基于注采平衡的合理注气量确定方法研究

Study on Method of Determining Reasonable Gas Injection Volume Based on Injection-Production Balance

确定合理注气量是注气开发方案设计中的重要环节。基于注采平衡要求,结合流体高压物性参数,推导分析低渗油藏注气开发过程中注气量的变化规律,在此基础上引入经济极限换油率,结合数值模拟,形成了一种计算确定合理注气量的方法。以南海西部WSX-1油田A1区块为例,介绍应用合理注气量确定方法的过程。注气突破前,保持同一采油速度,所需注气量随地层压力的降低而减少;在同一地层压力保持水平下,所需注气量随采油速度的增加而增加。注气突破后要维持注采平衡关系,注气量需大幅增加,此时将经济极限换油率作为控制条件,则注气量存在一个最佳经济值。在A1区块如实施顶部注烃类气辅助重力驱油,其合理注气量在突破前为6×10^4m^3/d,突破后为16×10^4m^3/d。

The design of gas injection volume is very important for the preparation of gas injection development plan.Based on the requirement of injection-production balance and the fluid PVT parameters,the variation law of gas injection rate in the process of gas injection development in low permeability reservoirs is deduced and analyzed.On this basis,the economic limit oil exchange rate is introduced,and a method of determining reasonable gas injection rate is formed by combining with numerical simulation.Taking Block A1 of WSX-1 Oilfield in the western South China Sea as an example,the process of determining reasonable gas injection rate is introduced.The results show that the required gas injection decreases with the decrease of formation pressure under the same oil production rate before gas breakthrough.At the same pressure level,the required gas injection increases with the increase of oil recovery rate.After the breakthrough,to maintain the balance between injection and production,the gas injection volume needs to increase substantially.Meanwhile,taking the economic limit oil exchange rate as the control condition,the gas injection volume has an optimal economic value.If top hydrocarbon gas injection assisted gravity flooding is implemented in Block A1,the reasonable gas injection volume is 6×10^4m^3 before breakthrough and 16×10^4m^3 after breakthrough.