柴达木盆地三湖地区第四系气藏形成与“烟囱效应”

Gas Chimney Effect and Formation of Quaternary Gas Pool in Sanhu Area, Qaidam Basin

高分辨率地震资料表明,柴达木盆地三湖地区第四系气藏周围发育有气烟囱。第四系具有较高的地温梯度,深部发育了低幅超压;甘森泉-小柴旦基底断裂影响气藏构造的完整性;第四系饱含高矿化度地层水泥岩构成的盖层可以起到一定的封盖作用。这些因素相互作用,最终导致了气烟囱的形成。气烟囱的发育可以解释第四系天然气组分、重烃碳同位素等体现出来的混源特征,解决第四系各层序源岩生烃潜力和含气储量之间存在的矛盾。总之,气烟囱作为天然气的垂向运移通道对该区第四系气藏的成藏起到重要作用。

The high resolution seismic data show that gas chimneys exist around Quaternary gas reservoirs in Sanhu area of Qaidam basin. The Quaternary system is characterized by high geothermal gradient, with low scope of overpressure in its deep and shale caprock saturated with formation water of high salinity. The Gansenquan-Xiaochaidan basement faults affect the integrality of gas reservoir structures. These interacted factors result in the formation of gas chimney. The existence of gas chimney can explain the mixed source characters of Quaternary gas composition and ethane carbon isotope, thus resolving the contradictions between source rock hydrocarbon- generating potentials and gas reserves of each sequence. In conclusion, the gas chimney as a vertical path of natural gas migration plays an important role in Quaternary gas accumulation in this area.