| Aiming at the problems of the preset throtile device in the Sulige gas field such as failure of setting and difficulty in unsealing,this paper is based on the preset throttle device applied in the field with the support of the project commissioned by the Changqing Oilfield Oil and Gas Technology Research Institute.The shape memory alloy is applied to the throttle locking mechanism,and the deformation of the shape mcmory alloy(NiTi alloy spring)is driven by downhole high temperature to set the lock anchoring,and the overall structure of the preset throttle and the design of key components are completed.The throttle has the advantages of controllable setting time,accurate setting,and no need for hammer to drop.Further,based on the finite element method,the influence of the structure and technology parameter changes on the setting and unsealing performance was studied and analyzed,and the parameters were optimized.The main research contents are as follows:(1)Completed the combination of downhole throttling technology and shape memory alloy application theory.The mechanism of gas well hydrate generation was analyzed,and the mathematical models of choke prssure drop and choke temperature drop were constructed.Utilizing the stress-strain relationship of shape memory alloy materials during heating and the thermodynamic properties of shape memory alloy materials during shrinkage,combined with the principle of downhole throttling,the ihermodynamic model of downhole shrinkage of shape memory alloy materials is deduced,and the shape memory alloy materials during throttling.(2)The structural design and key parameters determination of the new preset throttle device have been completed.The feature of the designed throttle device is that the NiTi alloy spring is applied to thc locking mechanism and the NiTi alloy spring is driven by high temperature downhole to make it shrink and deform so as to realize the setting of the throttle device.The overall scheme design and structural design of throttle devicc anchoring mechanism(lock block),sealing mechanism,anchoring mechanism(NiTi alloy spring)and throttle were carried out,and the key process paramcters of thrttle device(throttle device minimum down into the depth,throttle diameter)were determined.(3)The setting and unsealing performance analysis and paramcter uptimization of the shrinkage of the NiTi alloy spring during setting and the salvage force during unsealing were analyzed and calculated.The analysis shows that the setting and unsealing performance of the anchoring mechanism of the throttle device meets the design requirements.The structure and technology parameters of the lock block were optimized.It is preferable that the equivalent stress is smaller and the salvage force is the smallest when the thickness of the lock block is 11 mm and the contact angle is 45°.At this time,the setting and unsealing performance is better.(4)The setting and unsealing performance analysis and structural optimization of the throttle device sealing mechanism have been completed.Based on the hyperelastic theory and nonlinear contact theory,the influence of the sealing mechanism and the change of structure and technology parameters on the contact stress during setting and the friction force during unsealing were studied and analyzed by using the APDL command tool.The analysis shows that the setting and unsealing performance of the throttle device sealing mechanism meets the design requirements.Using the response surface method to optimize the structure and technology parameters of the sealing mechanism,the optimization results show that when the sealing angle is 60°,the sealing width is 5.34mm,and the sealing chamfer is 0.25mm,the contact stress is the largest and the friction force is the smallest.At this time,the setting and unsealing performance is better.At the end of the paper,relevant operating procedures are put forward for the designed new preset throttle device,which can provide reference opinions for on-site operations. |
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