钻软硬交错地层时钻头弯矩及转角的计算方法

CALCULATION OF BENDING MOMENT AND DEVIATION ANGLE IN FORMATIONS WITH DIFFERENT DRILLABILITY

本文详细地分析了从软地层钻入硬地层前后,钻头上产生弯矩的原因及计算方法。根据软硬地层的可钻性不同,钻速及相应的地层对钻头的反作用力也不同的原理,推导了在钻过交界面前后钻头的转角、钻具的反力矩及软硬地层中不同钻速与时间的关系式及微分方程,给出了方程的解。求解结果表明,钻头的转角和弯矩是随时间的延长而逐渐增大,在全部钻完交界面时达到最大值;钻头弯矩与交错层的可钻性、下部钻具的结构和钻头的几何尺寸有关,并且与所加的钻压成正比。

The interaction of rock and bit has got increasing attention in hole deviation control and directional drilling. When a bit drills from a soft formation to a hard formation, the difference in rock drillabilities will cause a change in drilling speed for the same bit, and a change in formation reaction on the bit. The equations of the formation reaction, the bending moment on the bit, the deviation angle and the counter torque on the bottom hole assembly are given in this paper. Solution of the differential equations show that the bending moment and deviation angle increase with time and reach a maximum when drillling through the interface from soft to hard formation. The bending moment can be related to the formation drillability, BHA configuration and drill bit size, and is proportional to the applied WOB.