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Research on Analysis Method of Reliability of Drilling String in Vertical Well

Author: LiWenFei
Tutor: GuanZhiChuan
School: China University of Petroleum
Course: Oil and Gas Well Engineering
Keywords: Vertical wells Drillstring Fatigue failure Cumulative damage Fatigue crack Reliability
CLC: TE921
Type: PhD thesis
Year: 2008
Downloads: 499
Quote: 0
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Abstract


Field data analysis showed that 80% of the drill string failure is caused due to fatigue. Using the method of theoretical analysis, combined with field data, analysis of the safety and reliability of the vertical wells drillstring. Drillstring buckling occurs, with the rotation of the drill string, the vibration caused by alternate drill string stress, alternating stress fatigue crack drill string continuously expansion led to the fracture of the drill string. According to the principle of energy derived drillstring buckling pitches and drill pressure model of the relationship between speed, torque, to help determine the location of the drill string in the wellbore, calculated drillstring stress. Consider fatigue factors in the the drillstring stress analysis on the basis of the the drillstring strength check model, based on static load compared with the conventional method, to improve the security of the strength of the drill string design. Combined with field data, the analysis of the variation of the of drillstring fatigue strength coefficient drilling parameters, obtained while drilling pressure, the increase of the speed, depth and reduce important conclusions and the application of the results also shows that the strength of the drill string checking must consider Importance of fatigue. Thread through the drill string joint force analysis, the establishment of the deformation coordination equation screw threads under axial load and bending loads and boundary conditions, each lap of thread load suffered formula is derived. The results show that when the drillstring connector uneven force becomes, with increasing the fillet radius of the bottom of the screw thread, the thread at the stress concentration factor is reduced; strength coefficient is increased. Drillstring fatigue S? N curve and corrected Miner linear fatigue cumulative damage theory of measure established a drillstring fatigue to accumulated damage calculation method easy drillstring fatigue damage. Examples show that with increasing depth of the well, the drill string injury is reduced; the drillstring fatigue damage is increased, as the speed increases, the order downwardly switchover drillstring is the best way, and the switchover after 6 times drill The column overall damage equilibrium. Deduced the drill collars fatigue S? The N curves expressions can calculate certain reliability under the the drill collars fatigue life convenient for engineering applications. Drill string fatigue crack crack open with a peel-off surface composite assumptions in the the drillstring stress analysis on the basis of, proposed, relatively close to the actual drill string, and the establishment of open and tear the surface recombination type crack growth rate calculation model. The analysis showed that, with the WOB, the speed increases, the number of cycles of the drill string is decreased. Established according to the law of drillstring size parameters, the parameters of the material properties and drilling parameters data distribution based on reliability theory, from the perspective of probability drillstring reliability calculation method to overcome the safety factor selected empirical, has a certain advanced nature.

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CLC: > Industrial Technology > Oil and gas industry > Oil machinery and equipment and automation > Drilling machinery equipment > Drill bits,drilling tools
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