底部钻具组合动力学模型及涡动特性仿真

Dynamics model and whirl features' simulation of bottom hole assembly

根据转子动力学理论,把底部钻具组合(BHA)简化成Jeffcott转子模型,同时考虑不同钻压形式对BHA的作用建立BHA的动力学模型,并对BHA的动力学特性进行数值仿真。结果表明:钻压的形式只影响恢复力项,对动力学模型的一般形式无影响;在不同钻压形式的作用下,BHA的动力学特性总体上保持一致;钻压为常数时BHA主要体现为经过一段时间的波动后转为规则向后涡动的特性,钻压为波动值时底部钻具组合也主要体现为向后涡动的特性,但BHA更容易贴着井壁运动。

According to the theory of rotor dynamics,bottom hole assembly（BHA） was seemed as Jeffcott＇s rotor model.And a dynamic model of BHA was established by taking into account different forms of weight on bit and its dynamic properties were simulated.The results show that weight on bit has nothing to do with the model form but the restoring force.With the different forms of weight on bit,the dynamic properties of model are coincident as a whole.The dynamic features of BHA mainly reflect in the volatility over a period of time and change to the regular backward whirl when weight on bit is constant,while the properties of BHA also mainly reflect as the regular backward whirl but the motion of BHA can be easier to cling to the borehole wall when weight on bit is not constant.