论文部分内容阅读
气体钻井有着较高的机械钻速在很大程度上归因于钻头水眼处的焦耳–汤姆森低温效应。这种效应对井底岩石产生了热冲击应力,使得井底岩石的强度降低,进而促进了机械破岩的作用。首先建立了非对称冷却条件下井底岩石的温度场的分布模型,并以此建立了井底岩石三维动态热应力分布模型,对气体钻井井底热冲击应力进行了深入的剖析。其次,通过莫尔–库仑准则,对岩石的黏聚力变化进行了分析,得出随着冷却时间的加长,岩石强度迅速降低,有利于岩石的破坏。最后,为验证理论模型,对砂岩岩样进行液氮冷却试验,并对其进行声波实时测量,声波的首波波幅也有明显的延迟,说明冷却处理对岩心内部结构产生了很大影响。
The high ROP for gas drilling is due in large part to the Joule-Thomson cryogenic effect at the bit’s waterhead. This effect produces thermal shock stress on the bottom hole rock, which decreases the strength of the rock at the bottom of the hole and further promotes the mechanical rock breaking. Firstly, the distribution model of temperature field of bottom hole rock under asymmetrical cooling conditions is established. Based on this, the 3D dynamic thermal stress distribution model of bottom hole rock is established, and the thermal shock stress of gas bottom hole is analyzed in depth. Secondly, according to the Mohr-Coulomb criterion, the change of cohesion of rock is analyzed. It is concluded that the strength of rock decreases rapidly with the increase of cooling time, which is in favor of rock destruction. Finally, in order to verify the theoretical model, the sandstone samples were subjected to liquid nitrogen cooling test and the real-time measurement of acoustic waves was carried out. The amplitude of the first wave of the acoustic wave was also obviously delayed, indicating that the cooling process had a great influence on the internal structure of the core.