CO2地质封存是当前温室气体减排的关键技术之一,而CO2突破压是CO2地质封存中盖层密封性评价的重要指标之一,它主要通过室内试验获取。目前,室内测试常用的方法包括间接法和直接法,间接法主要采用压汞法,直接法主要采用连续法、分步法、驱替法和脉冲法。在调研国内外CO2突破压室内试验研究工作的基础上,介绍了几种方法的测试原理与流程、误差来源分析以及适用范围:压汞法测试简单快速,但表面张力与接触角的转化、测试过程中孔隙结构破坏等问题导致准确度较低;分步法基于突破压定义而提出,测试准确度较高,但测试时间较长,低渗盖层岩石通常需要长达数月时间;连续法测试结果较为准确,但忽略了流体的流动黏滞阻力,且流量变化滞后于压力变化,故测试结果较易被高估;国内油气行业主要采用驱替法测试盖层突破压,测试过程快速,但结果的转化与校正比较繁琐;脉冲法以分步法为基础作了改进,兼顾了准确性和效率性,但存在数据解释的问题,特别是脉冲法获得的残余压差Psnapoff?和突破压真实值Pbreakthrough之间的差距。分析、对比了几种测试方法的原理、流程和误差来源,推荐了各个方法的适用范围,并提出了突破压测试技术的研究需求。
CO2 breakthrough pressure is a key parameter of caprock sealing efficiency evaluation for CO2 geological storage technology, which is one critical technology for greenhouse gas mitigation. It is mainly acquired by laboratory tests, including indirect and direct methods. The indirect methods mainly consist of mercury intrusion porosimetry. The direct methods consist of continuous injection method, step-by-step method, displacement method and pulse decay method (residual capillary pressure approach). Based on a literature review of existing laboratory breakthrough pressure measurement methods, measurement principles, testing procedures, error sources analysis and application ranges are introduced. Mercury injection method can obtain breakthrough pressure quickly, however, its measuring accuracy is comparatively low due to the impacts of such factors as conversion from mercury-air condition into CO2-brine condition including surface tension and contact angle, damage of porous structures, and so on. Step-by-step approach is based on the definition of breakthrough pressure. This approach has a high accuracy, but it is time-consuming. It always costs several months to conduct one test on caprock samples with a low permeability. Continuous injection approach also has a good accuracy, but it could over-estimate the CO2 breakthrough pressure due to the neglect of pressure gradient in the water phase and the delay between flow rate change and pressure change. Displacement method is widely used in natural gas industry in China. The experiment process is easy and timesaving; however, conversion and correction of the experiment results are complicated and high experience-dependent. Pulse decay method, which stems from step-by-step approach, has certain accuracy and efficiency. However, the difference between snap-off pressure and breakthrough pressure is still not clearly explained. At last, the application range and research demands of CO2 breakthrough pressure measurements are recommended based on the measurement principles, experiment procedures and error sources.