川西拗陷中段气藏稀有气体来源与烃类运移研究

Noble Gas Origin and Hydrocarbon Migration in the Central Area of the Western Sichuan Depression

川西拗陷中段的孝泉、新场与合兴场气藏的3 He 4 He值为 2 .0 1～ 6 .93,40 Ar 3 6Ar值为 372～ 739,绝大部分He与 2 0 %～ 6 0 %的Ar为地壳放射性成因气。地壳放射性成因4He、40 Ar(简写为40 Ar )的含量比值4He 4 0Ar 同气藏埋藏深度有着很好的函数关系 ,并同含量高达 93%～ 99%的CH4有很好的相关性。说明来源于基底的4He、40 Ar 在进入气藏前已同烃类充分混合 ;这些气体在拗陷东坡深处呈水溶相及气水混相向储层渗透运移 ;北环隆带CH4作为稀有气体载体 ,携带4He、40 Ar 向气藏扩散聚集。

Seven noble gas samples were collected from the Xiaoquan, Xinchang and Hexinchang fields in the central area of Western Sichuan Depression. The measured 3He/ 4He and 40Ar/ 36Ar ratios of the samples range from 2.01 to 6.93, and 372 to 739, respectively. Almost all He and 20%～60% Ar of the samples are crustal radiogenic(* denotes radiogenic origin). The calculated 4He/ 40Ar * ratio shows as a function of depth, and has a correlation with the CH 4 concentration, occupying up to 93 % to 99 % by volume of the gas samples. These characteristics suggest: 1)The basement-derived 4He and 40Ar * were well mixed with the CH 4 prior to entrapment into gas reservoirs. 2)Within the deeper region of the eastern slope of the depression these gases for gas-water mixture phase and gas-saturated water phase infiltrate into the sampled reservoir.3) In the northern circus-uplift zone of central area of the depression the CH 4 acts as a carrier phase for noble gases, and carries with 4He and 40Ar * to migrate diffusely into the overlying reservoirs.