超临界二氧化碳浸泡对页岩力学性质影响的实验

Experiment on mechanical properties of shale soaked with supercritical carbon dioxide

超临界二氧化碳在页岩油气等非常规油气藏的勘探开发中极具潜力,通过室内二氧化碳浸泡实验系统,对不同压力和温度浸泡下页岩岩心力学性质变化进行实验研究和机制阐释。结果表明:浸泡初期岩心膨胀,随后有所收缩,最后趋于平缓;浸泡后页岩弹性模量和泊松比均增大;在临界压力附近,力学性质发生急剧变化,压力继续增大,力学性质变化平缓,弹性模量和泊松比平均增幅分别为43.4%和36.6%;随着温度增加,弹性模量和泊松比逐渐增大,最大增幅分别为138.4%和24.7%。页岩力学性质变化对CO_2压力变化不敏感,而CO_2温度影响较为明显和复杂,对力学参数随温度变化给出了定量化描述,为超临界二氧化碳勘探开发页岩气在岩石力学等方面提供了一定数据支撑和理论依据。

Supercritical carbon dioxide as fracturing or displacement fluid has great potential in exploration and development of unconventional reservoirs such as shale oil and gas. In this study, the mechanical properties of shale rocks soaked with carbon dioxide soaking were investigated via indoor experiments under different pressure and temperature conditions. The experimental results show that the shale rock core expanded in the beginning of the soaking, then contracted, and finally leveled off. Its elastic modulus and Poisson’s ratio increased after the soaking. At near the critical pressure of CO2, the mechanical property of the core changes sharply, and then it becomes stable as pressure further increases. The average increments of the elastic modulus and the Poisson’s ratio are of 43.4% and 36.6%, respectively. With the increase of temperature, the elastic modulus and Poisson’s ratio increases gradually, and the maximum increase for the two parameters is of 138.4% and 24.7% respectively. The change of the mechanical properties of shale is not very sensitive to CO2 pressure, but the influence of temperature is obvious and complex. A quantitative description of the mechanical parameters of shale rocks soaking in CO2 under high temperature and pressure conditions was given, which can provide guidelines for the application of supercritical carbon dioxide in shale gas exploitation in terms of rock mechanics.