Analysis Of Drill String Dynamic Characteristics In Horizontal Well Hole

With the development of new drilling technology and the deepening of oil and gas exploration, lots of advanced technology such as horizontal wells, multilateral wells, rotary steerable drilling and geo-steering drilling have received a high degree attention and been developed rapidly. How to predict and control borehole trajectory scientifically and effectively has always been the emphases and difficulties in drilling engineering field. The drill string dynamics research is the cornerstone of the whole drilling engineering and it is becoming more necessary to study the drill string dynamics characteristic in horizontal well hole.In this paper, there are two main research methods. Firstly, get an intuitive understanding about the dynamics characteristic of horizontal drill string by indoor simulated experiment. Then, establish a numerical model for analyzing the dynamics characteristic of horizontal drill string. What’s more, solve the numerical model and try to optimize it through the simulation experiment results. Finally, analyze the dynamics characteristics and motion trajectory characteristics of drill string comprehensively.The similarity criterion of simulation experiment has been deduced by the method of dimensional analysis and a simulation experimental device for investigating the motion states of bottom drilling string in horizontal well has been designed and built up according to the geometric similarity ratio 1:10. The device can measure WOB, rotary speed, lateral vibration and bit side force at the same time as the drilling parameters changed. On the basis of simulation experiment device, drill string dynamics characteristics in horizontal well have been analyzed including lateral displacement, lateral vibration frequency, motion trajectory and fluctuating weight on bit.Apply the theory of rotor dynamics from the perspective of mechanical vibration and fully consider the influence of weight of drill string, fluctuating weight on bit, friction between drill string and the wall of well and drilling fluid, established a numerical model for analyzing horizontal drill string dynamics characteristics through energy method. In addition, discretized the generalized coordinates of the numerical model by using assumed mode method, and deduce the differential iteration format of the numerical model by Newmark—β method. Finally, analyzed the dynamics characteristics of drill string and verified the rationality of the numerical model.Using the numerical model established in this paper, firstly, analyzed the influence of WOB and rotary speed to drill string dynamics characteristics and motion trajectory of the center of drill string, achieved the dynamics characteristics of drill string in horizontal well and the law of drill string motion trajectory. Secondly, analyzed well hole parameters comprehensively, including deviation angle, rock’s modulus of elasticity and friction between drill string and the well wall rock. For another, the influence of drilling fluid has been studied and figured out the influence rule of gravity to drill string dynamics characteristics and motion trajectory. A full understanding of rotary drill string dynamics characteristics and motion law in horizontal well has been achieved.Realized bit side force by the indoor measurement and divided the bit side force into azimuth force and inclination force. The change law of bit side force has been analyzed by simulation experiment. On the basis of the change rule of bit side force, the drilling tendency of horizontal well hole has been analyzed.