镇泾地区长8、长6段储层特征及成岩作用对孔隙的改造

研究鄂尔多斯盆地镇泾地区三叠系延长组长8、长6段砂岩储层特征,探讨成岩作用对储层孔隙演化的影响。通过钻井岩心、薄片鉴定、扫描电镜、物性分析等资料,对长8、长6段储层特征及成岩作用进行了系统研究,开展孔隙演化定量计算,定性和定量分析了成岩作用对孔隙的改造。结果表明:长8、长6段属典型的低孔、低渗储层,成分成熟度中等,结构成熟度低;储集空间类型主要为粒间孔、粒间溶孔、长石溶孔和岩屑溶孔,少见溶(裂)缝;压实(压溶)、溶蚀、胶结作用为最主要的成岩作用。定量计算表明,砂岩原始孔隙度平均为35.96%,砂岩储层主要经历了早期强压实减孔阶段(-17.38%)、中晚期胶结作用减孔阶段(-16%)和晚期溶蚀作用增孔阶段(+6.82%)。早期强压实作用是长8、长6段砂岩储层低孔低渗的主要原因,胶结作用则进一步强化了低孔低渗特征。

Reservoir characteristics of Chang 8 and Chang 6 members of Yanchang Formation in Zhenjing area of Ordos Basin and pore transformation caused by diagenesis

Based on the application of drilling core,thin section identification,scanning electron microscope and physical property analysis,the reservoir characteristics and diagenesis of Chang 8 and Chang 6 members are systematically studied.Quantitative calculation of pore evolution is carried out and the diagenesis modification of pores is analyzed qualitatively and quantitatively in order to study the characteristics of sandstone reservoirs in Chang 8 and Chang 6 members of Triassic Yanchang Formation in Zhenjing area,Ordos Basin and discuss the influence of diagenesis on reservoir pore evolution.The results show that the Chang 8 and Chang 6 members are typical low porosity and low permeability reservoirs with medium compositional maturity and low structural maturity.The types of reservoir spaces are mainly intergranular pores,intergranular dissolved pores,feldspar dissolved pores and debris dissolved pores,with minor dissolved(fractured)fractures.Compaction(pressure solution),dissolution and cementation are the most important diagenesis.Quantitative calculation shows that the average original porosity of sandstone is 35.96%,and the sandstone reservoir mainly experienced the stage of early strong compaction and porosity reduction(-17.38%),the stage of middle and late cementation and porosity reduction(-16%),and the stage of late dissolution and porosity increase(+6.82%).Correlation analysis shows that the early strong compaction is the main reason for low porosity and low permeability of sandstone reservoirs in Chang 8 and Chang 6 members,while cementation further strengthens the characteristics of low porosity and low permeability in the area.