鄂尔多斯盆地高桥地区盒8段砂岩储层致密成因

运用常规薄片、铸体薄片、扫描电镜及恒速压汞等实验手段,对鄂尔多斯盆地高桥地区盒8段储层特征进行研究,并以孔隙演化过程为线索分析了储层致密成因。研究结果表明:盒8段储层主要为岩屑石英砂岩、石英砂岩与岩屑砂岩,成分成熟度和结构成熟度均较高,储层物性差;砂岩分选性好,初始孔隙度整体较高,平均可达34.7%;受岩石组分、埋深及煤系烃源岩酸性流体的影响,压实作用强烈,破坏了大约20.4%的原生孔隙度,胶结作用破坏了其余13.9%的原生孔隙度,原生孔隙几乎被破坏殆尽;早期溶蚀产生的孔隙被压实作用破坏,而晚期溶蚀作用较弱,仅增加了大约3.4%的次生孔隙度,难以大幅度改善储层物性。因此,成岩期原生孔隙被破坏殆尽及次生孔隙形成较少共同导致该区储层致密。

Origin Mechanism of Tightness from the He 8 Section Sandstone Reservoir in Gaoqiao Area of Ordos Basin,China

Through conventional section, cast section, SEM samples and constant-rate mercury injection technology, characteristics of He 8 reservoir in Gaoqiao area of Ordos Basin were studied, and its origin mechanism of tightness was analysed based on pore evolution. The following conclusions were obtained. The rock types of He 8 reservoir were mainly lithic quartz sandstone, quartz sandstone and lithic sandstone, the compositional maturity and the textural maturity of sandstone were high, but its reservoir property was low. The selectivity of sandstone was good, the initial porosity overall was higher, about 34.7% on average. On the one hand, due to the effects of rock components, buried depth, acidic fluids of coal measure hydrocarbon source rock, and the compaction was strong, 20.4% primary porosity was destructed. On the other hand, cementation destroyed 13.9% of the remaining primary porosity, leading to the complete loss of most primary pore. The compaction was destructive for the pore formed by the early dissolution, at the same time, the later dissolution was weak, only increased by 3.4% secondary porosity, it was hard to improve the reservoir property remarkably. So, in the diagenesis stage, the complete loss of most primary pore and the less formation of secondary pore common lead to the tight reservoir.