram of induced effects of Cl- on carbon chain"

Fig. 9

Hydrocarbon generation models of saline lacustrine source rocks of Paleogene in western Qaidam Basin"

Fig. 10

Hydrocarbon accumulation models of Paleogene in western Qaidam Basin"

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