高凝油藏中蜡沉积对开发效果的影响

Impact of wax deposition on development of high pour-point reservoirs

针对高凝油注水开发中蜡析出造成孔隙堵塞、渗透率下降这一问题,推导蜡沉积量与孔隙度、渗透率变化关系,建立水驱油藏渗流场与蜡沉积的耦合模型,对比地表水常温及适当升温(25、35、45、55、65℃)注入时,含水饱和度分布及孔隙度、渗透率降低情况。结果表明:注入冷水导致近井地带温度降至析蜡点以下,蜡晶颗粒大量析出,地层采出水(45℃,不加热)回注时,注水1 a后水井附近30 m温度受到影响,平均累积沉积量约占孔隙体积的4%;随着温度降低,含水饱和度前缘跃变程度减弱,渗透率与初始渗透率比值由93%降到72%;地层冷伤害随时间延长加剧,但增加速率逐渐减小,并逐渐向油层深部推进。

There has been lack of research on the effect of solid wax deposition to for^nation damage. To address this issue, solid deposition modeling was conducted to simulate the process of wax deposition in reservoirs with high pour-point oils, in which the impact of solid deposition on porosity and permeability was considered. The relationship between the amount of wax deposited and the induced porosity and permeability change was derived. The effect of injected water temperature （25-65 益）on the distribution of water saturation,and the reduction of porosity and permeability was investigated. The simulation results show that cold water injection can reduce the reservoir temperature to below the pour-point of oil. One year injection of the produced water （45 益）can also affect the reservoir temperature in near wellbore region up to 30 m,in which the amount of the cumulative wax deposited can be accounted for about 4% of the pore volume. The gradual reduction of reservoir tem-perature can affect the water saturation front and cause the ratio of real permeability to initial permeability dropped from 93 % to 72% . With continuous water injection,the increasing trend of deposited wax volume and permeability reduction near well-bore can be reduced and it spreads to the deep reservoir gradually.