川西坳陷飞仙关组三段鲕滩储层特征与成岩作用研究

Diagenesis and characteristics of oolitic beach carbonate reservoirs in the third member of the Feixianguan Formation in West Sichuan Depression

对川西坳陷下三叠统飞仙关组的天然气勘探一直未获得突破，但在该区野外露头发现了鲕粒滩相沉积，显示飞仙关组三段（简称飞三段）有可能成为该区重要的潜在海相储层。为此，利用野外露头样品，通过普通薄片．铸体薄片、阴极发光薄片观察及样品扫描电镜观察，结合部分样品的物性、微量元素分析测试结果，对该区飞三段鲕粒碳酸盐岩的储层特征、成岩作用进行了研究。结果显示，汉旺野外露头剖面飞三段下亚段鲕粒灰岩以海底成岩作用为主，两期胶结作用强烈，而不完全的埋藏白云岩化未能有效增加孔隙空间，使得最终孔隙度较小；汉旺剖面的飞三段上亚段及大飞水剖面飞三段鲕粒白云岩则主要以埋藏成岩作用为主，次生孔隙发育，埋藏白云岩化与溶蚀作用是孔隙发育的关键。研究结果表明，成岩作用是造成川西坳陷飞三段鲕粒碳酸盐岩样品物性差异的关键因素。

Carbonates of oolitic beach facies are found in the outcropped third member of the Feixianguan Formation(Fei-3 Member)in West Sichuan Depression,indicating an important potential target for gas exploration.Based on detailed microscopic observation of ordinary thin section,cast thin section,cathodoluminescence thin section and scanning electron microscopic observation of outcrop samples,and in combination with the measured porosity,permeability and trace elements of some samples,we study the characteristics and diagenesis of the carbonate reservoirs of oolitic beach facies in the Fei-3 Member in this area.The oolitic limestone in the Lower Fei-3 Member in the Hanwang outcrop is mainly of submarine diagenesis with two stages of strong cementation.However,the incomplete burial dolomitization cannot effectively enlarge pore space,resulting in a relatively small ultimate porosity.In contrast,the oolitic dolomite of the Upper Fei-3 Member in the Hanwang outcrop and the Fei-3 Member in the Dafeishui outcrop is mainly of burial diagenesis with well-developed secondary porosity.Burial dolomitization and dissolution are the major mechanisms of pore development.It is believed that diagenesis is the key factor leading to the difference of physical properties of the oolitic carbonates in West Sichuan Depression.