注CO2前置段塞+N2顶替提高采收率机理

SJ油田为一低渗透油藏,天然能量低。受CO2气源不足以及油井管柱抗腐蚀能力差的限制,持续的CO2-EOR不适合SJ油田的实际情况。鉴于此,一个改进的对策是用N2推动的CO2前置段塞驱代替持续的CO2驱油。本文根据SJ油田先导试验区的流体特征,对比了连续注入CO2驱油和N2推动的CO2前置段塞混相驱油的效果和机理。在注CO2、N2细管驱替效率及最小混相压力实验测试基础上,通过注CO2、N2与地层原油多级接触混相驱机理相态模拟,长细管前置CO2混相驱替+后续N2段塞顶替驱替机理一维数值模拟研究,分析了前置CO2段塞+后续N2顶替驱油时原油与注入气的互溶情况、气驱界面张力变化规律、气驱过程中C2—C6的中间烃组分在油气两相中的分布、气驱过程中油气两相的黏度以及密度变化。结果表明SJ油田实施前置CO2段塞+后续N2顶替驱油时,后续的N2与前置的CO2段塞不会出现严重的扩散弥散,注气前缘仍能保持CO2的富集并实现稳定的混相驱油即在注气总量相同的情况下,N2推动的CO2前置段塞驱可以获得与持续的CO2驱相同的驱油效果;同时减少了CO2的注入量,从而可减缓CO2长期注入对油井管柱产生的腐蚀。所得认识对CO2驱提高采收率技术的改进和发展具有一定的启发作用。

Mechanism Research of Enhancement Oil Recovery by CO2 Slugs Pushed by N2

SJ oil reservoir’s permeability is low and its natural energy is poor.However,because of the inadequate CO 2 source and the poor resistance of the pipelines to CO 2-corrosion,the continuous CO 2 injection is unavailable in the field.In that case,another improved strategy is the replacement of the continuous CO2 injection by CO 2 slugs pushed by N 2.Based on the formation hydrocarbon characteristics of the pilot test block,we try to compare the mechanism of CO 2 slugs drive pushed by N 2 with the continuous CO 2 drive.After we tested the recovery percent and minimum miscibility pressure(MMP)of CO 2 slugs drive pushed by N 2 and CO 2 drive by slim tube experiments,our research are the multiple contact simulation of CO 2 drive and N 2 drive and the one-dimensional simulation of long slim tube of CO 2 slugs pushed by N 2.We analyse the intermiscibility of gas slug and the crude oil,the interfacial tension between gas phase and liquid phase,the concentration of C 2-C 6 in the two phases,density and viscosity of such two phases.The simulation results indicate no serious diffusion and dispersion of CO 2 and N 2 occur when CO 2 slug pushed by N 2 displaces the crude oil during the long slim tube test.The CO 2 concentration of the multicontect front is in a high level to keep a stable miscible displacement front to drive oil.CO 2 slugs pushed by N 2 can gain the same oil recovery with continuous CO 2 flooding in the same volume of gas injection.Such gas slug displacementreduce the amount of CO 2,so it can slow the CO 2-corrosion to the pipelines caused by the continuous CO 2 injection.The cognition provides inspiration function for the development and improvement CO 2-EOR.