陇东地区长9油层组砂岩储层成岩作用精细研究

Diagenesis of sandstone reservoir of Chang 9 oil reservoir set in Longdong area, Ordos Basin

长9油层组是鄂尔多斯盆地陇东地区最具石油勘探潜力的地层单元之一,而有关该地层单元的储层特征研究非常薄弱,成为制约该区长9油层组高效勘探开发的难点。在薄片鉴定、扫描电镜、镜质体反射率和物性分析的基础上,对陇东地区长9油层组砂岩储层特征进行了深入研究。结果表明:有利储层发育的岩性主要为水下分流河道微相的中—细粒岩屑长石砂岩和长石砂岩,是储层发育的物质基础;机械压实和方解石、石英及伊/蒙混层、伊利石、高岭石和浊沸石等次生矿物的胶结作用对孔喉具有不同程度的封堵,是储层孔隙缩减、渗透率降低的主要原因;早期次生绿泥石环边和伊/蒙混层环边胶结物虽然占据了部分孔隙和降低了储层的孔隙度与渗透率,但同时也增强了砂岩的抗压实能力和抑制了次生石英沉淀,是部分原生粒间孔隙得以保存和有利储层发育的重要条件;深部有机酸热液对不稳定组分的溶蚀作用有利于各类次生孔隙的发育,对改善储层的孔渗性贡献最大,是形成优质储层的关键。

Chang 9 oil reservoir set is one of the potential hydrocarbon exploration targets in Longdong area, Ordos Basin, while its reservoir features are not clear and became a constraint on the efficient exploration and development of Chang 9 oil reservoir set. Based on the data of thin section, SEM, vitrinite reflectance and physical properties, this paper studied the reservoir features of Chang 9 oil reservoir set. The results show that the favorable rock types comprise medium to fine-grained lithie arkoses and feldspathic sandstones of underwater distributary channel microfacies, and they are the foundation for the reservoir development. Mechanical compaction and cementation of calcites, quartz, illite/smectite, illite, kaolinite and laumontite occluded the pores in different degrees, and they are the main causes for the reduced porosity and permeability. Early authigenic chlorite rim and illite/smeetite rim cements enhanced the capacity of compaction resistance, inhibited quartz cementation, and saved large numbers of primary intergranular pores. Hydrothermal dissolution by deep organic acid has greatest contributions to improve the porosity and permeability ofthe reservoirs by producing secondary pores, and it is crucial for the development of the high quality reservoirs.