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文章通过水平井井内切点以上非垂直井段钻柱弯曲刚性对轴力和摩擦力的影响分析，采用了弹性梁的变形微分方程以及单元体的静力平衡和力矩平衡关系，建立了钻井时轴力的二维计算模式，同时，对切点以下导向动力钻具组合采用纵横弯曲法大变形进行分析时，考察了动力钻具结构弯曲角的影响，得出导,向动力钻具三弈矩方程组，并对DTU钻具组合中第二段梁内存在方向相反的两个结构变角对其梁柱左右端角增量及变形前后的梁柱右端痊移进行分析，得出了DTU钻具组合的井底钻压计处模式，并给出了利用钻井时的钻重的视压力，计算出井底钻压的方法及步骤。

A RESEARCH ON BOTTOM HOLE BIT WEIGHT IN A HORIZONTAL WELL

Through analyzing the influence of drill stem buckling rigidity of the non vertical interval above wellbore tangential point of a horizontal well on axial force and friction force,a 2 D calculation mode of the axial force during drilling is set up in the paper by applying elastic beam deformation differential equation and the relation between the static equilibrium of unit body and its moment balance.Meanwhile three bending moment equation group of steerable dynamic drilling tool is derived in consideration of the effect of the structural bending angle of the dynamic drilling tool,when the steerable dynamic drilling tool assemblage under wellbore tangential point is analyzed by use of longitudinal transversal bending strong deformation method.The downhole bit weight calculation mode of DTU drilling tool assemblage is obtained through analyzing the two structural bending angles with a contrary direction in the second interval of the bean column in the assemblage,the rotary angle increments at the left and right ends of its bean column and the displacement value at the right end of the bea ncolumn before and after deforming.Finally,the method and procedure of calculating downhole bit weight by use of the drilling weight and apparent pressure during drilling are proposed in the paper also.