浅薄层稠油油藏氮气泡沫调驱适应性研究

Flexibility study on nitrogen-foam flooding for shallow-thin heavy oil reservoirs

针对河南油田某区块稠油粘度大、油层厚度薄、蒸汽吞吐后期汽窜超覆现象严重,急需转变热采开发方式,利用室内物理模拟实验和数值模拟方法,进行了氮气泡沫调驱的适应性研究。实验结果表明,发泡剂静态性能综合评价指数有利于发泡剂的统一筛选;在蒸汽和发泡剂基本注入参数相同的条件下,热泡沫(蒸汽伴随)的发泡剂利用率较高,单位质量发泡剂产油量比冷泡沫(蒸汽不伴随)高24.4%;多层合注合采时各层启动压差受泡沫注入方式和渗透率级差的双重影响,冷泡沫注入时各级启动压差随渗透率级差呈线性增长,热泡沫注入时则呈对数式增长;此外,不同渗透率层对采出程度贡献度差异较大,泡沫对中、低渗透层动用率相近。在实验基础上,利用数值模拟得到的氮气泡沫调驱最优方案为:采用氮气泡沫段塞式注入,在蒸汽注入速度为4.5t/(d·m),发泡剂质量分数为0.5%的条件下,泡沫段塞最佳注入量为0.01倍孔隙体积,最佳地面气汽比为20∶1,最佳采注比为1.3∶1,最佳泡沫段塞停注时间为90d。

Due to high viscosity, thin reservoir and the serious situation of steam channeling and overriding, it is urgent for Henan specific oil field to change its development pattern. Based on physical experiments and numerical simulation, the suitability of nitrogen-foam flooding is studied. As indicated in the experiments, it is beneficial to use foam static comprehensive evaluation index to unify the criteria of foam screening. Under the same condition of steam and foam injection parameters, compared with cold foam flooding,the oil production of unit foaming agent of hot foam flooding stays 24.4 percents higher. In the development of multi-layer co-injection and combined reservoir, start-up pressure of each layer is affected by foam injection pattern and permeability contrast. When injected with cold foam, the start pressure of each layer increases linearly along with the increase of permeability grade. But, for hot foam, this value increases in function of power. Because of permeability divergence, each layer s contribution to the recovery percent is different,and to middle and low level permeability layers, foam has the similar producing degree. The optimized program of nitrogen-foam flooding is determined that the appropriate foaming injection mode is slug injection, and on the condition that the steam injection rate is 4.5t/(d·m) and foaming agent mass concentration of 0.5%, the optimum injection volume is 0.01 PV; the optimum gas(steam)-gas(nitrogen) ratio is 20:1; the optimum production factor is 1.3:1 and the best foam spacing interval is 90 days.