Research On Performance Tests And Evaluation Of Controllable Flexible Sealing In Snubbing Service

Snubbing service is an advanced workover job process.When there is wellhead pressure,snubbing service equipment will control the wellhead pressure to realize wellhead seal and conduct pulling and down string or increase production.The main advantage is the ability to minimize the formation pollution and energy loss,high efficiency,safe,reliable,meeting the requirements in energy saving and emission reduction.Many foreign countries even stipulate oilfield workover job must be implemented with snubbing service,and snubbing service in China also shows the vigorous development.It will have a broader application space and the market in the future.In snubbing service environment the blowout preventer seal rubber core plays a role on sealing,the bottom hole high-pressure,and has a decisive impact on the success of snubbing service.Its process and characteristics determine this seal type is controllable flexible seal.Snubbing service controllable flexible seal material is a polymer with high comprehensive properties,and the deformation and force status of these polymers under external force determine the mechanical properties of the material under snubbing service environment;the surface friction and wear properties between the polymer and the tubing string determine the controllability of the flexible seal vice performance good or bad.The experimental study on the mechanical properties and surface friction and wear properties of snubbing service controllable flexible seal material is significant to improve the snubbing service controllable flexible seal properties.On the basis of the analysis in the superelasticity mechanical behavior of the controlled flexible sealing.material with snubbing service,the author makes compression experiments under snubbing service conditions with three flexible sealing materials,nitrile rubber(NBR),hydrogenated nitrile rubber(HNBR),and new polyurethane(PU)elastomer,analysis of the constitutive equation of the three materials in a compressed state,calculates their adaptability in different snubbing service operating conditions,and summarizes the mechanical properties that snubbing service controlled flexible sealing material should have.By friction and wear experiments,the author analyzes friction performance of snubbing service controlled flexible sealing material and wear mechanism of the three materials,and compares their wear in different abrasive wear conditions,studies how the friction coefficient and mechanical properties affect the wear.At last,the author provides the evaluation methods about snubbing service controlled flexible sealing.The main contents and results are as follows:(1)Make compression experiments with snubbing service controlled flexible sealing.Snubbing service controlled flexible sealing in the working state mainly bear compressive stress,by compressive experiments,determine the compressive stress-strain curves of the three flexible seal material NBR,HNBR and PU elastomer,by using ansys,determine the constitutive models and parameters of the three materials with compression deformation.(2)By use of the different constitutive models and parameters of the three kinds of snubbing service controllable flexible sealing,in snubbing service working environment,make controllable flexible sealing rubber core model by ansys,study the stress-strain of the three sealing materials in different formation pressure conditions,analysis of the adaptability of the three sealing materials,summarizes the performance that snubbing service controllable flexible sealing material should have.(3)By the friction experiments made by friction and wear testing machine,analyze a change law the friction properties of snubbing service controllable flexible sealing materials changes with load(pressure)and speed(sliding velocity),and compare how their friction coefficients are different.(4)Through the field experiments,analysis the wear mechanism of three kinds of snubbing service controllable flexible sealing rubber cores,come to that abrasive wear is the main factor to affect HNBR and PU rubber core sealed,for the NBR rubber core with larger friction coefficient,friction and wear is the main factor to affect the sealing performance.By comparing the abrasive and wear of the point contact,line contact and surface contact experiments and analysis,the article summarizes the characteristics of the three sealing materials in the wear surface state and the product of different abrasive wear conditions,research the wearing effect of the coefficient of friction and material mechanical properties of materials.(5)The article says the evaluation method of the snubbing service controllable flexible sealing performance,its sealing failure displays tearing of the material,the material yield,the excessive wear of sealing pair,for three kinds of failure form,the paper has given the different evaluation methods.