准中沙窝地地区三工河组砂岩致密化过程与机理

Study on Densification Process and Mechanism of Tight Sandstone in Sangonghe Formation of Shawodi Area,Central Junggar Basin

准噶尔盆地三工河组砂岩的致密化过程复杂,致密化机理及致密化过程与油气成藏时间的配置关系不清,直接影响深部油气藏的勘探开发进程。通过铸体薄片观察、扫描电镜分析、荧光分析和碳酸盐胶结物的碳氧同位素分析,建立成岩事件序列,重塑致密化过程,揭示了砂岩致密化与油气成藏间的关系。研究表明,沙窝地地区三工河组砂岩储层为孔洞型储层,经历了复杂的成岩事件改造和叠加。砂岩储层致密化的关键控制因素为压实作用和胶结作用。油气充注时砂岩并不致密,其孔隙度可达20%~28%。砂岩的致密与古油气藏的破坏密切相关,古油藏破坏过程中的BSR反应导致有机成因方解石胶结物的形成,从而使储层物性降低,成为低孔低渗储层。

The densification process of sandstone reservoir in Sangonghe Formation of Junggar Basin is complex,the allocation relationship between the mechanism and process of densification and hydrocarbon accumulation time is not clear,which directly affects the exploration and development process of deep oil and gas reservoirs.Based on casting thin slice observation,scanning electron microscope analysis,fluorescence analysis and the carbon and oxygen isotope analysis of carbonate cements,the diagenetic event sequence is established,the densification process is reconstructed,and the relationship between sandstone densification and hydrocarbon accumulation is revealed.The study indicates that the sandstone reservoir of Sangonghe Formation in Shawodi area is vuggy reservoir,and it has undergone the transformation and superposition of complex diagenetic events.The key control factors of the sandstone reservoir densification are compaction and cementation.The sandstone is not tight during oil and gas filling,and its porosity can reach 20%~28%.The densification of the sandstone is closely related to the destroy of ancient oil reservoir.BSR during the destroy of the ancient oil reservoir is responsible for the formation of organic calcite cements,which reduces the reservoir physical properties to low porosity and low permeability reservoir.