东海盆地西湖凹陷平湖构造带致密砂岩储层成岩成藏的耦合关系

Coupling relationship between diagenetic evolution and oil and gas accumulation of tight sandstone reservoir in Pinghu structural belt in Xihu depression, Eastern Sea Basin

以平湖构造带平湖组中下段为例,基于烃源岩及油气的地球化学特征,尝试利用流体包裹体系统分析技术厘定的油气充注史结合储层岩石学恢复的孔隙度演化史,得到研究区致密砂岩储层成岩演化与成藏之间具有＂独特＂的耦合关系,从而识别出该区存在2种不同成因类型的致密砂岩油气藏。即第1期（16.2~13.8 Ma）油充注于储层致密化之前,在浮力作用下进入储层,形成＂后成型＂致密油藏;第2期（5~0 Ma）油气充注于储层逐渐致密化时期,在浮力和毛细管压力共同作用下进入储层,形成＂边成藏边致密型＂油气藏。同时分别对应2种不同的成藏模式,即＂早期侧向充注古构造、晚期改造＂的复合成藏模式和＂原油从源岩垂向充注于圈闭,同时受后来天然气气侵改造＂的成藏模式。

Taking Pinghu group of middle and lower section in Pinghu structural belt as an example, based on the geochemical characteristics of hydrocarbon source rocks and oil and gas, this paper a unique coupling relationship between diagenetic evolution and oil and gas accumulation of tight sand reservoir in the study area was demonstrated by combining hydrocarbon charging history by fluid inclusion system analysis technology and porosity evolution which was restored by reservoir petrology. It identified two different genetic types of tight sandstone oil and gas reservoirs. The first phase of oil during 13.8-16.2 Ma charged before reservoir densification by buoyancy, which belongs to ＂subsequent＂ tight sand oil reservoir. The second phase of oil and gas during 5-0 Ma charge accompanied with reservoir densification by buoyancy and capillary pressure. Two different genetic types of tight sandstone oil and gas reservoirs have different accumulation models. One is oil laterally migrated to paleostructure in early stage, which was reformed by tectonic movement in later stage. The other is oil migrated upward from hydrocarbon source rocks to trap, which was reformed by gas washing.