温度对超深井非水化地层安全钻井的影响

超深井钻井中普遍存在高温高压等地质环境,钻井过程中经常发生喷、漏、卡、塌等复杂情况。为减少复杂情况发生、研究了温度对井壁稳定性的影响,探讨了井周有效应力、岩石力学性质及钻井液密度随温度变化的规律。研究发现温度变化会产生热应力,导致孔隙弹性系数变化,从而改变井周有效应力的分布;温度升高岩石力学性质逐渐变差,并有可能产生热开裂现象,从而引发井漏、井塌等复杂事故;高温高压井中压力和温度同时起作用,但温度效应更加明显,将引起钻井液当量密度降低。综合考虑以上3 个方面,认为温度对超深井地层安全钻进具有重要影响,钻井过程中应该尽量减少起下钻次数,保持钻井液循环,该研究结果可为进一步确定合理的安全密度窗口及入口钻井液密度提供依据。

Effect of temperature on safe drilling of ultra-deep well in non-hydration formations

To prevent the occurrence of complicated situations, the effect of temperature on borehole wall stability is studied. In this paper, the law that the circumferential effective stress, the rock mechanical properties and the drilling fluid density changed with temperature is discussed. It is found that the change of temperature could result in thermal stress, and thus enable the Biots factors to change. As a result, the distribution of circumferential effective stress is changed. As the temperature increases, the rock mechanic properties get poor. Thermal cracking may occur, which ultimately results in lost circulation and the collapse of wells. Temperature and pressure play a role on HTHP wells at the same time, but the temperature effect is more obvious, which will result in the decrease of ECD. On the basis of the above analysis, it is concluded that temperature has a major impact on the security of ultra-deep formation drilling. So it is critical to minimize the number of tripping and keep the drilling fluid circulation during the course of drilling. This is useful for determining a reasonable safe density window and imported density of drill fluid.