致密砾岩油藏CO_(2)吞吐提高采收率可行性研究

Feasibility of enhanced oil recovery by CO_(2) huff-n-puff in tight conglomerate reservoir

基于原油与CO_(2)以及CO_(2)与储层岩石相互作用,揭示环玛湖致密砾岩油藏CO_(2)提高采收率机理。利用高温高压核磁共振系统在孔隙尺度下监测了基质岩心CO_(2)吞吐过程中原油饱和度的变化,研究CO_(2)吞吐提高采收率可行性。采用岩心压裂和驱替系统开展三维物理模拟实验研究,研究裂缝对CO_(2)吞吐提高采收率的影响。实验结果表明,CO_(2)能够有效地溶解在原油中,补充地层能量,降低原油黏度,且改善储层润湿性。基质岩心中,衰竭式开采时的原油主要产于大孔隙,CO_(2)吞吐能有效启动中孔隙和小孔隙,衰竭式开采后,三轮次的吞吐能够提高采收率23.1%左右,而第一轮次的贡献率最大,为15.1%,裂缝的存在能够增大原油与CO_(2)接触面积,减小原油渗流阻力,最终提高采收率27.1%。实验结果从孔隙尺度揭示了CO_(2)吞吐提高致密砾岩油藏采收率的可行性。

Based on the interactions between CO_(2)and crude oil,CO_(2)and conglomerate,the enhanced oil recovery(EOR)mechanism of CO_(2)huff-n-puff has been revealed in Huanmahu tight conglomerate reservoir.Meanwhile,a high temperature and high pressure nuclear magnetic system was applied to monitor the change of oil saturation during experimental processes at pore scale in cores of substrates.Core fracturing and displacement system were used to investigate the effects of fractures on EOR during CO_(2)huff-n-puff.The experimental results indicated that CO_(2)could effectively dissolve in crude oil to replenish formation energy,reduce oil viscosity and improve wettability.Moreover,the crude oil produced in depletion development was in large pores,while that in medium pores and small pores could be effectively activated by CO_(2)huff-n-puff.After depletion development,three cycles of huff-n-puff could enhance oil recovery by 23.1%,among which the first cycle contributed most with factor of 15.1%.The existence of fractures could increase the contact area between crude oil and CO_(2)and decrease the flow resistance of crude oil,and finally the EOR is up to 27.1%.All the results reveal the feasibility of CO_(2)huff-n-puff to improve oil recovery in tight conglomerate reservoirs from pore scale.