火山碎屑岩储层异常高孔隙成因——以南贝尔凹陷东次凹北洼槽为例

Origin of anomalously high porosity in pyroclastic reservoirs: a case study on the northern region of the east sub-sag in Nanbeier sag

南贝尔凹陷东次凹北洼槽铜钵庙组—南屯组发育火山碎屑岩储层,在纵向上存在5个异常高孔隙带,其深度分布范围分别为1 450～1 500m、1 560～1 775m、1 840～2 030m、2 110～2 230m、2 330～2 520m。针对上述5个异常高孔隙带,应用普通薄片、铸体薄片、铸体图像分析、扫描电镜、黏土矿物X射线衍射等多种测试手段,对其成因进行研究。研究结果表明:异常高孔隙的形成主要与凝灰质成分的溶蚀溶解作用有关,凝灰质成分易于发生溶蚀是形成异常高孔隙的根本原因;有机质热演化过程中产生的有机酸是溶蚀溶解作用得以进行的主要营力;有利的沉积相带空间配置关系是控制异常高孔隙带空间分布的主要因素;高岭石向绿泥石转化产生的无机酸对于异常高孔隙的形成有一定贡献。

Pyroclastic rocks of Tongbomiao-Nantun Formation are an important oiI reservoir in the northern region of the east sub-sag in Nanbeier sag. Vertically there are five anomalously high porosity zones at depths of 1 450- 1 500 m, 1 560-1 775 m, 1 840-2 030 m, 2 110-2 230 m and 2 330-2 520 m, respectively. The origin of the anomalously high porosity zones was studied by applying vari- ous measurements, such as normal thin-section, cast thin-section, cast image analysis, scanning electron microscope and X-ray dif- fraction of clay minerals. The result showed that the genesis of anomalously high porosity is directly bound up with the corrosion and dissolution of tuffaceous components. The susceptibility of tuffaceous components to corrosion is a key reason for the formation of a- nomalously high porosity, and the organic acid generated in thermal evolution of organic matter is a main force to drive corrosion and dissolution. The suitable space relation of sedimentary facies is a primary factor controlling the distribution of anomalously high po- rosity zones. Besides, the inorganic acid produced during the process of transformation from kaolinite to chlorite can make a certain contribution to anomalously high porosity.