Design And Optimization Of High Temperature And High Pressure All-Metal Soluble Bridge Plug

Soluble bridge plugs are now widely used in unconventional oil and gas resources pumping bridge plug injection process because of their advantages of self-dissolving in the well,reducing operation process and improving fracturing efficiency.For the soluble bridge plugs in the downhole work often fail to seal the rubber cylinder,low pressure-bearing capacity and other problems,this paper takes the bi-directional seated all-metal soluble bridge plugs with high pressure-bearing and load-bearing force as the research object,proposes the use of soluble magnesium alloy instead of soluble rubber,and designs a bi-directional force-bearing soluble bridge plug with high pressure-bearing through structural design optimization,seating process simulation and contact mechanics performance analysis.The main results are as follows:(1)High temperature and high pressure resistant full-metal soluble bridge plug structure design.The bridge plug structure design mainly contains anchoring mechanism,sealing mechanism,center tie rod and other parts.The anchoring mechanism mainly contains three parts,namely,slip base,slip seating pin and cone.The slip base is made of high strength soluble magnesium alloy with dovetail structure;the slip seating pin is made of hard zirconium oxide ceramic with cylindrical structure;the cone is made of conical cylinder structure with the same material choice as the slip base.The sealing structure mainly contains two parts: metal seal ring and gasket ring.Both the metal seal ring and gasket ring are made of soluble magnesium alloy with high elongation.The center tie bar is a rod structure made of stainless steel.(2)Setting process simulation and mechanical performance analysis.This paper simulates the seating motion of the soluble bridge plug,and studies the deformation and stress distribution of the fracture ball cone sealing mechanism,the annular hollow sealing mechanism and the kava anchoring mechanism in the seating process.The results show that the bridge plug can complete the whole seating process when the axial displacement of the center tie rod is 64.50 mm.Under105 MPa fracturing load,the contact stress between fracture ball and cone is 700 MPa which is more than 3 times of the fracturing load,while the contact width is 3.86 mm which is more than1.5 mm,which is in accordance with the metal seal determination criterion,and the contact seal can be considered reliable during the fracturing process.The designed annular seal mechanism has a contact stress of 309 MPa and a contact width of 5.4 mm between the seal ring and the casing during seating and sealing,which meets the metal seal reliability requirements.The maximum local equivalent force of 436 MPa in the cavity wall of the cavity base during the seating and sealing process is greater than the tensile strength of the material 380 MPa,which indicates that the crushing phenomenon has occurred at the edge of the cavity wall and will affect the anchoring performance of the cavity and the casing.(3)Slip anchoring mechanism optimization.It was found that the uneven distribution of the seating pin post and casing bite depth in the axial direction would lead to insufficient bridge plug load capacity.In this paper,we study the effects of the changes of structural parameters of casing axis angle,casing depth,casing front end distance and casing inclination angle on the bite depth of the casing and the stress distribution of the casing base.The maximum bite depth and the extreme difference of bite depth are used as evaluation indexes,and orthogonal experiments are applied to obtain the optimal structural parameters of the cavity groove.The optimized cavity tooth groove axis angle is 28°,tooth groove depth is 6.7 mm,tooth end distance is 13 mm and cavity seating pin inclination angle is 65°.Compared with the pre-optimized cavity,the maximum equivalent force of the casing is reduced by 4.1% and the bite depth is increased by 4%.(4)Optimization of annular seal mechanism.Based on the designed seal ring structure,three seal ring optimized structures are proposed,and the effects of four different outer surface shapes of seal rings on their contact sealing performance with the casing are analyzed by contact stress,contact area,plastic strain,and support reaction force.The results show that the complex structure surface can strengthen the contact sealing performance of the seal ring.At the same cone displacement of 64.50 mm,the contact stress of the four structures differed by 15.6%,29.1% and 5.1%,the contact area differed by 15.7%,72.5% and 17.7%,the plastic strain differed by 1.51%,6.56% and 0.03%,and the support reaction force differed by 2.6% and 25.6%.The differences were 2.6%,25.8%,and 12.3%.The comprehensive performance of the four seal rings was compared,and it was found that the hyperbolic structure had the best sealing performance,the double groove structure was the second best,and the elliptical structure was the worst,so the hyperbolic seal ring structure was selected as the optimized annular hollow metal sealing mechanism.