Development of Thin Spherical Shell Fracture Disk Floating Collar
In order to solve the problem of the existing floating collar which are the sliding sleeve stuck and the unstable crushing pressure of the fracture disk and hard-to-pass of the subsequent tools due to the effect of the edge residual after the fracture disk crushing,and the higher tensile and internal compressive strength requirements during fracturing.A novel type floating collar was developed,which was assembled by a thin spherical shell fracture disk and a full bore shell structure.A high borosilicate thin spherical shell fracture disk for full pressure structures is designed,and is adopted the classic formula for thin spherical shell instability to determine the thickness of the thin spherical shell.The simulation results showed that when a pressure load of 60 MPa was applied to the upper outer surface,the maximum stress was concentrated on the inner side of the bottom boundary,with a magnitude of 590 MPa,which was higher than the compressive strength of high borosilicate glass,causing the fracture disk to shatter,Also designed a two-stage shell structure,with an inner diameter of Φ121.36 mm,which achieved a full bore diameter.During the simplified B-series experiment with a maximum tensile force of 2 565.32 kN and a maximum internal pressure of 102 MPa,the shell did not show any leakage,reaching the same strength as the connecting casing.Under two temperature conditions of room temperature and 180℃,simulated cyclic fracturing 100 times,no structural failure or leakage occurred.The floating collar has the characteristics of high compressive strength,stable cracked pressure and good passing performance for subsequent tool,which can meet the requirements of casing running and subsequent construction.
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