Research On Dynamic Mechanical Characteristics Of PDC Bit Under Complex Motion Conditions

PDC bit is widely used in oil and gas drilling,and the footage has reached more than 90%of the total footage of drilling rock breaking.In the process of PDC bit drilling,the motion and force conditions are very complex.Longitudinal vibration,transverse vibration and torsional vibration,will occur during drilling.Therefore,the motion and stress state of PDC bits can not be obtained by theoretical analysis alone,so it is necessary to simulate the drilling process of PDC bits.At present,the drilling simulation of PDC bit is mainly static simulation under ideal motion conditions,which will deviate greatly from the actual situation.Aiming at the above problems,this paper simulates the drilling process of PDC bit under complex motion conditions on the basis of previous studies.The main research contents are as follows:Based on the geometry of PDC bit and considering the accuracy and efficiency of calculation,this paper establishes the simulation model of PDC bit.According to the need of PDC bit drilling simulation,the bottom hole is discretized and a three-dimensional bottom hole discrete model is established.The cutting process of rock is realized.The calculation of cutting parameters such as cutting volume,cutting arc length and cutting area is completed.Real-time updating of bottom hole.The mechanical model of the interaction between PDC bit cutting teeth and rock is deduced theoretically.It is found that the error between the calculated results and the experimental data is relatively large Based on BP neural network algorithm,the mapping relationship between cutting tooth structure parameters,cutting parameters,rock properties and cutting loads is obtained,and the cutting mechanical model is established,which is verified by the single-teeth cutting experimental data.According to PDC bit simulation model,bottom hole model and cutting mechanics model,the cutting load of PDC bit under given motion conditions is calculated.The dynamic model of the interaction between PDC bit and rock during drilling is established.On this basis,considering the influence of drill string on PDC bit,dynamic models of longitudinal vibration,transverse vibration and torsional vibration of PDC bit during drilling are established.,which solved by using explicit newmark algorithm.PDC bit dynamics simulation software is developed by Matlab.The dynamic simulation of PDC bit is completed.