低渗透裂缝性油藏自发渗吸渗流作用

Spontaneous imbibition in fractured low permeability reservoir

裂缝和基质中流体渗吸作用是低渗透裂缝性油藏注水开采依据的重要机理。通过自发渗吸实验研究低渗透裂缝性油藏在不同渗透率级别下岩心的渗吸驱油机理,结果表明,该类油藏的油层渗吸体系因毛细管力较高,其渗吸过程为毛细管力支配下的逆向渗吸,毛细管力在吸渗过程中可作为驱油的动力;渗吸早期产油量高,约50 h后产油量明显降低,最后基本不产油。低渗透裂缝性油藏岩心自发渗吸采出程度平均为12%,其自发渗吸采出程度随渗透率的增大而增大,当渗透率大于2×10-3μm2时,自发渗吸采出程度的增加并不明显,孔隙结构越好越有利于自发渗吸作用发生。由于岩心和油藏储层尺寸存在差异,因此对实验结果进行等比例关系处理,使实验值可以用来预测实际油田开发指标。

Imbibition function of fluid in the fracture and matrix is a very important mechanism in low permeability reservoir during water flooding. The oil displacement process of different low permeability cores was studied by imbibition experiment. The result shows that the imbibition process in this type of oil reservoir is an inverse imbibition controlled by higher capillary force in the system,and the capillary force is helpful to the displacement process in imbibition. The imbibition production mainly occurs in the early imbibition process,and becomes fewer and fewer after 50 h in the later period,and there is almost no production in the final period. Mostly,the imbibition oil recovery of the fractured low permeability reservoir is 12% in average and increases with the permeability. But when the permeability is more than 2×10-3μm2,the imbibition oil recovery has few increases. Better pore structure is favorable to spontaneous imbibition. Calculated by isometric method,the experimental result may be applied to forecasting the actual oilfield development for various cores and reservoirs.