| With the deepening exploration of the oil and gas, the highly deviated wells have gradually been used in the drilling industry as a cost-effective mean. However, as a result of the high oblique and big horizontal displacement, there exist some outstanding problems with the highly deviated wells such as high large friction torque in the drilling development, difficult borehole extending, low penetration rate and so on. For the stress state of the drill string in the wellbore is very complex, application limitations and problems of drilling statics become more prominent. How to correctly understand the drilling dynamics behavior of highly deviated wells is particularly important.The passage is aimed at the weak understanding of the drill strings’dynamic mechanical behavior problems in the process of drilling highly deviated wells, on the basis of literature research, it has established a high-angle wells full well drill string and wellbore (casing wall) finite element modeling method based on finite element software, combined with the indoor test and field drilling data to guide this study to further optimize simulation analysis, and conduct drill string dynamics numerical simulation application research of highly deviated wells. It has improved the high-angle wells drill string dynamics theory and application technology.First, it has conducted the drill string system performance analysis of a high angle well, and settled the key issues in the research of full well drill string dynamics of highly deviated wells.(1) The contact model of drill string and borehole wall:according to the contact state of drill string and borehole wall in the three-dimensional hole, it has comparatively analyze the advantages and disadvantages of penalty function method, Lagrange multiplier method and extended Lagrange multiplier method of the finite element software, to determine the passage’s selection of extended Lagrange multiplier method.(2) The model of drilling fluid damping:it has analogy analyzed the research’s achievement of the forces of straight string in the fluid in marine engineering wave mechanics, and get the drag coefficient of the drilling fluid movement of the drill string to be the damping force in the drill string dynamics analysis, so it makes the simulation analysis meet the reality condition;(3) The study about the interactive of bit and rock equivalents the contact process of the drill string and rock to a friction coefficient model, and it proposes a weak coupling model of WOB and torque on this basis, which makes the simulation more practical.Secondly, according to the actual drilling trajectory and BHA, a finite element model of the whole well drill string has been established, and it achieves a depth of two highly deviated wells full well the drill string dynamics simulation, studing the drill string dynamics of highly deviated wells combined with hook load, torque, contact force, acceleration and other features, and it has a drilling safety qualitative analysis, meanwhile, it proves the feasibility of the drill string dynamics simulation methods of high-angle wells full well. On this basis, it proves the validity of the drill string dynamics simulation method of highly deviated wells full well.Finally, a simulation techniques is applied for full hole drilling-string dynamics of highly deviated wells. It.analyzes the differences between load transfer rules during operations and load transfer rules with different casing structure (inclination, depth) parameters, giving guidance and advice on the imposed WOB、lowering friction reducing twisting layout tool in the drilling. According to the simulation results of the friction torque reduction nipple, it proves that this simulation technology can satisfy the needs of practical engineering; eventually forms a drilling-string system dynamics simulation software of highly deviated wells, providing both guidance and help for highly deviated well design, equipment selection and drilling practices. |
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