单相流体对砂岩强度特性的影响

在CO2地质封存过程中，CO2注入深部岩层，引起地层孔隙流体组分和压力的改变，影响岩层的力学稳定性，可能导致储盖层破裂、地表隆起，并引发中小规模地震等不良后果。以砂岩为试验研究对象，以CO2、N2、H2O作为孔隙流体介质，通过控制和调节流体的温度和孔隙压力，开展了单相流体作用下岩石三轴压缩力学特性对比试验，分析了单相流体耦合作用下岩石强度、弹性模量和泊松比等基本力学参数。研究发现，高压孔隙流体使干燥砂岩的峰值强度和弹性模量均出现不同程度降低，泊松比却有较为明显的升高现象，且影响作用从大到小依次为H2O、CO2、N2。孔隙流体降低了干燥砂岩的脆性，并增强了塑性变形，且含水砂岩塑性最强。孔隙流体对砂岩力学特性影响程度取决于流体与岩石矿物成分的相互作用强弱，分析认为砂岩中不同矿物成分对CO2、N2、H2O的选择性吸附导致孔隙流体对砂岩强度影响差异明显，且作用效应从大到小依次为H2O、CO2、N2。

Influence of single-phase fluid on strength characteristics of sandstone

In the process of CO2 geological storage, the mechanical stability of rock can be influenced by changes in the composition and pressure of pore fluid due to CO2 injection into deep rock stratum. In addition, adverse consequences may further arise, such as reservoir caprock rupture, surface uplifting, and small and medium scale earthquakes. The triaxial compression tests of rock were conducted to compare the effects of pore fluid media of supercritical CO2, N2 and H2O under single-phase fluid. The fluid temperature and pore fluid pressure were controlled and adjusted to analyse the strength, elastic modulus and Poisson's ratio under single-phase fluid coupling. It was found that the peak strength and elastic modulus of dry sandstone were reduced at various degrees by high-pressure pore fluid. However, Poisson’s ratio increased obviously, and the impacts of pore fluid were H2O, CO2 and N2 in the descending order. The pore fluid decreased the brittleness of dried yellow sandstone and enhanced plastic deformation to a certain degree. Besides, the water-bearing sandstone had the strongest plastic property. The effect of pore fluid on mechanical properties of sandstone depended on the strength of interaction between the fluid and mineral composition of rock. The selective absorption of CO2, N2 and H2O by different mineral compositions of sandstone resulted in a significant difference in the effect of pore fluid on sandstone strength. The action effects ranked as H2O, CO2 and N2 in the ascending order.