Dynamic And Reliability Research Of Drill Stem Considered Clearance Between Drill Stem And Formation

The domestic and foreign research indicated that, the position with failure of the drill pipe mostly occurs in the part which the axial load and the torque load is in the smallest spot, some scholars and the overseas research facility think it is closely related with rotational speed and clearance between the drilling tool and the wall of a well. This article unifies the national natural fund subsidization project"the new drilling engineering research under complex drilling condition well"(50234030), and study dynamic and reliability research of drill stem considered clearance between drill stem and formation, the achievement obtained had the good application prospect in the petroleum well drilling profession. The summary in the present paper research is as follows:(1) Theory analysis of drill stem considered clearance between drill and formationThe rotary stem in vertical well is a very complex self exciting vibration system with much supporting. It is extremely difficult to carry on the theoretical analysis and the numerical simulation to this kind of system. This article first studied the transverse vibration as well as the bending stress of a single drill stem which caused by the whirling motion.Because the drill stem vibrates in the drilling fluid, the influence caused by the drilling fluid can not be ignored. This article studied how the drilling fluid influences the transverse vibration natural frequency thinking of clearance between the drill stem and the formation.The longitudinal vibration is important in the dynamic character. This article studied the longitudinal vibration of the drill stem and numerical simulation of longitudinal vibration is calculated using finite element method. This method can simulate longitudinal vibration and the harmonic response of the drill stem. The whirl of the drill stem can affect the dynamic character of drill stem greatly, it is thought more energy would be used to overcome the friction while whirling. The whirl character is greatly correlated with clearance between the drill stem and formation. The whirl character of the bottom hole assembly is studied in this article.(2) Lagrange model and ALE fluid and solid coupling model of collision between drill stem and the wall of a wellBased on the collision characteristic between the drill stem and the wall of a well, the Lagrange method was introduced to the collision analyzes between the drill stem and the wall of a well. The matrix differential equations containing strain and stress were obtained using the momentum equation, the mass-conservation equation, the energy equation and time integral method. The non-polynomial displacement function considering the reference configuration and the current configuration three-dimensional space drill stem and the wall of a well also found. The integral stiff matrix was established using 8-node hexahedron solid elements to solve the collision between the drill stem and formation. This article studied collision mechanism and stress field and the strain field change situation during the contact process.The arbitrary Lagrange-Euler (ALE) fluid-solid coupling model of well, stem and formation is established. The drill-drilling fluid system in collision is studied by ALE method The ALE method allows deformation and displacement in fluid area. This article uses ALE method to describe the fluid, and use Lagrange to describe the solid area. Stress and strain of the drill stem is obtained considering the fluid influence.(3) How the clearance influencing the normal drilling and casing drillingThis article finally discussed how the clearance influences the normal drilling and casing drilling, from whirling frequency, tool wear and fatigue failure of drill stem. When the clearance between the drill stem and formation decreased and the rotate speed increased, the fatigue strength of drill tem will decrease. The fatigue failure in casing drilling occurs more than normal drilling.(4) The drill stem reliability research considering clearanceThis article using clearance analysis and CAE technology studied the drill stem reliability, combining the domestic and foreign research aspect the achievement and based on this article research progress. Casing drilling reliability considering clearance and how to avoid casing and drill stem resonance point also was taken into account , because the clearance in normal drilling process are different from casing drilling process.