鄂尔多斯盆地南部山西组——下石盒子组致密砂岩成岩演化

鄂尔多斯盆地南部上古生界山西组—下石盒子组致密砂岩成岩作用影响着储层物性,但缺乏深入研究,严重制约了进一步的勘探开发。根据地质特征,通过铸体薄片、扫描电镜、阴极发光,结合孔渗数据研究了鄂尔多斯盆地南部山西组—下石盒子组致密砂岩储层特征及成岩演化规律。结果表明:鄂尔多斯盆地南部山西组—下石盒子组致密砂岩成岩作用复杂,包括破坏性的压实、压溶、胶结作用,建设性的溶解作用及保持性的高岭石、绿泥石胶结作用。压实作用是造成原生孔隙损失的主要因素,其次为胶结作用。成岩演化经历了同生期—早成岩A期、早成岩B期、中成岩A期及中成岩B期4个阶段,早成岩期结束时,石英砂岩原始孔隙降为9.2%,岩屑石英砂岩及岩屑砂岩原始孔隙降为16.2%,晚成岩作用至今,石英砂岩孔隙度持续减少到2%以下,岩屑石英砂岩由于溶蚀作用,孔隙度有所增加,为3%。鄂尔多斯盆地南部上古生界山西组—下石盒子组致密砂岩成岩特征及成岩演化可进一步深化该区储层致密化和优质储层成因认识,指导后期的油气勘探开发。

Diagenetic evolution of tight sandstone of Shanxi-Lower Shihezi formations in the southern Ordos Basin

The diagenesis of the tight sandstones affected the physical properties of the reservoir in the ShanxiLower Shihezi formations. The relative research is poor,which severely restricted further exploration and development. Based on the study of geological conditions,the characteristics and the diagenetic evolution of the tight sandstone were studied through analysis and testing methods such as cast slices,scanning electron microscopy,cathodoluminescence,and related porosity and permeability data. The results showed that the diagenesis of the tight sandstones was complex,including destructive,constructive and retentive diagenesis. Compaction,pressure solution and cementation were destructive diagenesis,dissolution was constructive diagenesis,while kaolinite and chlorite cementation were retentive diagenesis. Compaction was the major factor of porosity loss,followed by cementation. The diagenetic evolution was divided into syndiagenetic phase,early A phase,early B phase,middle A phase and middle B phase. After early phase,the original porosity of quartz sandstone reduced to 5.2%,while the original porosity of detrital quartz sandstone reduced to 16.2%. From the late phase to present,the porosity of quartz sandstone had continued to decrease by less than 2%,while the porosity of debris sandstone increased to 3% for the reason of dissolution. The analysis of diagenetic characteristics and diagenetic evolution had a great significance for further understanding of the characteristics of tight sandstone reservoirs,and the later petroleum exploration and development in the south of Ordos Basin.