中文摘要：

井底压差和三向地应力是钻井过程中影响井底岩石应力分布的主要因素,从而影响钻井机械钻速。主要针对欠平衡、平衡、过平衡和气体钻井4种钻井条件下三向地应力对井底应力分布进行定量研究。在井底岩石力学分析的基础上,建立了考虑正断层模型下的三向地应力、液柱压力和孔隙压力因素时的井底岩石流-固耦合模型,采用数值计算方法进行求解。结果表明,三向地应力差相同时,井底面岩石最大主应力与井底压差无关,井底面岩石最小主应力随井底压差增大而增大;不同钻井条件下井底面最小主应力与水平最小地应力无关,且随水平最大地应力增大而减小;不同钻井条件下井底面最大主应力与水平最大地应力无关,当井底压差存在时,其随水平最小主应力增加而减小后逐渐趋于稳定;当气体钻井时,其与水平最小主应力也无关。针对走滑断层和逆断层模型时的井底应力场尚需进一步研究。不同井底压差和三向地应力时井底岩石应力分布的定量化研究为实际钻井条件下钻头破岩机制研究和快速高效破岩提供理论基础。

英文摘要：

The bottom-hole differential pressure and the three-dimensional in-situ differential stress are the main factors during drilling that affect the distribution of the bottom-hole rock stress;and then affect the drilling speed.The purpose of the article is to quantitatively study the effect of the three-dimensional in-situ stress on the bottom-hole stress distribution under the overbalanced,balanced,underbalanced and air drilling condition.On the basis of the mechanical analysis of the bottom-hole rock,the fluid-solid coupling model with the factors of the three-dimensional in-situ stress of the normal fault,fluid column pressure and pore pressure is set up,without analytical solution of the model;and then the numerical solution method is used to resolve it.The results show that the maximum principal stresses of the bottom-hole surface under different drilling conditions are the same;the minor principal stress increases with the increase of the bottom-hole differential pressure.The minor principal stress decreases with the increase of the horizontal maximum in-situ stress,and keeps stable when the horizontal minimum in-situ stress changes under differential drilling condition.The maximum principal stress of the bottom-hole surface firstly decreases with the increase of the horizontal minimum in-situ stress and keeps stable with the existence of the differential pressure and it keeps stable during air drilling while the horizontal minimum in-situ stress changes,and keeps stable when the horizontal maximum in-situ stress changes under differential drilling condition.Distribution of the bottom-hole stress field of the reverse fault and strike-slip fault is to be studied.Quantitative study of the bottom-hole stress distribution with differential pressure of bottom-hole and three-dimensional in-situ stress provides a numerical stimulation method for study of bottom-hole stress field under actual drilling condition and is the theoretical basis for faster and more efficient drilling.