蒸汽CO_2复合驱驱油效率和CO_2的注入时机

Experimental Study on Oil Displacement Efficiency and CO_2 Injection Opportunity of Steam CO_2 Combination Flooding

新疆油田稠油储量丰富,现阶段开发方式仍以蒸汽吞吐和蒸汽驱为主,但已进入开发中后期,油汽比、产油量均较低。为了进一步提高稠油采收率,以M区特稠油为研究对象,通过室内实验系统研究了高渗低压油藏下非混相蒸汽-CO_2驱相对于纯蒸汽驱的驱油效率以及不同残余油饱和度下蒸汽-CO_2的驱油效率。研究结果表明:注蒸汽吞吐一段时间后转蒸汽-CO_2驱,相较于纯蒸汽驱,驱油效率可提高34.1%;蒸汽-CO_2驱具有气水交替驱的特征;过早注入CO_2,渗流通道会提前被打开,蒸汽过早地与孔道中大部分原油接触,导致原油乳化,使得部分乳化原油很难被驱扫出来;残余油饱和度为45%时,最终驱油效率可达到87%,是实验中CO_2的最佳注入时机。在实际开发过程中,要通过产水率判断蒸汽通道是否打开来决定CO_2的注入时机。

Heavy oil reserves in Xinjiang oilfields are abundant,and the main development methods at the present stage are still steam stimulation and steam flooding. However,the oil-steam ratio and oil production are lower at the middle and late development stages. In order to improve the recovery rate,it is urgent to change development method. In this paper,the M-zone crude was taken as the research object,the oil-displacement efficiency of immiscible steam-CO2 flooding relative to the pure steam flooding in the high-permeability and low-pressure oil reservoirs and the steam-CO2 in different residual oil saturations were studied systematically through laboratory experiments. The results showed that when the development method changed to steam-CO2 flooding from steam stimulation after a certain time,the oil displacement efficiency increases by 34.1%. The steam-CO2 flooding had the gas and water alternating flooding characteristics. If CO2 was injected too early,the percolation channel would be opened in advance. The steam would contact most of the crude oil in the tunnel prematurely,which resulted in that the crude oil was emulsified and some emulsified crude oil was difficult to be swept out. When the residual oil saturation was 45%,the final oil displacement efficiency could reach up to 87%,which was the best CO2 injection opportunity in the experiment. However,in the actual development process,the CO2 injection opportunity should be determined through judging whether the steam channel was open by the water production rate.