塔河油田强底水砂岩油藏CO2/N2驱提高采收率机理

塔河油田强底水砂岩油藏开发后期,受强非均质性和底水锥进影响,大部分水平井出现了点状水淹,导致低产低效井增多,油藏含水率不断上升,井间剩余油动用难,且该油藏具有高温、高盐特点,常规提高采收率技术难以取得较好开发效果。因此,本文主要通过高温高压三维物理模型进行油藏的模拟,采用注CO2/N2（体积比为7:3）混合气提高强底水砂岩油藏采收率。一方面,CO2与原油易混相,能够大幅度地提高驱油效率;另一方面,N2具有较好的压锥效果,在一定程度上抑制了强底水快速锥进,提高油藏的波及系数。这样使“驱油”与“压锥”进行有机结合,大大提高了油藏采收率。同时,对比不同注气方式、不同注气速度和不同注采部位等驱油条件,优选注气参数。实验结果表明：注入CO2/N2后地层原油体积膨胀了21%,粘度降低了24.9%;CO2/N2混合气与原油的最小混相压力为39.62 MPa;优选出了最佳的注入参数：注气速度为1 mL/min（提高采收率幅度为14.25%）、注气方式为水气交替注入（提高采收率幅度为15.8%）、注采部位为高注低采（提高采收率幅度为14.5%）。研究结果为塔河油田强底水砂岩油藏CO2/N2混合气驱先导试验提供可靠实验依据。

Study on enhanced oil recovery mechanism of CO2/N2 flooding in Tahe Oilfield sandstone reservoirs with strong bottom water

Late development of bottom water sandstone reservoir in Tahe Oilfield, by the strong heterogeneity and bottom water coning effects, most of the horizontal well in the dot flooded, lead to low Wells increase, reservoir water cut rising, interwell remaining oil use hard, have the characteristics of high temperature, high salt, and the reservoir to improve oil recovery technology is difficult to obtain better development effect. Therefore, in this paper, reservoir simulation was mainly carried out through high-temperature and high-pressure three-dimensional physical model, and CO2/N2 (7:3 volume ratio) mixture injection was adopted to improve recovery efficiency of strong bottom water sandstone reservoir.On the one hand, CO2 was miscible with crude oil, which could greatly improve oil displacement efficiency. On the other hand, N2 had a good coning effect, which inhibited the fast coning of strong bottom water to a certain extent and improved the reservoir sweep coefficient. In this way, the organic combination of "oil displacement" and "pressing cone" greatly improved the oil reservoir recovery. At the same time, oil displacement conditions such as different gas injection methods, different gas injection speeds and different injection and production locations were compared. The optimum gas injection parameters were optimized. The experimental results show that the oil volume expanded by 21% and the viscosity decreases by 24.9% after CO2/N2 injection. The minimum miscible pressure of CO2/N2 mixture and crude oil is 39.62 MPa. The optimal injection parameters are selected as follows: gas injection rate is 1 mL/min (enhanced oil recovery rate is 14.25%), gas injection method is alternate injection of water and gas (enhanced oil recovery rate is 15.8%), and injection and production location is high injection and low recovery (enhanced oil recovery rate is 14.5%). The results provide a reliable experimental basis for the pilot test of CO2/N2 mixed gas flooding in Tahe Oilfield sandstone reservoir with strong bottom water.