海洋深水井钻井过程中井筒温度的变化规律

Changing laws of wellbore temperature during offshore deepwater well drilling

海洋深水油气井钻井过程中,现有的井筒循环温度场计算模型虽然综合考虑了钻井液在循环过程中诸如海水对流换热、隔水管及钻井液、地层导热等多种因素对井筒温度的影响,但却忽略了钻进导致的温度差异,与实际情况不符。为了给深水钻井的钻井液密度设计、井壁稳定性分析等相关工作提供更加准确可靠的依据,在不钻进只循环钻井液过程的温度模型求解温度场的基础上,对补充钻进工况的计算模型应用有限差分法和高斯迭代法进行求解,进而通过节点更新的算法,分析了不同机械钻速的钻进过程对深水钻井井筒温度纵向变化规律的影响。研究结果表明:①同一深度,不同机械钻速下全井温度场的计算结果有明显差异,1000 m水深的井底随钻温度差异接近10℃;②钻进过程的循环温度场对时间的敏感性远高于机械钻速,与不考虑机械钻速的井筒温度场相比,考虑机械钻速情况下的井筒温度场呈整体增大的变化规律。结论认为,利用该方法可以更好地分析海洋深水钻井过程中井壁稳定性和管柱工况等实际问题,其结果更加符合生产实际。

When the existing calculation model of wellbore circulating temperature field is used to analyze the drilling process of offshore deepwater oil/gas wells,it takes into account the influence of many factors on the wellbore temperature(such as convection heat transfer of seawater,riser and drilling fluid,and formation heat conduction),but neglects the temperature difference caused by the drilling in actual fields.In order to provide more accurate and reliable data for related work in deepwater drilling,such as drilling fluid density design,borehole stability analysis,and so on,this paper calculated the temperature field using the temperature model for the process of circulating drilling fluid without drilling.Then,the calculation model of supplementary drilling condition was solved by means of the finite difference method and the Gauss iteration method.Finally,the influence of the drilling process with different rates of penetration on the longitudinal variation laws of wellbore temperature in deepwater wells was analyzed using the node updating algorithm.And the following research results were obtained.First,at the same depth,the calculated temperature fields of the whole well at different rates of penetration are obviously different,and the difference of the bottom hole temperature while drilling at a water depth of 1000 m is close to 10℃.Second,in the process of drilling,the circulating temperature field is more sensitive to time than to the rate of penetration.And compared with the wellbore temperature field without considering the rate of penetration,the one with consideration of the rate of penetration presents a law of overall increase.It is concluded that by virtue of this new method,the practical problems in the process of offshore deepwater drilling can be analyzed better,e.g.borehole stability and pipe string working conditions,and the actual production can be reflected more accurately.