A Study On The Degree Of Casing Wear Considering The Buckling And Whirling Effects Of The Drill String

Casing wear is one of the main factors affecting wellbore integrity.Accurately predicting the degree of casing wear has significant practical significance in ensuring wellbore integrity and preventing safety accidents.In the actual drilling process,due to the vibration of the drill string and the bending of the wellbore trajectory,the shape and motion of the drill string are very complex.When the drill string is compressed beyond a certain critical load,it is in a state of sinusoidal buckling,spiral buckling,or whirling motion.After the drill string buckles,the gap between it and the inner wall of the casing becomes smaller,making it easier to scratch the inner wall of the casing.The whirling of the drill string can cause friction between the drill string and the inner wall of the casing,thereby inducing casing wear.In order to obtain more accurate prediction results of casing wear,this thesis analyzes the impact of drill string buckling and drill string whirling on casing wear.The research work and important conclusions are as follows:Identified the mechanism of casing wear under the impact of drill string friction on casing and the factors affecting casing wear.A finite element dynamic model was established for the stable state,sinusoidal buckling state,and helical buckling state of the drill string.Through dynamic simulation,the whirling characteristics of the drill string at different positions in the two buckling states were analyzed.The results indicate that the whirling of the two buckling states of the drill string mainly occur in the bottom hole assembly,and overall,the whirling gradually decay from the bottom of the well to the wellhead direction.A calculation model for casing wear volume was established,and the casing wear volume corresponding to different parts of three types of drill strings was quantitatively analyzed.The degree of casing wear was compared between the sinusoidal or spiral buckling state drill string and the stable state drill string,and the impact of sinusoidal or spiral buckling on casing wear was investigated.The results indicate that when the drill string undergoes sinusoidal or spiral buckling,the wear of the casing at each position of the entire wellbore section will increase.Among them,the increase in casing wear caused by the spiral buckling section of the drill string is the most significant compared to the stable state,with an increase of 767.91% under the working conditions of 100 r/min drill string speed and 40 k N drilling pressure.Taking the spiral buckling drill string as the research object,the influence of key parameters such as drill string speed and drilling pressure on whirling of the spiral buckling drill string and the degree of casing wear was investigated.The results indicate that if the influence of critical speed on the spiral buckling state of drill string whirling and casing wear is ignored,as the drill string speed increases,whirling of the spiral buckling drill string becomes more severe,and the degree of casing wear becomes deeper;As the drilling pressure increases,the spiral buckling drill string whirls more violently,and the degree of casing wear deepens.When the drilling pressure reaches a certain critical value,continuing to increase the drilling pressure will significantly increase the degree of drill string whirl,significantly increase the degree of friction between the drill string and the casing,and sharply deepen the degree of casing wear.