塔里木盆地塔中16石炭系低含油饱和度油藏成因机理

Genetic Mechanism of Carboniferous Low-Oil Saturation Reservoirs in Tazhong-16 Well Block

塔中16石炭系油藏位于塔里木盆地塔中地区,具有低含油饱和度的油层分布在相对低孔-渗的储层中,而高GOI值的水层分布在高孔-渗储层中的特征.为阐明其特殊的成因机理,利用石油包裹体丰度（GOI）分析方法,结合圈闭演化历史开展了详细研究.结果表明,现今油层和水层的样品都具有较高的GOI值（5.6%～32.0%）,暗示在地质历史时期形成了古油层,GOI值与孔隙度和渗透率具有正相关关系.高孔-渗储层优先充注油气,形成具有高含油饱和度、高GOI值的油层,低孔-渗储层充注油气较少,形成具有低含油饱和度,相对低GOI值的油层.而古油层泄漏的过程中,高孔-渗储层中聚集的油气也更容易泄漏,形成高GOI值水层,低孔-渗储层中充注的油气泄漏较少,形成低含油饱和度油层.综合分析认为：不同孔-渗条件储层的差异充注和成藏后的差异泄漏,是塔中16石炭系低含油饱和度油藏的形成机理.深化并研究了多期演油气区的成藏机理,对于深入认识多期演化背景的致密砂岩油气勘探潜力具有指导意义.

The Tazhong-16Carboniferous oil reservoir,located in the central Tazhong area,has the characteristics of low-oil saturation layers preferentially accumulated in the low porosity and permeability sandstone reservoirs and water layers exist in high porosity and permeability reservoirs.Grains containing Oil Inclusion（GOI）method was applied to further understand the mechanisms of the low-oil saturation layers in this field.Most GOIvalues in both current oil layers and water layers range from 5.6%to 32%,suggesting abundant paleo-oil charge and large amount of oil leak from filled oil layers.The GOIvalues have positive correlation with high porosity and permeability,indicating oil preferentially charge reservoirs with high porosity and permeability forming oil layers with high-oil saturation.When oil leaks from a trap,the larger pores are drained more easily than the smaller ones,resulting in a decrease of residual oil saturation with increasing porosity and permeability in drained reservoirs.The framework of the Tazhong-16Carboniferous trap changed during the Late Triassic can be responsible for the large amount of oil leak.Preferential oil charge and preferential leak of the accumulated oil in reservoirs with different porosity and permeability during oil remigration is the mechanism of the formation of water layers with high GOIvalues and the low-oil saturation layers.Petroleum reservoirs in basins with complex evolution history usually experienced multiple phases of petroleum charge and post-accumulation alteration process.Thus,understanding the origin,charge history and physicochemical alteration processes associated with oil accumulation and preservation become critical for successful petroleum exploration in basins with complex evolution history.