低渗透油藏不稳定注水岩心实验及增油机理

Core Experiment and Stimulation Mechanism of Unstable Waterflooding in Low Permeability Reservoirs

根据长庆油田低渗透油藏典型储集层特征,开展并联岩心和双层岩心实验,模拟非均质低渗透油藏不稳定注水驱油效果。由于岩心实验可视性较差,建立层间非均质和层内非均质数值模拟模型,依据渗流场变化,揭示不稳定注水增油机理。结果表明,对于层间非均质储集层,相较于连续注水,不稳定注水能够促进较低渗透层水驱前缘推进,发挥毛细管力驱油作用,提高较低渗透油层采收率,其中短注长停方式的采收率提高幅度最大;对于层内非均质储集层,不稳定注水能够在储集层中产生压力振荡,使较高渗透层和较低渗透层之间发生流体交渗,增大注入水在较低渗透层中的波及,提高较低渗透层采收率,从而提高油藏总采收率。

According to the typical characteristics of low permeability reservoirs in Changqing oilfield,parallel core and double-layered core experiments were carried out to simulate the effect of unstable waterflooding in heterogeneous low permeability reservoirs.Due to the poor visibility of core experiments,numerical models for simulating interlayer and intralayer heterogeneous reservoirs were established,which may reveal the stimulation mechanism of unstable waterflooding according to the change of flow field.The results show that for interlayer heterogeneous reservoirs,compared with continuous waterflooding,unstable waterflooding can promote the advancement of the flooding front in the layers with lower permeability,and give full play to capillary force in oil displacement,so unstable waterflooding can significantly improve the oil recovery of the layers with lower permeability,and the pattern of short-term injection combined with long-term quit can enhance the recovery rate the most.For intralayer heterogeneous reservoirs,unstable waterflooding can generate pressure oscillations in the layers to enable the fluid percolation between the higher permeability layers and the lower permeability layers,so that the sweep efficiency of injected water in the lower permeability layers is increased and the recovery rate of the lower permeability layers is enhanced,thereby increasing the total oil recovery rate of the reservoir.