Geofluids

Research Article

Geochemistry and Genesis of Oil and Gas Seeps in the Junggar Basin, NW China: Implications for Hybrid Petroleum Systems

Table 3

Genetic classification and geochemical characteristics of oil-gas seeps in the Junggar Basin.


Genetic types	Basic information				Typical molecular geochemical characteristics
Genetic types	Region	Formation	Oil source	Secondary alteration	δ¹³C (‰; EOM)	Alkanes	Terpanes	Steranes

Type 1	NW	T₂k, K₁tg	P₁f	TIC: UCMs 177: 25-norhopanes (severe biodegradation)	−28.90‰ to −27.50‰	β-Carotane (rich)		DRS: C₂₇<C₂₈<C₂₉;

Type 2	SE, E	P₂l (SE), J₁b (E)	P₂l/P₂p	TIC: UCMs (light biodegradation)	−29.80‰ to −29.20‰	β-Carotane (rich);		DRS: C₂₇<C₂₈<C₂₉;

Type 3	SM (Qigu)	J₃q	J	None	−28.30‰ to −27.80‰	β-Carotane (no);		DRS: C₂₇<C₂₈<C₂₉;

Type 4	SM (Anjihai and Huoerguosi)	E_2-3a	K	TIC: UCMs (light biodegradation)	−30.40‰ to −28.80‰	β-Carotane (high);		DRS: C₂₇>C₂₈<C₂₉;

Type 5	SW (oil seeps)	E_2-3a, N₂d	E (+J)	TIC: UCMs (light biodegradation)	−29.6‰ to −28.1‰	β-Carotane (rich);		DRS: C₂₇>C₂₈<C₂₉;
Type 5	SW (gas seeps)	E_2-3a, N₂d	J	None	δ¹³C₁: −43.7‰ to −42.4‰ δ¹³C₂: −26.7‰ to −26.2‰	/	/	/

“/” denotes not applicable. Note: DRS = distribution of regular steranes; SII = sterane isomerization index; D/R = ratios of diasteranes to regular steranes.