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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。
Bottomhole pressure difference and three-direction ground stress are the main factors influencing rock stress distribution during drilling, which affects the drilling penetration rate. The three-direction in-situ stress underbalanced, balanced, overbalanced and gas drilling conditions is used to quantitatively study the bottomhole stress distribution. Based on the rock bottom mechanics analysis, a fluid-solid coupling model of rock bottomhole is established when three-direction geostress, liquid column pressure and pore pressure are taken into account in the normal fault model. The numerical calculation method is used to solve this problem. The results show that the maximum principal stress of the bottom rock is independent of the pressure difference at the bottom of the well, and the minimum principal stress of the bottom rock increases with the bottom hole pressure difference. The minimum principal stress The minimum horizontal stress has nothing to do with the maximum horizontal stress increases and decreases; under different drilling conditions, the maximum principal stress on the bottom of the well has nothing to do with the maximum horizontal stress; when the bottom hole pressure difference exists, it decreases with the minimum horizontal principal stress Small gradually gradually stabilized; when the gas drilling, it has nothing to do with the minimum level of the main stress. For the strike-slip fault and reverse fault model when the bottom hole stress field needs further study. The quantitative study of rock bottomhole stress distribution under different bottomhole pressure difference and three-direction ground stress provides the theoretical basis for the study of rock breaking mechanism and fast and high-efficiency rock breaking under actual drilling conditions.