Analysis Of Torsional Vibration Characteristics For The Drill Pipe In Core Drilling And Related Applications

Force of the drill string is relatively complicated in core drilling, the vibrationgenerated by the interference of the extemal environmental is inevitable. Usually,vibration mainly has four forms: the lateral vibration, longitudinal vibration, torsionalvibration, coupling vibration. No matter how the drill string vibration exists, it’sinfluential on the drilling process. For example, the torsional vibration, which can causethe drill string intense resonance and lead to the drill pipe fatigue, failure, or seriousdrilling accidents.Due to the traditional elastic-plastic strength theory and numerical analysis in theinterpretation of drill string vibration problems are relatively sketchy and complex, so it isnecessary to find a new research method instead. The finite element analysis method isapplied to the simulation analysis of drill pipe in this context.This paper focuses on the formation mechanism about the deep drill stringtorsional vibrations. Based on it, we have a study on the negative impacts of thevibrationin for drilling process and the drill string itself, and then we have a discussionabout the Ⅰ、Ⅲ type crack grouth rate for the drill string under the composite load(such as alternating bending stress, radial circumferential stress, etc.) so as to estimationthe fatigue life for the drill pipe. By choosing appropriate Ansys finite element type, theauthor builds the simulation model of the parameters’ drill string. To improve theefficiency of finite element analysis software, the author uses the ADPL languages,which can directly assign a variable to the real constants, are able to get the modelanalysis results quickly.In this paper, the author mainly investigates the torsional vibration characteristicsfor the drill string in one ideal vertical hole. Firstly, we established a drill stringtorsional vibration mechanical model, which is similar to the actual drilling condition.And then we solve this equation, analyzing the motion law of the drill string virbration.By using the Ansys sofeware, we analyze the dynamics of the drill string. We study thevariation of natural frequency of torisions undering some different factors (such asambient temperature, mud density, drill hole wall space, etc.). At the same time, theauthor gets the inherent vibration patterns of drill string before six order, and analysisthe relationship between vibration response, drilling depth and BHA. Further, the authorhas a discussion about the linear structural in response to the results of the post withstand changes over time when harmonic load, and makes a prediction about thecontinued dynamic characteristics of drill string. Conversely, analytic results provide areference basis for determining the rig’s critical rotating speed of resonance，optimizingthe rig drilling BHA, dealing the weak parts of the mechanical on drill, which are veryimportant to guide the vibration in drilling engineering.Based on the results of the drill string torsional vibration analysis, the authordiscusses the vibration problem in Dagangshan Hydropower Station deep-hole curtaingrouting hole drilling work. By combining with coring data and high frequencyborehole inclinometer data, the author analyses the influence of the vibration on thequality of drill hole in curtain grouting. Because the drill string vibration and boreholebending are a mutual causal, in order to guarantee the apex deviation is undering thecontrol by the design range, we put forward some measures to prevent drill piperesonance occurs according to the features of this project. Practice has proved that,Ansys drill string torsional vibration analysis results really have higher economic value,significant effect, and can improve the quality of engineering greatly.