Simulated Experiment of Dynamic Characteristics of Pendulum Bottom-hole assembly under gas drilling conditions

Stabilizer is not used or used seldom in gas drilling to ensure the downhole safety.At this time , bottom-hole assembly bends easily resulted in well deviation.One of the main reasons of the well deviation in the gas drilling is dynamic characteristics of the bottom-hole assembly (BHA).Through laboratory experiment,the dynamic characteristics of the BHA were simulated under the conditions of the gas drilling and various drilling parameters.And its influence on the well deviation was analyzed.The result shows that drilling parameters,wall friction factors and others have significant effect on motion state of BHA.Under certain WOB,when the rotation speed is lower than the critical rotation speed,the BHA may be at stable forward whirling or regular oscillation.When the rotation speed is near the critical rotation speed ,sympathetic vibration occurs and the BHA may move irregularly or whirl reversely.When the rotation speed is higher than the critical rotation speed,the BHA may be at stable backward whirling.The backward whirling is favorable for deviation control.The increased WOB is not good for deviation control.Some necessary measures should be taken for reducing fiction factor and alleviating drill string vibration during the gas drilling.It makes BHA whirl backward stably along with the borehole wall,which will improve the effect of borehole deviation control.