特低渗透—致密砂岩成岩作用特征及其差异性分析——以鄂尔多斯盆地陇东地区延长组为例

根据大量岩石薄片观察、扫描电镜和X?衍射分析,研究陇东地区典型区块三叠系延长组长6—长8段特低渗透—致密砂岩的岩石学特征、孔隙成因等,探讨成岩作用类型及主要控制因素,剖析延长组长6与长8成岩作用的差异性。研究表明:该区砂岩经历的成岩作用主要有压实作用、胶结作用、溶解作用等,建立了三角洲和重力流成岩演化模式序列,研究区目前处于中成岩A?B期;并从储层形成的物源、沉积环境、古气候等方面的差异性,探讨了华庆区块长63和马岭区块长81成岩作用差异性的成因。由于长6较长8粒度细、杂基含量较高,其压实作用强,原生粒间孔保存较少,早期绿泥石膜胶结不发育,含铁碳酸盐胶结物及自生伊利石含量高,砂岩储层物性较差。

Diagenesis characteristics and difference analysis of ultra-low permeability and tight sandstone: Taking Yanchang Formation in Longdong area of Ordos Basin as an example

Based on plenty of rock thin section observation, scanning electron microscopy （SEM） and X-ray diffraction analysis, such characteristics of petrology and pore formation of low permeable-tight sandstone petrology members Chang-6 and Chang-8 of Yanchang Formation, furthermore, the diagenesis and its main controlling factors are discussed, thus the difference of sandstone reservoir in members Chang-6 and Chang-8 of Yanchang Formation are analyzed. The research results indicate that the diagenesis sandstone experienced includes compaction, cementation, dissolution and so on, the sequence model of diagenetic evolution of sedimentary setting of delta and sediment gravity flow was established, the rock record of the study area is experiencing the phase A-B of medium-term diagenesis. Forthermore, the difference of sandstone reservoir in Chang-63 sub-member of Yanchang Formation in Huaqing area and Chang-81 sub-member of Yanchang Formation in Maling area in Ordos Basin are discussed, primarily in the terms of the provenance, sedimentary environment, the palaeoclimate of reservoir formation. Comparing the sandstone reservoirs of member Chang-6 with that of Chang-8 of Yanchang Formation, such differences, i.e., the finer granularity, higher proportion of matrix content, stronger compaction, less primary intergranular pore, less early chlorite membrane cementation, higher content of iron carbonate cement and authigenic illite content, result to the poor reservoir physical property.