超低渗透油藏CO2吞吐利用率实验研究

CO₂吞吐技术是开发特低渗透、超低渗透油藏的有效方式，但吞吐过程中CO₂的利用率如何亟待研究。利用长庆油田某超低渗透油藏天然岩心进行了室内CO₂吞吐物理模拟实验，分析了不同注入压力下CO₂吞吐的采收率规律和CO₂利用率。研究发现，CO₂吞吐的累计采收率随着注入压力的升高而增大，并逐渐减缓；CO₂利用率随着吞吐轮次的增加明显降低，前4轮CO₂吞吐中CO₂的利用率较高；提高CO₂注入压力使CO₂-原油体系达到近混相或者混相状态，不仅能够获得更高的采收率，而且不会显著增加CO₂气源方面的成本。研究结果表明，油田应用CO₂吞吐技术时采用近混相或者混相方式进行4个轮次的吞吐，能够取得较好的开发效果和经济效益。 

CO2 Utilization Ratio Simulation during a CO2 Huff-and-Puff Process in Ultra-Low Permeability Oil Reservoirs

CO₂ huff-and-puff is an effective method in the development of extra-low permeability and ultra-low permeability reservoirs.In order to use this technique to cut the cost and increase oil recovery in oilfields,the gas utilization ratio during CO₂ huff-and-puff process was investigated.CO₂ huff-and-puff tests using ultra-low permeability cores from Changqing Oilfield were carried out to investigate oil recovery factors and CO₂ utilization under different injection pressures.The test results show that ultimate oil recovery increases with the increase of injection pressure and the increasing amplitude would decrease gradually.In addition,CO₂ utilization ratio is relatively high in the first four cycles,but is significantly reduced with the increase of huff-and-puff cycles.The increasing of injection pressure can make the CO₂-crude oil system enter into a miscible phase condition, which is beneficial for obtaining higher oil recovery without significant increase of the cost of CO₂ supply.The results show that CO₂ huff-and-puff with four cycles will be close to miscible condition and could achieve better development effect and economic benefits.