向斜成藏理论及其石油地质意义

Theory of petroleum accumulation in syncline and its significance to petroleum geology

传统的石油成藏理论适用于中高渗透储层,流体的渗流特征是达西渗流,主要作用力是浮力,油气分布在构造高部位或砂体高部位,主要是寻找圈闭。但是在低-超低渗透储层和致密储层中,流体的渗流特征是非达西渗流,传统理论不再适用,油水不能发生正常的重力分异,流体在超压作用下以幕式排烃方式发生初次运移,石油在储层中运移要以非达西渗流方式通过变形才能缓慢通过,这种运移必然降低流速产生滞留效应导致石油在低部位大量滞留并聚集成连续油藏。这种滞留油藏的产生,可以形成背斜区圈闭含油、斜坡区相对高部位含水、而相对低部位却连续含油的油水倒置现象。由于滞留油藏无需构造和岩性边界圈闭,无需统一压力系统和油水边界,改变了传统上的圈闭找油模式,拓展了油气藏的概念,形成了低-超低渗透储层、非常规、致密油等成藏研究的理论基础。向斜成藏理论的提出,是对传统石油成藏理论的重要补充,拓展了油气勘探领域,使油气勘探从构造高部位转向构造低部位,增大了石油资源量,对勘探开发具有重要的指导作用。

The conventional petroleum geology theory is suitable for the reservoirs with high permeability and fluid flows obeying Darcy law with buoyancy effect mechanism,and oil and gas are situated at the high position of structure and sand body,and they are always structural reservoirs.But this theory does not apply to the reservoirs with low and ultra-low permeability or tight reservoirs where fluid flows obey non-Darcy law,and oil and gas cannot be separated by gravitation.On the condition of overpressure expulsion,flow primarily migrates as episodic expulsion manner,the oil droplets gradually deform and pass through the pore throats as non-Darcy flow.This low speed migration must lead to the stagnant mechanism that oil stagnates and accumulates in the lower area and form continuous reservoirs.This stagnation accumulation reservoirs will cause the phenomenon that oil accumulates in anticline area,or oil accumulates at low position of slope but water accumulates at high position,which is the oil-gas inversion.The stagnation accumulation reservoirs which have no structure,no lithology traps,no unified temperature-pressure systems and oil-water contacts have changed the traditional trap exploration method,expanded the concept of reservoir,and formed the fundamental theory for the research field such as reservoirs with low and ultra-low permeability and unconventional and tight reservoirs.Theory of petroleum accumulation in syncline is an important supplement to traditional petroleum geology.This theory expands the exploration area,changes the exploration target from high position of structure to low position,extremely increases the petroleum source and is regarded as important guiding principle for the petroleum exploration and development.