四川盆地东北部飞仙关组暴露浅滩、非暴露浅滩与储层关系

The exposed and unexposed shoals and their bearings on the carbonate reservoirs in the Feixianguan Formation in the northeastern part of the Sichuan Basin

关键词:  下三叠统  飞仙关组  浅滩  四川盆地东北部

Key words:  Lower Triassic  Feixianguan Formation  shoal  northeastern part of the Sichuan Basin

摘要:

四川盆地东北部飞仙关组中发育大量浅滩相沉积,不同地区浅滩形成时的古地理背景及海平面升降情况不同,导致沉积物岩性及储集性能截然不同。广元、通江、南江、巴中地区浅滩位于下三叠统飞仙关组三段,形成于海平面上升过程,沉积物一直处于被海水淹没状态,未曾暴露,岩性为灰色亮晶鲕粒灰岩、亮晶砂屑灰岩,颗粒间全被方解石晶体充填,岩石孔隙度和渗透率低,储集性能相对较差。达县宣汉地区浅滩位于飞仙关组二段中,沉积基底为一水下高地,形成于海平面下降过程;沉积物经常暴露于潮上,发生白云岩化和大气淡水溶蚀作用,埋葬后岩石又发生了重结晶作用和进一步溶蚀作用,岩性为砂屑白云岩、溶孔白云岩、残余鲕粒白云岩夹少量灰岩、鲕粒灰岩,岩石中晶间孔、粒间孔及溶孔丰富,孔隙度高,渗透率好,储集性能极佳。油气勘探时要注意寻找类似达县宣汉地区飞仙关组二段中的暴露浅滩型储层。

Abstract:

The shoal deposits crop out over a wide area of the Feixianguan Formation in the northeastern part of the Sichuan Basin. The palaeogeographic settings and sea-level changes during the shoal formation are interpreted to be major controls on the differences of lithology and reservoir quality in different parts of the basin. The shoals in the Guangyuan-Tongjiang-Nanjiang-Bazhong zone are confined to the third member of the Lower (Triassic) Feixianguan Formation, and formed during the rising phases of sea level. The sediments were always drowned by sea water, and even never cropped out on the surface. The lithologies contain grey oosparite and sparry calcarenite completely filled by calcite crystals. These rocks are characterized by low porosity and permeability and poor reservoir quality. The shoals in the Daxian-Xuanhan zone appear in the second member of the Feixianguan Formation. The sedimentary basement is represented by a subaqueous rise created during the falling phases of sea level. The sediments commonly cropped out in the supratidal zone have been subjected to the dolomitization and dissolution of meteoric water. After burial, the rocks have also been subjected to the (recrystallization) and further dissolution. The lithologies include dolarenite, porous dolostone and residual oolitic dolostone intercalated with minor amount of limestone and oolitic limestone, which are characterized by abundant intercrystal porosity, interparticle porosity and dissolution openings, high porosity, good permeability and reservoir quality. This kind of reservoir rocks in the second member of the Feixianguan Formation in the Daxian-(Xuanhan) zone may provide a good example for the future petroleum exploration.