Metal Stator Lining Linetype Design Of Positive Displacement Motor And Tube Hydroforming Method Research

With the rapid growth of domestic demand for crude oil, and drilling workload increased year by year, thus promoted the development and application of downhole drilling tools. Some advanced efficient drilling tools and new technologies were developed and applyed, and played a key role for improving the comprehensive technical and economic index of oil and gas drilling. Positive displacement motor(PDM) as one of the most widely used downhole tools, Especially with PDC bits, can get a higher economic efficiency. As the drilling technology progress and increasingly complex wells, it is inevitable to improve deep or superdeep well drilling technology, and under high temperature, high pressure, high stress conditions formations. However, general PDM stators are poor resistance to high temperature, and can’t meet the needs of the drilling environment. Therefore, the metal stator will play a key role in the development of the oil drilling.However, metal stator lining which is a large length-diameter ratio screw curved iso-wall thickness tube is processing difficulties to use the traditional method, and poor fit precision. Based on the above consideration, tube hydroforming(THF) is presented to process metal stator lining, so as to acquire high-performance PDM with high precision and high temperature resistance. THF process is an integral plastic processing method, involving with geometric nonlinearities, material nonlinearities and nonlinear boundary conditions. The influence factors also include material mechanics performance, tube geometrical shapes, die geometrical shapes, loading path and technological parameter. Therefore, the THF process is complex.In the paper, the main study object is metal stator lining linetype design and THF process, the following researches were completed:(1) Based on the forming principle of gear pair, the unified parametric equation of motor was built. Since the metal stator lining can’t compensate linetype kink, based on the unified parametric equation, linetype curvature and fixed contact point maximum curvature were chose to evaluate contact conditions and sealing property of motor linetype. The optimized objective function of linetype parameters was built by open area, offset distance, centrifugal inertia force of rotor and maximum sliding speed, so as to design the linetype with high volumetric efficiency, smooth continuous and reliably sealing for metal stator lining.(2) Based on elastoplastic deformation and cylinder problem theory, the stress strain states of metal stator lining in the THF process was analyzed. Ultimately The tube material selected stainless steel304in the paper, which is large plastic deformation and high forming strength. Several material mechanics parameters parameters had measured according to the test. The result provided the theoretic foundation for building metal stator lining mechanical model and tube THF numerical simulation.(3) The finite element model of parametric sensitivity analysis for metal stator lining THF process was built. Three evaluation criterias of metal stator screw lining forming quality are presented as "fillet stick mold coefficient, thickness relative error, forming quality coefficient" against the special section shape. Consideration the effect of tube size, dies load, loading paths and friction coefficient, the selection criteria was acquired. According to the spring back analysis results, the spring back had affected forming quality less. Thus, the precision of metal stator lining can be satisfied by external pressure forming.(4) The experimental apparatus was designed for Tube THF tests, and based on the results of numerical simulation, the THF tests was carryed forward. The results show that the experimental results primarily agreed with numerical simulation results, so numerical simulation could provide theoretical basis for early stage of metal stator lining forming experiment and application, and could effectively improve the efficiency of forming parameters design and save tests cost. Therefore, based on the numerical simulation and experimental method, it is feasible to obtain the metal stator lining with high forming quality.Through the theoretical derivation, numerical modeling and THF test, the results can provide the theoretic foundation for acquiring metal stator lining with high precision and lowcost, and will play a key role for the development of special blocks and the sustainable development of oilfield drilling. Furthermore, the research of metal stator lining PDM can promote the industry development in China, and provide the powerful technical support for the development of drilling technology.