超临界二氧化碳浸泡对页岩力学性能的影响

超临界二氧化碳对岩石力学性能的影响是非常规油气藏钻探开发的基础问题。依据井下工况,研制超临界二氧化碳浸泡实验装置,研究超临界二氧化碳浸泡条件下,页岩的力学性能变化规律。试验结果表明:随着时间的增加,页岩的抗压强度降低至稳定值,弹性模量升高至稳定值,泊松比降低至稳定值。相比于氮气实验,超临界二氧化碳弱化岩石力学性质的能力更强,说明超临界二氧化碳更有利于破岩。相比于清水实验,清水浸泡后页岩抗压强度一直下降,不利于井壁稳定,二氧化碳浸泡后页岩抗压强度下降至稳定值,有利于井壁稳定。浸泡不同岩石发现,岩石抗压强度均降低,但是降低幅度不同,说明超临界二氧化碳可渗入各种不同岩石,改变岩石力学性质,有利于提高破岩效果,加快钻井速度。研究结果为超临界二氧化碳钻完井技术的发展提供了依据。

Effects of Supercritical Carbon Dioxide Immersion on Mechanical Properties of Shale

The influence of supercritical carbon dioxide on the mechanical properties of rock is the fundamental problem in the development of unconventional oil and gas reservoirs. Under actual condition, the supercritical carbon dioxide immersion test device has been designed, then the variation of mechanical properties of shale during supercritical carbon dioxide immersion has been studied. The results show that, with the increase of duration, the compressive strength of shale decreases to a stable value, the elastic modulus increases to a stable value, and the poisson ratio decreases to a stable value. Compared with the nitrogen experiments, the shale becomes weak easily during supercritical carbon dioxide immersion, indicating that supercritical carbon dioxide is more conducive to rock breaking. Compared with the clear water experiments, the compressive strength of the shale always decreases with the increase of the clear water immersion duration, which is bad for wellbore stability, the compressive strength of the shale decreases to a stable value during supercritical carbon dioxide immersion, which is good for wellbore stability. Compared with different rocks, the compressive strength of all rocks decreased, but the magnitude of decrease of every rock is different, indicating that the supercritical carbon dioxide can penetrates into the many kinds of rocks and change the mechanical properties of rocks, which is beneficial to improve the rock breaking effect and speed up the drilling. The research results provide a basis for the development of supercritical carbon dioxide drilling and completion technology.