Pear-shaped Expander Research

With the oilfield development, a lot of artificial stimulations, such as high pressure water injection, steam injection and large scale fracturing, have been applied in the production, in order to improve the production of oil wells. Casing is prone to deformation, dislocation damage etc., due to the influence of artificial stimulation, cementing quality, complicated geological condition of reservoir, corrosion of CO2and SO2and material quality of casing. According to incomplete statistics, the casing-damaged well quantity that had increased year by year exceeded15million in CNPC in2009, which have caused incalculable direct and indirect economic losses. Repair of casing damage wells have become a realistic problem urgently to be solved in the oilfield. Pear-shaped casing swage has been widely used in oil field workover operation, due to its simple operation, strong durability and lower cost. However, the theoretical analysis model of the shaping process and the analysis of optimization design scheme of the pear-shaped casing swage are rare. So a detailed research of reshaping technology of the pear-shaped casing swage has been done in this thesis.First, serious consequences of casing damage and the necessity of casing repair operation are studied by a survey of casing damage and its research status at home and abroad. Meanwhile, a research is done about the mechanism and the type of casing damage. Also, the frequently-used reshaping technologies of the casing deformation are analysed.Second, a mechanics model of reshaping process of the pear-shaped casing swage is established on the basis of the elastic-plastic theory analysis of casing. And the reshaping force (RSF) is calculated on the mechanics model.Third, a reshaping test is done using pear-shaped casing swages, and the diameters of which are122mm,125mm,128mm and131mm. The reliability of mechanics model is verified by results of the reshaping test. And the influences to RSF of taper angle of the pear-shaped casing swage and the casing ovality is studied on the basis of the mechanics model. Meanwhile, a diameter range optimization design scheme of the pear-shaped casing swage is proposed on the analysis of wear degree of the pear-shaped casing swage, RSF, pull force and springback of the casing.Last, the finite element simulation method is applied to analyse the reshaping process of the pear-shaped casing swage. And a change trend is studied about the Mises equivalent stress of the casing. A comparative method is applied to analyse the RSFs resulted from finite element simulation, reshaping test and mechanics model. Meanwhile, the finite element model is used to analyse the diameter range optimization design scheme of the pear-shaped casing swage. In addition, the finite element simulation method is also devoted to analyse the reshaping process of the pear-shaped casing swage in different confining pressures. And equations between RSF and confining pressure are established through the linear fitting mathematical method on the basis of result of the finite element simulation.The reshaping test, the mechanics model, the finite element model and the equations between RSF and confining pressure established in this thesis provide theoretical support and reference for the field repair work of the deformated casing.