砂岩储集层致密与成藏耦合关系——以鄂尔多斯盆地西峰—安塞地区延长组为例

Coupling relationship between sandstone reservoir densification and hydrocarbon accumulation: A case from the Yanchang Formation of the Xifeng and Ansai areas, Ordos Basin

以鄂尔多斯盆地西峰地区长8段和安塞地区长6段为研究对象,通过镜下包裹体荧光鉴定、孔隙度演化模拟以及石油充注临界实验,确定西峰—安塞地区三叠系延长组砂岩储集层致密与成藏时间的先后顺序。镜下包裹体荧光鉴定发现,延长组砂岩储集层普遍存在石英次生加大边夹沥青和烃类包裹体现象;孔隙度演化模拟表明,成藏期延长组砂岩储集层孔隙度大于10%,未达到致密状态;石油充注临界条件实验发现当西峰地区长8段和安塞地区长6段砂岩孔隙度小于10%时,即使在加压条件下,石油仍不能充注进入砂岩。综合研究表明鄂尔多斯盆地西峰—安塞地区延长组砂岩储集层先成藏后致密,为典型的"后成型"致密砂岩油藏。成藏期之后,压实作用和自生矿物胶结作用才使得延长组砂岩储集层致密化。

The Chang 8 member of the Xifeng Area and the Chang 6 member of the Ansai Area are taken as examples to define the relationship between the sandstone densification and accumulation from fluid inclusion identification, simulation of sandstone porosity evolution, and analysis of oil charge critical experiment. The fluid inclusion fluorescence shows that there is quartz overgrowth containing the residual asphalt and hydrocarbon inclusions existing in the sandstone reservoir of Yanchang Formation. The simulation of porosity evolution shows that the sandstone reservoir was not tight sandstone during the key accumulation period for the porosity was greater than 10%. The oil charge critical experiment indicates that the oil cannot charge into the sandstone if the porosity is less than 10% in Xifeng and Ansai, even under pressurized conditions. The results demonstrate that the Yanchang Formation of Xifeng Area and Ansai Area in the Ordos Basin is a typical ＂postforming＂ tight sandstone hydrocarbon reservoir in which the sandstone undergoes densification after oil accumulation. The compaction and cementation following the oil charging lead to the densification of sandstone.