四川盆地天然气成藏条件及其勘探方向

四川盆地系在刚性结晶基底上由克拉通海相原型盆地同造山前陆盆地和后造山前陆盆地先后演化而成的克拉通前陆盆地。整体封存构造保存条件是该盆地天然气成藏的主体地质背景和晚期成藏保存的主要条件。加里东和印支两期的古隆起对油气的早期聚集和破坏具有双重作用,但有利于晚期成藏。盆地的保存条件可划分为整体封存、残留封存和缺乏封存三类构造保存单元,并由此可划分出三个相应的构造保存单元组合区。盆地的天然气成藏条件总体良好,影响因素主要是水动力条件和断层。该盆地有T_3,P_2~1,P_1~(1+2),S_1,∈_1和 Z_2六套主力烃源岩和 Z_2—∈_1,∈_1—S,S—P_1,p—T_2,T_3—J 五套成油气体系。今后深化勘探的方向为:(1)川东石炭系向斜带的低缓构造、潜伏构造、高陡背斜带两翼的高陡潜伏构造,特别是构造复合圈闭;(2)川东北—川北开江—梁平、城口—鄂西等海槽为中心的以陆棚边缘滩、碳酸盐岩深缓坡台地;(3)川西—川中的须家沟组原生气藏和侏罗系次生气藏。评价该盆地可以从反向思维入手,即对油气藏破坏条件进行区域和目标评价。

Accumulation and Preservation Conditions of Natural Gas in Sichuan Basin

Sichuan Basin is an inheriting basin evolved from Z-T_2 craton marine primary basin,T_3-J synorogenic foreland basin and K -E postorogenic foreland basin. Tectonic holistic preservation is the main geologic setting of natural gas accumulation and the significant condition of late gas replacement and preservation. Cratonic and Indosinian paleo-uplifts plays a double role of both early accumulation and destruction. In the basin, the preserva- tion conditions can be divided into three types of structural preservation units,i.e.the holistic,the remnant and the lack seal units,to which there are three combinatorial areas of seal units corresponding. The preservation conditions of gas reser- voirs are well in general although hydrodynamics and faults are the main effecting factors. There are six major source rocks (T_3, P_2~1,P_1~(1+2),S_1,∈_1 and Z_2)and five petroleum systems (Z_2-∈_1,∈_1-S,S-P_1,P-T_2 and T_3-J)in this basin, among which commercial gas reserves are offered except the ∈_1-S system.Also,some potential and prospecting traps, reservoirs and areas are proposed by the author.The author suggests that a reversed thinking can be taken in basin evalua- tion,for example the regional and prospecting target evalua- tions can be dealt with from destruction conditions of reser- voirs.