气体钻井井底岩石热应力分析

Thermal stress analysis on bottom hole rock in gas drilling

为研究焦耳-汤姆逊冷却效应产生的低温气体与地层的传热现象,采用热传导和热弹性理论方法求得井底温度,建立井底岩石稳态温度和热应力分布模型,并分析井底岩石稳态和非稳态情况下温度和热应力的分布规律。结果表明:井底附近岩石存在低温区,径向热应力和由负压差产生的'拉应力'叠加之后加强了井底岩石向井眼变形的趋势,促使井底岩石破裂;井底岩石热应力随井底气体温度降低而增大,保持适当的井底温度有利于钻头破碎岩石及机械钻速提高;时间对于井底岩石热应力的影响较大,在研究井底低温问题时不可忽略其影响。

Heat transfer phenomena between low temperature gas caused by Joule-Thomson cooling effect and formation were studied. The bottom hole temperature was calculated by heat conduction and thermoelasticity theory method. A steady state temperature and thermal stress distribution model of bottom hole rock was developed, and the distribution laws of bottom hole rock temperature and thermal stress under steady and unsteady state were analyzed. The results show that a low temperature zone exists near bottom hole, the radial thermal stress together with the tensile stress generated by negative pressure differ- ence enhances the bottom hole rock deformation to the wellbore and leads to rock breaking. The bottom hole rock thermal stress increases with bottom hole gas temperature decreasing, and maintaining certain bottom hole temperature helps rock breaking and the penetration rate increase. Time has a major influence on bottom hole rock thermal stress, and the effect of time can＇t be ignored when the low temperature bottom hole problems are studied.