论文部分内容阅读
钻井井壁稳定是钻井过程中的复杂性问题。当水平井筒穿过储层天然裂缝时,天然裂缝可能在较小的井底流体压力下发生剪切破坏,造成井壁垮塌。为此,基于弹性力学和岩石力学理论,并考虑岩石孔隙弹性和热弹性效应影响,推导了井壁主应力计算式。视天然裂缝为地层中的结构弱面,基于主应力与天然裂缝法向的空间位置关系,得出了天然裂缝法向与井壁最大主应力夹角计算式,结合弱面结构剪切破坏准则,得到维持井壁稳定的最小井底流压数学求解模型,提出了模型求解和井壁稳定流压获取方法。通过公式推导及计算实例分析可知:天然裂缝倾角和走向、原地应力和水平井方位将影响钻井过程中防止井壁垮塌的最小井底流体压力的设计,也即影响安全钻井液密度的选择。
Drilling shaft wall stability is a complication in drilling. As horizontal boreholes pass through natural fractures in the reservoir, natural fractures may shear under small fluid pressure in the bottomhole, causing collapse of the borehole wall. Therefore, based on the theories of elasticity and rock mechanics, and taking into account the influence of rock pore elasticity and thermoelasticity, the formula for calculating the principal stress of borehole wall is deduced. Considering the natural fracture as the weak surface in the stratum, based on the spatial relationship between the principal stress and the natural fracture normal, the formula for calculating the angle between the normal direction of the natural fractures and the maximum principal stress of the wellbore is obtained. Combined with the shear failure criterion , The mathematical model of the minimum bottom hole flow pressure to maintain wellbore stability was obtained and the model solution and the steady pressure acquisition method of wellbore stability were proposed. Through formula derivation and calculation example analysis, the natural fracture inclination and direction, in-situ stress and horizontal well orientation will influence the design of the minimum borehole fluid pressure to prevent collapse of the wellbore during drilling, that is to say, the choice of the density of the safe drilling fluid.