孔喉结构对CO_2驱储层伤害程度的影响

Influence of pore throat structure on reservoir damage with CO_2 flooding

在CO_2驱提高采收率的过程中,CO_2与原油、基质矿物的相互作用会对储层孔喉结构造成一定的伤害。为了揭示孔喉结构对CO_2驱储层伤害程度的影响,利用高压压汞、扫描电镜结合核磁共振技术,通过室内物理模拟实验确定岩心样品的孔喉堵塞程度,评价了不同孔喉结构的岩心样品在CO_2驱过程中的伤害程度,明确了CO_2驱储层伤害机理。实验结果表明:CO_2驱过程中产生的沥青质沉积及酸化作用对储层孔隙度的影响很小,实验岩心样品的孔隙度降幅为1%左右,而渗透率受到的伤害程度较高,Ⅲ类孔隙结构岩心的渗透率降幅达20.55%,且渗透率越低、孔喉结构越差,渗透率受到伤害的程度越高;孔喉堵塞程度与孔喉结构参数成正相关关系,孔喉结构越差,中值半径越小,越容易发生孔喉堵塞;Ⅰ类孔隙结构岩心的孔喉堵塞程度较低,Ⅲ类孔隙结构岩心的孔喉堵塞程度明显增高,最高可达到34.32%。该研究结果可为CO_2驱现场高效应用提供依据。

In the process of enhancing oil recovery by CO2 flooding,the interaction of CO2 with crude oil and matrix minerals will damage the pore throat structure of reservoir.In order to reveal the influence of pore throat structure on reservoir damage during CO2 flooding,nuclear magnetic resonance(NMR)combined with high pressure mercury injection and scanning electron microscopy was used to determine the plugging degree of pore throat in core samples through laboratory physical simulation experiments,and the damage degree of core samples with different pore throat structures during CO2 flooding was evaluated,to clarify the reservoir damage mechanism.The experimental results show that asphaltene deposition and acidification produced during CO2 flooding have little effect on reservoir porosity,and the porosity of core samples decreased by about 1%.While the damage to permeability is greater,and the permeability of core with type Ⅲ pore structure decreased by 20.55%.The lower the permeability and the worse the pore throat structure,the greater the damage to permeability.The plugging degree of pore throat is positively correlated with pore throat structure parameters.The worse the pore throat structure is,the lower the median radius is,the easier the pore throat plugging will occur.The rate of pore throat plugging in type I pore structure cores is low,and the degree of pore throat plugging in type III pore structure cores is obviously increased,up to 34.32%.The results can provide a basis for efficient application of CO2 flooding in the field.