Simulation Of Dynamic Seal Performance Of The Rubber Core In Ram Bop With Snubbing

The snubbing.service can reduce the pollution to the reservoir,maximize the protection of original formation and improve the working environment.At the same time,the snubbing service can safeguard the oilfield stable yield of later period and its unique advantage has been widely recognized in the industry.Ram preventer is the core of the snubbing service,realizing the online sealing by the rubber core of open and being closed to control the wellhead sealing,and completing work with snubbing.Therefore,the sealing ability and life of the rubber core is the key factor of the snubbing service.Although the domestic development of ram preventer seal pressure is higher and higher and ram preventer pressure can reach 140 mpa,it can not be used to seal the dynamic sealing or rotating and the life of the seal is less than half of the same abroad products.At present,the pressure level of the rubber core that can be used to dynamic sealing is less than 35 MPa domestically,which restricts the development of the domestic snubbing service for overhaul,ultra-high pressure,the special type Wells with pressure operation.Therefore,developing the rubber core of which the dynamic sealing pressure is greater than 35 MPa,which is very necessary and urgent.First of all,the paper obtains rubber core working conditions and the characteristics of load by the analysis of the working process of the snubbing service and studying the structure,materials and working principle of the rubber core which is existing in the domestic and foreign and is used to the snubbing service.Combining with engineering practice,the paper analyses the mechanical behavior of the rubber core used by the oil field,and establishs the physical model of the rubber core.According to the theory of fluid seal and seal criterion,the paper analyses the static and dynamic sealing mechanism of rubber core.Secondly,the paper obtains the stress strain curve of the material of the rubber core by the mechanics performance test,and determines the suitable model for the rubber core to express rubber material constitutive model by contrasting several rubber constitutive relation for software fitting.Then,based on the constitutive model of rubber material,using ABAQUS software to establish ram preventer rubber core seal string static simulation model,the paper gets the stress distribution of the rubber core in relatively static state,and competes with the failure place of the rubber core in the oil field to verify its correctness.Based on the static simulation model,The paper analyses the influence of thewellbore pressure,the liquid pressure of piston rod,the rubber material to the distribution of the Mises stress,contact stress,gets the rule,and provides the reference of optimization selection of the structure of the rubber core size and working condition.Finally,based on the finite element analysis,the paper optimizes the rubber core material and the structure of the size of the wear resistant block.The main results are as follows:(1)Ogden model is best for characterization of constitutive relationship of rubber material commonly being used by the rubber core.(2)The contact pressure between the sealing surface is the main measure of rubber core sealing performance.(3)The hydraulic force is not too big,otherwise the Mises stress of rubber core exceed the allowable stress value of the material,and reduce the service life of the rubber core;Under the effect of wellbore pressure,the failure position of rubber core concentrated on the four horns of the contact area of rubber matrix and top and bottom of ram,and the top area is serious.(4)The wellbore pressure is the main factor that the top area of wear resistent block is abrased seriously;Friction coefficient between the string and wear resistant block should not be too big,or the abrasion of wear resistant block will be accelerated.(5)When the rubber matrix materials is hardness of 75 butyronitrile and s and k parameter of wear-resistant block is 10 and 8,the width is 108,rubber core can be used for the snubbing service that the dynamic sealing pressure is no more than 35 MPa.When the rubber matrix materials is hardness of 80 butyronitrile and s and k parameter of wear-resistant block is 10 and 8,the width is 108,rubber core can be used for the snubbing service that the dynamic sealing pressure is no more than 50 MPa.