水化-温度协同作用对龙马溪组深层页岩声波传播特性及力学强度影响实验研究

Experimental study on the effect of hydration and temperature synergism on acoustic wave propagation and mechanical strength of Longmaxi deep shales

摘要:

深层页岩具有高水敏性及高温特性，水化-温度协同效应对泥页岩物理及力学性质存在较大影响。以四川盆地龙马溪组深层页岩为研究对象，基于XRD衍射、扫描电镜、水化-温度协同浸泡、超声波及室内力学压缩等实验获取了页岩在不同温度条件下浸泡后的裂缝参数、声波参数和力学参数。研究结果显示：在常温（24 ℃）及高温（120 ℃）环境下，随浸泡时间增加，声波能量产生衰减，高温环境下纵、横速度下降幅度分别是常温环境下的1.41倍和1.71倍；水化作用导致岩样裂缝参数产生变化并具有阶段性，声波衰减系数及水化结构损伤系数在水化初期、中期、末期，分别呈现快速增加、缓慢增加和趋于稳定的趋势，高温环境下声波衰减系数及水化损伤系数分别是在常温环境下的1.72和2.98倍；浸泡后页岩力学参数出现劣化，岩样抗压强度、弹性模量、内摩擦角及粘聚力呈阶段式下降，高温环境下页岩力学参数降幅分别是常温环境下对应力学参数降幅的1.24、1.42、2.06和1.39倍。研究结论可为优化深层页岩水平井钻井地质设计及调整钻井液密度提供一定理论依据。

Abstract:

Deep shale exhibits high water sensitivity and high-temperature characteristics， and the coupled effects of hydration and temperature have a significant impact on the physical and mechanical properties of shale. Using deep shale samples from the Longmaxi Formation in the Sichuan Basin as the research subject， fracture parameters， ultrasonic parameters， and mechanical parameters of the shale after immersion under different temperature conditions were obtained through experiments involving X-ray diffraction （XRD）， scanning electron microscopy （SEM）， hydration-temperature coupled immersion tests， ultrasonic testing， and laboratory mechanical compression.The experimental results reveal that， the energy of ultrasonic waves decayed with increasing immersion time under both ambient temperature （24°C） and high-temperature （120°C） conditions. The reduction in longitudinal and transverse wave velocities in the high-temperature environment was 1.41 and 1.71 times greater， respectively， than that under ambient conditions. Hydration caused changes in the fracture parameters of the shale， showing a phased behavior. The ultrasonic attenuation coefficient and hydration-induced structural damage coefficient increased rapidly in the early stages of hydration， increased gradually in the middle stages， and tended to stabilize in the late stages. The ultrasonic attenuation coefficient and hydration damage coefficient at high temperatures were 1.72 and 2.98 times higher， respectively， than that under ambient conditions. Additionally， the mechanical properties of the shale deteriorated after immersion， with compressive strength， elastic modulus， internal friction angle， and cohesion showing a staged decline. Under high-temperature conditions， the reduction in these mechanical parameters was 1.24， 1.42， 2.06， and 1.39 times greater， respectively， than that under ambient conditions. The findings of this study provide a theoretical basis for optimizing geological designs for horizontal drilling in deep shale formations and for adjusting drilling fluid densities.