复杂结构井旋转下套管数学模型建立与分析

随着复杂结构井钻井技术发展,井斜角和方位角随着井深复杂变化引起常规套管下入方式难度大,旋转下套管技术可有效解决套管下入的难题,但该方面的理论模拟分析报道较少,增加了旋转下套管技术应用的盲目性和低效性。综合运用软杆和刚杆模型的优点并考虑井眼轨迹对模型计算条件影响,建立了旋转下套管数学模型;结合实例井对比了大钩载荷和模拟的轴向应力,验证了模型的正确性;在此基础上,探讨了常规和不同旋转速度下套管的摩阻,并分析了不同摩阻系数条件下的摩阻分布特征。实例分析表明：相同井深下,旋转下套管摩阻小于常规下套管摩阻,并且旋转速度越快,下套管摩阻越小;当旋转速度分别为15r/min和20r/min时,井底处摩阻降低幅度分别为12.13%和19.17%;造斜率越大,摩阻越高,导致套管下入到指定深度难度加大;钻井液摩阻系数越大,套管下入难度越高;在井深1401.5m,裸眼段摩阻系数分别为0.21和0.29,常规下套管摩阻分别为46.51kN和57.49kN。该模型能准确预测下套管摩阻,对复杂结构井的套管下入具有指导意义。

Research on the developing mathematical model considering the running casing with rotating in complex structure well

With the development of drilling technology in complex structural wells, it is difficult to run casing by conventional methods due to the complex change of deviation angle and azimuth angle with well depth. The running - casing with rotating technology can solve the problem of running casing effectively, but few theoretical analysis was reported in this field, which increases the blindness and inefficiency of the application of running casing with rotating technology. The mathematical model of rotating casing running is obtained by using the advantages of soft rod and rigid rod model comprehensively and considering the influence of wellbore trajectory on model calculation conditions. The correctness of the model is verified by comparing the load of the hook with the simulated axial stress. On this basis, the friction of casing under normal and different rotating speeds is discussed, and the friction distribution characteristics under different friction coefficients are analyzed. The case analysis indicates that the casing friction with rotation is less than that of conventional method in the same well depth, and the faster the rotation speed is, the smaller the casing friction is. When the rotation speeds of casing are 15 r/min and 20 r/min, the decrease degree of the friction resistance at the bottom are 12.13% and 19.17%, respectively; The greater the slope is, the higher the friction, leading to the casing be more difficult to run into the specified depth; the greater the friction coefficient of drilling fluid is, the higher the difficulty of running casing is; the friction coefficient of open hole section is 0.21 and 0.29 at the depth of 1401.5 m, corresponding to the friction of conventional casing be 46.51 kN and 57.49 kN, respectively. The developed model can accurately predict casing friction, which has guiding significance for running casing in complex structural wells.