鄂尔多斯盆地东南缘延长组长6砂岩孔喉类型及演化特征

鄂尔多斯盆地东南缘宜川-旬邑地区中生界延长组长6段主要为三角洲前缘沉积环境,局部发育湖底滑塌扇体.岩心观察、薄片分析、扫描电镜及压汞测试表明:长6砂岩的孔隙类型以残余原生粒间孔为主;其次为溶蚀孔隙,以长石溶孔为主;见少量构造裂缝及微缝.多是片状喉道和弯片状喉道,喉道小,孔隙结构差,以细孔-微喉型为主.砂岩初始孔隙为34.59%,压实作用和胶结作用损失27.81%孔隙度,溶蚀作用仅新增次生孔隙0.84%,造成长6砂岩现今平均孔隙度在7%～8%之间,形成储集空间以残余原生粒间孔为主的低孔-超低孔致密砂岩储层.

THE PORE TYPES AND ITS EVOLUTION CHARACTERISTIC IN THE CHANG 6 SANDSTONES IN THE SOUTHEAST MARGIN OF ORDOS BASIN

The Cenozonic Chang 6 formation in the Yichuan-Xunyi area on the southeast margin of Ords basin occurs mainly under the front sedimentation environment of delta and locally under sublake-fan.The core and slice observation and calculation and the scanning electron microscope and pressure Hg analysis show that sandstones of Chang 6 formation are mostly feldspar detritus sandstone and detritus feldspar sandstone and the residual protozonal intergranular pore and the dissolution pore are the main pore types with the poor pore structure.Compaction and cementation reduced 27.81% of the pore and dissolution increased 0.84% of the pore thus the protozonal porosity of the sandstones is reduced from 34.59% to 7%-8% with the tight sandstone reservoir formed.The reservoir space is mostly the protozonal intergranular pore.