注CO_2前置段塞+N_2顶替提高采收率机理

Mechanism Research of Enhancement Oil Recovery by CO_2 Slugs Pushed by N_2

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。

SJ oil reservoir＇s permeability is low and its natural energy is poor. However, because of the inadequate CO2 source and the poor resistance of the pipelines to CO2-corrosion, the continuous CO2 injection is unavailable in the field. In that case, another improved strategy is the replacement of the continuous CO2 injection by CO2 slugs pushed by N2. Based on the formation hydrocarbon characteristics of the pilot test block, we try to compare the mechanism of CO2 slugs drive pushed by N2 with the continuous CO2 drive. After we tested the recovery percent and minimum miscibility pressure （MMP） of CO2 slugs drive pushed by N2 and CO2 drive by slim tube experiments, our research are the multiple contact simulation of CO2 drive and N2 drive and the one-dimensional simulation of long slim tube of CO2 slugs pushed by N2. We analyse the intermiscibility of gas slug and the crude oil, the interracial tension between gas phase and liquid phase, the concentration of C2-C6 in the two phases, density and viscosity of such two phases. The simulation results indicate no serious diffusion and dispersion of CO/ and N2 occur when CO2 slug pushed by N2 displaces the crude oil during the long slim tube test. The CO2 concentration of the multicontect front is in a high level to keep a stable miscible displacement front to drive oil. CO2 slugs pushed by N2 can gain the same oil recovery with continuous CO2 flooding in the same volume of gas injection. Such gas slug displacementreduce the amount of CO2, so it can slow the CO2-corrosion to the pipelines caused by the continuous CO2 injection. The cognition provides inspiration function for the development and improvement CO2-EOR.