低渗特低渗注水储层梯形保护技术研究与应用

Study and Application of Trapezoidal Protection Technology for Low and Ultra-Low Permeability Reservoirs Subjected to Water Injection

在低渗特低渗储层注水过程中,通常存在水化膨胀、水锁、贾敏等严重储层损害,增大渗流阻力与注水压力损耗,使注水压力高、注水压力上升速率快、吸水指数低,甚至注不进水,注水储层长期欠注,且对注水储层实施解堵的效果虽然显著但有效期短,导致见效井产量和油气采出程度低。为解决该难题,目前通常往注入水中长期不间断地加入防膨剂、表面活性剂来减缓水化膨胀和毛细管效应导致的注水储层损害,但由于需长期补加药剂、成本高、效果也不理想。基于储层水化膨胀不仅与外来流体矿化度有关,而且与矿化度从高到低的降低速率也存在密切关系的认识,研发/筛选了小阳离子型梯形防膨保护剂A和梯形润湿保护剂B。按照一定时间间歇、从高到低的浓度梯度顺序往注入水中加入梯形防膨保护剂A和梯形润湿保护剂B,直至最后使储层适应注入水性质而无需加入梯形保护剂,即可控制注水储层水化膨胀和毛细效应发生。大量节省药剂使用量和成本,达到“经济、高效”补充储层能量并大幅提高水驱油效率的目的。称该技术为注水储层梯形保护技术。现场应用表明,在同一注水工作制度下,较低的成本而大幅提高了单井日注水量、大幅缓减了注水压力上升速率,满足了配注要求,为低渗特低渗注水储层能量补充提供了一项关键技术。

In the process of injecting water into low and ultra-low permeability reservoirs,serious damage to reservoirs often occurs,such as hydration swelling,water lock,and Jamin effect,increasing flow resistance and water injection pressure loss,and giving rise to high water injection pressure,rapid increasing in water injection pressure,low water absorption index,and even inability to get water injected into reservoir.As a result,reservoirs subjected to water injection have insufficient water injected into them for a long time,and the effectiveness of plugging removal measures cannot last long in such reservoirs,though they are effective.Consequently,beneficiary wells have low production and oil and gas recover percent.In order to solve this problem,it is a common practice to inject anti-swelling agent and surfactant into the injection water for a long time without interruption to mitigate the damage to reservoirs caused by hydration swelling and capillary effect.However,due to the demand for long-term injection of chemicals,production cost is high,and the effect is not so satisfactory.In this study,small cationic trapezoidal anti-swelling protectant A and trapezoidal wetting protectant B were developed and screened out based on the understanding that the hydration swelling of reservoirs is not only related to the TDS of foreign fluid,but also has a close relationship with the decrease rate of TDS.Both of them were injected into the injection water at a certain time interval and a concentration gradient from high level to low level until reservoirs were adapted to the properties of the injection water and demanded no more injection of protectants.This means that,at this point,hydration swelling and capillary effect of the reservoirs subjected to water injection were controlled.With the two protectants,a lot of chemicals and costs have been saved,and cost-effective replenishment of reservoir energy and significant increase in the efficiency of water flooding have been achieved.This technology is referred to as trapezoidal protection technology for reservoirs subjected to water injection.Field application shows that,under the same water injection regime,the daily water injection volume of a single well was significantly increased at a lower cost,and the rise rate of injection pressure was significantly slowed down,which met the requirements of injection allocation,providing a key technology to replenish energy for low and ultra-low permeability reservoirs subjected to water injection.