超低渗透油藏CO_2吞吐利用率实验研究

CO_2 Utilization Ratio Simulation during a CO_2 Huff-and-Puff Process in Ultra-Low Permeability Oil Reservoirs

CO_2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CO_2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CO_2吞吐物理模拟实验,分析了不同注入压力下CO_2吞吐的采收率规律和CO_2利用率。研究发现,CO_2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;CO_2利用率随着吞吐轮次的增加明显降低,前4轮CO_2吞吐中CO_2的利用率较高;提高CO_2注入压力使CO_2-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CO_2气源方面的成本。研究结果表明,油田应用CO_2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。

CO2huff-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 CO2huff-and-puff process was investigated.CO2huff-and-puff tests using ultra-low permeability cores from Changqing Oilfield were carried out to investigate oil recovery factors and CO2utilization 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,CO2utilization 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 CO2supply.The results show that CO2huff-and-puff with four cycles will be close to miscible condition and could achieve better development effect and economic benefits.