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天环坳陷北部地区山西—下石盒子组具有天然气勘探前景,但砂岩储集特征不清,加强储层特征研究是适应本区勘探形势的需要。文章运用铸体薄片、物性测试、孔隙图像分析、压汞和扫描电镜等多种测试方法对砂岩的组构特征、孔隙类型、物性特征及孔喉系统进行研究,明确了砂岩储集性能。通过对砂体沉积微相类型、砂岩组构特征和主要成岩作用的研究,对该区储层发育的控制因素进行了分析。该区有利储层主要发育在平原分流河道、水下分流河道和河口坝沉积微相砂体中。压实压溶作用和胶结作用使粒间孔隙损失严重,高岭石晶间孔隙和凝灰质填隙物溶蚀孔隙构成了砂岩储集空间的主体,最终形成了微细喉道—中孔—低渗的天然气储层。

SANDSTONE RESERVOIR CHARACTERISTICS OF SHANXI-LOWER SHIHEZI FORMATION IN NORTH TIANHUAN DEPRESSION

The Shanxi—Lower Shihezi Formation in North Tianhuan Depression is of prospects for exploring for natural gas,however the sandstone reservoir characteristics are not clear.It is suited to the demand on the exploration situation in this region to strengthen the research on reservoir characteristics.The fabric features,pore type,petrophysical property and pore throat system of the sandstones were studied by applying these methods,such as cast thin sections,petrophysical test,pore image analysis,mercury injection test and scanning electron microscopy,etc.thus clarifying the sandstone reservoir characteristics.Through analyzing the types of sedimentary microfacies of the sand bodies and the fabric features and principal diageneses of the sandstones,it was thought that the beneficial reservoirs in this region are mainly developed in the sedimentary microfacies sand bodies of the plain distributary river channels,subaqueous distributary river channels and debouch bars;compaction and cementation made the intergranular pores' being greatly lost;and the sandstone reservoir spaces are mainly composed of the intercrystal pores of kaolinite and the solution pores of tuffaceous filler,thus forming the gas reservoirs with fine throats,medium porosities and low permeabilities finally.