不同温度超临界CO_(2)对页岩力学特性的影响

Effects of Supercritical CO_(2) at Different Temperatures on Shale Mechanical Properties

我国西南地区页岩气储层地温通常在60℃以上,采用超临界CO_(2)强化其开采效率是研究前沿。通过试验模拟不同温度超临界CO_(2)作用于页岩,分析其力学性质变化,并探讨不同温度超临界CO_(2)对页岩作用机理,主要研究结果表明:随着浸泡温度升高和浸泡时间增长,页岩抗拉强度、三轴抗压强度和弹性模量均发生不同程度的弱化,其中抗拉强度的损失率最大,这3种力学参数与浸泡时间均呈负指数变化,浸泡温度加速页岩弱化速度并在浸泡初期起主要作用。分析表明:浸泡温度通过提高溶蚀速度增加页岩矿物的溶蚀程度,增大页岩孔隙度和降低胶结强度,通过页岩升温膨胀,促进微裂隙生成,浸泡时间通过累积溶蚀提高了页岩矿物的溶蚀程度;另一方面,通过页岩吸附CO_(2)膨胀累积增长,促进微裂隙萌生,进而劣化页岩力学性质。

The geothermal temperature of shale gas reservoirs in southwest China is usually above 60℃.The current research frontier is to use supercritical CO_(2) to improve its extraction efficiency.Experiments were conducted to simulate the effects of supercritical CO_(2) at different temperatures on shale,the changes in its mechanical properties were analyzed,and the effect mechanism of supercritical CO_(2) at different temperatures on shale were discussed.The main research results show that as the immersion temperature increases and the immersion time increases,the shale tensile strength,triaxial compressive strength and elastic modulus all have different degrees of weakening.Among them,the loss rate of tensile strength is the largest.These three mechanical parameters and immersion time all show negative exponential changes.The immersion temperature accelerates the shale weakening rate,and plays a major role in the early stage of soaking.The analysis shows that the immersion temperature increases the dissolution rate to increase the dissolution degree of shale minerals,increase the porosity of the shale and reduce the cementation strength.And the formation of micro-cracks can be promoted through the shale heating and expansion.The immersion time increases the dissolution degree of shale minerals through cumulative dissolution.On the other hand,through the expansion and accumulation of CO_(2) adsorbed by shale,the micro-cracks initiation is promoted,and then the mechanical properties of shale are deteriorated.