Drill Pipe Joints And Casing Friction And Wear Problems Of Experimental And Theoretical Research

Drilling time will be lasted and lateral force on casing exerted by drill pipe will increase in case of drilling deep well, ultradeep well, high inclined hole, extended reach well and horizontal well, therefore, friction and wear between casing and drill pipe became a severe problem. It can lead to not only quick wear and early failure of drill pipe but also the decrease of collapse resistance and burst resistance of casing string, which could cause casing collapse, casing deformation and casing leak, even well bore abandonment. Thereby, this paper has carried through an in-depth study on wear mechanism between tool joint of drill pipe and casing, problems caused by wear and measures to deal with wear based on researches at home and abroad. The research contents include:In order to reveal mechanism of wear occurred between tool joint and casing, distribution of the contact pressure between the tool joint and casing for different loads was obtained with finite element method. Furthermore, the mathematical model of maximum contact pressure and the wear depth on casing was established. The results have given the reason of tool joint with one side hardbanding and double sides hardbanding could reduce casing wear, and the theoretical foundation and technical guidelines to technology of tool joint hardbanding.This paper has illustrated mechanism of heat checking of tool joint, hence measures against heat checking was put forward. Especially for the longitudinal heat checking of tool joint, the hoop toughness criterion of tool joint material was put forward to prevent the heat checking. Based on analysis for field failure cases, minimal hoop impact work by means of mechanical calculation has been obtained, which can be used to modify the relevant contents of API RP7G.By using finite element method, full-scale tests and the strain survey method, as for the crescent-shaped wear casing, this paper has discussed on mechanism of casing collapse and its influence on casing collapse. Furthermore, computing method for both uniform wear and crescent-shaped wear situation was introduced, which can be used directly for casing string design.According to the researches on working principle of wear-resistant alloy, the ideas on selecting the new-typed wear-resistant alloy were put forward, which are "equilibrium wear design" and "stability" concept. Three kinds of new wear-resistant alloy that can be used for hardbanding on tool joint were developed, and wear experiments have showed that its property is as good as or better than that of abroad.The highlights of this paper include: hoop toughness criterion for longitudinal heat checking of tool joint was introduced firstly; failure criterion for crescent-shaped wear casing was established according to the results of full-scale collapse tests; new-typed alloy for hardbanding of tool joint was developed, its property has showed good performance in the tests.