超临界二氧化碳泡沫在低渗多孔介质内的渗流特性及渗流机理研究

Foam technology has great application prospects on enhancing and stablizing oil production from unconventional reservoirs and as well on increasing the geological storage efficiency of Carbon Dioxide. Accordingly we propose in this project to carry out relevent studies focusing on flow characteristics and flow mechanism for supercritical CO2 foam flow in low permeability porous media. Research works will be conducted in following three aspects. 1. Experimental studies on flow characteristics for supercritical CO2 foam flow in low permeability porous media. X-Ray CT instrument will be employed to visualize the dynamic foam flow process and to obtain the water saturation distribution along the sample core. In the mean time, pressure drop along the foam flow direction will also be recorded to perform systematic studies on macroscopic foam flow characteristics in porous media. 2. Experimental studies on supercritical CO2 foam rheology. With accurately measured resistance characteristics for foam flow in microchannels or channles with different internal shapes, a foam rheology model will be built based on two phase system to help understainding the cause of high foam apparent viscosity and analyzing the mechanisms of foam flow behavoir in low permeability porous media from microscopic viewpoint. 3. Simulation studies on supercritical CO2 foam flow in low permeability porous media. A simple but robust stochastic foam population balance model will be proposed for properly describing supercritical CO2 foam generation, development and collapse in low permeability porous media. Based on the proposed model with taking into consideration of Non-Darcy effect, numerical simulations will be carried out to study supercritical CO2 foam flow characteristics and mechanisms in low permeability porous media.

基于泡沫技术在增产与稳产非常规原油资源及提高二氧化碳地质埋存效率方面的巨大应用前景，本项目对超临界CO2泡沫在低渗多孔介质内的渗流特性和渗流机理进行针对性研究。研究内容包括三个方面： 1. 超临界CO2泡沫在低渗介质内渗流特性的实验研究。采用CT测试技术可视化低渗介质内超临界CO2泡沫的动态渗流过程并获得介质内液相饱和度的变化规律，再结合沿程渗流压力的同步测量，对其宏观渗流特性进行系统研究。2. 超临界CO2泡沫流变学特性研究。通过测量微细通道及不同形状通道内泡沫的流动特性，建立基于两相体系的泡沫流变学模型，从微观上理解其高表观粘度的成因并对其在低渗介质内的渗流机理进行探讨。3. 超临界CO2泡沫在低渗介质内渗流过程的模拟研究。基于统计原理建立简单且能正确描述泡沫在介质内生成、发展和湮灭等动态过程的泡沫数目守恒模型。同时考虑非达西渗流现象，利用数值方法对其渗流特性及渗流机理进行分析和研究。

基于泡沫技术在原油增产及二氧化碳地质埋存方面的巨大应用前景，本项目对超临界CO2泡沫在低渗多孔介质内的渗流特性和渗流机理开展了针对性研究。研究内容包括三个方面： 1. 超临界CO2泡沫在低渗介质内三相渗流特性的实验研究。采用CT测试技术可视化储层介质内CO2泡沫的三相动态渗流过程，并结合渗流压降测量，探讨了系统压力、不同气体种类、泡沫质量及不同渗透率对CO2泡沫驱替特性的影响。然后利用微CT测试技术对超临界CO2泡沫的三相驱替特性及高压CO2流体在低渗介质内三相驱替特性进行了实验研究。结果表明CO2泡沫可在水驱过程结束后获得更高的油相采收率，而当CO2与驱替油相达到混相状态时，CO2流体对油相的驱替效果增加明显。 2. 超临界CO2泡沫流变学特性研究。实验结果表明，超临界CO2泡沫及液态CO2泡沫呈现剪切变稠的非牛顿流体特性，而气态CO2及N2泡沫则呈现剪切变稀的非牛顿流体特性。流变学特性研究结果可从机理上理解泡沫流体高表观粘度的成因并对其在低渗介质内的渗流机理进行探讨。3. 超临界CO2泡沫在低渗介质内渗流过程的模拟研究。创新性地提出并采用随机泡沫守恒模型，通过引进泡沫生成速率、泡沫最大数目及泡沫相对渗透率减小系数，综合考虑了粘性力、毛管力及表面张力的综合作用，针对泡沫渗流过程的入口及出口效应，以及其在非均质介质内的渗流特性开展了详细的数值模拟研究工作。数值计算结果无论在定性和定量上均与相应的实验结果达成一致，说明计算模型能够从机理上反映多孔介质内泡沫渗流机理，从而对泡沫在多孔介质内的渗流特性进行正确分析。本项目的研究结果对于深刻理解超临界CO2泡沫在低渗介质内的多相渗流特性及渗流机理、进而指导其在强化采油与碳地质埋存方面的工业实践有着重要意义。