西湖凹陷古近系花港组砂岩储层致密化与油气充注关系

Relationship between sandstone reservoirs densification and hydrocarbon charging in the Paleogene Huagang Formation of Xihu Depression,East China Sea Basin

东海盆地西湖凹陷致密砂岩气资源丰富,近年来古近系花港组成为勘探热点层位,但储层的致密化及与油气充注关系不明制约着花港组致密砂岩气的有效勘探和经济开发。在花港组储层特征的基础上,划分及厘定储层成岩作用类型与演化序列,恢复并揭示储层致密化过程及与油气充注的匹配关系。研究表明,西湖凹陷花港组储层砂岩主要经历压实、胶结和溶蚀3种成岩作用,压实作用是导致花港组储层孔隙损失和致密化的根本原因;并经历同生阶段、早成岩阶段(A、B期)和中成岩阶段(A、B期)共3阶段5期次的成岩演化过程;在中成岩阶段A 2期时成岩环境开始由酸性向碱性发生转变,并伴随着晚期碳酸盐、硅质等胶结作用发育以及机械压实作用持续增强,储层逐渐趋于致密化;结合与油气主成藏期(7~0 Ma)的耦合关系将研究区花港组储层划分为3种类型:成藏未致密型储层、成藏同步致密型储层、成藏已致密型储层。研究梳理了西湖凹陷花港组储层特征、成岩演化序列、储层致密化及与油气充注的耦合关系,为下一步研究区致密砂岩气的勘探提供理论支持。

The tight sandstone gas resources in Xihu Depression of the East China Sea Basin are abundant.In recent years,the Paleogene Huagang Formation is a hot spot for exploration.However,the unclear densification of the reservoir and the matching relationship with the oil and gas charge restrict the effective exploration and economic development of the tight sandstone gas of the Huagang Formation.This study reveals the reservoir densification process and its relationship with hydrocarbon charging based on the analysis of sandstone reservoir characteristics,the classification and evolution of diagenesis type and evolution sequence.The study shows that the reservoir sandstone mainly undergoes three diagenesis processes:compaction,cementation and dissolution.Compaction is the root cause of sandstone pore loss and densification in the Huagang Formation reservoir during burial diagenesis.The formation experienced a total of three stages and five periods of diagenetic evolution,including the syngenetic stage,the early diagenetic stage(A,B period)and the middle diagenetic stage(A,B period).At the A 2 period of the middle diagenetic stage,the diagenetic environment began to change from acidic to alkaline,accompanied by cementation of late carbonate and siliceous.When the strength of mechanical compaction continued to increase,the reservoir gradually became denser.Combined with the coupling relationship between oil and gas accumulation period(7-0 Ma),the Huagang Formation reservoirs in the study area are divided into three types:accumulated reservoir,synchronous dense reservoir,accumulated dense reservoir.The study combs the reservoir characteristics,diagenetic evolution sequence,reservoir densification and coupling relationship with hydrocarbon charging in the Huagang Formation of Xihu Depression,providing theoretical support for the exploration of tight sandstone gas in the next study area.