鄂尔多斯盆地西部长6砂岩致密化过程分析

通过储层物性、铸体薄片和带能谱仪的扫描电镜，对鄂尔多斯盆地西部长6砂岩的致密化过程进行定量研究。研究表明，鄂尔多斯盆地西部长6超低渗透砂岩的原始沉积物孔隙度为39.3%，渗透率为22400×10-3 μm2，其致密化过程分为2个阶段；早成岩阶段的压实作用和方解石及绿泥石膜胶结作用，导致砂岩的孔隙度和渗透率急剧下降到8.0%和0.17×10-3 μm2，砂岩转化为超低渗透储层；中成岩阶段A期的油气充注成藏过程中，油气携带有机酸性流体进入超低渗透储层，长石与有机酸性流体发生反应，产生长石溶蚀孔隙，使孔隙度和渗透率提高到11.6%和0.61×10-3 μm2；鄂尔多斯盆地西部长6超低渗透砂岩致密与成藏的配置关系为"先致密后成藏，边成藏边扩容增渗"。 

ANALYSIS ON DENSIFICATION PROCESS OF CHANG 6 SANDSTONES IN WESTERN ORDOS BASIN

By core physical property, casting slice, scanning electron microscope analysis with energy disperse spectroscopy, the densification process of Chang 6 sandstones in western Ordos Basin was studied quantitatively. The study showed that the initial porosity and permeability of sandstones in the area were 39.3% and 22400×10-3 μm2 respectively, and its densification process was divided into two stages. In the course of early diagenesis stage, both calcite and chlorite coat cements and mechanical compaction caused the sandstones into ultra-low permeability reservoir whose porosity and permeability were 8.0% and 0.17×10-3 μm2 apart. During hydrocarbon accumulation in middle diagenesis stage A, hydrocarbon with organic acid came into this ultra-low permeability sandstones, and under organic acid circumstance feldspar dissolution formed secondary pore, which made porosity and permeability up to 11.6% and 0.61×10-3 μm2 individually. So the relationship between the densification process of Chang 6 sandstone and hydrocarbon accumulation is first densification then accumulation and accumulation with increased porosity and permeability.