A mathematical model for predicting the attenuation of measurement while drilling (MWD) pressure pulses in aerated drilling was proposed using the two-phase flow model and considering the momentum and energy exchange at the phase interface, gravity of each phase, viscous pipe shear and other closing conditions. The small perturbation theory was used to solve the mathematical model; then, a model was established to compute the velocity and attenuation coefficient of mud pulse signal, and the simulated result of the model is in line with the measured attenuation in field test. With the mathematical model, the influencing factors for mud pulse attenuation were simulated and analyzed. The results reveal that the gas holdup, system pressure and pulse frequency are the major influencing factors. In case of low gas holdup (0-5%), as the gas holdup increases, the pulse velocity decreases drastically, and as it further increases, the pulse velocity tends to be flattened; whereas the attenuation coefficient increases gradually with the increase of gas holdup and begins to decline when it reaches maximum. At the same gas holdup, the mud pulse signal shows higher velocity under a high system pressure, and the attenuation coefficient increases faster with increase of the gas holdup under a low system pressure. Both pulse velocity and attenuation coefficient increase gradually with the increase of pulse frequency, and tend to be a stable high value when the frequency exceeds 100 Hz.%基于两相流体模型,考虑相界面的动量和能量交换、各相重力及管面黏性剪切力等封闭条件,建立充气钻井随钻测量(MWD)脉冲信号衰减的数学模型.利用小扰动理论求解数学模型,得到钻井液脉冲信号传播速度和衰减系数计算模型,模型计算结果与现场试验实测的脉冲信号衰减结果吻合较好.利用该模型计算并分析了钻井液脉冲信号衰减的影响因素,结果表明,持气率、系统压力和脉冲频率是影响钻井液脉冲信号衰减的重要因素.低持气率(0～5％)时钻井液脉冲信号的传播速度随持气率的增加而迅速降低,随着持气率的持续增加,其变化逐渐趋于平缓；而其衰减系数则随着持气率的增加逐渐增大,并在达到最大值之后开始下降.相同持气率时,高系统压力下钻井液脉冲信号具有更快的传播速度；低系统压力下钻井液脉冲信号的衰减系数随持气率增加上升速率更快.钻井液脉冲信号传播速度和衰减系数随脉冲频率的增加而逐渐增大,并都在脉冲频率大于100 Hz后逐渐趋于一个较高的稳定值.图5表1参14
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