鄂尔多斯盆地榆林气田山西组2段砂岩成岩作用及孔隙演化

Diagenesis and Porosity Evolution of the Lower Permian Shanxi -2 Member Sandstone in Yulin Gasfield, Ordos Basin

榆林气田下二叠统山西组2段为一套辫状河三角洲沉积,储集岩主要为石英砂岩、岩屑石英砂岩,平均孔隙度5.36%,平均渗透率4.58×10-3μm2,是典型的低孔低渗储层。以岩心观察为基础,结合薄片鉴定、扫描电镜、阴极发光及物性分析等资料进行研究,认为山2段砂岩经历了压实作用、胶结作用、交代作用、溶解作用、粘土杂基的充填作用等多种成岩作用,目前已达到晚成岩阶段A期。成岩作用是控制该区储层物性的关键因素,孔隙演化经历了原生孔隙的破坏、次生孔隙的形成和次生孔隙的破坏三个阶段。各类次生孔隙占总孔隙度的55.3%,其中岩屑溶孔18.4%,粒间溶孔10.8%,晶间孔26.1%。

Lower Permian Shanxi 2 sandstone was a set of braided river deltaic sediments, which is comprised of quartz sandstone and lithic quartz sandstone.It is a typical gas reservoir with low porosity(average of 5.36%) and low permeability (average of 4.58×10-3μm2) in Yulin Gasfield, Ordos Basin. It is shown that having undergone compaction, cementation, metasomatism, dissolution and filling of clay matrix, the diagenetic evolution of the sandstone is within late diagenetic stage (Stage A). Porosity evolution in the rock has experienced destruction of primary porosity and construction and then re-destruction of secondary porosity. By statistical, secondary porosity reaches 55.3% of the gross porosity,which indicates that the diagenesis has a great effect in control of the reservoir property in this area.