Erosion Resistance of Rubber Core of BOP Ram During Shut-in Process
A large amount of fluid carrying rock debris rapidly flows out of the well when a blowout or well kick occurs.During the process of closing the blowout preventer(BOP)ram,solid particles in the drilling fluid will erode the rubber core of the ram.To address this issue,the work aims to determine the optimal erosion model for nitrile rubber and predict the erosion amount of the rubber core quantitatively,so as to provide a basis for evaluating the sealing performance of the rubber core after shut-in.Firstly,based on the erosion test of rubber specimens,the optimal parameters of the erosion model suitable for nitrile rubber material were obtained through inversion analysis by the Levenberg-Marquardt(LM)optimization algorithm.Then,this erosion model with optimal parameters was assigned to the elements of the sealing rubber core via a user defined function(UDF).A numerical model of the flow field near the BOP pipe ram was established during the shut-in process by Fluent.Finally,the erosion resistance of the rubber core was simulated,and the variation of the removal of the rubber core material with the duration of shut-in was discussed.As a result,an improved Finnie erosion model was determined by which the relationship between the erosion rate and impact angle was calculated for the rubber specimens.The maximum relative error between the predicted results and the experimental ones was only 5.77％.It could be used to simulate the erosion resistance of nitrile rubber components.By the improved Finnie model,the erosion resistance of the sealing rubber core of BOP ram was calculated during the shut-in process.It was found that the erosion of the rubber core by rock-carrying drilling fluid mainly occurred at the lip edge,the high-speed collision zone of cuttings.The erosion rate of the rubber core was linearly positively correlated with the sand content and nonlinear with the flow rate of the drilling fluid.As the opening of the ram decreased,the erosion rate grew exponentially.Under the parameter conditions proposed,when the opening of the ram was 104 mm,26 mm and 6 mm,the material removal rate of the rubber core was 1.52 mm3/s,5.22 mm3/s and 28.3 mm3/s,respectively.Therefore,the most serious erosion happened to the rubber core in the last shut-in period and before the gate was about to be closed.For the whole shut-in process,the material removal of the rubber core increased with the shut-in duration.Shut-in periods of 3 s and 8 s resulted in core removal of 5.04 mm3 and 13.43 mm3,respectively.In conclusion,both the timing and duration of closing the BOP ram during a blowout or a well kick is crucial to the management of the incident.It is necessary to comprehensively evaluate the effect of shut-in duration on wellhead dynamic loads and erosion of rubber core.Then,a scientific shut-in plan should be developed to ensure the safety of the wellbore,surface equipment and construction personnel.
BOP ramsealing rubber coreerosion modelinversion analysisshut-in process
万方数据
维普
