低渗致密气藏注超临界CO_2驱替机理  

Mechanism of supercritical CO_2 flooding in low-permeability tight gas reservoirs

作　　者：史云清[1,2] 贾英[1,2] 潘伟义[1,2] 严谨[1,2] 黄磊[3] 

机构地区：[1]中国石化石油勘探开发研究院,北京100083 [2]中国石化海相油气藏开发重点实验室,北京100083 [3]中国石油勘探开发研究院,北京100083

出　　处：《石油与天然气地质》2017年第3期610-616,共7页Oil & Gas Geology

基　　金：国家科技重大专项(2016ZX05048003-004);中国石油化工股份有限公司科技部项目(P15031);中国石油化工股份有限公司科技部基础前瞻项目(G5800-14-ZS-KJB033-5)

摘　　要：为了提高低渗致密气藏采收率,探索研究将CO_2注入气藏中,实验与数模相结合论证超临界CO_2驱替天然气的驱替机理。首先,通过超临界CO_2-天然气相态实验研究CO_2与天然气混合规律。平衡相行为实验定量测定了储层条件CO_2与天然气的物性参数,结果表明CO_2与天然气的物性差异有利于CO_2驱替天然气提高采收率以及封存。超临界CO_2-天然气扩散实验论证了CO_2与天然气混合过程中驱替前沿的混合程度,结果表明CO_2在天然气中的扩散度不高,可形成较窄的互溶混相带,实现CO_2有效驱替。在分析了CO_2与天然气混合特征的基础上,开展致密储层CO_2驱替天然气长岩心驱替实验。实验结果表明,CO_2提高天然气采收率12%,超临界CO_2驱可有效提高致密气采收率。最后,以相态及驱替实验为基础,应用数值模拟方法,建立了长岩心模型,单注单采倾角机理模型及背斜模型,系统证实了超临界CO_2驱替天然气的驱替机理。通过分析认为,CO_2与天然气驱替前沿部分混溶,一方面保持了气藏压力,另一方面超临界CO_2沉降在气藏圈闭下部形成"垫气"提高了天然气采收率。从实验及数值模拟两方面系统论证超临界CO_2的驱替机理,为探索注CO_2提高天然气采收率选区评价奠定了基础。The mechanism of supercritical CO_2 flooding in gas reservoirs was studied through both laboratory and numerical simulations to explore ways to increase recovery of low-permeability tight gas reservoirs. Behaviors of mixing supercritical CO_2 with natural gas were observed first to reveal the mixing patterns of the two phases. A laboratory quantitative measurement was carried out for an equilibrium phase behaviors to define the in-situ physical properties of both carbon dioxide and natural gas. The results show that the differences between the properties of the two gases are favorable for CO_2-based flooding and storage in gas reservoirs. A supercritical CO_2-natural gas diffusion test offered opportunities for observing behaviors of mixed gas front during flooding process. The result indicates that CO_2 does not diffuse much in natural gas and can form only a narrow mixing phase belt,which is good for an effective CO_2 displacement. Based on an analysis of CO_2 and natural gas mixing behaviors,we carried out a CO_2 displacement experiment on a long core from tight gas reservoirs. The results show that gas recovery rate can be increased by 12% after supercritical CO_2 flooding. Finally,based on the experiments,we used numerical simulation method to establish long core model,single injector-single producer dip mechanism model as well as anticline model. These models were then used to systematically verify the mechanism of supercritical CO_2 displacing natural gas. It suggests that a higher gas recovery is possible because of a partial mixing of natural gas with CO_2 at the flooding fronts helping maintain gas reservoir pressure and of a supercritical CO_2 ＂pad＂formed at the lower part of gas traps favorable for gas recovery. The displacement mechanisms expounded through both laboratory works and numerical simulations provide a basis for selecting potential CO_2 flooding target in tight gas reservoirs.

关 键 词：数值模拟 天然气 CO2驱 低渗致密气藏 提高采收率 

分 类 号：TE37[石油与天然气工程—油气田开发工程]