白云凹陷北坡珠江组陆架边缘三角洲前缘砂体储层特征及控制因素

Continental shelf margin delta front sandstone reservoirs in the Zhujiang Formation,northern Baiyun depression,Zhujiangkou Basin: Characteristics and controlling factors

采用铸体薄片、岩石薄片、扫描电镜和压汞实验、物性分析等测试资料,对珠江口盆地白云凹陷北坡珠江组陆架边缘三角洲前缘砂体储层特征及控制因素进行研究。结果表明,该储层主要为灰色中细粒岩屑砂岩,成分成熟度、结构成熟度均较低。储集空间以次生孔隙为主,其次为剩余原生粒间孔、原生孔隙等。储层具有排驱压力较高、配位数较高、孔喉半径小和孔喉分选性较差的孔隙结构特点,为中-低孔、中-低渗型储层。储层发育受沉积相和成岩作用的复合控制,水下分流河道砂体储集物性明显优于其它微相砂体。成岩作用过程主导储层物性变化,砂岩储集体中的原生储集空间因机械压实作用、胶结作用而大幅降低,后期溶蚀作用产生较多的次生储集空间,尤其是长石的溶蚀极大改善了本区储层物性,导致储集体中溶蚀性次生孔隙为主要的储存空间。

The characteristics and controlling factors are dealt with on the basis of thin section identification,scanning electron photomicrographs,mercury injection experiment and physical properties of the continental shelf margin delta front sandstone reservoirs in the Zhujiang Formation,northern Baiyun depression,Zhujiangkou Basin.The sandstone reservoirs dominated by grey medium- to fine-grained lithic sandstones are characterized by relatively low compositional and textural maturity,abundant secondary porosities with minor amount of residural primary intergranular porosity and primary porosity,relatively higher driving pressures and coordination numbers,relatively smaller pore throat sizes and poor sorting,and thus interpreted as the reservoir rocks with the medium to low porosity and medium to low permeability. The sandstone reservoirs are primarily constrained by sedimentary facies and diagenesis. The delta front subaqueous distributary channel microfacies is believed to be most favourable facies zone for the development of the sandstone reservoirs,followed by the delta front channel mouth bar microfacies.The destructive diagenesis such as mechanical compaction and cementation may reduce the porosity and permeability while the constructive diagenesis such as dissolution and cracking may facilitate the improvement of the porosity and permeability of the sandstone reservoirs.